Human insulin receptor substrate-2: gene organization and promoter characterization

Insulin receptor substrate-2 (IRS-2) belongs to a family of cytoplasmic adaptor proteins, which link insulin, IGF-1, and cytokine receptor tyrosine kinases to signaling pathways regulating metabolism, growth, and differentiation (1-3). IRS-2-deficient mice display all characteristics of type 2 diabetes, suggesting that dysfunction of the IRS-2 gene may contribute to the pathogenesis of human type 2 diabetes (4). Based on its progesterone inducibility, we have recently cloned and sequenced a full-length human IRS-2 cDNA containing an open reading frame (ORF) of 4,014 bp and 5'- and 3'-untranslated regions (UTRs) of 516 and 2,466 bp (5). Although the IRS-2 gene has previously been thought to lack introns within the coding region (6,7), the amino acid sequence predicted from our cDNA sequence differed at its very COOH-terminal end from an IRS-2 protein sequence derived from genomic IRS-2 sequences. Therefore, we carefully analyzed the genomic structure of the IRS-2 gene and found that the IRS-2 gene contains an intron that disrupts the ORF. Characterization of promoter and 5'-flanking regions of IRS-2 by sequencing, reporter gene assays, and chromatin structure analysis suggests that elements conferring progesterone inducibility are not located immediately upstream of the gene promoter.