P42 MAPK PHOSPHORYLATES 80 KDA MARCKS AT SER-113

It is demonstrated here that p42 MAPKinase (p42 MAPK) phosphorylates t he Myristoylated Alanine-Rich C-Kinase Substrate (MARCKS) at Ser-113. In permeabilised Swiss 3T3 cells activation of protein kinase C (PKC) leads to p42 MAPK activation, but only the protein kinase C sites in M ARCKS become phosphorylated and not Ser-113. The mitogen platelet-deri ved growth factor (PDGF) elicits the same response. These results demo nstrate that while Ser-113 is a substrate for p42 MAPK in vitro and ca n be phosphorylated in vivo as shown by Taniguchi et al. [(1994) J. Bi ol, Chem, 269, 18299-18302], its phosphorylation is not subject to acu te regulation by p42 MAPK in Swiss 3T3 cells.