Possible mechanism of chemo-resistance under hypoxia and the effect of expressed ASC on hypoxia-mediated cell death in pancreatic cancer

LB-49 We previously demonstrated that an apoptosis-associated speck-like protein, ASC, can regulate p53-mediated chemosensitivity and TNF-α-induced apoptosis (Nature Cell Biol 2004, Oncogene 2006). We also showed the preliminary data that ASC is inducible by hypoxia, and regulates hypoxia-mediated cell death (AACR 2006). Others have demonstrated that hypoxia causes chemo-resistance and accelerates the tumor progression, invasiveness, and metastasis in pancreatic cancer, and thus, one of the reasons for the poor prognosis of pancreatic cancer is considered to be a hypoxic circumstance due to its hypovascularity. In this study, we investigated more detailed roles of ASC under hypoxia- mediated cell death using pancreatic cancer cells. ASC expression was preserved in 5 of 7 pancreatic cancer cell lines (71%). Among them, PK-1 was suitable for our experiment because expressions of ASC, wild-type p53, hypoxia-inducible factor (HIF)-1α, and other apoptosis-related genes were well preserved. ASC induction under 1% hypoxic condition was HIF1α-dependent but p53-independent. Two representative chemotherapeutic agents for pancreatic cancer, 5-FU and Gemcitabine, promoted cell death of PK-1 with p53-dependent manner; however, 1% hypoxia caused chemo-resistance to these drugs. Western blot of this condition showed that a pro-apoptotic gene, Bax, decreased and anti-apoptotic genes, IAP-2 and survivin, increased under hypoxia. These results suggest that although hypoxia induces both pro-apoptotic (ASC induction) and anti-apoptotic condition (Bax repression, and IAP-2 and survivn inductions), total balance seemed to be anti-apoptotic dominant, which might be explanation for chemo-resistance. To overcome this anti-apoptotic dominant condition, adenovirus expressing ASC were infected into PK-1 cells. Expressed ASC induced cell death even under the 20% normoxia, and hypoxia enhanced such ASC-mediated cell death. Our data demonstrate the possible mechanism of chemo-resistance under hypoxia in pancreatic cancer cells, and suggest that ASC might become a new treatment strategy for pancreatic cancer.