Investigation of possible involvement of several genes related to development of hepatocarcinogenesis in rats.
A comparative study on the possible involvement of several genes in the susceptibility of chemical carcinogenesis was carried out using carcinogen-resistant DRH rat and -sensitive Donryu and F344 rats. Previously, we observed that the induction of glutathione S-transferase placental form (GST-P) in the liver of Donryu rats by 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) was significantly greater than that of DRH rats. In the present study, we tentatively determined base sequences of the enhancer region including GPE-I and GPE-II (GST-P enhancers I and II) of GST-P genes of DRH, Donryu and F344 rats, but we did not observe any nucleotide polymorphism around these regions. Furthermore, the mRNA levels of silencer binding protein (NFA-1) for the GST-P promoter of rat liver were also similar in the DRH and Donryu rats. Since clonal expansion of putative preneoplastic GST-P-positive foci in the DRH rat liver was significantly suppressed during 3'-Me-DAB administration, we examined whether two opposite growth controlling factors, TGF-alpha and TGF-beta, may participate in such suppression of growth. It was supposed that mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R), at least in part, activates TGF-beta preproprotein. However, we observed that the levels of M6P/IGF2R mRNA in the livers of DRH were not higher than those of Donryu rats after being fed 3'-Me-DAB for 8 weeks. Another important factor in the carcinogenesis is insulin-like growth factor II itself. Although liver tumors induced by 3'-Me-DAB in F344 had high levels of IGF-II mRNA, little IGF-II gene expression existed in normal adult livers of Donryu, F344 and DRH rats. High levels of IGF-II mRNA were detected similarly in the livers of neonates from all these three strains of rats. Finally, we detected a significant increase of AFP (alpha-fetoprotein) mRNA in the livers of Donryu rats around 6 to 8 weeks from the start of 3'-Me-DAB feeding, which is in parallel with detrimental effects of this carcinogen on these rats. A reduced induction of AFP mRNA was observed in DRH rats under the same conditions. Further study will be needed to explain the lower tumor susceptibility in the DRH rat.
Todaka
N
N
Department of Biochemistry, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
Higashi
K
K
Yan
Y
Y
Abe
T
T
Yamashiro
K
K
Hiai
H
H
D000818:Animals; D001483:Base Sequence; D004742:Enhancer Elements, Genetic; D015972:Gene Expression Regulation, Neoplastic; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D005982:Glutathione Transferase / Q000235:genetics; D007335:Insulin-Like Growth Factor II / Q000235:genetics; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000235:genetics*; D008297:Male; D008749:Methyldimethylaminoazobenzene; D008969:Molecular Sequence Data; D051381:Rats; D011916:Rats, Inbred F344; D011919:Rats, Inbred Strains; D016212:Transforming Growth Factor beta / Q000235:genetics; D000509:alpha-Fetoproteins / Q000235:genetics
D016212:Transforming Growth Factor beta; D000509:alpha-Fetoproteins; D008749:Methyldimethylaminoazobenzene; D007335:Insulin-Like Growth Factor II; D005982:Glutathione Transferase