Glucose-6-phosphatase (G6Pase) catalyzes the final step in the gluconeogenic and glycogenolytic pathways, the hydrolysis of glucose-6-phosphate (G6P) to glucose and phosphate. This paper describes the identification and characterization of a cDNA and the gene encoding the mouse ubiquitously expressed G6Pase catalytic subunit-related protein (UGRP). The open reading frame of this UGRP cDNA encodes a protein (346 amino acids (aa); M r 38 755) that shares 36% overall identity (56% similarity) with the mouse G6Pase catalytic subunit (357 aa; M r 40 454). UGRP exhibits a similar predicted transmembrane topology and conservation of many of the catalytically important residues with the G6Pase catalytic subunit; however, unlike the G6Pase catalytic subunit, UGRP does not catalyze G6P hydrolysis and does not contain a carboxy-terminal di-lysine endoplasmic reticulum retention signal. UGRP mRNA was detected by RNA blot analysis in every mouse tissue examined with the highest expression in heart, brain, testis and kidney. Database analysis showed that the mouse UGRP gene is composed of six exons, spans ∼4·2 kbp of genomic DNA and is located on chromosome 11 along with the G6Pase catalytic subunit gene. The UGRP gene transcription start sites were mapped by primer extension analysis, and the activity of the mouse UGRP gene promoter was analyzed using luciferase fusion gene constructs. In contrast to the G6Pase catalytic subunit gene promoter, the UGRP promoter was highly active in all cell lines examined.

The initial stages of diabetic nephropathy are characterized, in part, by expansion of the mesangial matrix and thickening of the glomerular basement membrane which are caused by increased extracellular matrix (ECM) protein synthesis and reduced degradation, a consequence of decreased matrix metalloproteinase (MMP) activity. These changes have been largely attributed to the effects of hyperglycemia such that the potential contribution of impaired insulin action to alterations in the ECM have not been studied in detail. We have shown here that insulin stimulates collagenase-1 fusion gene transcription in the MES 13 mesangial-derived cell line. Multiple collagenase-1 promoter elements are required for the full stimulatory effect of insulin but the action of insulin appears to be mediated through an activator protein-1 (AP-1) motif. Thus, mutation of this AP-1 motif abolishes insulin-stimulated collagenase fusion gene transcription and, in isolation, this AP-1 motif can mediate a stimulatory effect of insulin on the expression of a heterologous fusion gene. This suggested that the other collagenase-1 promoter elements that are required for the full stimulatory effect of insulin probably bind accessory factors that enhance the effect of insulin mediated through the AP-1 motif. In MES 13 cells, the AP-1 motif is bound by Fra-1, Fra-2, Jun B and Jun D. Stimulation of collagenase-1 fusion gene transcription by insulin requires activation of the mitogen-activated protein kinase (MEK) pathway since inhibition of MEK-1 and -2 blocks this effect. The potential significance of these observations with respect to a role for insulin in the pathophysiology of diabetic glomerulosclerosis is discussed.