title: Induction of glutathione-S-transferase mRNA levels by chemopreventive selenocysteine Se-conjugates.
abstract: Several selenocysteine Se-conjugates (SeCys-conjugates) prevent against chemically induced carcinogenesis. Bioactivation to selenols (RSeH) by beta-lyases is thought to be critical, but the mechanism of tumor suppression remains unclear. Induction of phase II biotransformation enzymes is a possible mechanism of chemoprevention. In this study, we evaluated the isoform-selective induction of glutathione-S-transferase (GST) at the mRNA level using a quantitative reverse transcriptase polymerase chain reaction assay. In cultured primary rat hepatocytes and H35 Reuber rat hepatoma cells, SeCys-conjugates time-dependently increased mRNA levels of GST Alpha isoforms and GST Pi, but not of GST Mu isoforms. Se-allyl-L-selenocysteine, the most potent chemopreventive SeCys-conjugate so far known, was also the most active GST inducer. After exposure for 24hr, it elevated GSTA2, GSTA3, GSTA5, and GSTP mRNA levels in primary hepatocytes 3.2+/-0.4-, 1.9+/-0.1-, 4.3+/-0.3-, and 2.9+/-0.3-fold, respectively. Se-allyl-D-selenocysteine was significantly less active, suggesting that stereoselective conversion of SeCys-conjugates to selenols is involved in GST induction. In H35 Reuber hepatoma cells, where conversion of SeCys-conjugates to selenols was 2-6-fold lower than in primary hepatocytes, GST induction was also much lower than in primary hepatocytes. SeCys-conjugates did not induce cytochrome P450 1A1, 2B1/2, or 3A1. This indicates that SeCys-conjugates are monofunctional inducers of phase II biotransformation enzymes. The present results suggest that induction of GST expression contributes to the chemopreventive activity of SeCys-conjugates.
authors.affiliation: Leiden/Amsterdam Center for Drug Research, Division of Molecular Toxicology, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
authors.forename: Peter A C
authors.initials: PA
authors.lastname: 't Hoen
authors.forename: Martijn
authors.initials: M
authors.lastname: Rooseboom
authors.forename: Martin K
authors.initials: MK
authors.lastname: Bijsterbosch
authors.forename: Theo J C
authors.initials: TJ
authors.lastname: van Berkel
authors.forename: Nico P E
authors.initials: NP
authors.lastname: Vermeulen
authors.forename: Jan N M
authors.initials: JN
authors.lastname: Commandeur
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis; D004790:Enzyme Induction / Q000187:drug effects; D005982:Glutathione Transferase / Q000096:biosynthesis*; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D008190:Lyases / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis / Q000187:drug effects; D051381:Rats; D018036:Selenium Compounds / Q000378:metabolism; D017279:Selenocysteine / Q000737:chemistry / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D012333:RNA, Messenger; D018036:Selenium Compounds; C442270:selenol; D017279:Selenocysteine; D003577:Cytochrome P-450 Enzyme System; D005982:Glutathione Transferase; D008190:Lyases