Abstract 1860: MDM2 stabilizes and induces HIF-1α levels during reoxygenation of cancer cells

Abstract

Abstract Hypoxia stimulates several pathways that are critical to cancer cell growth and survival, including activation of vascular endothelial growth factor (VEGF) transcription. Overexpression of VEGF and the extent of neo-angiogenesis are closely correlated with increase in tumor size and cancer metastases. The main regulator of hypoxia-induced angiogenesis is the hypoxia inducible factor (HIF)-1α which regulates the transcription of various target genes including VEGF. Stabilization of HIF-1α in cancer cells could enable tumor progression and results in poor survival. In this respect, the multifunctional mouse double minute 2 homolog (MDM2) oncoprotein has been gaining significant amount of attention. The MDM2 oncoprotein has been shown to exert both p53-dependent and p53-independent roles in oncogenesis. It is also well established that MDM2 gene amplification can occur in diverse human malignancies that include soft tissue sarcomas, neuroblastoma, cancers of the brain, breast, ovary, cervix, lung, colon, prostate, and bone. Mechanisms underlying induction and stabilization of HIF-1α in normoxic conditions are less clearly understood. Our present data indicated that the normoxic expression level of HIF-1α was significantly higher (p<0.0001) in LNCaP-MST as compared with LNCaP cells. When we treated the cells with the MDM2 inhibitor nutlin-3, the levels of HIF-1α was significantly down regulated. These results were further correlated with the differences in subcellular compartmentalization and degradation of HIF-1α. Findings from our lab shows the degradation rate of HIF-1α protein in both the nuclear and cytoplasmic compartments of LNCaP (non-transfected) and LNCaP-MST (MDM2 transfected) cells. In LNCaP cells, the degradation of HIF-1α protein occurs within 8 min in cytoplasmic (99%) and 10 min in nuclear compartments (75%). Whereas, in LNCaP-MST cells, the degradation rate of HIF-1α protein was slower even at 10 min of reoxygenation in both cytoplasmic (70%) and nuclear compartment (40%). Our results suggest that, MDM2 could play the role of master regulator in stabilizing HIF-1α even after reoxygenation. Further studies in this direction will shed more light on the in-depth mechanisms involved in the regulation of HIF-1α in MDM2 positive cancers. (This project was supported by The Royal Dames of Cancer Research Inc., Ft. Lauderdale, Florida). Citation Format: Thanigaivelan Kanagasabai, Rohin Chand, AmyAman Kaur, Sivanesan Dhandayuthapani, Olena Bracho, Appu Rathinavelu. MDM2 stabilizes and induces HIF-1α levels during reoxygenation of cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1860.