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Type: Journal article
Title: Differential activities of murine single minded 1 (SIM1) and SIM2 on a hypoxic response element - Cross-talk between basic helix-loop-helix/Per-Arnt-Sim homology transcription factors
Author: Woods, S.
Whitelaw, M.
Citation: Journal of Biological Chemistry, 2002; 277(12):10236-10243
Publisher: Amer Soc Biochemistry Molecular Biology Inc
Issue Date: 2002
ISSN: 0021-9258
Organisation: Centre for the Molecular Genetics of Development
Statement of
Susan L. Woods and Murray L. Whitelaw
Abstract: The basic-helix-loop-helix/Per-Arnt-Sim homology (bHLH/PAS) protein family comprise a group of transcriptional regulators that often respond to a variety of developmental and environmental stimuli. Two murine members of this family, Single Minded 1 (SIM1) and Single Minded 2 (SIM2), are essential for post-natal survival but differ from other prototypical family members such as the dioxin receptor (DR) and hypoxia inducible factors, in that they behave as transcriptional repressors in mammalian one hybrid experiments and have yet to be ascribed a regulating signal. In cell lines engineered to stably express SIM1 and SIM2, we show that both are nuclear proteins that constitutively complex with the general bHLH/PAS partner factor, ARNT. We report that the SIM factors, in combination with ARNT, attenuate transcription from the hypoxia inducible Erythropoietin (EPO) enhancer during hypoxia. Such cross talk between coexpressed bHLH/PAS factors can occur through competition for ARNT, which we find evident in SIM repression of DR induced transcription from a xenobiotic response element reporter gene. However, SIM1/ARNT, but not SIM2/ARNT, can activate transcription from the EPO enhancer at normoxia, implying the SIM proteins have the ability to bind hypoxia response elements and affect either activation or repression of transcription. This notion is supported by co-immunoprecipitation of EPO enhancer sequences with the SIM2 protein. SIM protein levels decrease with hypoxia treatment in our stable cell lines, although levels of the transcripts encoding SIM1 and SIM2 and the approximate 2h half lives of each protein are unchanged during hypoxia. Inhibition of protein synthesis, known to occur in cells during hypoxic stress in order to decrease ATP utilisation, appears to account for the fall in SIM levels. Our data suggests the existence of a hypoxic switch mechanism in cells which coexpress HIF and SIM proteins, where upregulation and activation of HIF-1a is concomitant with attenuation of SIM activities.
Keywords: Kidney
Cells, Cultured
Cell Line
Cell Nucleus
Proto-Oncogene Proteins c-myc
Transcription Factors
Repressor Proteins
DNA, Complementary
Adenosine Triphosphate
Microscopy, Fluorescence
Blotting, Western
Precipitin Tests
Blotting, Northern
Electrophoresis, Polyacrylamide Gel
Transcription, Genetic
Binding, Competitive
Amino Acid Sequence
Response Elements
Helix-Loop-Helix Motifs
Protein Structure, Tertiary
Protein Binding
Sequence Homology, Amino Acid
Genes, Reporter
Genetic Vectors
Time Factors
Molecular Sequence Data
Basic Helix-Loop-Helix Transcription Factors
Hypoxia-Inducible Factor 1, alpha Subunit
Enhancer Elements, Genetic
DOI: 10.1074/jbc.M110752200
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Appears in Collections:Aurora harvest 6
Centre for the Molecular Genetics of Development publications
Molecular and Biomedical Science publications

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