FUNCTIONAL-ANALYSIS OF DESMOPLAKIN DOMAINS - SPECIFICATION OF THE INTERACTION WITH KERATIN VERSUS VIMENTIN INTERMEDIATE FILAMENT NETWORKS

We previously demonstrated that truncated desmoplakin I (DP I) molecul es containing the carboxyl terminus specifically coalign with and disr upt both keratin and vimentin intermediate filament (IF) networks when overexpressed in tissue culture cells (Stappenbeck, T. S., and K. J. Green. J. Cell Biol. 116:1197-1209). These experiments suggested that the DP carboxyl-terminal domain is involved either directly or indirec tly in linking IF with the desmosome. Using a similar approach, we hav e now investigated the behavior of ectopically expressed full-length D P I in cultured cells. In addition, we have further dissected the func tional sequences in the carboxyl terminus of DP I that facilitate the interaction with IF networks. Transient transfection of a clone encodi ng full-length DP I into COS-7 cells produced protein that appeared in some cells to associate with desmosomes and in others to coalign with and disrupt IF Deletion of the carboxyl terminus from this clone resu lted in protein that still appeared capable of associating with desmos omes but not interacting with IF networks. As the amino terminus appea red to be dispensable for IF interaction, we made finer deletions in t he carboxyl terminus of DP based on blocks of sequence similarity with the related molecules bullous pemphigoid antigen and plectin. We foun d a sequence at the very carboxyl terminus of DP that was necessary fo r coalignment with and disruption of keratin IF but not vimentin IF. F urthermore, the coalignment of specific DP proteins along keratin IF b ut not vimentin IF was correlated with resistance to extraction by Tri ton. The striking uncoupling resulting from the deletion of specific D P sequences suggests that the carboxyl terminus of DP interacts differ entially with keratin and vimentin IF networks.