Calcineurin enhances acetylcholinesterase mRNA stability during C2-C12 muscle cell differentiation

Treatment of C2-C12 mouse myoblasts with the immunosuppressant drug cyclosp orin A (CsA) enhances the increase in acetylcholinesterase (AChE) expressio n observed during skeletal muscle differentiation. The enhanced AChE expres sion is due primarily to increased mRNA stability because CsA treatment inc reases the half-life of AChE mRNA, but not the apparent transcriptional rat e of the gene. Neither tacrolimus (FK506), an immunosuppressive agent with a distinct structure, nor cyclosporine H, an inactive congener of CsA, alte rs AChE expression. The enhanced AChE expression is associated with the mus cle differentiation process, but cannot be triggered by CsA exposure before differentiation. Myoblasts and myotubes of C2-C12 cells express similar am ounts of cyclophilin A and FKBP12, immunophilins known to be intracellular- binding targets for CsA and tacrolimus, respectively. However, cellular lev els of calcineurin, a calcium/calmodulin-dependent phosphatase known to be the cellular target of ligand-immunophilin complexes, increase 3-fold durin g myogenesis. Overexpression of constitutively active calcineurin in differ entiating cells reduces AChE mRNA levels and CsA antagonizes such an inhibi tion. Conversely, overexpression of a dominant negative calcineurin constru ct increases AChE mRNA levels, which are further enhanced by CsA. Thus, a C sA sensitive, calcineurin mediated pathway appears linked to differentiatio n-induced stabilization of AChE mRNA during myogenesis.