Description of a utrophin associated protein complex in lipid raft domains of human artery smooth muscle cells

The dystrophin-associated protein complex (DAPC) is a multimeric complex that links the extracellular matrix to the actin cytoskeleton, and in some cases dystrophin can be substituted by its autosomal homologue utrophin to form the utrophin-associated protein complex (UAPC). Both complexes maintain the stability of plasma membrane during contraction process and play an important role in transmembrane signaling. Mutations in members of the DAPC are associated with muscular dystrophy and dilated cardiomyopathy. In a previous study with human umbilical cord vessels, we observed that utrophin colocalize with caveolin-1 (Cav-1) which proposed the presence of UAPC in the plasma membrane of vascular smooth muscle (VSM). In the current study, we demonstrated by immunofluorescence analysis, co-immunoprecipitation assays, and subcellular fractionation by sucrose gradients, the existence of an UAPC in lipid raft domains of human umbilical artery smooth muscle cells (HUASMC). This complex is constituted by utrophin, β-DG, ε-SG, α-smooth muscle actin, Cav-1, endothelial nitric oxide synthase (eNOS) and cavin-1. It was also observed the presence of dystrophin, utrophin Dp71, β-SG, δ-SG, δ-SG3 and sarcospan in non-lipid raft fractions. Furthermore, the knockdown of α/β-DG was associated with the decrease in both the synthesis of nitric oxide (NO) and the presence of the phosphorylated (active) form of eNOS; and with a reduction in the downstream activation of some cGMP signaling transduction pathway components. Together these results show the presence of an UAPC complex in HUASMC that may participate in the activity regulation of eNOS and in the vascular function.