Adiponectin receptor 1 C-terminus interacts with PDZ-domain proteins such as syntrophins

The utrophin-beta 2 syntrophin complex regulates adipocyte lipid droplet size independent of adipogenesis

Utrophin is a widely expressed cytoskeleton protein and is associated with lipid droplets (LDs) in adipocytes. The scaffold protein beta 2 syntrophin (SNTB2) controls signaling events by recruiting distinct membrane and cytoskeletal proteins, and binds to utrophin. Here we show that SNTB2 forms a complex with utrophin in adipocytes. SNTB2 protein is strongly diminished when utrophin is low. Of note, knock-down of utrophin or SNTB2 enhances LD growth during adipogenesis. SNTB2 reduction has no effect on basal and induced lipolysis, and insulin-stimulated phosphorylation of Akt is normal. The antilipolytic activity of insulin is enhanced in adipocytes with low SNTB2, while knock-down of utrophin has no effect. Uptake of exogenously supplied oleate and linoleate is comparable in scrambled and SNTB2 siRNA-treated cells. In the fibroblasts, diminished SNTB2 is associated with lower proliferation. CCAAT/enhancer-binding protein alpha and sterol regulatory element-binding proteins which are critical transcription factors for adipogenesis are normally expressed. Consequently, maturation of cells with SNTB2 knock-down is not grossly impaired. In fibroblasts, SNTB2 is localized to filamentous and vesicular structures which are distinct from beta actin, alpha tubulin, endoplasmic reticulum, early endosomes, lysosomes and mitochondria. Collectively, our data provide evidence that the utrophin-SNTB2 complex regulates LD size without affecting adipogenesis.

Absence of Dystrophin Disrupts Skeletal Muscle Signaling: Roles of Ca2+, Reactive Oxygen Species, and Nitric Oxide in the Development of Muscular Dystrophy

Dystrophin is a long rod-shaped protein that connects the subsarcolemmal cytoskeleton to a complex of proteins in the surface membrane (dystrophin protein complex, DPC), with further connections via laminin to other extracellular matrix proteins. Initially considered a structural complex that protected the sarcolemma from mechanical damage, the DPC is now known to serve as a scaffold for numerous signaling proteins. Absence or reduced expression of dystrophin or many of the DPC components cause the muscular dystrophies, a group of inherited diseases in which repeated bouts of muscle damage lead to atrophy and fibrosis, and eventually muscle degeneration. The normal function of dystrophin is poorly defined. In its absence a complex series of changes occur with multiple muscle proteins showing reduced or increased expression or being modified in various ways. In this review, we will consider the various proteins whose expression and function is changed in muscular dystrophies, focusing on Ca(2+)-permeable channels, nitric oxide synthase, NADPH oxidase, and caveolins. Excessive Ca(2+) entry, increased membrane permeability, disordered caveolar function, and increased levels of reactive oxygen species are early changes in the disease, and the hypotheses for these phenomena will be critically considered. The aim of the review is to define the early damage pathways in muscular dystrophy which might be appropriate targets for therapy designed to minimize the muscle degeneration and slow the progression of the disease.

Evaluation of the specificity of four commercially available antibodies to alpha-syntrophin

Alpha-syntrophin (SNTA) is an adaptor protein that regulates several signaling pathways. To analyze expression of SNTA immunoblot assays must be performed. Here, the specificity of four commercially available SNTA antibodies has been evaluated in immunoblot experiments using liver tissues of wild-type and SNTA-deficient mice. While one of the antibodies reacts with SNTA, two antibodies specifically recognize beta 2 syntrophin (SNTB2). The antigen detected by the fourth antibody has not been identified but is different from SNTA and SNTB2. Therefore, only one of the four tested antibodies is appropriate to analyze SNTA protein levels by immunoblot.