β-Arrestin2 directly or through GRK2 inhibits PKCβII activation in a ubiquitination-dependent manner

The GRK/β-arrestin and PKC/PKA mediate the homologous and heterologous regulation of G protein-coupled receptors (GPCRs), respectively. Interaction between the two pathways is one of the most important issues in understanding the regulation of GPCRs. The present study investigated the regulatory effect of GRK2 and β-arrestins on PKC activation. The roles of GRK2 and β-arrestins in the functional regulation of PKC were assessed by determining their influence on PKC autophosphorylation and intracellular translocation. Radioligand binding assay was utilized to characterize intracellular trafficking of dopamine D₂R, D₃R, and β₂ adrenergic receptor (β₂AR). The subdomains involved in the mutual interactions among GRK2, β-arrestin2, and PKCβII were determined by in vitro binding assay. Various point mutants of key regulatory players were combined with knockdown cells of GRK2, β-arrestins, and Mdm2 to functionally correlate the biochemical changes with functional outcomes. GRK2 and β-arrestin2 mutually inhibited the PKCβII autophosphorylation, a hallmark of PKCβII activation. β-Arrestin2 ubiquitination was required for the inhibitory activities of GRK2 as well as β-arrestin2. Furthermore, GRK2 facilitated β-arrestin2 ubiquitination, thus to enhance the inhibitory actions of β-arrestin2 on PKCβII activity. Aforementioned processes were also involved in the GRK2/β-arrestin2-mediated inhibition of the D₂R, D₃R, and β₂AR endocytosis. The present study provides new insights into the intricate interactions between the homologous and heterologous GPCR regulation pathways. In addition, a novel regulatory role of GRK2 was proposed for the ubiquitination of β-arrestin in the context of the PKC-mediated heterologous regulation of GPCRs.