title: The putative tumor suppressor Tsc-22 is downregulated early in chemically induced hepatocarcinogenesis and may be a suppressor of Gadd45b.
abstract: Tsc-22 is a novel tumor suppressor gene that represents a new class of transcription factors that has transcriptional repressor activity. We found Tsc-22 downregulation in livers from B6C3F1 mice following treatment for 2 weeks with carcinogenic doses of the antianxiety drug oxazepam (2500 ppm) or the peroxisome proliferator Wyeth-14,643 (500 ppm) but not with two other carcinogens such as o-nitrotoluene or methyleugenol or three noncarcinogens including p-nitrotoluene, eugenol, or acetaminophen. The expression of Tsc-22 was also repressed in B6C3F1 mouse liver tumors that were induced by several chemicals from 2-year carcinogenicity studies as well as in spontaneous liver tumors. To identify potential Tsc-22 target genes in mouse liver, we transfected small interference RNA (SiRNA) designed to inhibit Tsc-22 into murine liver BNL-CL.2 cells. We selected two potential transcriptional targets of Tsc-22, growth arrest and DNA damage-inducible gene 45 beta (Gadd45b) and leucine zipper, putative tumor suppressor 2 (Lzts2) to test based on our previous complementary DNA microarray studies, showing that expression of these cancer-associated genes was increased when Tsc-22 was repressed. SiRNA treatment of BNL-CL.2 cells with Tsc-22 oligonucleotides but not nonspecific oligonucleotides decreased RNA and protein expression of Tsc-22 by 80-90%, while expression of Gadd45b gene, but not Lzts2, was increased over time after an initial decrease. Treatment of these cells with oxazepam for 48 h also resulted in decreased Tsc-22 and increased Gadd45b expression. These data provide evidence that Tsc-22 is a suppressor of Gadd45b expression, which may contribute to an early antiapoptotic response.
authors.affiliation: Laboratory of Molecular Carcinogenesis, Toxicology Operations Branch, Environmental Toxicology Program, National Institute of Environmental Health Sciences, National Institute of Health, Research Triangle Park, NC 27709, USA. kotorogzo@yahoo.co.jp
authors.forename: Mari
authors.initials: M
authors.lastname: Iida
authors.forename: Colleen H
authors.initials: CH
authors.lastname: Anna
authors.forename: Nicole D
authors.initials: ND
authors.lastname: Gaskin
authors.forename: Nigel J
authors.initials: NJ
authors.lastname: Walker
authors.forename: Theodora R
authors.initials: TR
authors.lastname: Devereux
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism*; D002273:Carcinogens / Q000633:toxicity*; D045744:Cell Line, Tumor; D015536:Down-Regulation; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D016147:Genes, Tumor Suppressor / Q000187:drug effects*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced* / Q000235:genetics; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D020411:Oligonucleotide Array Sequence Analysis; D010076:Oxazepam / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D000097642:GADD45 Proteins
chemical_list: D000943:Antigens, Differentiation; D002273:Carcinogens; D010076:Oxazepam; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D053773:Transforming Growth Factor beta1; D025521:Tumor Suppressor Proteins; C490125:Gadd45b protein, mouse; D000097642:GADD45 Proteins; C490983:Tgfb1i4 protein, mouse