The Role of DOC-2/DAB2 Protein Phosphorylation in the Inhibition of AP-1 Activity

Abstract

T. (1998) Endocrinology 139, 3542-3553). However , its mechanism of action is not understood completely. This study delineates the functional significance of DOC-2/DAB2 protein phosphorylation and demonstrates that in vivo activation of protein kinase C (PKC) by 12-O-tetradecanoylphorbol-13-acetate (TPA) induces DOC-2/DAB2 phosphorylation, including a ser-ine residue at position 24. Mutation of Ser 24 to Ala reduced DOC-2/DAB2 phosphorylation by PKC. Using a synthetic Ser 24 peptide (APS 24 KKEKKKGSEKTD) or re-combinant DOC-2/DAB2 as substrates, PKCII, PKC, and PKC (but not casein kinase II) directly phospho-rylated Ser 24 in vitro. This indicates that DOC-2/DAB2 is a PKC-specific substrate. Since expression of wild-type DOC-2/DAB2, but not the S24A mutant, inhibited TPA-induced AP-1 activity in prostatic epithelial cells, phos-phorylation of Ser 24 appears to play a critical role in modulating TPA-induced AP-1 activity. Taken together, these data suggest that PKC-regulated phosphorylation of DOC-2/DAB2 protein may help its growth inhibitory function.