Megakaryoblastic leukemia 1, a potent transcriptional coactivator for serum response factor (SRF), is required for serum induction of SRF target genes.
Megakaryoblastic leukemia 1 (MKL1) is a myocardin-related transcription factor that we found strongly activated serum response element (SRE)-dependent reporter genes through its direct binding to serum response factor (SRF). The c-fos SRE is regulated by mitogen-activated protein kinase phosphorylation of ternary complex factor (TCF) but is also regulated by a RhoA-dependent pathway. The mechanism of this pathway is unclear. Since MKL1 (also known as MAL, BSAC, and MRTF-A) is broadly expressed, we assessed its role in serum induction of c-fos and other SRE-regulated genes with a dominant negative MKL1 mutant (DN-MKL1) and RNA interference (RNAi). We found that DN-MKL1 and RNAi specifically blocked SRE-dependent reporter gene activation by serum and RhoA. Complete inhibition by RNAi required the additional inhibition of the related factor MKL2 (MRTF-B), showing the redundancy of these factors. DN-MKL1 reduced the late stage of serum induction of endogenous c-fos expression, suggesting that the TCF- and RhoA-dependent pathways contribute to temporally distinct phases of c-fos expression. Furthermore, serum induction of two TCF-independent SRE target genes, SRF and vinculin, was nearly completely blocked by DN-MKL1. Finally, the RBM15-MKL1 fusion protein formed by the t(1;22) translocation of acute megakaryoblastic leukemia had a markedly increased ability to activate SRE reporter genes, suggesting that its activation of SRF target genes may contribute to leukemogenesis.
Cen
Bo
B
Department of Biological Sciences, Columbia University, 1212 Amsterdam Avenue, New York, NY 10027, USA.
Selvaraj
Ahalya
A
Burgess
Rebecca C
RC
Hitzler
Johann K
JK
Ma
Zhigui
Z
Morris
Stephan W
SW
Prywes
Ron
R
D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D005799:Genes, Dominant; D017930:Genes, Reporter; D016762:Genes, fos; D006801:Humans; D051379:Mice; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D027602:Serum Response Element; D026362:Serum Response Factor / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
D004268:DNA-Binding Proteins; C431575:MRTFA protein, human; C478036:MRTFB protein, human; D015514:Oncogene Proteins, Fusion; C431574:RBM15 protein, human; D016601:RNA-Binding Proteins; D026362:Serum Response Factor; D015534:Trans-Activators; D014157:Transcription Factors; C072545:p62TCF protein, human; C489525:p62TCF protein, mouse; D020742:rhoA GTP-Binding Protein