Depletion of pro-oncogenic RUNX2 enhances gemcitabine (GEM) sensitivity of p53 -mutated pancreatic cancer Panc-1 cells through the induction of pro-apoptotic TAp63

// Toshinori Ozaki 1 , Mizuyo Nakamura 1 , Takehiro Ogata 1 , Meijie Sang 1, 2 , Hiroyuki Yoda 3 , Kiriko Hiraoka 3 , Meixiang Sang 1, 4 , Osamu Shimozato 1 1 Laboratory of DNA Damage Signaling, Chiba Cancer Center Research Institute, Chiba, Japan 2 Department of Regenerative Medicine, Graduate School of Medicine and Pharmatheutical Science, University of Toyama, Toyama, Japan 3 Laboratory of Cancer Genetics, Chiba Cancer Center Research Institute, Chiba, Japan 4 Research Center, Fourth Hospital of Hebei Medical University, Shijiazhuang, China Correspondence to: Toshinori Ozaki, email: tozaki@chiba-cc.jp Keywords: gemcitabine, mutant p53, pancreatic cancer, RUNX2, TAp63 Received: February 16, 2016      Accepted: September 25, 2016      Published: October 04, 2016 ABSTRACT Recently, we have described that siRNA-mediated silencing of runt-related transcription factor 2 (RUNX2) improves anti-cancer drug gemcitabine (GEM) sensitivity of p53 -deficient human pancreatic cancer AsPC-1 cells through the augmentation of p53 family TAp63-dependent cell death pathway. In this manuscript, we have extended our study to p53 -mutated human pancreatic cancer Panc-1 cells. According to our present results, knockdown of mutant p53 alone had a marginal effect on GEM-mediated cell death of Panc-1 cells. We then sought to deplete RUNX2 using siRNA in Panc-1 cells and examined its effect on GEM sensitivity. Under our experimental conditions, RUNX2 knockdown caused a significant enhancement of GEM sensitivity of Panc-1 cells. Notably, GEM-mediated induction of TAp63 but not of TAp73 was further stimulated in RUNX2 -depleted Panc-1 cells, indicating that, like AsPC-1 cells, TAp63 might play a pivotal role in the regulation of GEM sensitivity of Panc-1 cells. Consistent with this notion, forced expression of TAp63α in Panc-1 cells promoted cell cycle arrest and/or cell death, and massively increased luciferase activities driven by TAp63-target gene promoters such as p21 WAF1 and NOXA . In addition, immunoprecipitation experiments indicated that RUNX2 forms a complex with TAp63 in Panc-1 cells. Taken together, our current observations strongly suggest that depletion of RUNX2 enhances the cytotoxic effect of GEM on p53 -mutated Panc-1 cells through the stimulation of TAp63-dependent cell death pathway even in the presence of a large amount of pro-oncogenic mutant p53, and might provide an attractive strategy to treat pancreatic cancer patients with p53 mutations.