Caveolin-1 regulates TGF-β superfamily signaling in vitro Recently, caveolin-1 has drawn attention as a regulator of TGF-β superfamily signaling. Caveolin-1 binds to and suppresses activation of the type I receptor of TGF-β1, which induces growth arrest in nonmuscle cells (35). Consistently, the binding affinity of caveolin-1 with type I TGF-β1 receptor decreases after stimulation Inhibitors,research,lifescience,medical with TGF-β1. In addition, caveolin-1 associates with the type II receptor of TGF-β1 (36–38). Caveolin-1 also facilitates ligand–bound TGF-β1 receptors internalization and degradation via the formation of endocytic vesicles with ubiquitin-ligase (39, 40).

In addition, caveolin-1 interacts with type II and type I receptors of bone morphogenic proteins (BMPs) in vivo (41). These findings indicate that caveolin-1 regulates TGF-β superfamily signaling, including TGF-β1 and BMPs, at its receptor level. Caveolin-3 suppresses myostatin signaling through its type

I receptor in vitro Upon consideration of molecular analogy and tissue distribution, Inhibitors,research,lifescience,medical Inhibitors,research,lifescience,medical we hypothesized that caveolin-3 inhibits myostatin signaling in a similar manner to that of inhibition of caveolin-1 to multiple TGF-β superfamily signaling in nonmuscle cells. We found several caveolin-3 binding motifs (7); ΦXΦXXXXΦXXΦX, where Φ indicates aromatic or aromatic-like amino acids in the cytoplasmic kinase domain of type I serine/threonine myostatin receptors, ALK4/5 (42). Therefore, we cotransfected caveolin-3 Inhibitors,research,lifescience,medical and these type I myostatin receptors in COS-7 monkey kidney cells and found that caveolin-3 colocalized with type I myostatin receptor. Crizotinib mw Immunoprecipitation and subsequent immunoblot analysis revealed

that caveolin-3 associates with the type I myostatin receptor. In addition, phosphorylation level of the type I myostatin receptor decreased with the addition of caveolin-3 in cells cotransfected with constitutively active type I receptor and caveolin-3. Moreover, caveolin-3 eventually suppressed subsequent intracellular myostatin signaling; the phosphorylation level Inhibitors,research,lifescience,medical of an R-Smad of myostatin, Smad2 as well as the transcription level of the Smad-sensitive (CAGA)12-reporter gene. Therefore, caveolin-3 suppresses the the myostatin signal at its type I receptor level, in a similar manner to caveolin-1 for TGF-β1 signaling in vitro. Caveolin-3 deficient muscles exhibit enhanced intracellular myostatin signaling We previously generated transgenic (Tg) mice overexpressing mutant caveolin-3 (CAV-3P104L) to develop a mouse model of LGMD1C/AD-RMD (11). The skeletal muscle phenotype of the transgenic mice showed severe myopathy with loss of caveolin-3. To determine whether caveolin-3 regulates myostatin signaling in vivo, we generated and characterized the double-transgenic mice showing myostatin deficiency and myostatin inhibition.