Duchenne Muscular Dystrophy (DMD) is an X-linked genetic disease caused by the absence of dystrophin, which links the cytoskeleton to the membrane-bound dystrophin-associated glycoproteins (DAG). Increased levels of intracellular calcium in muscle cells is one of the causes of muscle damage in DMD and we have proposed that the increased calcium influx enters through a class of stretch activated channels (SACs) (Yeung et al., 2005) which are thought to be encoded by TRPC1 (Maroto et al., 2005). The aim of the present investigation is to understand the link between dystrophin absence and increased activity of SACs. Caveolin-3 is a membrane-bound protein which locates DAG to the caveolae and whose overexpression also leads to a dystophic phenotype. In smooth muscle TRPC1 has been shown to interact with caveolin-1 (Lockwich et al., 2000). Src kinase co-fractionates with caveolin-3 (Song et al., 1996) and can also activate channels from the TRPC family (Kawasaki et al., 2006). We therefore studied the levels of expression and interaction of caveolin-3, TRPC1 and Src kinase in mdx mice, a mouse model which also lacks dystrophin expression. Caveolin-3 was increased in mdx mouse (Western Blot). This increase was confirmed by immunohistochemistry using skeletal muscle cryosections, showing higher levels of caveolin-3 both at the sarcolemma region and in the cytoplasm. TRPC1 was also increased in mdx mouse (Western Blot, immunohistochemistry). Over 50% of caveolin and TRPC1 co-localized at the sarcolemma region and their interaction was confirmed using co-immunoprecipitation. pY418-Src, the active form of Src kinase, was increased in mdx mouse. These results suggest that that caveolin-3 links dystrophin to TRPC1 and raise the possibility that Src kinase might be involved in the overactivity of the channel encoded by TRPC1.
Kawasaki BT, Liao Y & Birnbaumer L (2006) Proceedings of the National Academy of Science USA, 103: 335-40.
Lockwich TP, Liu X, Singh BB, Jadlowiec J, Weiland S & Ambudkar IS. (2000) Journal of Biological Chemistry, 275: 11934-42.
Maroto R, Raso A, Wood TG, Kurosky A, Martinac B & Hamill OP. (2005) Nature Cell Biology, 7: 179-185.
Song KS, Scherer PE, Tang Z, Okamoto T, Li S, Chafel M, Chu C, Kohtz DS & Lisanti M. (1996) Journal of Biological Chemistry, 271: 15160-5.
Yeung EW, Whitehead NP, Suchyna TM, Gottlieb PA, Sachs F & Allen DG. (2005) Journal of Physiology, 562: 367-380.