[Show abstract][Hide abstract] ABSTRACT: Cells from multiple origins contribute to vascular smooth muscle cell (VSMC) development. Phenotypic heterogeneity of VSMCs is associated with their point of developmental origin; however, the mechanisms driving such differences are unknown. We here examined the mechanisms controlling vascular bed-specific differences in Rgs5 expression during development. Rgs5 levels were similar across different regions of the vasculature in neonatal animals but were >15-fold higher in descending aortas compared with carotid arteries of adult mice. Thus, vessel bed-specific changes in regulation of Rgs5 expression occurred during vessel maturation. Examination of adult Rgs5-LacZ reporter mice revealed lower Rgs5 expression in VSMCs originating from the third (carotid artery) branchial arch compared with those originating in the fourth and sixth (aortic B segment, right subclavian, and ductus arteriosus) branchial arches. Indeed, a mosaic Rgs5 expression pattern, with discreet LacZ boundaries between VSMCs derived from different developmental origins, was observed. Furthermore, Rgs5-LacZ expression was correlated with the site of VSMC origin (splanchic mesoderm ≈ local mesenchyme > somites > proepicardium > mesothelium). Surprisingly, Rgs5 reporter activity in cultured carotid artery- and descending aorta-derived cells did not recapitulate the differences observed in vivo. Consistent with a developmental origin-specific epigenetic mechanism driving the observed expression differences in vivo, the Rgs5 promoter showed increased methylation on CpG dinucleotides in carotid arteries compared with that in descending aortas in adult but not in neonatal mice. In vitro methylation of the Rgs5 promoter confirmed that its activity is sensitive to transcriptional down-regulation by CpG methylation. These data suggest that an origin-dependent epigenetic program regulates vascular bed- and maturation state-dependent regulation of VSMC-specific gene transcription.
No preview · Article · Sep 2011 · The FASEB Journal
[Show abstract][Hide abstract] ABSTRACT: RGS2 and RGS5 are inhibitors of G-protein signaling belonging to the R4/B subfamily of RGS proteins. We here show that RGS2 is a much more potent attenuator of M1 muscarinic receptor signaling than RGS5. We hypothesize that this difference is mediated by variation in their ability to constitutively associate with the plasma membrane (PM). Compared with full-length RGS2, the RGS-box domains of RGS2 and RGS5 both show reduced PM association and activity. Prenylation of both RGS-box domains increases activity to RGS2 levels, demonstrating that lipid bilayer targeting increases RGS domain function. Amino-terminal domain swaps confirm that key determinants of localization and function are found within this important regulatory domain. An RGS2 amphipathic helix domain mutant deficient for phospholipid binding (L45D) shows reduced PM association and activity despite normal binding to the M1 muscarinic receptor third intracellular loop and activated Galpha(q). Replacement of a unique dileucine motif adjacent to the RGS2 helix with corresponding RGS5 residues disrupts both PM localization and function. These data suggest that RGS2 contains a hydrophobic extension of its helical domain that imparts high efficiency binding to the inner leaflet of the lipid bilayer. In support of this model, disruption of membrane phospholipid composition with N-ethylmaleimide reduces PM association of RGS2, without affecting localization of the M1 receptor or Galpha(q). Together, these data indicate that novel features within the RGS2 amphipathic alpha helix facilitate constitutive PM targeting and more efficient inhibition of M1 muscarinic receptor signaling than RGS5 and other members of the R4/B subfamily.
Preview · Article · Dec 2007 · Journal of Biological Chemistry