A novel molecular mechanism involved in the crosstalks between homologous and PKC-mediated heterologous regulatory pathway of dopamine D 2 receptor.

Protein kinase C (PKC) is one of the major effectors involved in the heterologous regulatory pathways of G protein-coupled receptors (GPCRs). On the other hand, GRK2 and β-arrestins are the players of homologous regulatory pathway of GPCRs that affect the receptor functions in agonist-selective manner. Even though two pathways can occur independently, crosstalks between two pathways add more diverse modes of regulations on GPCR functions. Even if extensive studies have been conducted, a commonly applicable molecular mechanism involved in the crosstalks between two regulatory pathways has yet to be elucidated. Here we show that PKCβII was phosphorylated at its activation loop of kinase domain (T500) through constitutive interaction with phosphoinositide-dependent kinase 1 (PDK1) that is phosphorylated at S214. With agonist stimulation, dopamine D2 receptor interacted with 14-3-3η in GRK2/β-arrestin2-dependent manner, resulting in the recruitment of PDK1. The PDK1 recruited to 14-3-3η was dephosphorylated at S241 and dissociated from PKCβII, abrogating the phosphorylation of PKCβII at T500. This signaling cascade resulted in the inhibition of PKCβII functions, including its phosphorylation in the C-terminal tail, intracellular translocation, and kinase activity. Thus, this study revealed a novel and commonly applicable molecular mechanism involved in the inhibition of PKCβII functions through GRK2/β-arrestin2-mediated homologous pathway of GPCRs. The results obtained in this study could be expanded to other GPCRs and provide new strategies for the treatment of PKCβII-related disorders.