STIM1 negatively regulates Ca2{+} release from the sarcoplasmic reticulum in skeletal myotubes

Stromal interaction molecule 1 (STIM1) mediates store-operated Ca2+ entry (SOCE) in skeletal muscle. However, the direct role(s) of STIM1 in skeletal muscle, such as Ca2+ release from the sarcoplasmic reticulum (SR) for muscle contraction, have not been identified. The times required for the maximal expression of endogenous STIM1 or Orai1, or for the appearance of puncta during the differentiation of mouse primary skeletal myoblasts to myotubes, were all different, and the formation of puncta was detected with no stimulus during differentiation, suggesting that, in skeletal muscle, the formation of puncta is a part of the differentiation. Wild-type STIM1 and two STIM1 mutants (Triple mutant, missing Ca2+-sensing residues but possessing the intact C-terminus; and, E136X, missing the C-terminus) were overexpressed in the myotubes. The wild-type STIM1 increased SOCE, while neither mutant had an effect on SOCE. It was interesting that increases in the formation of puncta were observed in Triple mutant as well as in wild-type STIM1, suggesting that SOCE-irrelevant puncta could exist in skeletal muscle. On the other hand, overexpression of wild-type or Triple mutant, but not E136X, attenuated Ca2+ releases from the SR in response to KCl (evoking excitation-contraction coupling (ECC) via activating dihydropyridine receptor (DHPR)) in a dominant-negative manner. The attenuation was removed by STIM1 knockdown, and STIM1 was co-immunoprecipitated with DHRP i...

Source: BJ Signal - May 14, 2013 Category: Biochemistry Authors: K Lee, J Woo, J Hwang, C Hyun, C Cho, D Kim, E Lee Tags: BJ Signal Source Type: research