Dystrophin/α1-syntrophin scaffold regulated PLC/PKC-dependent store-operated calcium entry in myotubes

In skeletal muscles from patient suffering of Duchenne Muscular Dystrophy and from mdx mice, the absence of the cytoskeleton protein dystrophin has been shown to be essential for maintaining a normal calcium influx. We showed that a TRPC store-dependent cation influx is increased by loss of dystrophin or a scaffolding protein alpha 1-syntrophin, however the mechanisms of this calcium mishandling are incompletely understood. First of all, we confirmed that TRPC1 but also STIM1 and Orail are supporting the store-operated cation entry which is enhanced in dystrophin-deficient myotubes. Next, we demonstrated that inhibition of PLC or PKC in dystrophin-deficient myotubes restores elevated cation entry to normal levels similarly to enforced minidystrophin expression. In addition, silencing alpha 1-syntrophin also increased cation influx in a PLC/PKC dependent pathway. We also showed that alpha 1-syntrophin and pLC beta are part of a same protein complex reinforcing the idea of their inter-relation in calcium influx regulation. This elevated cation entry was decreased to normal levels by chelating intracellular free calcium with BAPTA-AM. Double treatments with BAPTA-AM and PLC or PKC inhibitors suggested that the elevation of cation influx by PLC/PKC pathway is dependent on cytosolic calcium. All these results demonstrate an involvement in dystrophin-deficient myotubes of a specific calcium/PKC/PLC pathway in elevation of store-operated cation influx supported by the STIM1/Orai1/TRPC1 proteins, which is normally regulated by the alpha 1-syntrophin/dystrophin scaffold. (C) 2012 Elsevier Ltd. All rights reserved.