Phosphorylation-dependent binding of 14-3-3 to Par3β, a human Par3-related cell polarity protein

Mammalian Par3α and Par3β/Par3L participate in cell polarity establishment and localize to tight junctions of epithelial cells; Par3α acts via binding to atypical PKC (aPKC). Here we show that Par3β as well as Par3α interacts with 14-3-3 proteins in a phosphorylation-dependent manner. In the interaction, Ser-746 of Par3β and the corresponding residue of Par3α (Ser-814) likely play a crucial role, since replacement of these residues by unphosphorylatable alanine results in a loss of interacting activity. The mutant Par3 proteins with the replacement are correctly recruited to tight junctions of MDCK cells and to membrane ruffles induced by an active form of the small GTPase Rac in HeLa cells. Thus, the interaction with 14-3-3 appears to be dispensable to Par3 localization. Consistent with this, the Par3α-14-3-3 interaction does not inhibit the Par3α-aPKC association required for the Par3α localization, although the aPKC-binding site lies close to the Ser-814-containing, 14-3-3-interacting region.