ABSTRACT
Beta-arrestins are multifunctional adaptors that mediate the desensitization, internalization, and some signaling functions of seven-transmembrane receptors (7TMRs). Agonist-stimulated ubiquitination of beta-arrestin2 mediated by the E3 ubiquitin ligase Mdm2 is critical for rapid beta(2)-adrenergic receptor (beta(2)AR) internalization. We now report the discovery that the deubiquitinating enzyme ubiquitin-specific protease 33 (USP33) binds beta-arrestin2 and leads to the deubiquitination of beta-arrestins. USP33 and Mdm2 function reciprocally and favor respectively the stability or lability of the receptor beta-arrestin complex, thus regulating the longevity and subcellular localization of receptor signalosomes. Receptors such as the beta(2)AR, previously shown to form loose complexes with beta-arrestin ("class A") promote a beta-arrestin conformation conducive for binding to the deubiquitinase, whereas the vasopressin V2R, which forms tight beta-arrestin complexes ("class B"), promotes a distinct beta-arrestin conformation that favors dissociation of the enzyme. Thus, USP33-beta-arrestin interaction is a key regulatory step in 7TMR trafficking and signal transmission from the activated receptors to downstream effectors.
Subject(s)
Arrestins/metabolism , Proto-Oncogene Proteins c-mdm2/metabolism , Receptors, Cell Surface/metabolism , Signal Transduction , Ubiquitin Thiolesterase/metabolism , Ubiquitin-Protein Ligases/metabolism , Animals , Cell Line , Endosomes/drug effects , Endosomes/enzymology , Enzyme Activation/drug effects , Extracellular Signal-Regulated MAP Kinases/metabolism , Humans , Kinetics , Models, Biological , Protein Binding/drug effects , Protein Transport/drug effects , Signal Transduction/drug effects , Ubiquitination/drug effects , Vasopressins/pharmacology , beta-ArrestinsABSTRACT
Monokines (i.e., interleukin [IL]-12, -18, and -15) induce natural killer (NK) cells to produce interferon-gamma (IFN-gamma), which is a critical factor for immune surveillance of cancer and monocyte clearance of infection. We show that SET, which is a potent inhibitor of protein phosphatase type 2A (PP2A) activity, is highly expressed in human CD56bright NK cells, which produce more IFN-gamma than CD56dim NK cells. SET was up-regulated upon monokine stimulation of primary human NK cells. Furthermore, ectopic overexpression of SET significantly enhanced IFN-gamma gene expression in monokine-stimulated NK cells. In contrast, RNAi-mediated suppression of SET expression renders NK cells inefficient in producing high levels of IFN-gamma in response to monokine costimulation. Mechanistically, suppression of PP2A activity by SET is important for IFN-gamma gene expression in NK cells. In fact, treatment of primary human NK cells with the PP2A activator 1,9-dideoxy-forskolin, as well as administration of the drug to C57BL/6 mice, significantly reduced NK-dependent IFN-gamma production in response to monokine treatment. Further, SET knockdown or pharmacologic activation of PP2A diminished extracellular signal-regulated kinase 1/2, p65RelA, signal transducer and activator of transduction 4 (STAT4), and STAT5 activity in monokine-stimulated NK cells, potentially contributing to the reduction in IFN-gamma gene expression. Thus, SET expression is essential for suppressing PP2A phosphatase activity that would otherwise limit NK cell antitumoral and/or antiinflammatory functions by impairing NK cell production of IFN-gamma.
