We isolated a cDNA clone, pAH1005, originating from the 6.8-kilobases mRNA of the rat ascites hepatoma cell line, AH60C. The sequence was highly expressed in various tumor tissues and tumor lines in rats, mice and humans. In rats, the expression of the sequence was also observed in fetal liver of 7 and 10 days of gestation, to some extent in the regenerating liver, yet was sparse in normal adult tissues. Additionally, this expression was induced when adult rat hepatocytes in primary monolayer cultures proliferated by the addition of epidermal growth factor and insulin. Southern blot analysis showed no major gene amplification and rearrangement between DNAs from hepatoma and normal liver of the same species. In addition, in vitro nuclear transcription assay revealed that a genomic clone corresponding to the pAH1005 hybridized to the nascent RNA from isolated nuclei of AH60C but not from those of normal rat liver. All these observations suggest that the expression of the conserved sequence we isolated is closely associated with cell growth and is regulated at the transcriptional level.
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