Browsing Department of Pathology: Faculty Research and Presentations by Title
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Switched alternative splicing of oncogene CoAA during embryonal carcinoma stem cell differentiation.Alternative splicing produces functionally distinct proteins participating in cellular processes including differentiation and development. CoAA is a coactivator that regulates transcription-coupled splicing and its own pre-mRNA transcript is alternatively spliced. We show here that the CoAA gene is embryonically expressed and alternatively spliced in multiple tissues to three splice variants, CoAA, CoAM and CoAR. During retinoic-acid-induced P19 stem cell differentiation, the expression of CoAA undergoes a rapid switch to its dominant negative splice variant CoAM in the cavity of the embryoid body. CoAM functionally inhibits CoAA, and their switched expression up-regulates differentiation marker Sox6. Using a CoAA minigene cassette, we find that the switched alternative splicing of CoAA and CoAM is regulated by the cis-regulating sequence upstream of the CoAA basal promoter. Consistent to this, we show that p54(nrb) and PSF induce CoAM splice variant through the cis-regulating sequence. We have previously shown that the CoAA gene is amplified in human cancers with a recurrent loss of this cis-regulating sequence. These results together suggest that the upstream regulatory sequence contributes to alternative splicing of the CoAA gene during stem cell differentiation, and its selective loss in human cancers potentially deregulates CoAA alternative splicing and alters stem cell differentiation.
Transcriptional Coactivator and Oncoprotein CoAACoAA contains two copies of RNA recognition motifs (RRM) and an intrinsic transactivation domain rich in repetitive tyrosines and glutamines (YxxQ domain). Previously, CoAA has been shown to be a transcriptional coactivator that stimulates transcriptional activation and regulates alternative splicing. A pattern and profile search revealed that the YxxQ domain in CoAA shared significant pattern homology with the oncogenic EWS activation domains (EAD) in TET family proteins, including, TLS/FUS, EWS and TAFII 68. It was further demonstrated that CoAA’s YxxQ domain and EWS’ EAD also shared functional similarities. Based on these findings, this work investigated the aberration of CoAA in cancers and its pathophysiological significance. The results showed that the CoAA gene was amplified in a high percentage of inflammation-related human cancers with recurrent loss of the 5’ regulatory element upstream of its promoter. This genomic aberration resulted in CoAA protein overexpression, which in turn, induced the transformation of NIH3T3 cells. Subsequently, it was shown that the lost 5’ regulatory element could modulate the alternative splicing of the CoAA gene during stem cell differentiation and that the unbalanced expression of CoAA and its splice variant, CoAM could potentially impact the cell differentiation process. To further characterize the regulation of CoAA alternative splicing, two conserved trans-splicing events between CoAA and its downstream RBM4 were identified. These events yield a novel zinc finger- containing coactivator, CoAZ, and a non-coding splice variant, ncCoAZ. Both variants regulated their parental genes’ mRNA expression as well as activities, suggesting a linked control between CoAA and RBM4. Moreover, the expression patterns of CoAA, RBM4 and their trans-splicing variants switched during neural stem cell differentiation, resulting in lineage-specific expression of each variant. Our phylogenetic analysis suggests that mammalian CoAA and RBM4 share a common ancestor with the Drosophila melanogaster gene, Lark. In this regard, the trans-splicing events between CoAA and RBM4 represent a functional regulation preserved during evolution. This study established the connection between CoAA and human cancer and provides evidence for CoAA’s involvement in the regulation of cell differentiation. Moreover, this study is the first to report a functional trans-splicing variant in mammalian cells.
The Transcriptional Profile of Mesenchymal Stem Cell Populations in Primary Osteoporosis Is Distinct and Shows Overexpression of Osteogenic InhibitorsPrimary osteoporosis is an age-related disease characterized by an imbalance in bone homeostasis. While the resorptive aspect of the disease has been studied intensely, less is known about the anabolic part of the syndrome or presumptive deficiencies in bone regeneration. Multipotent mesenchymal stem cells (MSC) are the primary source of osteogenic regeneration. In the present study we aimed to unravel whether MSC biology is directly involved in the pathophysiology of the disease and therefore performed microarray analyses of hMSC of elderly patients (79â 94 years old) suffering from osteoporosis (hMSC-OP). In comparison to age-matched controls we detected profound changes in the transcriptome in hMSC-OP, e.g. enhanced mRNA expression of known osteoporosis-associated genes (LRP5, RUNX2, COL1A1) and of genes involved in osteoclastogenesis (CSF1, PTH1R), but most notably of genes coding for inhibitors of WNT and BMP signaling, such as Sclerostin and MAB21L2. These candidate genes indicate intrinsic deficiencies in self-renewal and differentiation potential in osteoporotic stem cells. We also compared both hMSC-OP and non-osteoporotic hMSC-old of elderly donors to hMSC of â ¼30 years younger donors and found that the transcriptional changes acquired between the sixth and the ninth decade of life differed widely between osteoporotic and non-osteoporotic stem cells. In addition, we compared the osteoporotic transcriptome to long term-cultivated, senescent hMSC and detected some signs for pre-senescence in hMSC-OP.
Transcriptional Regulation by Tbx2Tbx2 is a member of an evolutionarily conserved transcriptional regulatory gene family. Little is known about the molecular mechanisms underlying the function of Tbx2. Because connexin43 (Cx43) and Tbx2 are both expressed in neural crest derivatives in pharyngeal arches and because the promoter of Cx43 contains direct repeats of T (Brachyury) half sites, it is hypothesized that Tbx2 regulates Cx43 and other genes important for neural crest cell functions. TBX2 DNA binding affinity was analyzed by eletrophoretic mobility shift assays. Transcriptional regulation of the Cx43 promoter by Tbx2 was analyzed using reporter constructs. These results suggest that Cx43 is a bona fide target gene o(Tbx2 and that Tbx2 negatively regulates Cx43 gene expression by binding to TCACAC sites. Moreover, dye-coupling assays showed that Tbx2 upregulation led to decreased junctional coupling. To identify other genes that may be regulated by Tbx2, a differential gene expression profile was determined using GEM1 microarrays. CellSpace knowledgebase was used to perform functional assignments to 72>x2-regulated genes. This analysis indicated that Tbx2 might be involved in different fundamental cell functions. Tbx2 upregulates proliferation genes, downregulates tenascinC, and upregulates nidogen. In conclusion, together with Cx43 repression, Tbx2 may signal neural crest cells to stop migration and start proliferation. Gene cluster analysis also suggested a potential role for Tbx2 in osteogenesis. In accord, Tbx2 expression was detected in chondrocytes and osteocytes both in long bone and membranous bones.