Abstract 2907: AMPK induction, lysosomal acidification and melanoma survival increased by p53 dysfunction are counteracted by inhibiting autophagy

BACKGROUND. In contrast to the majority of human tumors which harbour p53 mutations, melanomas preferentially have BRAF V600E or NRAS(Q61K) mutations accompanied by dysfunction of the p53 tumor suppressor gene, which may help progression from nevi to invasive melanoma. Although ultraviolet radiation accelerates BRAF-driven melanomagenesis by targeting TP53 (Viros A. et al, Nature. 2014;511:478-82), some evidences for an anomalous wt p53 response to radiation in melanomas are a dysfunctional pro-apoptotic DNA damage response which can be enhanced by radiation sensitizers like halogenated pyrimidines (Rieber M, Rieber MS.Cancer Biol Ther. 2008;7:1561-6), and a report that p53 knockdown in melanoma cells resulted in decreased proliferation (Avery-Kiejda KA1, Bowden NA, Croft AJ, Scurr LL, Kairupan CF, Ashton KA, Talseth-Palmer BA, Rizos H, Zhang XD, Scott RJ, Hersey P.BMC Cancer. 2011;11:203) .PURPOSE. Since activation of AMPK by AMP inhibits ATP-consuming metabolic pathways during metabolic stress which may cause autophagy, we investigated the possible role of melanoma p53 status in modulating response to AMPK activators and autophagy inhibitors, in physiological 5mM glucose. EXPERIMENTAL. Genetically-matched NRAS-mutant human melanoma cells with unequal p53 mutational status were exposed to different glucose levels in the presence of AMPK inducers including autophagy modulators. Formation of autophagic vesicles were quantitated by cytometric red/gree acridine orange fluorescence Apoptosis-associated PARP cleavage was studied by specific immune blotting. RESULTS. AMPK induction in response to AICAR was greater than that of metformin and was increased in mutant p53 cells, which also showed greater resistance to autophagy inhibition. Greater AMPK activation correlated with increased lysosomal acidification in mutant p53 cells. CONCLUSIONS. Our results identify a role for a) p53 dysfunction in enhancing the response to AMPK activators and autophagy to favour tumor cell survival, b) autophagy inhibitors in counteracting pro-survival AMPK signaling. Citation Format: Valery Chavez-Perez, Mary Strasberg-Rieber, Manuel Rieber. AMPK induction, lysosomal acidification and melanoma survival increased by p53 dysfunction are counteracted by inhibiting autophagy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2907. d