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GPCR kinase 2 (GRK2)/β-arrestins and protein kinase A (PKA)/protein kinase C (PKC) mediate homologous and heterologous regulations of GPCRs, respectively. Conventional protein kinase C enzymes (PKCs), as exemplified by PKCβII, selectively inhibit internalization of dopamine D 2 receptor and β 2 adrenoceptor in a β-arrestin- but not GRK2-dependent manner. PKCβII interacts with β-arrestin2 upon autophosphorylation at T250, and inhibits the receptor internalization by decreasing the ubiquitination of β-arrestin2. PKCβII interferes with the interaction between β-arrestin2 and MDM2 in the cytosol, resulting in the redistribution of MDM2 to the nucleus. Subsequently, deubiquitination of β-arrestin2 and inhibition of agonist-induced receptor internalization follow. Thus, our study suggests that the extent of β-arrestin ubiquitination and the autophosphorylation status of PKCs determine PKCβII-mediated inhibition of homologous regulatory processes of GPCRs. [ABSTRACT FROM AUTHOR]

Dopamine D2 receptor (D2R) has been shown to activate extracellular signal‐regulated kinases (ERKs) via distinct pathways dependent on either G‐protein or β‐arrestin. However, there has not been a systematic study of the regulatory process of D2R‐mediated ERKs activation by G protein‐ versus β‐arrestin‐dependent signaling since D2R stimulation of ERKs reflects the simultaneous action of both pathways. Here, we investigated that differential regulation of D2R‐mediated ERKs activation via these two pathways. Our results showed that G protein‐dependent ERKs activation was transient, rapid, reached maximum level at around 2 min, and importantly, the activated ERKs were entirely confined to the cytoplasm. In contrast, β‐arrestin‐dependent ERKs activation was more sustained, slower, reached maximum level at around 10 min, and phosphorylated ERKs translocated into the nucleus. Src was found to be commonly involved in both the G protein‐ and β‐arrestin‐dependent pathway‐mediated ERKs activation. Pertussis toxin Gi/o inhibitor, GRK2‐CT, AG1478 epidermal growth factor receptor inhibitor, and wortmannin phosphoinositide 3‐kinase inhibitor all blocked G protein‐dependent ERKs activation. In contrast, GRK2 and β‐Arr2 played a main role in β‐arrestin‐dependent ERKs activation. Receptor endocytosis showed minimal effect on the activation of ERKs mediated by both pathways. Furthermore, we found that the formation of a complex composed of phospho‐ERKs, β‐Arr2, and importinβ1 promoted the nuclear translocation of activated ERKs. The differential regulation of various cellular components, as well as temporal and spatial patterns of ERKs activation via these two pathways, suggest the existence of distinct physiological outcomes. [ABSTRACT FROM AUTHOR]