title: Expression profile and down-regulation of argininosuccinate synthetase in hepatocellular carcinoma in a transgenic mouse model.
abstract: BACKGROUND
  Argininosuccinate synthetase (ASS) participates in urea and nitric oxide production and is a rate-limiting enzyme in arginine biosynthesis. Regulation of ASS expression appears complex and dynamic. In addition to transcriptional regulation, a novel post-transcriptional regulation affecting nuclear precursor RNA stability has been reported. Moreover, many cancers, including hepatocellular carcinoma (HCC), have been found not to express ASS mRNA; therefore, they are auxotrophic for arginine. To study when and where ASS is expressed and whether post-transcriptional regulation is undermined in particular temporal and spatial expression and in pathological events such as HCC, we set up a transgenic mouse system with modified BAC (bacterial artificial chromosome) carrying the human ASS gene tagged with an EGFP reporter.
  
  
  RESULTS
  We established and characterized the transgenic mouse models based on the use of two BAC-based EGFP reporter cassettes: a transcription reporter and a transcription/post-transcription coupled reporter. Using such a transgenic mouse system, EGFP fluorescence pattern in E14.5 embryo was examined. Profiles of fluorescence and that of Ass RNA in in situ hybridization were found to be in good agreement in general, yet our system has the advantages of sensitivity and direct fluorescence visualization. By comparing expression patterns between mice carrying the transcription reporter and those carrying the transcription/post-transcription couple reporter, a post-transcriptional up-regulation of ASS was found around the ventricular zone/subventricular zone of E14.5 embryonic brain. In the EGFP fluorescence pattern and mRNA level in adult tissues, tissue-specific regulation was found to be mainly controlled at transcriptional initiation. Furthermore, strong EGFP expression was found in brain regions of olfactory bulb, septum, habenular nucleus and choroid plexus of the young transgenic mice. On the other hand, in crossing to hepatitis B virus X protein (HBx)-transgenic mice, the Tg (ASS-EGFP, HBx) double transgenic mice developed HCC in which ASS expression was down-regulated, as in clinical samples.
  
  
  CONCLUSIONS
  The BAC transgenic mouse model described is a valuable tool for studying ASS gene expression. Moreover, this mouse model is a close reproduction of clinical behavior of ASS in HCC and is useful in testing arginine-depleting agents and for studies of the role of ASS in tumorigenesis.
authors.affiliation: Institute of Microbiology & Immunology, National Yang-Ming University, Taipei, Taiwan. benson.shiue@gmail.com.
authors.forename: Shih-Chang
authors.initials: SC
authors.lastname: Shiue
authors.affiliation: Department of Medical Research, Taipei Veterans General Hospital, Taipei, 112, Taiwan. mzhuang@vghtpe.gov.tw.
authors.forename: Miao-Zeng
authors.initials: MZ
authors.lastname: Huang
authors.affiliation: Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan. tftsai@ym.edu.tw.
authors.forename: Ting-Fen
authors.initials: TF
authors.lastname: Tsai
authors.affiliation: Institute of Neuroscience, National Yang-Ming University, Taipei, Taiwan. acchang@ym.edu.tw.
authors.forename: Alice Chien
authors.initials: AC
authors.lastname: Chang
authors.affiliation: Department of Preclinical Sciences, Faculty of Medicine and Health Sciences, Universiti Tunku Abdul Rahman, Selangor, Malaysia. chookb@utar.edu.my.|Centre for Stem Cell Research, Universiti Tunku Abdul Rahman, Selangor, Malaysia. chookb@utar.edu.my.
authors.forename: Kong Bung
authors.initials: KB
authors.lastname: Choo
authors.affiliation: Department of Animal Science, Chinese Culture University, Taipei, Taiwan. hqr2@faculty.pccu.edu.tw.|Graduate Institute of Biotechnology, Chinese Culture University, Taipei, Taiwan. hqr2@faculty.pccu.edu.tw.
authors.forename: Chiu-Jung
authors.initials: CJ
authors.lastname: Huang
authors.affiliation: Institute of Microbiology & Immunology, National Yang-Ming University, Taipei, Taiwan. su31659@gmail.com.|Department of Medical Research, Taipei Veterans General Hospital, Taipei, 112, Taiwan. su31659@gmail.com.|Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan. su31659@gmail.com.
authors.forename: Tsung-Sheng
authors.initials: TS
authors.lastname: Su
mesh_terms: D000818:Animals; D001124:Argininosuccinate Synthase / Q000235:genetics* / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology*; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009928:Organ Specificity; D013047:Specific Pathogen-Free Organisms
chemical_list: C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D001124:Argininosuccinate Synthase