Cell-cycle arrest by PD184352 requires inhibition of extracellular signal-regulated kinases (ERK) 1/2 but not ERK5/BMK1

摘要

Serum and growth factors activate both the canonical extracellular signal-regulated kinase (ERK) 1/2 pathway and the ERK5/big mitogen-activated protein kinase 1 (BMK) 1 pathway. Pharmacological inhibition of the ERK1/2 pathway using PD98059 and U0126 prevents cyclin D1 expression and inhibits cell proliferation, arguing that the ERK1/2 pathway is rate limiting for cell-cycle re-entry. However, both PD98059 and U0126 also inhibit the ERK5/BMK1 pathway, raising the possibility that the anti-proliferative effect of such drugs may be due to inhibition of ERK5 or both pathways. Here we characterize the effect of the novel mitogen-activated protein kinase/ ERK kinase (MEK) inhibitor, PD184352, on the ERK1/2 and ERK5 pathways in the Chinese hamster fibroblast cell line CC139. In quiescent cells, serum-stimulated ERK1 activity was completely inhibited by PD184352 with an IC50 below 1 muM, whereas ERK5 activation was unaffected even at 20 muM. Serum-stimulated DNA synthesis and cyclin D I expression was inhibited by low doses of PD184352, which abolished ERK1 activity but had no effect on ERK5. Similarly, in cycling cells PD184352 caused a dose-dependent G, arrest and inhibition of cyclin D1 expression at low doses, which inhibited ERK1 but were without effect on ERK5. These results indicate that the antiproliferative effect of PD184352 is due to inhibition of the classical ERK1/2 pathway and does not require inhibition of the ERK5 pathway.