Adapter protein involved in asymmetrical cell division and cell polarization processes. Probably involved in the formation of epithelial tight junctions. Association with PARD3 may prevent the interaction of PARD3 with F11R/JAM1, thereby preventing tight junction assembly. The PARD6-PARD3 complex links GTP-bound Rho small GTPases to atypical protein kinase C proteins (PubMed:15761148). Regulates centrosome organization and function. Essential for the centrosomal recruitment of key proteins that control centrosomal microtubule organization (By similarity). Interacts with ECT2 ('Thr-359' phosphorylated form) and PRKCI. Interacts with PALS1 and CRB3 (By similarity). Interacts with PARD3. Interacts with GTP-bound forms of CDC42, RHOQ/TC10 and RAC1. Interacts with the N-terminal part of PRKCI and PRKCZ. Part of a complex with PARD3, CDC42 or RAC1 and PRKCI or PRKCZ. Part of a complex with LLGL1 and PRKCI. Interacts with MAP2K5. Interacts with TGFBR1; involved in TGF-beta induced epithelial to mesenchymal transition. Interacts with DCTN1 and PCM1 (By similarity). Colocalizes with GTP-bound CDC42 or RAC1 at membrane ruffles and with PARD3 at epithelial tight junctions. Recruited to the centrosome by a microtubule and dynein-dynactin-dependent mechanism. The PB1 domain mediates interactions with MAP2K5. The pseudo-CRIB domain together with the PDZ domain is required for the interaction with Rho small GTPases. The PDZ domain mediates the interaction with CRB3. Phosphorylated by the TGF-beta receptor. Belongs to the PAR6 family.