Genetic alterations in N-bis(2-hydroxypropyl)nitrosamine-induced rat transplantable thyroid carcinoma lines: analysis of the TSH-R, G(alpha)s, ras and p53 genes.
It has recently been shown that point mutations of the TSH-R or G(alpha)s genes are associated with autonomous hyperfunctioning thyroid adenomas and differentiated carcinomas. We therefore screened for mutations in the TSH-R, G(alpha)s, ras and p53 genes in nine rat transplantable thyroid carcinoma lines derived from tumors induced by DHPN as a chemical carcinogen. Mutations were identified using single-strand conformation polymorphism and DNA sequencing analysis. Point mutations in G(alpha)s codon 201 (CGC-->CAC) were detected in three lines (33%), resulting in a heterozygous alteration (Arg-->His) in the expressed G(alpha)s protein. The mean intracellular cAMP level (2.30 +/- 0.27 nmol/mg) of the three mutated cell lines was significantly increased as compared with that of the lines (1.54 +/- 0.32 nmol/mg) without the G(alpha)s mutation (P < 0.01, by paired t-test). Also, these three cell lines had an activating mutation in Ki-ras codon 12 (GGT-->GAT). One TSH-R gene mutation was found with a base substitution in codon 636 (TGC-->TGT) but no amino acid change. No p53 gene (exons 5-8) mutations were detected in any of the cell lines analyzed. The results suggest that mutational activation of the G(alpha)s gene may play a tumorigenic role through constitutive activation of the cAMP pathway and that G-->A point mutations in the G(alpha)s and ras genes in thyroid carcinomas directly reflect interaction of the chemical carcinogen with guanine residues in DNA.
Kitahori
Y
Y
Second Department of Pathology, Nara Medical University, Shijo-cho, Kashihara, Japan.
Naitoh
H
H
Konishi
N
N
Ohnishi
T
T
Hiasa
Y
Y
D000818:Animals; D002273:Carcinogens; D019204:GTP-Binding Proteins / Q000235:genetics*; D016158:Genes, p53 / Q000235:genetics*; D011905:Genes, ras / Q000235:genetics*; D009374:Neoplasms, Experimental / Q000139:chemically induced / Q000235:genetics; D009602:Nitrosamines; D017354:Point Mutation; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011989:Receptors, Thyrotropin / Q000235:genetics*; D013964:Thyroid Neoplasms / Q000139:chemically induced / Q000235:genetics*; D014407:Tumor Cells, Cultured
D002273:Carcinogens; D009602:Nitrosamines; D012333:RNA, Messenger; D011989:Receptors, Thyrotropin; C012457:diisopropanolnitrosamine; D019204:GTP-Binding Proteins