REGULATION OF ERCC-1 MRNA EXPRESSION BY INSULIN

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Summary of work: Expression of DNA repair enzymes, which includes ERCC-1, may be under the control of hormonal and growth factor stimulation. In this study, it was observed that insulin increased ERCC-1 mRNA levels both in Chinese hamster ovary cells overexpressing human insulin receptors (HIRc cells) and in fully differentiated 3T3-L1 adipocytes. To investigate the mechanisms underlying the increase in ERCC-1 gene expression in HIRc cells, a variety of pharmacological tools known to inhibit distinct signaling pathways were used. None of these inhibitors affected the amount of ERCC-1 mRNA in unstimulated cells. The pretreatment of cells with two chemically unrelated phosphatidylinositol 3'-kinase inhibitors, wortmannin and LY294002, failed to block the 2-fold increase in ERCC-1 mRNA by insulin. Likewise, inhibition of pp70 S6 kinase by rapamycin had no apparent effects on this insulin response. In contrast, altering p21ras-dependent pathway with either manumycin, an inhibitor of Ras farnesylation, or PD98059, an inhibitor of the mitogen-activated protein kinase/extracellular-response kinase (ERK) kinase, suppressed the induction of ERCC-1 mRNA by insulin (P<0.001). Furthermore, inhibition of RNA and protein synthesis negatively regulated the expression of this insulin-regulated gene (P<0.005). These results suggest that insulin enhances ERCC-1 mRNA levels by activation of the Ras-ERK-dependent pathway without involvement of the phosphatidylinositol 3'-kinase/pp70 S6 kinase. The notion that hormones and growth factors could control expression of DNA repair genes in mammalian cells is of great interest. High glucose concentrations found in diabetic conditions results in DNA damage in a variety of cell types associated with perturbation of DNA repair synthesis. Such impairment in DNA repair may result in aberrant gene expression leading to degenerative disorders which includes diabetic microangiopathy. Efforts are underway to assess whether expression of DNA repair genes is altered in diabetic conditions.