Doctor of Philosophy (Ph.D.)
Degree Granting Department
Biology (Cell Biology, Microbiology, Molecular Biology)
Meera Nanjundan, Ph.D.
Patrick Bradshaw, Ph.D.
Younghoon Kee, Ph.D.
Sandy Westerheide, Ph.D.
cancer, Chemotherapeutics, EVI1, lipid droplets, miR-494, SnoN/SkiL
Genomic aberrations are primary contributors to the pathophysiology of cancer . Dysregulated expression of genes located within these aberrations are important predictors of chemoresistance, disease prognosis, and patient outcome . This dissertation is focused on understanding the regulation and/or functions of specific genes located at dysregulated genomic regions such as 3q26 and 14q32 in the biology of ovarian and renal cancer, respectively.
Serous epithelial ovarian cancer (EOC) manifest amplification at the 3q26.2 locus , an observation consistent with the cancer genome atlas (TCGA) . The most amplified gene in this region is EVI1 which has been extensively studied in hematological malignancies . However, its contribution to the pathophysiology of solid cancers remains unknown. We hypothesized that dysregulated EVI1 and SnoN/SkiL expression (located at the 3q26.2 amplicon) leads to the altered cellular functional response, thereby contributing to the pathophysiology of ovarian cancer. Our group has previously shown that EVI1 splice forms may exhibit altered subcellular localization and functional properties relative to the wild type form . In Chapter 3 of this dissertation, we identified that EVI1 splice forms could modulate epithelial-mesenchymal transition. Our findings indicate that siRNA construct targeting the splice junction between exon 2 of MDS1 to exon 2 of EVI1, (reduces the expression of MDS1/EVI1 and EVI1Del190-515 splice forms) increases epithelial cell markers while decreasing mesenchymal markers and reducing migratory potential of ovarian and breast cancer cells.
SnoN/SkiL, another gene overexpressed at the 3q26 is reported by our group to be induced upon As2O3 treatment in ovarian cancer cells via unknown mechanisms . This induction of SnoN opposes the apoptotic cell death pathway induced by the drug treatment . We have previously identified that the PI3K/AKT pathway (also dysregulated in ovarian cancer ) contributes to the up-regulation of SnoN upon treatment with As2O3 . However, SnoN is regulated via multiple mechanisms including post-translational modifications . Additionally, c-Ski (a homolog of SnoN) is regulated post-transcriptionally by numerous miRNAs in cancer cells [19-22]. In Chapter 4, we attempted to identify potential miRNAs that could regulate SnoN expression post-transcriptionally. We discovered that miR-494 reduces both SnoN mRNA and protein levels. Our experimental outcomes also demonstrate that miR-494 further sensitizes ovarian cancer cells to drug treatment.
Interestingly, miR-494 is located at the 14q32 region which has been shown to be down-regulated in renal cancers . Several reports indicate miR-494 to be involved in tumor suppressive responses including apoptosis and cell cycle arrest in various cancers [24-26]. However, its role in renal cancer biology remains unknown. We hypothesized that miR-494 elicits a tumor suppressive response in renal cancer cells. Through our studies in Chapter 5, we demonstrate that miR-494 reduces cell viability and increases apoptotic response in renal cancer cells. We also show that miR-494 increases LC3B mRNA and protein levels. A 3’UTR luciferase assay indicated that LC3B may be a potential target of miR-494. Intracellular lipid droplets (LDs) increased in miR-494 expressing in a LC3B-dependent manner. This was accompanied with reduced intracellular cholesterol content, increased mitochondrial structural disorganization, and altered Drp1 localization.
The outcome of our findings have improved our understanding of the regulation and functional response of these genes/miRNAs (EVI1, SnoN, and miR-494) in ovarian and renal cancers. The studies reported in Chapter 5 identified a novel function of miR-494 in increasing LDs and reducing renal cell survival. However, additional studies are warranted to fully understand the underlying mechanism of increased LDs formation in miR-494 expressing cells and the implication of miR-494 and other miRNAs at the 14q32 region in renal cancer biology. In future, these studies will aid in the development of better treatment strategies which will contribute towards the management of cancer.
Scholar Commons Citation
Dutta, Punashi, "Genomic Aberrations at the 3q and 14q loci: Investigation of Key Players in Ovarian and Renal Cancer Biology" (2015). Graduate Theses and Dissertations.