Insulin is known to regulate the transcription of almost 100 genes indicating that this represents a major action of this hormone. For a few of these genes specific cis-acting elements, referred to as insulin response sequences/elements (IRSs/IREs), have been identified through which insulin regulates their transaction. This information is important since various investigators have speculated that a defect in insulin-regulated gene transcription may explain some aspects of non-insulin dependent diabetes mellitus (NIDDM). Moreover, it has recently been shown that a mutation in the apolipoprotein CIII (apo CIII) IRS, resulting in a loss of insulin-regulated apo CIII gene transcription, is one cause of hypertriglyceridemia in humans. A consensus IRS/IRE sequence has not emerged, instead most of the sequences identified to date appear unique. Based on what is known concerning the mechanisms by which other hormones regulate gene transcription, it seems very unlikely that insulin will use unique mechanisms to regulate every gene. Phorbol esters can regulate gene transcription through at least eight cis-acting elements and we believe that a similar situation will exist with respect to insulin-regulated gene transcription. Clearly this is a field still waiting for its general principles to emerge. A broad objective of this proposal is to use the gene encoding malic enzyme (ME) as a model system to further the understanding of the molecular mechanisms whereby insulin regulates gene transcription. The investigator's preliminary data suggests that, while insulin stimulates ME gene transcription and the second goal is to identify the trans-acting factor that this element binds. The relative basal expression of the ME gene has been genetically linked to the difference in the severity of diabetes seen in C57BL/KsJ-db/db as compared to C57BL/KsJ-db/db mice. The third objective of this proposal concerns the biochemical analysis of the basis for this variation in basal ME gene expression and the determination of whether an alteration in basal ME gene expression contributes directly to the pathophysiology of NIDDM. The investigator's preliminary data suggests that a transcription factor is differentially expressed in the mouse strains.
