Constitutive serum response factor activation by the viral chemokine receptor homologue pUS28 is differentially regulated by Gαq/11 and Gα16

The puzzling uniqueness of the heterotrimeric G15 protein and its potential beyond hematopoiesis

“…The presence of G15 biased the pharmacological profile of the k opioid receptor (Su et al 2009), again suggesting the existence of preformed receptor-G protein complexes. A similar interaction with G15 may even interfere with the activation of other G protein subtypes as shown for pUS28 (Moepps et al 2008), a viral GPCR characterized by elevated ligand-independent constitutive activity and by increased phosphorylation (Minisini et al 2003). This effect was unmasked because Gq/11 promotes serum response factor (SRF)-dependent transcriptional activity much more effectively than G15 or G14, and the overexpression of G15 reduced SRF effect by directly competing with Gq/11 for the chemokine-activated pUS28 (Moepps et al 2008).…”

Identification of Common Mechanisms by Which Human and Mouse Cytomegalovirus Seven-Transmembrane Receptor Homologues Contribute to In Vivo Phenotypes in a Mouse Model

“…Consistent with previous studies, fractalkine proved to be an inverse agonist for wt US28, which was converted to agonism in US28⌬C54. Fractalkine did not affect signaling of US28R129Q, US28RQ/⌬C54, or US28⌬N [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], confirming that the effects were G protein dependent and initiated by binding of fractalkine to US28. These results demonstrate that PLC-␤ signaling, chemokine binding, and endocytic properties of wt US28 and the US28 mutants used in this study were consistent with those in previous reports of transfected …”

“…In mouse embryonic fibroblasts (MEF) infected with either untagged wt US28 or mutant US28 recombinant MCMV, 125 I-CX 3 CL1 radioligand binding experiments, using methods similar to those described previously (16), demonstrated high-affinity binding by all viruses (Fig. 1C), except the negative control US28⌬N [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], which was disrupted for fractalkine binding (17). Endocytosis experiments using 125 I-CX 3 CL1 with MCMV-infected MEF (24 h postinfection [p.i.])…”

“…At steady state, US28⌬C54 and US28RQ/⌬C54 were expressed mostly at the cell surface, in contrast to wt US28, US28R129Q, and US28⌬N [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] (Fig. 1A).…”

“…US28 mutants comprised either a point mutation disrupting the DRY motif (US28R129Q), a truncation of the C terminus (US28⌬C54), or a dual R129Q/⌬C54 mutant (US28RQ/⌬C54). A US28 mutant with a deletion of Nterminal residues (US28⌬N [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]), which disrupted fractalkine binding (17,18), was included as a control in some studies.…”