Regulation of capacitative calcium entries by alpha 1-syntrophin: association of TRPC1 with dystrophin complex and the PDZ domain of alpha 1-syntrophin

Calcium mishandling in Duchenne dystrophic muscle suggested that dystrophin, a membrane-associated cytoskeleton protein, might regulate calcium signaling cascade such as calcium influx pathway. It was previously shown that abnormal calcium entries involve uncontrolled stretch-activated currents and store-operated Ca super(2+) currents supported by TRPC1 channels. Moreover, our recent work demonstrated that reintroduction of minidystrophin in dystrophic myotubes restores normal capacitative calcium entries (CCEs). However, until now, no molecular link between the dystrophin complex and calcium entry channels has been described. This study is the first to show by coimmunoprecipitation assays the molecular association of TRPC1 with dystrophin and alpha 1-syntrophin in muscle cells. TRPC1 was also associated with alpha 1-syntrophin in dystrophic muscle cells independently of dystrophin. Furthermore, glutathione S-transferase (GST) pulldown assays showed that TRPC1 binds to the alpha 1-syntrophin PDZ domain. Transfected recombinant alpha 1-syntrophin formed a complex with TRPC1 channels and restored normal CCEs in dystrophic muscle cells. We suggest that normal regulation of CCEs in skeletal muscle depends on the association between TRPC1 channels and alpha 1-syntrophin that may anchor the store-operated channels to the dystrophin-associated protein complex (DAPC). The loss of this molecular association could participate in the calcium alterations observed in dystrophic muscle cells. This study provides a new model for the regulation of calcium influx by interaction with the scaffold of the DAPC in muscle cells.