Nuclear factor kappa B (NF-kB) induced regulation of SLC2A4 gene expression: direct transcriptional control?

Abstract

Several components of Metabolic Syndrome are associated with inflammation. Among them, insulin resistance has been extensively associated with inflammation, playing important role in the genesis of type 2 diabetes mellitus (T2DM), as well as in the evolution of T1DM and T2DM. Reduced glucose uptake by adipose and muscle tissues is a feature in the insulin resistance, and that is clearly related to decreased expression of the solute carrier 2A4 (SLC2A4) gene, which encodes the glucose transporter 4 (GLUT4). However, the mechanisms involved in the SLC2A4 repression in that situation are unclear. It has been suggested that inflammatory cytokines, such as the Tumor Necrosis Factor alpha (TNF-alpha) are involved in the SLC2A4 repression. In a previous study, we showed that inflammatory activity in adipose tissue of obese mice was accompanied by decreased expression of SLC2A4 gene, and increased activity of Nuclear Factor kappa B (NF-kappa B) pathway; which mediates the effects of several cytokines, including TNF-alpha. However, the direct transcriptional control of SLC2A4 gene by NF-kappaB has never been described. Taking into account that the promoter region of SLC2A4 gene contains two sequences (-134/-112 and -82/-60 of mouse gene) highly homologous to known consensus NF-kappa B binding domain, we hypothesize that this transcriptional factor could act as a direct repressor of the SLC2A4 transcriptional activity. The aims (and experimental approaches) of the present study are: 1) to show the direct binding of NF-kappaB in the -134/-112 and -82/-60 domains of SLC2A4 gene in vitro (electrophoretic mobility assay - EMSA / gel shift and super supershift) and in vivo (chromatin immunoprecipitation assay - ChIP assay); 2) to show the functional activity of these domains (gel reporter assay); and 3) to show situations in which the SLC2A4 gene is regulated by NF-kappa B in adipose (3T3L1) and muscle (L6) cells challenged by TNF-alpha, oleic and linoleic fatty acids, estradiol, insulin, among others, as well as in tissues of obese mice and rats. We expect to reveal that in several situations the GLUT4 expression is transcriptionally regulated by NF-kappa B. This represents an alternative field of investigation of a mechanism by which we could enhance the GLUT4 expression, contributing to increase insulin sensitivity and improve glycemic control. (AU)