Modification of the composition of polycystin-1 multiprotein complexes by calcium and tyrosine phosphorylation

Abstract

Mutations in the PKD1 gene are responsible for >85% of autosomal dominant polycystic kidney disease (ADPKD). The protein product of PKD1, polycystin-1, is a large, modular membrane protein, with putative ligand-binding motifs in the extracelluar N-terminal portion, 9–11 transmembrane domains and an intracellular C-terminal portion with phosphorylation sites. A role for polycystin-1 as a cell surface receptor involved in cell–matrix and cell–cell interactions has been proposed. In this study, we have analyzed polycystin-1 and associated protein distribution in normal human epithelial cells and examined the role of cell–matrix versus cell–cell interactions in regulation of the assembly of polycystin-1 multiprotein complexes. Immunocytochemistry, sucrose density gradient sedimentation, co-immunoprecipitation analyses and in vitro binding assays have shown that polycystin-1 associates with the focal adhesion proteins talin, vinculin, p130Cas, FAK, α-actinin, paxillin and pp60c-src in subconfluent normal human fetal collecting tubule (HFCT) epithelia when cell–matrix interactions predominate. Polycystin-1 also forms higher S value complexes with the cell–cell adherens junction proteins E-cadherin, β- and γ-catenins in confluent cultures when cell–cell interactions are predominant. Polycystin-1 multiprotein complexes can be disrupted by cytochalasin D but not by colchicine, suggesting involvement of the actin cytoskeleton. Although inhibition of tyrosine phosphorylation by tyrphostin inhibits polycystin-1–FAK interactions, E-cadherin interactions are enhanced. High calcium treatment also increases polycystin-1–E-cadherin interactions.