Recent Submissions

  • Biomechanical behavior related to structure in normal and congenitally disordered elastic arteries

    Beall, Arthur C.; Department of Pharmacology and Toxicology (Augusta University, 1992-12)
  • The effects of retinoic acid-induced differentiation on neurotransmitter receptor content and signal transduction in a human neuroblastoma cell line

    Baumgartner, Melissa K.; Department of Pharmacology & Toxicology (Augusta University, 01/23/1993)
    The purpose of the present study was to establish the effects of retinoic acidindttced differentiation on muscarinic receptor populations and signal transduction pathways in the human neurroblastoma Sk-N-SH cells. The human neuroblastoma cell line Sk-N-SH was induced to differentiate by treatment with 1 uM retinoic acid for 7 days. Differentiation was characterized by profuse neurite outgrowth, a decrease in cell growth, and a 2~3 fold increase in the protein content of each cell. Muscarinic receptors were labelled-using [3H]N-methyl scopolamine. Muscarinic receptor density increased by approximately 36% after treatment for 7 days with retinoic acid (Bmax, control = 126 ± 13 fmol/mgprotein; Bmax, retinoic acid-treated= 170 ± 17 fmol/mg protein; p<0.05), corresponding to a 170% increase in receptor content per cell. The affinity of [3H]NMS for the receptors was somewhat lower in the differentiated cells (KD, control = 0.14 ± 0.04 nM; KD, retinoic acid-treated = 0.25 ± 0.0.4 nM; p<0.05). The guanine nucleotide sensitivity of agonist (carbamylcholine) binding to Sk-N-SH muscarinic receptors Was slightly decreased by differentiation. Reverse transcriptase/polymerase chain reaction (PCR) analysis using muscarinic receptor subtype specific primers revealed that the undifferentiatied Sk-N-SH cells transcribed mRNA for all 5 receptor subtypes; this pattern was not affected by differentiation. [3H]NMS displacement curves with subtype- selective receptor ligands (pirenzepine, m1; AFDX-116, m2; 4-DAMP, m3) indicated the predominant expression of m1 and m3 receptor subtypes, and differentiation did not affect the pharmacological profile of the expressed muscarinic receptor populations. Differentiation did not affect basal G protein GTPase activity. However, acetylcholine (100 uM) stimulation of G protein GTPase activity was decreased in differentiated cells (18 ± 1.8 pmol/min/mgprotein) compared to the undifferentiatied cells (23 ± 1 .0 pmol/ min/ mg protein) (p<0.05). Inhibition of acetylcholine--stimulated GTPase activity with selective muscarinic receptor antagonists indicated that the m3 antagonist (4-DAMP) was as effective as atropine in inhibiting activity by 80-100%. Selective m1 and m2 antagonists were less effective (30-40%) at inhibiting stimulated GTPase activity. There were no differences in inhibition of stimulated GTPase activity after differentiation. Immunoblots of control and retinoic acid-treated cells revealed no change in Goa, Gsa or Gp content after differentiation; however, 0.1% ethanol and retinoic acid-treated cells displayed a 30% decrease in expression of Gia3, and Gqa. Muscarine (0.1-100 uM) stimulated 45Ca influx into Sk-N-SH cells, and this uptake was inhibited by preincubation with atropine. The magnitude of the muscarinic receptor-mediated uptake was 50-60% lower in the differentiatied cells. Basal adenylate cyclase activity was depressed in the differentiated cells (2.5 pmol / min / mg protein) compared to the undifferentiated cells (8.4 pmol / min / mg protein) (p< 0.05). Forskolin (5 - 50 uM)-stimulated adenylate cyclase activity was not altered, however fractional stimulation was significantly (p<0.0001) increased in the differentiated cells. Differentiated cells displayed a slightly greater receptor-mediated inhibition of the adenylate cyclase activity by carbamylcholine (1 uM- 1 mM). It is demonstrated that in Sk-N-SH cells, retinoic acid-induced differentiation: 1) increases the size of the muscarinic receptor population (Bmax) while decreasing [3H]NMS binding affinity, 2) does not alter muscarinic receptor pharmacology, or the expression of. muscarinic receptor subtypes, 3) decreases muscarinic receptor-stimulated 45Ca flux 50-60% compared to undifferentiated cells, 4) depresses basal adenylate cyclase activity, increases fractional stimulation of forskolin-stimulated activity of adenylate cyclase, and may increase muscarinic receptor-mediated inhibition of adenylate cyclase activity, 5) does not alter basal G protein GTPase activity but depresses muscarinic receptor-stimulated high affinity GTPase activity suggesting muscarinic receptor-G protein coupling is altered, and 6) does not alter expression of Goa, Gsa and Gp content while Gia3 and Gqa are depressed in differentiated as well as in 0.1% e.thanol treated cells.
  • Profiling the HCA Receptor Family through BRET Analysis of GPCR-G-Protein and GPCR-Arrestin Interactions

    Saj, Dalia; Department of Biological Sciences; Department of Pharmacology & Toxicology (Augusta University, 2020-05)
    Increasing obesity rates have put the American population at higher risk for developing obesity-related medical conditions such as hypertension, heart disease, and diabetes. The hydroxycarboxylic acid (HCA) receptor family is a family of G protein-coupled receptors (GPCRs) that are expressed in adipose tissue and function as metabolic sensors, making them potential pharmaceutical targets in the treatment of obesity and other metabolic disorders. The HCA receptor family consists of the HCA1, HCA2, and HCA3 receptors, which are activated by hydroxycarboxylic acids such as lactate and 3-hydroxybutyric acid. We utilized bioluminescence resonance energy transfer (BRET) to study agonist-induced coupling of luciferase-tagged HCA receptors to Venus fluorescent protein-tagged G protein heterotrimers or arrestins. Our results indicate that the three HCA receptors couple to the Gαi/o subfamily of G proteins. The data additionally confirms a lack of coupling to the other G protein subfamilies (Gαs, Gαq, and Gα12/13), and lacks evidence of arrestin recruitment to HCA receptors. Overall, our study highlights the use of BRET as a powerful tool for analysis of GPCR signaling and demonstrates its possible use for future studies to determine the potency of potential drugs targeting HCA receptors as a therapy for health-related problems such as obesity.
  • CaMKIIβ association with F-actin in developing cortical neurons

    Lin, Yu-Chih; Department of Pharmacology and Toxicology (2008-08)
    Calcium/calmodulin-dependent protein kinase II (CaMKII) is a serine/threonine kinase that is best known for its role in synaptic plasticity and memory .. Although multiple roles of CaMKII have been identified in the hippocampus, its role in the developing cerebral cortex is less well understood. Immunostaining showed Ca~KII~, but not CaMKIIa was expressed in embryonic day 18 (E 18) cortical neurons at 4 days in vitro (DIV) and localized to a F-actin rich cytoskeletal structure we termed "micro spike". Further characterization of micro spikes revealed that micro spikes were composed of bundled actin, and were stable over time. Besides CaMKII~, several actin binding proteins, such as Arp3, cortactiti"and ~1-integrin were also colocalized in microspikes. Fluorescence recovery after photo bleaching (FRAP) analyses showed different dynamics of actin and CaMKII~ in microspikes compared to dendrite spines. The colocalization of CaMKII~ and F-actin in microspikes was dependent on the F-actin binding domain and the oligomerization domain. FRAP analyses confirmed the association of CaMKIIP with F-actin in microspikes was via the F-actin binding domain. This association was altered by the co-expression of CaMKIIa. FRAP analyses with stabilized F-actin using jasplakinolide or cytochalasin-D further indicated CaMKIIP, but not CaMKIIa, had a strong interaction with stable F-actin. Inhibiting calmodulin binding on CaMKII using a CaMKII inhibitor, KN93, dissociated CaMKIIP from stable F-actin. Increasing CaMKIIP activity with KCl or an active form of CaMKIIP, CaMKIIPT287D, also dissociated CaMKIIP from stable F-actin. A calmodulin binding mutant, CaMKIIPA303R, or a kinase dead mutant, CaMKIIPK43R, however, did not recover differently from wildtype CaMKIIp. The differential binding of CaMKIIP with F-actin shown in FRAP analyses correlated with CaMKIIP enrichment in microspikes and the prominence of microspikes. While overexpressed CaMKIIP increased the number of cells with microspikes, knockdown of CaMKIIP with shRNA reduced it. Taken together, these data suggested that CaMKIIP is associated with F-actin in cortical neurons, and this association is regulated by CaMKIIa and calcium signals · contributing to the stability of micro spikes.
  • SELECTIVITY AND PRODUCTIVITY OF GPCR-G PROTEIN INTERACTIONS

    Okashah, Najeah; Department of Pharmacology and Toxicology (Augusta University, 2020-03)
    Hundreds of human G protein-coupled receptors (GPCRs) converge on activation of four families of heterotrimeric G proteins. Individual receptors select a subset of G proteins in order to produce appropriate cellular responses. While the precise mechanisms of coupling selectivity are uncertain, the G alpha subunit carboxy (C) terminus is believed to be the primary region recognized by GPCRs. We directly assessed coupling between 14 representative GPCRs and 16 G alpha subunits, including one wild-type G alpha subunit from each of the four families and 12 chimeras with exchanged C termini. We found that Gi-coupled receptors were relatively selective for Gi1 heterotrimers, while Gs-, Gq-, and G12- coupled receptors were more promiscuous and always coupled in some measure to Gi1 heterotrimers. Our tests with G alpha subunit chimeras show that the G alpha subunit core and C terminus both play important roles in selectivity. This suggests that the key G protein determinants of selectivity vary widely, even for different receptors that couple to the same G protein. While promiscuous GPCR-G protein coupling is often observed. These interactions behave as expected with receptor-G protein coupling and activation being almost synonymous. Agonist bound GPCRs activate the G protein heterotrimers they interact with, while ignoring G protein subtypes that they cannot activate. However, we have shown that GPCRs can form unproductive complexes with G12 heterotrimers. Vasopressin 2 receptor (V2R) forms agonist-dependent complexes with G12 heterotrimers. Unlike V2R complexes with cognate Gs heterotrimers, V2R-G12 complexes do not dissociate when GDP or GTP is present. Stimulating V2R with arginine vasopressin (AVP) does not activate signaling responses downstream of G12 activation. Evaluation of several G12-coupled receptors demonstrated that agonist induced GPCR-G12 complexes have a wide range resistance to GDP. Like V2R receptors, formyl peptide 2 receptors (FPR2) and smoothened receptors (SMOR) formed complexes with G12 heterotrimers that were relatively resistant to GDP. Our results indicate that several GPCRs can form agonist-dependent unproductive complexes with G12 heterotrimers that are relatively resistant to GDP. Suggesting that for some GPCRs agonist-dependent association with G12 heterotrimers is weakly coupled to nucleotide exchange
  • EFFECT OF GABAERGIC NEURONS IN SUSCEPTIBLE VERSUS RESILIENT MALE RATS TO PTSD

    Dixon, Rachel; Mandavilli, Rohan; Department of Phychological Sciences; Department of Biological Sciences; Departmetn of Pharmacology & Toxicology; Bunting, Kristopher M; Alexander, Khadijah; Vazdarjanova, Almira; Augusta University (2019-02-13)
    Post-traumatic stress disorder (PTSD) is a psychological disorder that can occur after a traumatic event. Individuals with PTSD exhibit extreme anxiety and learning and memory difficulties. Once exposed, 12-35% develop PTSD with women twice as likely to be affected than men. Our goal is to discover underlying mechanisms to prevent PTSD, as we investigate the relevance of glutamic acid decarboxylase positive (GAD+) neurons on susceptible (SUS) and resilient (RES) male rats. SUS and RES phenotypes were assessed using the highly advanced RISP protocol to reveal susceptibility to a PTSD-like phenotype. The increase of GAD+ cells in the medial prefrontal cortex (mPFC) informs us that more GABAergic neurons are present, which can cause inappropriate recall. We will be examining if there is a difference in the number of GAD+ cells in the RES versus SUS male rats. To investigate, we used cryosectioned brains from SUS or RES rats. The brains were stained using immunohistochemistry to isolate the GAD+ neurons in the mPFC and were counted. The results of this experiment will be determined and examined at a later date closer to our presentation. We expect to see a SUS male rats to have a higher number of GAD+ neurons.
  • THE MECHANISM OF INVERSE AGONISTS ON HISTAMINE RECEPTORS, HISTAMINE RECEPTOR H1, AND HISTAMINE RECEPTOR H2

    Patel, Shrey P; Department of Phychological Sciences; Department of Pharmacology & Toxicology; Lambert, Nevin; Augusta University (2019-02-13)
    The experiment discusses the role of inverse agonist binding to receptors and how its effect cell signaling. The specific receptors that was focused on in the project was histamine receptor H1 (HRH1) and histamine receptor H2 (HRH2) which are types of G-protein coupled receptors (GPCR). Both receptors are activated when a ligand, specifically a histamine molecule, which binds to the receptor and activates the signaling pathway within the cell. The main protein within the signaling pathway is the G-protein which helps the cascade effect of the signal to other molecules. G-proteins are activated through GTP. An inverse agonist works like an agonist but will have an opposite end effect within the cell. It was originally thought that inverse agonist works the same way as an agonist to recruit a GTP and activate a G-protein for signaling. The experiment being tests tries to explain the opposite that the inverse agonist could activate the protein without GTP and continue to have its effect on the cell. Human embryonic cells were transfected with plasmids that contain sequences for the receptors and the G-protein, which were also tagged with a fluorophore to measure any bioluminescence with interaction of G-protein and the receptor when the ligands binds. From collecting data from the bioluminescence effect, it shows that there is an interaction a receptor and G-protein complex when the inverse agonist is bound.
  • Unconventional Coupling of 5HT7 receptors to Gs heterotrimers

    Adams, Elizabeth; Department of Pharmacology and Toxicology; Lambert, Nevin; Augusta University (2019-02-13)
    GPCRs play a major role in cell signaling through their interactions with heterotrimeric G proteins. In conventional models of GPCR-G protein coupling, agonist binding promotes a conformational change within the receptor, which then associates with G proteins, facilitating the exchange of GDP for GTP. GTP-bound G proteins dissociate from the receptor and exert their effects on downstream signaling molecules. Previous studies suggest that serotonin 5HT7 receptors associate with Gs�heterotrimers prior to agonist binding, and that 5HT7-Gs�complexes dissociate after the G protein is activated. Here we study this unconventional mode of coupling using bioluminescence resonance energy transfer (BRET) between luciferase-tagged 5HT7 receptors and Gs�heterotrimers labeled with Venus. Our results confirm that 5HT7 receptors interact with inactive (GDP-bound) Gs�heterotrimers in the absence of an agonist, and that this interaction is stabilized by the inverse agonist methiothepin. Stimulation with the endogenous agonist serotonin (5HT) decreased BRET between 5HT7 receptors and Gs, indicating that the activation of the receptor leads to 5HT7-Gscomplex dissociation. Interestingly, Gs�activation was not required for complex dissociation. These results are consistent with the hypothesis that 5HT7 receptors couple to Gs�heterotrimers via an unconventional mechanism involving ligand-sensitive complexes of receptors and inactive Gs.
  • The Study of 5ht-1d and 5ht-1f Receptor Interactions with Mini G Proteins via Bret Analysis

    Trang, Amy; Department of Chemistry & Physics; Department of Pharmacology and Toxicology; Spencer, Angela; Lambert, Nevin; Augusta University (2019-02-13)
    G protein-coupled receptors (GPCRs) are receptors involved in signal transduction, a process for converting extracellular signals into internal messages to elicit a cellular response. Signal transduction pathways involve activating various G protein subtypes (Gs, Gi/o, Gq/11 and G12/13) which typically lead to second messenger production. Traditionally, second messenger concentration assays are used to identify GPCR coupling with G protein(s), but they are not efficient in profiling GPCRs since they compare the concentrations from different downstream signals. Instead, novel tools, such as Bioluminescence Resonance Energy Transfer (BRET) and mini G (mG) proteins, can be used to profile GPCRs. BRET is a technique that provides quantitative data when protein-protein interaction occurs and requires the proteins of interest to be fused with either a bioluminescent protein or fluorescent protein. In this study, we used mG proteins representing each G protein subtype to identify 5-hydroxytryptamine (5-HT; serotonin) receptor coupling upon serotonin stimulation. Through BRET assays, we determined that both the 5-HT1D and 5-HT1F receptors couple primarily with the mGsiand mGo classes of mG proteins. This supports previous studies that these receptors couple to Gi/o proteins and suggests that the use of mG proteins in BRET assays is an effective tool for GPCR profiling.
  • The Role of T Cells in High Fat Diet Induced Hypertension and Vascular Dysfunction in Female Rats

    Taylor, Lia; Department of Pharmacology and Toxicology (2019-01-08)
    Hypertension is a leading risk factor for the development of cardiovascular disease (CVD) worldwide, affecting ~86 million adults in the United States alone. In general, the prevalence of hypertension is lower in premenopausal women than in age-matched men. Despite having lower risk than men, however, women represent more than half of all hypertension cases, and CVD is the leading cause of death in women worldwide. Women are also more likely than men to be obese and two-thirds of hypertension cases in the U.S. positively correlate with excessive weight gain due to the consumption of diets high in saturated fat. Dahl salt-sensitive rats (DSS) have traditionally been used to study salt-sensitive hypertension. However, previously, it has been shown that male DSS also exhibit a high fat diet (HFD)-induced increase in blood pressure (BP) at normal salt intake, which is attenuated by treatment with the lymphocyte inhibitor mycophenolate mofetil (MMF), suggesting a role for B and T cells in HF-induced hypertension in male animals. However, there is limited data on the role of HFD and T cell activation on BP in females. We hypothesized that HFD will promote hypertension and vascular dysfunction in female DSS and that these cardiovascular changes will be mediated by T cells. We demonstrate that female DSS are susceptible to HFD-induced hypertension and vascular T cell infiltration and activation similar to that of males. Since local inflammation in perivascular adipose tissue (PVAT) is linked to HFD-induced increases in BP and vascular dysfunction in males, we further investigated the impact of HFD on vascular function and the buffering capacity of PVAT in female DSS. HFD alone did not impair vascular function compared to normal fat diet (NFD) in female DSS. Interestingly, the buffering capacity of PVAT was also maintained in female DSS in response to a HFD despite increases in BP and vascular inflammation, likely due to overproduction of nitric oxide (NO). To directly assess the role of T cells on HFD-induced alterations of BP and vascular function in female DSS, we utilized female CD247-/- rats on the DSS background. HFD-induced increases in BP were completely abolished in CD247-/- . Further, the buffering capacity of PVAT was preserved in CD247-/- in response to a HFD. We conclude that T cells underlie the susceptibility of female DSS to HFD-induced hypertension. Further, vascular function and PVAT buffering capacity are maintained in female DSS despite fat-induced increases in BP and vascular inflammation, suggesting an adaptive response in the early stages of diet-induced obesity in which nitric oxide (NO) may play a key role.
  • Effect of chronic oral treatment with risperidone or quetiapine on cognitive performance and neurotrophin-related signaling molecules in rats

    Poddar, Indrani; Department of Pharmacology and Toxicology (8/7/2018)
    Antipsychotic (APs) drugs are among the top selling pharmaceuticals in the world and they have a variety of important therapeutic applications for neuropsychiatric disorders. However, there are a number of controversies related to this class of agents and many of the relevant questions are difficult to prospectively address in the clinical trial environment. For example, there have been multiple clinical trials for pro-cognitive agents in schizophrenia that have failed; however, the question of how chronic prior treatment with APs might influence the response to a pro-cognitive agent was not addressed. Moreover, there is clinical evidence that chronic treatment with some APs may lead to impairments in cognition, however, this issue and the potential molecular mechanisms of the deleterious effects have been not been prospectively addressed. Accordingly, the purpose of the work described in this dissertation was to prospectively address each of these issues in animals (specifically rats) were environmental conditions can be rigorously controlled. In each of the manuscripts included in this dissertation, two of the most commonly prescribed APs, risperidone and quetiapine were evaluated. In the work conducted in Manuscript 1, we established a therapeutic relevant dosing approach for rats (oral administration in drinking water) and reinforced the argument that these two APs are not pro-cognitive agents. Moreover, we determined that alpha-7 nicotinic acetylcholine receptor (nAChR) ligand like tropisetron has potential as an adjunctive medication in schizophrenia since the pro-cognitive effect was maintained in the presence of chronic AP treatment. In Manuscript 2, we concluded that chronic treatment with risperidone or quetiapine in rats can lead to impairments in a domain of cognition (recognition memory) that is commonly altered in neuropsychiatric disorders. Moreover, the negative effects of the APs appeared to be exacerbated over time. In Manuscript 3, we concluded that risperidone and quetiapine when administered chronically to rats have the potential to adversely affect neurotrophin-related signaling molecules that support synaptic plasticity and cognitive function. These data would suggest that the extensive prescribing of these APs across multiple conditions in patients ranging in age from the very young to the very old should be carefully reexamined. Key Words: antipsychotic, cognition, brain volume, schizophrenia, neurotrophin
  • Epigenetic Regulation of Adipogenic Differentiation And Lipid Metabolism: Role of Enhancer of Zeste Homolog 2 (EZH2)

    YIEW, KAN HUI; Department of Pharmacology and Toxicology (2017)
    Adipose tissue expansion in obesity promotes cardiometabolic disease, for which there is an urgent need to elucidate disease mechanisms and develop novel and effective medical therapies. In obesity, adipose tissues can potentially expand through adipocyte hypertrophy and/or hyperplasia, with the latter being a healthier mechanism of fat expansion. Adipocyte hyperplasia (via adipogenic differentiation) is inexplicably restrained in diet-induced obesity (DIO), however, and hypertrophy ensues, leading to inflammation, insulin resistance, and dysregulated adipose tissue lipid metabolism, which together contribute to cardiometabolic disease. The mechanisms of impaired adipogenic differentiation and lipid metabolism during DIO are unclear, with prior studies suggesting epigenetic dysregulation of histone deacetylase 9 (HDAC9, an endogenous repressor of adipogenic differentiation). The overall goal of my dissertation project is to investigate the role of Enhancer of Zeste Homolog 2 (EZH2), a histone methyltransferase, in the aforementioned processes. In Aim 1, we hypothesized that EZH2 promotes adipogenic differentiation by repressing HDAC9. EZH2 recruitment and histone 3 lysine 27 trimethylation (H3K27me3) modification were elevated at the HDAC9 gene promoter (p<0.05) concurrent with dramatic downregulation of HDAC9 mRNA levels (p<0.05) during adipogenic differentiation of primary human preadipocytes. This suggested a role for EZH2 in silencing HDAC9 gene expression. Counterintuitively, a highly selective EZH2 pharmacological inhibitor (GSK126), at a concentration that effectively blocked H3K27me3, led to increased lipid accumulation (p<0.05) in human adipocytes, without inhibiting adipocyte marker gene expression. Consistently, mice with adipose-specific EZH2 deletion (cKO) displayed significantly elevated body weight, adipose tissue mass, and adipocyte cell size. These phenotypic alterations could not be explained by differences in feeding behavior, locomotor activity, or metabolic energy expenditure, thereby suggesting that EZH2 regulates lipid metabolism. This hypothesis was explored in Aim 2. Human adipocytes treated with either an EZH2 inhibitor or vehicle exhibited comparable rates of de novo lipogenesis (DNL), fatty acid (FA) uptake, and basal/stimulated lipolysis. Consistently, cKO and littermate control mice displayed comparable in vivo and ex vivo basal/stimulated adipose lipolysis. EZH2’s function in other important metabolic pathways such as glycolysis and β-oxidation remain to be investigated. Collectively, our findings suggest a potential role of EZH2 in regulating adipocyte lipid metabolism.
  • A Data-Mining Strategy That Identifies Drugs and Genes Associated With Anti-Cancer Drug Sensitivity

    Schleifer, Robert John; Department of Pharmacology and Toxicology (2017)
    The success of cancer therapy for patients often hinges on the responsiveness of the cancer cells to therapeutics. Drug resistance to anti-cancer therapeutics, both intrinsic and acquired, has important clinical and scientific significance. Identification of drug resistance genes using traditional methodologies and translation of those findings to the clinic has proven challenging. We developed a predictive data mining-based bioinformatic framework using public patient data and high-throughput cancer cell drug screening data. This information was used for genome-wide rankings of putative drug resistance genes. Prominent drug resistance genes (e.g. ABCB1, EGFR, and AXL) were successfully identified by the pipeline, additional genes hypothesized to be novel drug resistance genes were then investigated. Experimental confirmation of the novel genes using knockdown technologies indicated a propensity for of decreased proliferation/viability of cancer cells and increased sensitivity for anticancer compounds after knockdown much like known drug resistance genes. We then assessed the potential of each gene as an anti-cancer therapeutic target by exploring how gene knockdown behaved with clinical anticancer compounds. A second arm of the data-mining pharmaco-genomic strategy involved identification of candidate compounds that decrease expression of drug resistance genes. Using the drug resistance gene AXL as a proof-of-concept, three compounds were identified that decreased AXL expression at sub-micromolar concentrations. These compounds were characterized using microarray and cell signaling studies and found to decrease cell cycle signaling as well as activity of the Akt, mTOR, and ERK pathways. This study illustrates a novel approach for rapid and efficient identification of drug sensitivity genes or gene expression altering compounds utilizing bioinformatic data-mining.
  • Circadian Clock in Angiotensin II Induced Hypertension and Vascular Disease

    Pati, Paramita; Department of Pharmacology and Toxicology (2015)
    Hypertension remains a major risk factor for cardiovascular disease and death. While clinical studies and guideline recommendations underscore the benefits of reducing sodium intake in the treatment of high blood pressure, recent human data suggest that underlying conditions of disease may confound these positive effects of low salt diets. Herein, we examined the influence of circadian dysfunction during experimental hypertension caused by angiotensin II (Ang II), a key peptide in blood pressure regulation. While a low salt diet caused the expected decrease in blood pressure in wild type (WT) mice, mice with disruption of the circadian clock exhibited a paradoxical response to low salt. Mice with disruption in the circadian clock component Period (Period-knockout/KO mice), were abolished in blood pressure rhythm due to an increase in daytime blood pressure. This impairment in blood pressure rhythm in Per-KO mice on the low salt diet was restored to rhythmic oscillation by the angiotensin receptor blocker losartan. Similarly, exogenous administration of Ang Il caused a non-dipping blood pressure phenotype in the Per-KO mice on a normal salt diet, which resulted in pathological thickening of the vasculature indicative of vascular disease. These effects were related to circadian rhythm as impairment in blood pressure caused by low salt was recapitulated in WT mice induced to circadian derangement by a shortened light cycle. Further thickening of the vasculature and increased renin levels were observed in Per-KO mice on a chronic low salt diet but not in WT mice. Moreover, disruption of the Period gene altered ATI receptor expression and other components of the renin-angiotensin system. These data suggest that circadian dysfunction may compromise the benefits of a low salt diet and support recent clinical data that raise caution to sodium restriction as a therapy for hypertension.
  • Involvement of arginase upregulation in diabetes- and angiotensin II-induced vascular dysfunction

    Bhatta, Anil; Department of Pharmacology and Toxicology (2015)
    Cardiovascular disease (CVD) is the number 1 killer of men and women in the United States and the world. Diabetes, hypertension, obesity, and aging are some of the risk factors for CVD. A major cause of morbidity and mortality in CVD is vascular dysfunction, which progresses rapidly as the risk factors progress. Vascular dysfunction is characterized by a constellation of blood flow reducing pathologies, including impaired vasorelaxation and elevated arterial stiffening. The mechanisms leading to these vascular abnormalities are not well understood. We tested the hypothesis that arginase, an enzyme in the urea cycle, mediates vascular dysfunction in hypertension and obesity related diabetes. Arginase (ARG) can compete with nitric oxide (NO) synthase for their common substrate, L-arginine. Increased arginase can also provide more ornithine for synthesis of polyamines via ornithine decarboxylase (ODC) and proline/collagen via ornithine aminotransferase (OAT), leading to vascular cell proliferation and collagen formation, respectively. We hypothesized that elevated arginase activity is involved in Ang II-induced vascular dysfunction and that limiting its activity can prevent these changes. We tested this by studies in C57BL/6J mice lacking one copy of the ARG1 gene that were treated with Ang II (1 mg/kg/day, 4 weeks). We demonstrated that Ang II induces smooth muscle cell proliferation, collagen synthesis, and arterial fibrosis and stiffness via a mechanism involving increased arginase activity. Furthermore, we examined the role of arginase in vascular dysfunctions and pathologies associated with obesity-related type 2 diabetes in mice fed with high-fat/high-sucrose (HFHS) diet for 6 months. This model produced a clinical presentation and pathophysiological relevance to the human condition in obesity related type 2 diabetes. We demonstrated that HFHS diet impaired endothelial dependent vasorelaxation and increased arterial stiffness in WT mice, but not in mice treated with arginase inhibitor ABH. Endothelial cell specific knockout of ARG1 (EC-A1-/-) in mice also prevented HFHS induced vascular dysfunctions. Aortic perivascular collagen deposition was significantly higher in HFHS mice compared to normal diet. Furthermore, marked increase in vascular cell adhesion molecule expression and macrophage infiltration into the aortic walls was observed with HFHS diet. Additionally, plasma lipid peroxidase activity, a measure of systemic oxidative stress, was also markedly increased in HFHS mice. These changes were prevented in ABH treated mice and EC-A1-/- mice. These studies suggest that enhanced ARG1 activity promotes vascular dysfunctions associated with elevated Ang II levels or obesity related diabetes.
  • A Novel Function of ADP-Ribosylation Factor 1 in Prostate Cancer Cell Proliferation through Activating the Mitogen-Activated Protein Kinase Pathway

    Davis, Jason E.; Department of Pharmacology and Toxicology (8/23/2016)
    The enhanced activation of the mitogen-activated protein kinase (MAPK) Raf-MEK-ERK1/2 pathway directly correlates with the growth, androgen-independence, and poor prognosis of prostate cancer. However, the underlying molecular mechanisms remain poorly understood. Here, we have demonstrated that ADP-ribosylation factor 1 (ARF1), a Ras-like small GTPase, was highly expressed in human prostate cancer cells and tissues. In addition, ARF1 was markedly activated in prostate cancer cells. More interestingly, oncogenic G protein-coupled receptors (GPCRs) strongly activated ARF1 and the activation was mediated through Gβγ subunits. These data indicate that GPCRs and heterotrimeric G proteins are the upstream activators of ARF1 in prostate cancer cells. Next, we determined the role of ARF1 in the MAPK activation and proliferation in prostate cancer cells. Lentiviral-mediated overexpression of ARF1 remarkably enhanced, whereas shRNA-mediated depletion of ARF1 dramatically reduced ERK1/2 activation in prostate cancer cells. In addition, disruption of both the Golgi localization of ARF1 and the Golgi structure substantially attenuated ERK1/2 activation in prostate cancer cells. In parallel with their effects on the MAPK activation, ARF1 overexpression greatly enhanced and ARF1 knockdown inhibited the proliferation of prostate cancer cells. These data suggest that ARF1, by its ability to activate the MAPK pathway likely at the Golgi, controls prostate cancer cell proliferation. We then investigated the consequence of pharmacologically inhibiting ARF1 activation. Small molecule inhibitors including brefeldin A, golgicide A, and Exo2 that specifically target Golgi-localized ARF1 markedly reduced both ERK1/2 activation and proliferation in prostate cancer cells. These results further indicate an important role of ARF1 activation in regulating the MAPK pathway and prostate cancer cell proliferation. Altogether, our data suggest a possible GPCR-G-ARF1-MAPK signaling pathway, which may be responsible for the hyperactivation of the MAPK ERK1/2 in prostate cancer and contributes to prostate cancer progression. Our results also imply a novel approach for prostate cancer therapy by targeting ARF1 activation
  • Calpain-2 Activates Akt via the TGF~ 1-mTORC2 Pathway in Pulmonary Artery Smooth Muscle Cells

    Abeyrathna, Prasanna; Deparment of Pharmacology and Toxicology (8/23/2016)
    Calpain is a family of calcium-dependent nonlysosomal neutral cysteine endopeptidases. Akt is a serine/threonine kinase that belongs to the AGC kinases and plays important roles in cell survival, growth, proliferation, angiogenesis, and cell metabolism. Both calpain and Akt are downstream signaling molecules of platelet-derived growth factor (PDGF) and mediate PDGF-induced collagen synthesis and proliferation of pulmonary artery smooth muscle cells (PASMCs) in pulmonary vascular remodeling. We found that inhibition of calpain-2 using the calpain inhibitor MDL28170 and calpain-2 siRNA attenuated Akt phosphorylation at serine-473 (S473) and threonine-308 (T308) as well as collagen synthesis and cell proliferation ofPASMCs induced by PDGF. Overexpression of calpain-2 in PASMCs induced dramatic increases in Akt phosphorylation at S4 73 and T308. Moreover, knockout of calpain attenuated Akt phosphorylation at S473 and T308 in smooth muscle of pulmonary arterioles of mice with chronic hypoxic pulmonary hypertension. The cell-permeable specific TGF~ receptor inhibitor SB431542 attenuated Akt phosphorylation at both S473 and T308 induced by PDGF and overexpressed calpain- 2 in PASMCs. Moreover, SB-431452 and knock down of ALK5 significantly reduced PDGF-induced collagen synthesis and cell proliferation of PASMCs. Nevertheless, neutralizing extracellular TGF~l using a cell-impermeable TGF~l neutralizing antibody did not affect PDGF-induced Akt phosphorylation at S473 and T308. Further, inhibition of mTORC2 by knocking down its component protein Rictor prevented Akt phosphorylation at S473 and T308 induced by PDGF and overexpressed calpain-2. These data provide the first evidence supporting that calpain-2 up-regulates PDGF-induced Akt phosphorylation via an intracrine TGF~ 1/mTORC2 mechanism.
  • Attenuating the Interaction Between Delta Protein Kinase C and the "d" Subunit of FIFo ATp Synthase Protects Against Cardiac Ischemia/Repferusion injury

    Walker, Matthew; Deparment of Pharmacology and Toxicology (6/3/2016)
    Cardiac ischemia / reperfusion (IR) injury most often results from the thrombotic blockade of the coronary arteries and is the most frequent cause of death in humans. Despite the significant role energy deprivation plays in cardiac IR injury, few studies have targeted the IR-induced impairment of the mitochondrial F1Fo ATP synthase. We have previously demonstrated delta protein kinase C (δPKC) involvement in cardiac myocyte energy deprivation via its interaction with the “d” subunit of F1Fo ATP synthase (dF1Fo) and have developed a peptide inhibitor [NH2YGRKKRQRRMLATRALSLIGKRAISTSVCAGRKLALKTIDWVSFDYKDDDDK- COOH] of this interaction. It targets to the mitochondrial matrix / inner membrane. The inhibitor peptide contains a FLAG epitope which allowed confirmation of its uptake into cardiac mitochondria. Our early studies in neonatal cardiac myocytes (NCMs) led us to the hypothesis that PKC inhibits ATP production in vivo via an interaction with dF1Fo to exacerbate cardiac IR injury. To directly test our hypothesis, we first utilized the Langendorff isolated heart model to show that PKC co-immunoprecipitates (co-IPs) with antisera to dF1Fo in myocardium exposed to simulated IR injury. Administration of the inhibitor peptide to the isolated rat hearts prior to cardiac IR attenuated the co-IP of 􀁇PKC with dF1Fo, improved recovery of contractility, diminished levels of tissue t-carbonyls and 4-hydroxy-2-nonenal (HNE), and reduced myocardial infarct size (as assessed by 2, 3, 5 triphenyltetrazolium chloride (TTC) staining) following simulated IR exposures. Additionally, this peptide enhanced ATP levels 2.1 fold, improved ADP-stimulated mitochondrial respiration, and attenuated Ca++-induced mitochondrial swelling in ischemic myocardium. We next evaluated the inhibitor peptide in an in situ rat coronary ligation model for its ability to protect live rats from cardiac IR injury. A 10 min coronary ligation increased the PKC-dF1Fo co-IP in the region at risk (RAR) by 5-fold which was attenuated by 71% with intravenous infusion of the inhibitor peptide. This response correlated with an enhancement of ATP levels, a 2-fold reduction in oxidative stress markers, improvement in systolic cardiac function, and a reduction in TTC monitored myocardial infarct size in the RAR. These results support further development of this peptide as a first-in-class-translational therapeutic for the treatment of cardiac IR injury.
  • Protein-Protein Interaction between G protein-coupled receptors and heterotrimeric G proteins

    Qin, Kou; Department of Pharmacology and Toxicology (2011-01)
    G protein-coupled receptors (GPCRs) interact directly with heterotrimeric G proteins to transduce physiological signals. Early studies of this interaction concluded that GPCRs (R) and G proteins (G) collide with each other randomly after receptor activation and that R-G complexes are transient (collision model). More recent studies have suggested that inactive R and G are preassembled as stable R-G complexes in cells (preassembly models). Using fluorescence recovery after photobleaching (FRAP) we examined the stability of complexes formed between cyan fluorescent protein-labeled a2Aadrenoreceptors (C-a2ARs) and G proteins in HEK293 cells. Labeled G proteins diffused in the plasma membrane with equal mobility in the absence and presence of immobile C- a2ARs. In contrast, a stable R-G interaction was detected when G proteins were deprived of nucleotides and C- a2ARs were active. Over-expression of regulator of G protein signaling 4 (RGS4) accelerated the onset of effector activation but did not alter the interaction between C- a2ARs and G proteins. At most a small fraction of C- a2ARs and G proteins exist as R-G complexes at any moment. However, applying similar technique and protocols, we demonstrated that immobilized M3R specifically decreases the mobility of Gaq heterotrimers on the plasma membranes of intact HEK293 cells, suggesting the existence of R-G preassembly. The C-terminus of M3R was determined to be both required and sufficient for preassembly. The M3R C-terminus contains a polybasic region (565KKKRRK570) located distal to the 8th a-helix domain. Substitution of this polybasic region with 6 electroneutral alanines (M3R6A) prevented preassembly. Permeabilization of cells with low ionic strength buffer resulted in enhanced R-G interaction, implicating electrostatic forces as a factor in the preassembly. We examined the functional properties of the mutant M3R6A, which showed decreases in acetylcholine potency compared with M3R. M3R6A produced active Gq at half the rate of M3R. Other Gq-coupled receptors, such as M1 and M5 muscarinic and a1a,a1b, aid adrenergic receptors, contain similar C-terminal polybasic regions. We found that both M5R and alb adrenoceptor (albAR) preassembled with Gq proteins. Our findings suggest that a polybasic regionmediated electrostatic mechanism could be a common mechanism of preassembly between Gq-coupled receptors and Gq proteins.
  • The Role of Lateral Diffusion in G-Protein-Coupled Receptor Signaling

    Lober, Robert M.; Department of Pharmacology and Toxicology (2006-05)
    In the standard model of G-protein-coupled receptor (GPCR) signaling, receptors and G-proteins are free to diffuse laterally within the plane of the plasma membrane, and these molecules encounter each other by random collision. It is possible that formation of the receptor-G-protein (R-G) complex precedes receptor activation, although the dynamics of this process have been challenging to observe in live cells. We have approached this problem by measuring the membrane diffusion and binding reactions of receptors and Gproteins. We examined the functional consequences of immobilizing receptors, G-proteins, and inwardly rectifying potassium (GIRK) channels at the cell surface by biotinylation and avidin crosslinking, and monitored intermolecular binding events reflected by receptor-imposed constraints on G-protein diffusion, as measured by fluorescence recovery after photobleaching. In whole-cell voltage-clamp recordings, we found that both mobile and immobile heterologous p-opioid receptors (MOR) activated endogenous GIRK channels in cerebellar granule neurons with kinetics and agonist sensitivity resembling native synaptic responses. In HEK 293 cells, immobile GIRK channels were activated by multiple populations of immobilized receptors and Gproteins. Immobilization of MOR constrained the apparent mobility of freely diffusing fluorescent Gaj/o-family proteins, indicating measurable binding reactions between the two protein types, but had no effect on the diffusion of unrelated membrane proteins or Gaq subunits. Transient binding reactions were highly specific, as determined by competition with unlabeled binding partners. RG binding was disrupted by receptor agonist or GTPase-deficient G-protein mutants. Neither receptor antagonists nor pertussis toxin blocked basal R-G binding. Furthermore, the Ga subunit amino terminus (amino acids 1-31) was sufficient for mediating R-G binding. Our results provide evidence for the free diffusion of receptors and Gproteins, as well as a pre-signaling binding-dissociation equilibrium between them that is altered upon activation. The frequency of collisions between receptors and G-proteins does not limit the rate of signaling in neurons, but by diffusion receptors can “swap” G-proteins that are not stably associated with GIRK channels. A three-stage sequential fit model of R-G coupling is suggested.

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