Abstract 3501: Puma/pBcl-2 axis influences sensitivity of cancer cells to multiple stimuli

Abstract

Abstract Bcl-2 is a central regulator of cell survival that is overexpressed in the majority of cancers cells.Previous reports indicated that Bcl-2 phosphorylation (S70) may provide a switch by which cellscan regulate the pro-survival functions of Bcl-2. But there is still controversy over the function of phosphorylatedBcl-2 (pBcl-2).In the presentstudy, Puma/pBcl-2 axis was found to play a key role in regulating the sensitivity of cancer cells to multiple stimuli.Based on immunoprecipitation, weobserved that the pro-apoptoticBH3-only protein Puma which was induced by paclitaxel competitively bound pBcl-2 (S70) and displaced Bim and Bax from pBcl-2(S70) in Hela and HL60 cells.Further study showed thatdepletion of Puma (siRNA), but not other BH3 only proteins, significantlydecreased paclitaxel-induced apoptosis.Bim/pBcl-2 and Bax/pBcl-2 complexeswere largely maintained when Pumawas reduced. These data indicated that the phosphorylation of Bcl-2(S70) enhancedits anti-apoptotic function and the induction of Puma could neutralize this effect. Similarly,the induced Puma was also responsible for Bim and Bax displacement from pBcl-2 (S70) when Hela and HL60 cellswere treated with DNA damage agents(cisplatin and etoposide).However, Pumacannot displace Bax or Bim when pBcl-2 (S70) was redundant in the cells expressedphospho-mimetic S70E-Bcl-2. It demonstrated that DNA damage induced apoptosis could be inhibit by pBcl-2 (S70) and the induction of Puma could antagonize pBcl-2 (S70). In a cell free system, mitochondria from Hela and HL60 cells which expressing the S70E-Bcl-2 wereincubated with different BH3 peptides. Cytochrome c release couldbe induced by a low concentration of Puma-BH3 peptide, but a higher concentrationwas necessary during Bimengagement.By contrast, Bad-BH3 and Noxa-BH3cannot initiate the release of cytochrome c.In conclusion, multiple stimuli activates the mitochondrial apoptoticpathway in cancer cells, in which Puma/pBcl-2(S70) axisplay a key role in a novel mechanism involving the displacement of Bim and Bax from pBcl-2 (S70)by Puma. In contrast with the debatable function of Bcl-2 phosphorylation (S70), this study provided evidence that the phosphorylation of Bcl-2 at S70 enhanced cell survivalin multiplestimuli triggered apoptosis. Citation Format: Yubo Liu. Puma/pBcl-2 axis influences sensitivity of cancer cells to multiple stimuli. [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 3501.