p42 MAPK phosphorylates 80 kDa MARCKS at Ser-113.

It is demonstrated here that p42 MAPKinase (p42 MAPK) phosphorylates the 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 MARCKS become phosphorylated and not Ser-113. The mitogen platelet-derived growth factor (PDGF) elicits the same response. These results demonstrate that while Ser-113 is a substrate for p42 MAPK in vitro and can be phosphorylated in vivo as shown by Taniguchi et al. [(1994) J. Biol. Chem. 269, 18299-18302], its phosphorylation is not subject to acute regulation by p42 MAPK in Swiss 3T3 cells.