Caveolin‐3 is not an integral component of the dystrophin glycoprotein complex

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Abstract
The dystrophin‐glycoprotein complex is a multi‐subunit protein complex that spans the muscle plasma membrane (sarcolemma) and forms a link between the intracellular cytoskeleton and the extracellular matrix. Caveolin‐3, the muscle specific form of caveolin, is also a major structural and regulatory integral membrane protein found at the sarcolemma. Oligomers of caveolin‐3 form the structural framework for small membrane pockets known as caveolae. We directly examined whether caveolin‐3 is an integral component of the dystrophin‐glycoprotein complex by examining four common biochemical and cellular properties of proteins integrally bound to the dystrophin‐glycoprotein complex. We found that caveolin‐3 de‐enriches with partial purification of the dystrophin‐glycoprotein complex although a small amount of caveolin‐3 is present. Sucrose gradient fractionation and laminin affinity chromatography completely separate this residual caveolin‐3 from the core components of the dystrophin‐glycoprotein complex. We also show that caveolin‐3 expression at the sarcolemma is not reduced in patients with primary mutations in either dystrophin or the sarcoglycans. This data demonstrates that localization of caveolin‐3 to the sarcolemma occurs independently of the dystrophin‐glycoprotein complex and that caveolin‐3 is not an integral component of the dystrophin‐glycoprotein complex.