Calcium regulation of myogenesis by differential calmodulin inhibition of basic helix-loop-helix transcription factors.
The members of the MyoD family of basic helix-loop-helix (bHLH) transcription factors are critical regulators of skeletal muscle differentiation that function as heterodimers with ubiquitously expressed E-protein bHLH transcription factors. These heterodimers must compete successfully with homodimers of E12 and other E-proteins to enable myogenesis. Here, we show that E12 mutants resistant to Ca(2+)-loaded calmodulin (CaM) inhibit MyoD-initiated myogenic conversion of transfected fibroblasts. Ca(2+) channel blockers reduce, and Ca(2+) stimulation increases, transcription by coexpressed MyoD and wild-type E12 but not CaM-resistant mutant E12. Furthermore, CaM-resistant E12 gives lower MyoD binding and higher E12 binding to a MyoD-responsive promoter in vivo and cannot rescue myogenic differentiation that has been inhibited by siRNA against E12 and E47. Our data support the concept that Ca(2+)-loaded CaM enables myogenesis by inhibiting DNA binding of E-protein homodimers, thereby promoting occupancy of myogenic bHLH protein/E-protein heterodimers on promoters of myogenic target genes.
Hauser
Jannek
J
Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden.
Saarikettu
Juha
J
Grundström
Thomas
T
D000595:Amino Acid Sequence; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000378:metabolism; D019281:Dimerization; D017930:Genes, Reporter; D051379:Mice; D008969:Molecular Sequence Data; D024510:Muscle Development; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism; D041681:NIH 3T3 Cells; D011401:Promoter Regions, Genetic / Q000235:genetics; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D051820:TCF Transcription Factors / Q000037:antagonists & inhibitors* / Q000737:chemistry; D058125:Transcription Factor 7-Like 1 Protein; D015533:Transcriptional Activation; D014162:Transfection
D051792:Basic Helix-Loop-Helix Proteins; D002118:Calcium; D002147:Calmodulin; D050505:Mutant Proteins; D017570:MyoD Protein; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D051820:TCF Transcription Factors; D058125:Transcription Factor 7-Like 1 Protein; C544913:Tcf7l1 protein, mouse