Browsing Theses and Dissertations by Title
Now showing items 1074-1075 of 1075
β-adrenergic receptor/β-arrestin-mediated microRNA maturation regulatory network: A new player in cardioprotective signalingChronic treatment with the β-blocker carvedilol (Carv) has been shown to reduce established maladaptive left ventricle (LV) hypertrophy and to improve LV function in experimental heart failure. However, the detailed mechanisms by which carvedilol improves LV failure are poorly understood. We previously showed that carvedilol is a β-arrestin-biased β1-adrenergic receptor ligand, which activates cellular pathways through β-arrestins in the heart independent of G protein-mediated second messenger signaling, a concept known as biased signaling. Here, we sought to (i) identify the effects of Carv on LV gene expression on a genome-wide basis and (ii) investigate whether Carv could regulate novel miR expression/biogenesis, thereby providing a novel mechanism for its cardioprotective effects. Gene expression profiling analysis revealed that subsets of genes are differentially expressed after Carv treatment. Further analysis categorized these genes into pathways involved in tight junction, cardiac response to malaria, viral myocarditis, glycosaminoglycan biosynthesis, and arrhythmogenic right ventricular cardiomyopathy (ARVC). Genes encoding proteins in the tight junction, malaria, and viral myocarditis pathways were upregulated in the LV by Carv, while genes encoding proteins in the glycosaminoglycan biosynthesis and ARVC pathways were downregulated by Carv. In addition, our findings also revealed that Carv indeed upregulates 3 mature miRs, but not their pre-miRs and pri-miRs, in a β-arrestin1/2-dependent manner. Interestingly, Carv-mediated activation of miR-466g or miR-532-5p, and miR-674 is dependent on β2AR and β1AR, respectively. Mechanistically, β-arrestins regulate maturation of 3 newly identified βAR/β-arrestin-responsive miRs (β-miRs) by associating with the Dicer complex as well as two RNA binding proteins (hnRNPK and dyskerin) on three pre-miRs. Cardiac cell approaches uncover that β-miRs act as gatekeepers of cardiac cell function by repressing deleterious targets. Our findings indicate a novel role for βAR-mediated β-arrestin signaling activated by Carv in miR maturation, which may be linked to its protective mechanism. Altogether, our findings indicate that (i) the gene expression changes may reflect the molecular mechanisms that underlie the functional benefits of Carv therapy and (ii) the novel role for βAR-mediated β-arrestin signaling activated by Carv in miR maturation, which may be linked to its protective mechanism.
Βeta-Arrestin1 and G Protein-Coupled Receptor Kinase5 Regulate Cancer ProgressionCancer is a leading cause of death worldwide, accounting for nearly seven million deaths per year. Available clinical data establish a protective effect of COX-2 inhibition on human cancer progression, but the appearance of unwanted side effects remains a major hurdle for the general application of COX-2 inhibitors as effective cancer therapeutics. Major COX-2 effectors are prostaglandins and we explored the idea that PGE2 promotes mitogenic signals that could be exploited for targeted therapy of cancer. PGE2 signals through EP1, EP2, EP3, and EP4 that belong to the superfamily of GPCR that have been demonstrated to signal through G proteins and βArrestins. In the first part of this thesis project we determined the role of βArrestins in PGE2-regulated cancer cell migration. We report that the COX-2 effector PGE2 signals selectively via EP4 to enhance A549 lung cancer cell migration. We further find that this mode of signaling requires the presence of βArrestin1 and tyrosine kinase c-Src activity. Hence, this study provides preclinical-based rationale for the selective targeting of EP4 to inhibit PGE2-induced lung cancer cell migration. In the second part of this thesis project we determined the role of G protein-coupled receptor kinase 5 (GRK5) in cancer cell proliferation and tumor growth. Recent studies have implicated distinct GRK roles in the regulation of non-GPCR substrates, some of which have well-defined roles in cancer progression such as tumor suppressor p53. Here we report that GRK5 is required for prostate cancer cell cycle progression, cell proliferation, and prostate tumor growth. We identified HDAC4 as a novel GRK5 substrate, whose gene and protein expression is regulated by its kinase activity. In addition, we found that serine 246 residue of HDAC4 is phosphorylated by GRK5, a site known to regulate HDAC4 activity and subcellular localization. GRK5 can also phosphorylate an HDAC4 fragment (419-670 amino acid residues) that also contains two important regulatory serine phosphorylation sites. As many studies have shown HDAC4 involvement in cancer, our findings may provide a possible mechanism of HDAC4 regulation by GRK5.