Protein kinase Cα inhibitor enhances the sensitivity of human pancreatic cancer HPAC cells to Clostridium perfringens enterotoxin via claudin-4

Protein kinase C (PKC) is overexpressed in cancer, including pancreatic cancer, compared with normal tissue. Moreover, PKC alpha is considered one of the biomarkers for the diagnosis of cancers. In several human cancers, the claudin tight junction molecules are abnormally regulated and are thus promising molecular targets for diagnosis and therapy with Clostridium perfringens enterotoxin (CPE). In order to investigate the changes of tight junction functions of claudins via PKC alpha activation in pancreatic cancer cells, the well-differentiated human pancreatic cancer cell line HPAC, with its highly expressed tight junction molecules and well-developed barrier function, was treated with the PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA). Treatment with TPA modified the activity of phosphoPKC alpha and caused an increase of the Snail family members Snail, Slug and Smad-interacting protein 1 and a decrease of E-cadherin. In HPAC cells treated with TPA, downregulation of claudin-1 and mislocalization of claudin-4 and occludin around the nuclei were observed, together with a decrease in the numbers of tight junction strands and an increase in phosphorylation of claudin-4. The barrier function and the cytotoxicity of CPE were significantly decreased on TPA treatment. All such changes after TPA treatment were prevented by inhibitors of panPKC and PKC alpha. These findings suggest that, in human pancreatic cancer cells, PKC alpha activation downregulates tight junction functions as a barrier and as a receptor of CPE via the modification of claudin-1 and -4 during epithelial to mesenchymal transition-like changes. PKC alpha inhibitors might represent potential therapeutic agents against human pancreatic cancer cells by use of CPE cytotoxicity via claudin-4.