title: Identification of argininosuccinate lyase as a hypoxia-responsive gene in rat hepatocytes.
abstract: OBJECTIVE
  The differential oxygenation of periportal and perivenous hepatocytes has been demonstrated as a major determinant in the zonated expression of certain metabolic pathways in the liver. We have searched for novel genes whose expression could be modulated by hypoxia in cultured rat hepatocytes.
  
  
  METHODS
  Primary cultures of rat hepatocytes were incubated under normoxic (21% oxygen) or hypoxic (3% oxygen) conditions for 6 h. Differences in gene expression under both conditions were analyzed using the technique of differential display by means of PCR.
  
  
  RESULTS
  We have identified the enzyme argininosuccinate lyase (ASL) as being downregulated by hypoxia. ASL is a cytosolic protein which participates in urea metabolism. ASL expression was time-dependently reduced in hypoxia. Hypoxia modulated the responses of this gene to the two main hormonal signals which induce ASL mRNA: glucocorticoids and cAMP. ASL mRNA levels decreased in response to ATP-reducing agents. CoCl2 mimicked the effect of hypoxia, suggesting the implication of a hemoprotein in this response. Hypoxia did not affect ASL mRNA stability, indicating that this effect occurs at the transcriptional level.
  
  
  CONCLUSIONS
  Our observations suggest that differences in oxygen levels across the hepatic parenchyma could participate in the zonated expression of ASL.
authors.affiliation: Unidad de Hepatologia y Terapia Génica, Departamento de Medicina Interna, Facultad de Medicina, Universidad de Navarra, Pamplona, Spain.
authors.forename: M U
authors.initials: MU
authors.lastname: Latasa
authors.forename: M V
authors.initials: MV
authors.lastname: Carretero
authors.forename: E R
authors.initials: ER
authors.lastname: García-Trevijano
authors.forename: L
authors.initials: L
authors.lastname: Torres
authors.forename: J M
authors.initials: JM
authors.lastname: Mato
authors.forename: M A
authors.initials: MA
authors.lastname: Avila
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D001123:Argininosuccinate Lyase / Q000235:genetics*; D015687:Cell Hypoxia; D005576:Colforsin / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D022781:Hepatocytes / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species; D014221:Triamcinolone / Q000494:pharmacology
chemical_list: D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D005576:Colforsin; D014221:Triamcinolone; D000255:Adenosine Triphosphate; D001123:Argininosuccinate Lyase