High glucose induces transactivation of the human paraoxonase 1 gene in hepatocytes.
Human serum paraoxonase 1 (PON1) is associated with high-density lipoprotein and inhibits oxidative modification of low-density lipoprotein in vitro. Therefore, PON1 is expected to protect against atherosclerosis in vivo. We and other investigators have shown that PON1 enzymatic activity is decreased in diabetic patients; however, an alteration in hepatic PON1 synthesis under hyperglycemic conditions remains unclear. We previously demonstrated that Sp1 is a positive regulator of PON1 transcription and that an interaction between Sp1 and protein kinase C (PKC) is a crucial mechanism for the effect of Sp1 on PON1 transcription in cultured HepG2 cells. Because several PKC isoforms are activated under hyperglycemic conditions, we examined the effect of d-glucose, which can activate the diacylglycerol-PKC pathway, on the transcription and expression of PON1. For a reporter gene assay, Huh7 human hepatocyte cell line incorporated with PON1 (-1232/-6)-luciferase expression vector was established using a cationic lipid method. d-Glucose dose dependently enhanced PON1 promoter activity. d-Glucose also enhanced both messenger RNA and protein expression of PON1. Increased PON1 expression was also detected in primary human hepatocytes treated with high d-glucose concentrations. Bisindolylmaleimide, a PKC inhibitor, significantly inhibited d-glucose-induced transactivation of PON1; and mithramycin, an inhibitor of Sp1, completely abrogated the transactivation. Our data suggest that high glucose concentrations transactivate the PON1 gene through Sp1 activation by PKC in cultured hepatocytes. Up-regulated hepatic PON1 expression under high glucose conditions may be a compensatory mechanism in diabetes in which antioxidant capacity, including PON1 enzymatic activity, is attenuated.
Ikeda
Yukio
Y
Department of Endocrinology, Metabolism and Nephrology, Kochi Medical School, Kochi University, Nankoku, Kochi 783-8505, Japan.
Suehiro
Tadashi
T
Arii
Kaoru
K
Kumon
Yoshitaka
Y
Hashimoto
Kozo
K
D043303:Aryldialkylphosphatase / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000378:metabolism / Q000502:physiology; D015533:Transcriptional Activation / Q000187:drug effects*; D014162:Transfection
D012333:RNA, Messenger; D016329:Sp1 Transcription Factor; D011493:Protein Kinase C; D043303:Aryldialkylphosphatase; C468406:PON1 protein, human; D005947:Glucose