INHIBITION OF MAPK PATHWAY BY A SYNTHETIC PEPTIDE CORRESPONDING TO THE ACTIVATION SEGMENT OF MAPK

Mitogen-activated protein kinase (MAPK) is activated by phosphorylatio n within its activation segment. Upon phosphorylation, the activation segment refolds to provide the active conformation of the enzyme. We r eported previously that a phosphorylation-sensitive secondary structur e could be formed in a 26-amino-acid long synthetic peptide correspond ing to the activation segment of Xenopus MAPK termed IDA (Inter-DFG-AP E) MAPK peptide (Tokmakov, A. A., ct al 1997, Biochem. Biophys. Res. C ommun. 236, 243-247). Here, we show that unphosphorylated IDA MAPK pep tide can inhibit in vitro both MAPK and MAPK kinase activities with th e inhibition constants of 82 and 18 mu M, respectively. Phosphorylated forms of the peptide were of little effect. IDA MAPK peptide did not inhibit significantly the activity of some other protein kinases, incl uding MAPK homologue p38 kinase, suggesting the specificity for MAPK a nd MAPK kinase. Microinjection of unphosphorylated IDA MAPK peptide in to immature Xenopus oocytes significantly suppressed progesterone-indu ced oocyte maturation by inhibiting activation of both MAPK and matura tion promoting factor. Similar inhibition of maturation was registered upon oocyte treatment with another specific inhibitor of MAPK pathway , PD098059. These results depict IDA MAPK peptide as a selective inhib itor of the MAPK pathway that can be used for the investigations of MA PK-mediated signaling: (C) 1998 Academic Press.