Extracellular regulated kinase (ERK) interaction with actin and the calponin homology (CH) domain of actin-binding proteins

An interaction between extracellular regulated kinase 1 (ERK1) and calponin has previously been reported (Menice, Hulvershorn, Adam, Wang and Morgan ( 1997) J. Biol. Chem. 272 (40), 25157-25161) and has been suggested to refle ct a function of calponin as a signalling molecule. We report in this study that calponin binds to both ERK1 and ERK2 under native conditions as well as in an overlay assay. Using chymotryptic fragments of calponin, the bindi ng site of ERK on calponin was identified as the calponin homology (CH) dom ain, an N-terminal region of calponin found in other actin-binding proteins . ERK also bound, in a gel overlay assay, alpha-actinin, a protein with two tandem CH domains, as well as a 27 kDa thermolysin product of alpha-actini n containing the CH domains of alpha-actinin. The CH domain of calponin cou ld compete with intact calponin or alpha-actinin for ERK binding. Titration of acrylodan-labelled calponin with ERK gave a K-a of 6 x 10(6) M-1 and ti tration of acrylodan-labelled calponin with a peptide from the alpha L16 he lix of ERK gave a K-a of 1 x 10(6) M-1. Recombinant ERK was found to co-sed iment with purified actin and induced a fluorescence change in pyrene-label led F-actin (K-a = 5 x 10(6) M-1). The interaction of ERK with CH domains p oints to a new potential function for CH domains. The interaction of ERK wi th actin raises the possibility that actin may provide a scaffold for ERK s ignalling complexes in both muscle and non-muscle cells.