Figure 5. MuRF1 and MuRF3 mediate MHC protein turnover in vivo.

(A and B) PTU was administered for 2 weeks to induce expression of β/slow MHC in WT, MuRF1^–/–, and MuRF3^–/– mouse hearts (n = 6 each). Expression of β/slow MHC (A) and α-MHC (B) mRNA as assessed by real-time PCR analysis was increased and decreased, respectively, to comparable levels after 2 weeks of PTU treatment in all genotypes. Terminating the administration of PTU treatment led to a normalization of β/slow MHC and α-MHC mRNA expression. (C) Immunoblotting of proteins from hearts of WT, MuRF1^–/–, and MuRF3^–/– mice showed a reduced degradation of β/slow MHC in MuRF1^–/– and MuRF3^–/– compared with WT mice. Anti-tubulin antibody was used as a control. (D) Immunoblots of lysates from C2C12 myoblasts (MB) and differentiating myotubes (MT; days of differentiation are indicated at top) transfected with MuRF1-myc or MuRF3-myc, using anti-MHC antibody show a reduced MHC content when MuRF1 or MuRF3 were coexpressed. Transfection of pcDNA3.1 was used as a control. Anti-myogenin, was used as a control for differentiation, and anti-myc and anti-tubulin antibodies were used as controls for input.