Rem, Rem2, Rad, and Gem͞Kir (RGK) represent a distinct GTPase family with largely unknown physiological functions. We report here that both Rem and Rad bind directly to Ca 2؉ channel ␤-subunits ( R em, Rem2, Rad, and Gem͞Kir (RGK) are members of a Ras-related GTPase subfamily (RGK family), with many unique characteristics that distinguish them from other members of the Ras superfamily (1-5). The common structure for all RGK proteins consists of a conserved Ras-related core domain, a series of nonconservative amino acid substitutions within regions known to be involved in guanine nucleotide binding and hydrolysis, a non-CAAX-containing C-terminal extension, and large N-terminal extensions relative to other Ras family proteins. The conservation of structural features within the RGK proteins suggests shared mechanisms of regulation and the control of common cellular signal transduction networks. However, RGK subfamily members differ from each other and from other Ras-related proteins in their putative effector (G2) domains, suggesting that they interact with distinct regulatory and effector proteins, and each exhibits distinct tissue-specific expression patterns (1-5). Thus, despite their conserved structural and biochemical properties, functional evidence to suggest a unified mechanism of action has been limited.In this study, we investigated the ability of Rem and Rad to regulate Ca 2ϩ channel activity. Our results demonstrate that, although both proteins have distinct effector interaction domains, they each bind directly to Ca V ␤ subunits and inhibit detectable ionic current expression from the native cardiac L type, but not from T type, Ca 2ϩ channels when coexpressed in human embryonic kidney (HEK)293 cells. The Rem protein is expressed in striated muscle cells, and we demonstrate that Rem inhibits L type Ca 2ϩ channel activity in differentiated C2C12 myotubes. Deletion analysis demonstrates that the C terminus of Rem plays an important role in Ca V ␤ subunit association and is necessary for regulation of channel activity. Taken together, these studies indicate that Rem functions as a potent regulator of L type Ca 2ϩ channel function in muscle and suggest that a conserved physiological role for the RGK GTPase gene family is the control of Ca 2ϩ channel activity via modulation of Ca V ␤ subunit function. Experimental ProceduresRNase Protection Assays and Cell Culture. C2C12DS and C2C12(E) mouse muscle myoblast cell lines were from Robert Krauss (Mount Sinai School of Medicine, New York) and were cultured and induced to differentiate as described (6). Primary mouse muscle cultures and MM14 cells were provided by

BACKGROUND.Beige adipose tissue is associated with improved glucose homeostasis in mice. Adipose tissue contains β3adrenergic receptors (β3-ARs), and this study was intended to determine whether the treatment of obese, insulin-resistant humans with the β3-AR agonist mirabegron, which stimulates beige adipose formation in subcutaneous white adipose tissue (SC WAT), would induce other beneficial changes in fat and muscle and improve metabolic homeostasis. METHODS.Before and after β3-AR agonist treatment, oral glucose tolerance tests and euglycemic clamps were performed, and histochemical analysis and gene expression profiling were performed on fat and muscle biopsies. PET-CT scans quantified brown adipose tissue volume and activity, and we conducted in vitro studies with primary cultures of differentiated human adipocytes and muscle. RESULTS.The clinical effects of mirabegron treatment included improved oral glucose tolerance (P < 0.01), reduced hemoglobin A1c levels (P = 0.01), and improved insulin sensitivity (P = 0.03) and β cell function (P = 0.01). In SC WAT, mirabegron treatment stimulated lipolysis, reduced fibrotic gene expression, and increased alternatively activated macrophages. Subjects with the most SC WAT beiging showed the greatest improvement in β cell function. In skeletal muscle, mirabegron reduced triglycerides, increased the expression of PPARγ coactivator 1 α (PGC1A) (P < 0.05), and increased type I fibers (P < 0.01). Conditioned media from adipocytes treated with mirabegron stimulated muscle fiber PGC1A expression in vitro (P < 0.001). CONCLUSION.Mirabegron treatment substantially improved multiple measures of glucose homeostasis in obese, insulinresistant humans. Since β cells and skeletal muscle do not express β3-ARs, these data suggest that the beiging of SC WAT by mirabegron reduces adipose tissue dysfunction, which enhances muscle oxidative capacity and improves β cell function.TRIAL REGISTRATION. Clinicaltrials.gov NCT02919176.

NIH (DK107646, DK112282, P20GM103527, and by CTSA grant UL1TR001998).

No abstract

Using microarray analysis, we identified a unique ras superfamily gene, termed RERG (ras-related and estrogen-regulated growth inhibitor), whose expression was decreased or lost in a significant percentage of primary human breast tumors that show a poor clinical prognosis. Importantly, high RERG expression correlated with expression of a set of genes that define a breast tumor subtype that is estrogen receptor-positive and associated with a slow rate of tumor cell proliferation and a favorable prognosis for these cancer patients. RERG mRNA expression was induced rapidly in MCF-7 cells stimulated by ␤-estradiol and repressed by tamoxifen treatment. Like Ras, RERG protein exhibited intrinsic GDP/GTP binding and GTP hydrolysis activity. Unlike Ras proteins, RERG lacks a known recognition signal for COOH-terminal prenylation and was localized primarily in the cytoplasm. Expression of RERG protein in MCF-7 breast carcinoma cells resulted in a significant inhibition of both anchorage-dependent and anchorageindependent growth in vitro and inhibited tumor formation in nude mice. These features of RERG are strikingly different from most Ras superfamily GTP-binding proteins and suggest that the loss of RERG expression may contribute to breast tumorigenesis.