PHOSPHORYLATION OF THE DESMOPLAKIN COOH TERMINUS NEGATIVELY REGULATESITS INTERACTION WITH KERATIN INTERMEDIATE FILAMENT NETWORKS

Desmoplakins (DPs) are the most abundant proteins in the innermost por tion of the desmosomal plaque and have been proposed to play a role in the attachment of intermediate filaments (IF) to cell-cell contact si tes. Our previous results suggest that the globular end domains of DP perform dual functions: first, to target DP to the desmosome via the N H2 terminus and second, to attach IF to the desmosomal plaque via the COOH terminus. When ectopically expressed in most cultured cells, the COOH terminus plus the rod domain (DP.Delta N.SerC23) exhibits strikin g coalignment with keratin IF networks. However, in certain cell types (e.g. PtK2) or in cells treated with forskolin to activate protein ki nase A, DP.Delta N.SerC23 exhibits a diffuse cytoplasmic distribution. A Variant molecule (DP.Delta N.GlyC23) in which a serine located 23 a mino acids from the COOH terminus is altered to a glycine, thereby dis rupting a protein kinase A consensus phosphorylation site, co-localize s with keratin IF networks regardless of cell type or forskolin treatm ent. Analysis of the phosphopeptide maps of these DP variants and endo genous DP is consistent with the phosphorylation of the serine 23 resi dues from the COOH terminus. These results suggest that phosphorylatio n of a specific residue in the DP COOH terminus may negatively regulat e its interaction with keratin IF networks.