PPARγ is a key target of butyrate-induced caspase-3 activation in the colorectal cancer cell line Caco-2

Abstract

Background: Butyrate, a potent histone deacetylase inhibitor, belongs to a promising new class of antineoplastic agents with the capacity to induce apoptosis of cancer cells. However, the underlying mechanisms of action have yet not been elucidated. Aim: To further investigate the molecular events involved in butyrate-induced caspase-3 activation in Caco-2 wild-type, empty-vector and dominant-negative PPARγ mutant cells along the signalling pathway. In this context, the involvement and up-regulation of PPARγ was examined. Results: Stimulation of cells with butyrate resulted in increased expression of PPARγ mRNA, protein, and activity as well as phospho-p38 MAPK protein expression and caspase-3 activity. Arsenite, a direct stimulator of p38 MAPK, also led to an increased PPARγ expression, thereby mimicking the effects of butyrate. In contrast, butyrate-mediated up-regulation of PPARγ was counteracted by co-incubation with the p38 MAPK inhibitor SB203580. Treatment of cells with butyrate resulted in both increased caspase-8 and -9 activity and reduced expression of XIAP and survivin. However, butyrate-mediated effects on these apoptosis-regulatory proteins leading to caspase-3 activation were almost completely abolished in Caco-2 dominant-negative PPARγ mutant cells. Conclusions: Our data clearly unveil PPARγ as a key target in the butyrate-induced signalling cascade leading to apoptosis via caspase-3 in Caco-2 cells.