Megakaryoblastic leukemia-1/2, a transcriptional co-activator of serum response factor, is required for skeletal myogenic differentiation.
Serum response factor (SRF) is required for the expression of a wide variety of muscle-specific genes that are expressed upon differentiation and is thus required for both striated and smooth muscle differentiation in addition to its role in regulating growth factor-inducible genes. A heart and smooth muscle-specific SRF co-activator, myocardin, has been shown to be required for cardiac development and smooth muscle differentiation. However, no such co-factors of SRF have been identified in the skeletal myogenic differentiation program. Myocardin and the related transcription factor megakaryoblastic leukemia-1 (MKL1/MAL/MRTF-A) can strongly potentiate the activity of SRF. Here we report the cloning of the third member of the myocardin/MKL family in humans, MKL2. MKL2 binds to and activates SRF similar to myocardin and MKL1. To determine the role of these factors in skeletal myogenic differentiation we used a dominant negative MKL2 to show that the MKL family of proteins is required for skeletal myogenic differentiation. Expression of the dominant negative protein in C2C12 skeletal myoblasts blocked the differentiation-induced expression of the SRF target genes skeletal alpha-actin and alpha-myosin heavy chain and blocked differentiation of the myoblasts to myotubes in vitro. C2C12 cells express both MKL1 and MKL2, but not myocardin, implicating MKL1 and/or MKL2 in the requirement for skeletal myogenic differentiation. MKL1 was predominantly cytoplasmic in C2C12 cells, with a small amount in the nucleus, however, no movement of MKL1 to the nucleus was observed upon differentiation.
Selvaraj
Ahalya
A
Department of Biological Sciences, Columbia University, 1212 Amsterdam Avenue, New York, NY 10027, USA.
Prywes
Ron
R
D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000166:cytology*; D015514:Oncogene Proteins, Fusion / Q000378:metabolism* / Q000502:physiology; D011485:Protein Binding; D026362:Serum Response Factor / Q000378:metabolism*; D014018:Tissue Distribution; D015534:Trans-Activators; D014157:Transcription Factors / Q000378:metabolism* / Q000502:physiology; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; C431575:MRTFA protein, human; C478036:MRTFB protein, human; D015514:Oncogene Proteins, Fusion; D026362:Serum Response Factor; D015534:Trans-Activators; D014157:Transcription Factors