12-Lipoxygenase metabolite 12(S)-HETE stimulates human pancreatic cancer cell proliferation via protein tyrosine phosphorylation and ERK activation

We previously reported that inhibition of the 12-lipoxygenase pathway abolished proliferation and induced apoptosis in several pancreatic cancer cell lines. Furthermore, the 12-lipoxygenase product 12(S)-HETE stimulated pancreatic cancer cell proliferation and reversed 12-lipoxygenase inhibitor-induced growth inhibition. We investigated the underlying mechanism for 12(S)-HETE-induced pancreatic cancer cell proliferation, using 2 human pancreatic cancer cell lines, PANC-I and HPAF. Cell proliferation was monitored by both thymidine incorporation and cell number. Western blotting was used to investigate the effect of 12(S)-HETE on cellular protein tyrosine phosphorylation as well as ERK, P38 MAPK and JNK/SAPK phosphorylation. 12(S)-HETE markedly stimulated proliferation of pancreatic cancer cells in a time- and concentration-dependent manner. In parallel, 12(S)-HETE induced tyrosine phosphorylation of multiple cellular proteins, while inhibition of tyrosine kinase by genestein abolished 12(S)-HETE-induced proliferation, indicating that intracellular protein tyrosine kinase activation is involved in the mitogenic effects of 12(S)-HETE. Following treatment with 12(S)-HETE, both ERK and P38 MAPK, but not JNK/SAPK, were phosphorylated. The specific MEK inhibitors PD098059 and U0126, which in turn suppress ERK, abolished 12(S)-HETE-stimulated proliferation. In contrast, inhibition of P38 MAPK with SB203580 did not affect 12(S)-HETE-stimulated pancreatic cancer cell proliferation. Furthermore, 12(S)-HETE-stimulated ERK phosphorylation was inhibited by genestein, indicating that tyrosine phosphorylation is essential for ERK activation. These findings suggest that both ERK and cellular protein tyrosine kinase activation are involved in 12(S)-HETE-induced pancreatic cancer cell proliferation but P38 and JNK/SAPK are not involved in this mitogenic effect.