Myogenic regulatory factors regulate M-cadherin expression by targeting its proximal promoter elements.

M- and N-cadherin are members of the Ca(2+)-dependent cell-cell adhesion molecule family. M-cadherin is expressed predominantly in developing skeletal muscles and has been implicated in terminal myogenic differentiation, particularly in myoblast fusion. N-cadherin-mediated cell-cell adhesion also plays an important role in skeletal myogenesis. In the present study, we found that both genes were differentially expressed in C2C12 and Sol8 myoblasts during myogenic differentiation and that the expression of M-cadherin was preferentially enhanced in slow-twitch muscle. Interestingly, most MRFs (myogenic regulatory factors) significantly activated the promoter of M-cadherin, but not that of N-cadherin. In line with this, overexpression of MyoD in C3H10T1/2 fibroblasts strongly induced endogenous M-cadherin expression. Promoter analysis in silico and in vitro identified an E-box (from -2 to +4) abutting the transcription initiation site within the M-cadherin promoter that is bound and differentially activated by different MRFs. The activation of the M-cadherin promoter by MRFs was also modulated by Bhlhe40 (basic helix-loop-helix family member e40). Finally, chromatin immunoprecipitation proved that MyoD as well as myogenin binds to the M-cadherin promoter in vivo. Taken together, these observations identify a molecular mechanism by which MRFs regulate M-cadherin expression directly to ensure the terminal differentiation of myoblasts.

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