The bHLH/Per-Arnt-Sim transcription factor SIM2 regulates muscle transcript myomesin2 via a novel, non-canonical E-box sequence.
Despite a growing number of descriptive studies that show Single-minded 2 (Sim2) is not only essential for murine survival, but also upregulated in colon, prostate and pancreatic tumours, there is a lack of direct target genes identified for this basic helix-loop-helix/PAS transcription factor. We have performed a set of microarray experiments aimed at identifying genes that are differentially regulated by SIM2, and successfully verified that the Myomesin2 (Myom2) gene is SIM2-responsive. Although SIM2 has been reported to be a transcription repressor, we find that SIM2 induces transcription of Myom2 and activates the Myom2 promoter sequence when co-expressed with the heterodimeric partner protein, ARNT1, in human embryonic kidney cells. Truncation and mutation of the Myom2 promoter sequence, combined with chromatin immunoprecipitation studies in cells, has lead to the delineation of a non-canonical E-box sequence 5'-AACGTG-3' that is bound by SIM2/ARNT1 heterodimers. Interestingly, in immortalized human myoblasts knock down of Sim2 results in increased levels of Myom2 RNA, suggesting that SIM2 is acting as a repressor in these cells and so its activity is likely to be highly context dependent. This is the first report of a direct SIM2/ARNT1 target gene with accompanying analysis of a functional response element.
Woods
Susan
S
School of Molecular & Biomedical Science (Biochemistry) and the Centre for the Molecular Genetics of Development, University of Adelaide, South Australia 5005, Australia. susan.woods@ucsf.edu
Farrall
Alexandra
A
Procko
Carl
C
Whitelaw
Murray L
ML
D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002460:Cell Line; D064211:Connectin; D019281:Dimerization; D024721:E-Box Elements; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D007668:Kidney / Q000196:embryology / Q000378:metabolism; D051379:Mice; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism; D032446:Myoblasts / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D015533:Transcriptional Activation
D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D064211:Connectin; D009124:Muscle Proteins; D012333:RNA, Messenger; C577287:MYOM2 protein, human; C577288:Myom2 protein, mouse; C417032:SIM2 protein, human