Graduate Defense: Madhuri Nandakumar

Thesis Information

Title: Role Of Hif1α In Osm-Induced Vegf

Program: Master of Science in Biology

Advisor: Dr. Cheryl Jorcyk, Biological Sciences

Committee Members: Dr. Julia Oxford, Biological Sciences and Dr. Allan Albig, Biological Sciences

Abstract

Vascular endothelial growth factor (VEGF) is a chemical signal produced by cells that stimulates angiogenesis. VEGF activation can be induced by hypoxic and non-hypoxic means in the presence of various cytokines. Oncostatin M (OSM) is an interleukin-6 (IL-6) family cytokine that has been shown to induce expression of vascular endothelial growth factor (VEGF) in astroglioma, hepatocellular and breast carcinoma. Under hypoxic conditions, VEGF expression is known to be dependent on the transcription factor hypoxia-inducible factor 1 alpha (HIF1α). The oxygen sensitive HIF1α subunit can also be induced in a non-hypoxic manner in the presence of cytokines that include OSM, IL6 and LIF which belong to the interleukin 6 (IL6) family. In order to understand the molecular mechanisms involved in OSM induced VEGF and elucidate the role played by OSM induced HIF1α, VEGF promoter – luciferase reporter studies were conducted on triple negative MDA-MB 231’s and luminal T47D breast cancer cell lines. The VEGF promoter studies revealed that while HIF1 and AP1 response element did not play a role on OSM induced VEGF promoter activity in the MDA-MB-231’s, mutating these sites brought down VEGF promoter activity in the T47D’s suggesting their significant role in this cell line. It was also observed that mutating the STAT3 response element on the promoter did not decrease VEGF expression levels in the cell lines used. Contrarily, evidence in the form of siRNA studies from the Jorcyk lab reveal the importance of STAT3 in OSM induced VEGF in both the triple negative MBA-MB-231 and the luminal T47D subtype. This highlights the presence of breast cancer subtype-specific differences in signaling mechanisms leading to VEGF secretion. Probing further into these differences could lead to targeted cancer therapies in the future. In addition, a study was undertaken to establish an alternate mechanism of OSM induced HIF1 α through JNK1 induced HSP90 via HDAC6 modulation. It was observed that OSM induced HSP90 in both MDA-MB-231 and T47D breast cancer cell lines but independently of JNK1 or HDAC6. A comparative study on changes in HSP90-lysine acetylation levels using two different exposures – OSM and a hypoxia chamber showed no significant differences at early time points in the triple negative MDA-MB-231’s. OSM treatment at late time points also did not change HDAC6 levels in these cells. These experiments collectively indicate that there was no evidence that HSP90 stabilized HIF1α via JNK1 and HDAC6 in the breast cancer cell lines used in the study undertaken. This also suggests the presence of other post translational modifications stabilizing HSP90 which could in turn effect HIF1α stability. Taken together this research suggests that HIF1α could be playing a direct role in OSM induced VEGF in a breast cancer subtype specific manner and that OSM induced HIF1α may not be regulated by JNK1 or HDAC6 in the both cell lines studied.