CLDN18 and pancreatic neoplasm: The upregulation of claudin-18 by TPA in human pancreatic cancer cell lines can be prevented by inhibitors of PKCδ, PKCε, and PKCα, whereas the upregulation of claudin-18 by TPA in hTERT-HPDE cells is prevented by inhibitors of PKCδ, PKCθ, and PKCα.