Evidence against the regulation of caldesmon inhibitory activity by p42/p44(erk) mitogen-activated protein kinase in vitro and demonstration of another caldesmon kinase in intact gizaard smooth muscle

p44(erk1) mitogen-activated protein kinase on the inhibitory activity of ca ldesmon and its C-terminal fragment H1,vas studied in vitro. Neither inhibi tion of actin-tropomyosin activated;ATPase of heavy meromyosin by caldesmon or H1, nor inhibition of the actin-tropomyosin motility over heavy meromyo sin by H1 aas significantly affected by the phosphorylation while only a mo derate effect on the actin-activated component of heavy meromyosin ATPase i nhibition was observed. Phosphopeptide mapping of caldesmon immunoprecipita ted from [ P-32]PO4-labelled intact gizzard strips revealed that it is pred ominantly phosphorylated at mitogen-activated protein kinase sites in unsti mulated tissue and that it is stimulated for 1 h with phorbol 12,13-dibutyr ate. We find that phorbol 12,13-dibutyrate also induces a transitory phosph orylation of caldesmon peaking at 15 min after addition and this phosphoryl ation is not attributed to mitogen-activated protein kinase, protein kinase C, Ca(/)(2+)calmodulin-dependent kinase II or casein kinase II. We suggest that a yet unidentified kinase, rather than mitogen-activated protein I;ki nase, may be involved in regulation of the caldesmon function in vivo. (C) 1999 Federation of European Biochemical Societies. The effect of direct pho sphorylation by recombinant.