2000 Volume 23 Issue 5 Pages 575-580
Since it is known that hypoxia increases inducible nitric oxide synthase (iNOS) gene expression through the hypoxia responsive element, it was hypothesized that nitric oxide could be a mediator of hypoxia to inhibit Cyp1a1 promoter activity. In order to test this hypothesis, we have undertaken a study to examine the effects of hypoxia and nitric oxide on Cyp1a1 promoter activity in Hepa I cells. Mouse Cyp1a1 5' flanking DNA, 1.6kb, was cloned into pGL3 expression vector in order to construct pmCyp1a1-Luc. Hepa I cells were tranfercted with pmCyp1a1-Luc and were treated with 10-9M 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) in the presence or absence of various hypoxic agents such as 10-6-10-4M cobalt chloride or 10-6-10-4M picolinic acid or 10-6-10-4M desferrioxamine. The luciferase activity of the reporter gene was measured from pmCyp1a1-Luc transfected Hepa I cell lysate which contains 2μg total protein using luciferin as a substrate. Hypoxic agents such as cobalt chloride, picolinic acid, and desferrioxamine showed inhibition of luciferase activity that was induced by 10-9M TCDD treatment in a dose dependent manner. Concomitant treatment of 1mM NG-nitro-l-arginine with 10-6-10-4M cobalt chloride or 10-6-10-4M desferrioxamine or 10-6-10-4M picolinic acid or 10-6-10-4M sodium nitroprusside recovered luciferase activity from the TCDD induced luciferase activity that was inhibited by hypoxic agents. These data demonstrated that nitric oxide might be a mediator of iron chelating agents and hypoxic agents to inhibit dioxin induced Cyp1a1 promoter activity in Hepa I cells.
