Direct Kinase Assay Screening for Inhibitors of MAP Kinase

An important convergence point involved in the signal transduction pathways of many different growth factors, hormones, and cytokines are the p42 and p44 serine/ threonine kinases called either MAP kinases (mitogen-activate protein kinases) or ERK 1 and ERK 2 (extracellular regulated kinases) (2 -4 ). MAP kinases are activated in cells upon stimulation with growth factors (e.g., insulin, platelet derived growth factor, epidermal growth factor) (5 -7 ), tumor promoters (e.g., phorbol 12-myristate 13-acetate) (8 ), antigen binding to T-cell receptors, and infection of cells by Salmonella sp. MAP kinase is also involved in cell-cycle control and becomes activated during M-phase of the cell cycle (9 ). As such, MAP kinase is of great interest in cancer studies including ovarian cancer. Studies on MAP kinase activation and regulation will lead to an improved understanding of intracellular signal transduction and involvement of this enzyme in key signaling process. It is therefore important to know how anticancer drugs if at all act on this kinase. MAP kinase is activated by sequential phosphorylation on both tyrosine and threonine residues by either the dual tyrosine/threonine kinase MEK (MAPK kinase) alone or by MEK in conjunction with an as yet undescribed kinase (2 ). The serine/threonine kinases RAF and MEKK (MAPK kinase kinase) phosphorylate and activate MEK, in turn, during intracellular signaling (6 ). Activation of MAPK is directly regulated by a specific MAPK phosphatase and indirectly regulated by protein kinase A activation, which results in inhibition of RAF activity in Mammalian cells (11 ).