Inhibition of β-Catenin signaling suppresses pancreatic tumor growth by disrupting nuclear β-Catenin/TCF-1 complex: Critical role of STAT-3

Aberrant activation of beta-catenin/TCF signaling is related to the invasiveness of pancreatic cancer. In the present study, we evaluated the effect of capsaicin on beta-catenin/TCF signaling. In a concentration and time-dependent study, we observed that capsaicin treatment inhibits the activation of dishevelled (Dsh) protein DvI-1 in L3.6PL, PanC-1 and MiaPaCa-2 pancreatic cancer cells. Capsaicin treatment induced GSK-3 beta by inhibiting its phosphorylation and further activated APC and Axin multicomplex, leading to the proteasomal degradation of beta-catenin. Expression of TCF-1 and beta-catenin-responsive proteins, c-Myc and cyclin D1 also decreased in response to capsaicin treatment. Pre-treatment of cells with MG-132 blocked capsaicin-mediated proteasomal degradation of beta-catenin. To establish the involvement of beta-catenin in capsaicin-induced apoptosis, cells were treated with LiCl or SB415286, inhibitors of GSK-3 beta. Our results reveal that capsaicin treatment suppressed LiCl or SB415286-mediated activation of beta-catenin signaling. Our results further showed that capsaicin blocked nuclear translocation of beta-catenin, TCF-1 and p-STAT-3 (Tyr705). The immunoprecipitation results indicated that capsaicin treatment reduced the interaction of beta-catenin and TCF-1 in the nucleus. Moreover, capsaicin treatment significantly decreased the phosphorylation of STAT-3 at Tyr705. Interestingly, STAT-3 over expression or STAT-3 activation by IL-6, significantly increased the levels of beta-catenin and attenuated the effects of capsaicin in inhibiting beta-catenin signaling. Finally, capsaicin mediated inhibition of orthotopic tumor growth was associated with inhibition of beta-catenin/TCF-1 signaling. Taken together, our results suggest that capsaicin-induced apoptosis in pancreatic cancer cells was associated with inhibition of beta-catenin signaling due to the dissociation of beta-catenin/TCF-1 complex and the process was orchestrated by STAT-3.