Expression of Gαz in C2C12 cells restrains myogenic differentiation

The recent identification of G alpha(z) expression in C2C12 myoblasts and its demonstrated interaction with the transcription factor Eya2 inferred an unanticipated role of G alpha(z) in muscle development. In the present study, endogenous G alpha(z) mRNA and protein expressions in C2C12 cells increased upon commencement of myogenesis and peaked at around 4-6 days after induction but were undetectable in adult skeletal muscle. Surprisingly, stable expression of recombinant G alpha(z) in C2C12 myoblasts strongly suppressed myotube formation upon serum deprivation, and the constitutively active mutant G alpha(z)QL exerted more pronounced effects. Transcriptional activities of reporter genes responsive to early (MyoD, MEF2 and myogenin) and late (muscle creatine kinase and myosin heavy chain) myogenic markers were reduced by transiently expressed G alpha(z)QL Membrane attachment of G alpha(z) was apparently required for the suppressive effects because a fatty acylation-deficient G alpha(z) mutant could not inhibit myogenin expression. Introduction of siRNA against G alpha(z) enhanced myogenin-driven luciferase activity and increased myosin heavy chain expression. Immunostaining of C2C12 cells over-expressing G alpha(z) showed delayed nuclear expression of myogenin and severe myotube deformation. G alpha(z) expression was accompanied by reduced levels of Rock2, RhoA and RhoGAP, enhanced expression of Rnd3, and a reduction of serum-responsive factor-driven reporter activity. These results support a novel role of G alpha(z) in restraining myogenic differentiation through the disruption of Rho signaling. (C) 2010 Elsevier Inc. All rights reserved.