MEK kinase 2 binds and activates protein kinase C-related kinase 2 - Bifurcation of kinase regulatory pathways at the level of an MAPK kinase kinase

MEK kinase 2 (MEKK2) is a 70-kDa protein serine/threonine kinase that has b een shown to function as a mitogen-activated protein kinase (MAPK) kinase k inase, MEKK2 has its kinase domain in the COOH-terminal moiety of the prote in. The NH,-terminal moiety of MEKK2 has no signature motif that would sugg est a defined regulatory function. Yeast two-hybrid screening was performed to identify proteins that bind MEKK2. Protein kinase C-related kinase 2 (P RK2) was found to bind MEKK2; PRK2 has been previously shown to bind RhoA a nd the Src homology 3 domain of Nck, PRK2 did not bind MEKK3, which is clos ely related to MEKK2. The MEKK2 binding site maps to amino acids 637-660 in PRK2, which is distinct from the binding sites for RhoA and Nck. This sequ ence is divergent in the closely related kinase PRK1, which did not bind ME KK2. In cells, MEKK2 and PRK2 are co-immunoprecipitated and PRK2 is activat ed by MEKK2, Similarly, purified recombinant MEKK2 activated PRK2 in vitro. MEKK2 activation of PRK2 is independent of MEKK2 regulation of the c-Jun N H,-terminal kinase pathway. MEKK2 activation of PRK2 results in a bifurcati on of signaling for the dual control of MAPK pathways and PRK2 regulated re sponses.