MEKK1 interacts with alpha-actinin and localizes to stress fibers and focal adhesions

Mitogen-activated protein (MAP) kinases orchestrate the effects of many ext racellular stimuli on cells. The serine/threonine protein kinase MEKK1 is a n upstream activator of the MAP kinases c-Jun N-terminal kinase/stress-acti vated protein kinase (JNK/SAPK), extracellular signal-regulated kinase (ERK ), and p38 as well as NF-kappa B. In a yeast two-hybrid interaction screen to identify proteins that bind to an N-terminal fragment of MEKK1 (amino ac ids 1-719), the actin-crosslinking protein ol-actinin was identified as a M EKK1-binding protein. Over-expressed MEKK1 co-immunoprecipitated with alpha -actinin in cell lysates. Both endogenous and over-expressed MEKK1 colocali zed with a-actinin along actin stress fibers and at focal adhesions. Residu es 221-559 of MEKK1 bound to purified cr-actinin in vitro, indicating that the interaction is direct, and this fragment localized to actin filaments i n cells. MEKK1 kinase activity was not required for association with actin filaments, because a catalytically inactive mutant of MEKK1 (MEKK1 D1369A) localized to stress fibers. These results provide strong evidence for the i nteraction between MEKK1 and alpha-actinin. Thus, restriction of the kinase to the actin cytoskeleton may serve to regulate its specificity towards do wnstream targets. Cell Motil. Cytoskeleton 43:186-198, 1999. (C) 1999 Wiley -Liss, Inc.