MEK/ERK signaling pathway regulates the expression of Bcl-2, Bcl-X(L), and Mcl-1 and promotes survival of human pancreatic cancer cells.

Growth factors are well known for their participation in the regulation of cell proliferation and survival. However, the intracellular signaling pathways by which growth factors promote survival are still poorly understood. In the present study, using the MIA PaCa-2 cell line, a well-established model of pancreatic cancer cells, we analyzed the roles of ERK1/2 activities in the regulation of cell survival and investigated some of the mechanisms involved. The ability of the MEK inhibitor PD98059 to modulate survival of the MIA PaCa-2 cells was evaluated, and the responses were correlated with expression of Bcl-2 homologs and caspases 1, 3, 6, 8, and 9 activities. Herein, we showed that inhibition of ERK1/2 activities caused (1) a G1 arrest; (2) a down-regulation of the expression levels of the anti-apoptotic homologs Bcl-2, Mcl-1, and Bcl-X(L) without affecting the pro-apoptotic levels of Bax and Bak; (3) a promotion of caspases 3, 6, 8, and 9 activities; (4) a stimulation of PARP cleavage; and (5) a programmed cell death by apoptosis. Our data suggest that activation of the ERK pathway functions to protect pancreatic tumor cells from apoptosis as well as to regulate their progression in the cell cycle.