CBP-Mediated FOXO-1 Acetylation Inhibits Pancreatic Tumor Growth by Targeting SirT

Here we investigated the potential mechanism of capsaicin-mediated apoptosis in pancreatic cancer cells. Capsaicin treatment phosphorylated JNK, FOXO1 and BIM in BxPC-3, AsPC-1 and L3.6PL cells. The expression of BIM increased in response to capsaicin treatment. Capsaicin treatment caused cleavage of caspase-3and PARP indicating apoptosis. Antioxidants tiron and PEG-catalase blocked capsaicin-mediated JNK/FOXO/BIM activation and protected the cells from apoptosis. Furthermore, capsaicin treatment caused a steady increase in the nuclear expression of FOXO-1 leading to increased DNA binding. Capsaicin-mediated expression of BIM was found to be directly dependent on the acetylation of FOXO-1. The expression of CBP was increased whereas SirT-1was reduced by capsaicin treatment. Using acetylation mimic or defective mutants, our result demonstrated that phosphorylation of FOXO-1 was mediated through acetylation by capsaicin treatment. JNK inhibitor attenuated the phosphorylation of FOXO-1, activation of BIM and abrogated capsaicin-induced apoptosis. Moreover, silencing FOXO1 by siRNA blocked capsaicin-mediated activation of BIM and apoptosis whereas overexpression of FOXO-1augmented its effects. Silencing Bim drastically reduced capsaicin-mediated cleavage of caspase-3 and PARP, indicating the role of BIM in apoptosis. Oral administration of 5mg/kg capsaicin substantially suppressed the growth of BxPC-3 tumor xenografts in athymic nude mice. Tumors from capsaicin-treated mice showed an increase in the phosphorylation of JNK, FOXO-1, BIM, and levels of CBP, cleavage of caspase-3, PARP and decreased SirT-1 expression. Taken together, our results suggest that capsaicin activated JNK and FOXO-1, leading to the acetylation of FOXO-1 through CBP and SirT-1. Acetylated FOXO1 induced apoptosis in pancreatic cancer cells through BIM activation.