HMGI-Y is an architectural transcription factor that regulates gene expression in vivo by controlling the formation of stereospecific multiprotein complexes on the AT-rich regions of certain gene promoters. Recently, we demonstrated that HMGI-Y is required for proper transcription of the insulin receptor (IR) gene. Here we provide evidence that transcriptional activation of the human IR promoter requires the assembly of a transcriptionally active multiprotein-DNA complex which includes, in addition to HMGI-Y, the ubiquitously expressed transcription factor Sp1 and the CCAAT-enhancer binding protein β (C/EBPβ). Functional integrity of this nucleoprotein complex is required for full transactivation of the IR gene by Sp1 and C/EBPβ in cells readily expressing IRs. We show that HMGI-Y physically interacts with Sp1 and C/EBPβ and facilitates the binding of both factors to the IR promoter in vitro. Furthermore, HMGI-Y is needed for transcriptional synergism between these factors in vivo. Repression of HMGI-Y function adversely affects both Sp1- and C/EBPβ-induced transactivation of the IR promoter. Together, these findings demonstrate that HMGI-Y plays significant molecular roles in the transcriptional activities of these factors in the context of the IR gene and provide concordant support for the hypothesis that, in affected individuals, a putative defect in these nuclear proteins may cause decreased IR expression with subsequent impairment of insulin signaling and action.
CITATION STYLE
Foti, D., Iuliano, R., Chiefari, E., & Brunetti, A. (2003). A Nucleoprotein Complex Containing Sp1, C/EBPβ, and HMGI-Y Controls Human Insulin Receptor Gene Transcription. Molecular and Cellular Biology, 23(8), 2720–2732. https://doi.org/10.1128/mcb.23.8.2720-2732.2003
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