Transcriptional regulation of human insulin receptor gene by the high‐mobility group protein HMGI(Y)

Abstract

We have previously identified two closely related nuclear binding proteins that specifically interact with two unique functional AT-rich sequences of the 5' regulatory region of the human insulin receptor gene. Expression of these nuclear binding proteins increases during myocyte and adipocyte differentiation, and in other tissues appears to correlate with insulin receptor content. We have hypothesized, therefore, that insulin receptor expression in the insulin target tissues is regulated at least in part by these nuclear proteins. Here we show data on purification and biochemical characterization of these DNA binding proteins. Using a conventional chromatographic purification procedure combined with electrophoresis mobility shift assay and immunoblot analyses, a unique approximately 15 kDa protein, either identical to or highly related to the architectural transcription factor HMGI(Y), has now been identified, suggesting an essential role for HMGI(Y) in regulating insulin receptor gene transcription. Direct evidence of HMGI(Y) insulin receptor promoter interactions is provided by functional analysis with the CAT reporter gene and by hormone binding studies in cells expressing HMGI(Y) antisense RNA. In these experiments, antisense HMGI(Y) specifically inhibits insulin receptor promoter function and insulin receptor protein expression, indicating that HMGI(Y) is required for proper transcription of insulin receptor gene. Moreover, our data consistently support the hypothesis that a putative defect in this nuclear binding protein may cause insulin receptor dysfunction with subsequent impairment of insulin signaling and action.

Mechanism of Lipid Induced Insulin Resistance: An Overview

“…We have found that FA induced pPKCε impairs HMGA1 [34]. During IR gene transcription HMGA1 migrates from heterochromatin to euchromatin region and activates IR promoter [48,50]. Interestingly, pPKCε phosphorylates HMGA1 which restricted its mobility and therefore unable to activate IR promoter resulting reduced IR expression.…”

Recent advances in the molecular genetics of type 2 diabetes mellitus

“…We previously found that HMGA1 is a key regulator of INSR gene expression [69][70][71] (Figure 4). Consistent with these findings, we identified two patients with insulin-resistant T2DM who had defects in HMGA1 expression and concomitant decreased INSR mRNA and protein in muscle, fat and circulating monocytes [72] .…”

Insulin Receptor and its Relationship with Different Forms of Insulin Resistance

“…It was observed that the HMGI-Y inhibition in cells up-regulating INSR , led to its down-regulation. In turn, HMGI-Y over-expression in cells down-regulating the INSR, led to its up-regulation [15]. Taken together, it has been suggested that HMGI-Y positively regulates the expression of INSR.…”

“…Accordingly Brunetti et al suggested that the proteins binding to these regions play a crucial role in the spatial expression of ISNR [13]. Further experiments revealed that these regions (C2 and E3) are bound by high mobility group proteins (HMGI-Ys), in this way activating INSR gene transcription [15]. Electrophoretic mobility shift assay (EMSA) and Western blot experiments using nuclear proteins isolated from human lymphocyte IM-9 cell line enabled identification of the protein, which was named IR-DBP (Insulin Receptor DNA Binding Protein) and was highly similar to HMGI-Y proteins.…”