Molecular study of signaling-pathway genes in experimental rat thyroid carcinoma.
BACKGROUND
A study was conducted on histological patterns and biomolecular changes in Goitrogen-induced experimental rat thyroid tumors. The link between the histological types observed and N-ras, B-raf, and PI3KCA gene mutations widely reported in human thyroid cancers was explored.


METHODS
An analysis was done on paraffin-embedded tumor tissue sections from Wistar rats receiving 1% potassium perchlorate (KClO(4)) added to the ad libitum drinking-water supply over an 18-month period. Three experimental subgroups were formed, each comprising 10 thyroids: subgroup I (control) consisted of thyroids from untreated controls; subgroups II and III (experimental) consisted of thyroids from KClO(4)-treated rats, displaying capsular, vascular, or both invasion but no metastasis (II), or distant metastasis (III). DNA was extracted from paraffin-embedded tissues. To test for the genetic mutations most widely reported in human thyroid cancers, exon 1 of the N-ras gene, exons 9 and 20 of the PI3KCA gene, and exon 15 of the B-raf gene were amplified and sequenced.


RESULTS
All tumors were of the follicular type. None of the 20 experimental rat thyroids displayed the expected gene mutations reported in humans. However, 90% of them contained four new B-raf gene mutations and all were silent and did not cause an amino acid substitution in the protein chain.


CONCLUSIONS
Biomolecular analysis suggested that N-ras, PI3KCA, and B-raf gene mutations may not be involved in thyroid tumor formation using the experimental procedure applied in this study. But the four mutations in B-raf, though without functional repercussions, may be a specific marker for this tumor type.
Departamento de Citología e Histología Normal y Patológica, Universidad de Sevilla, Sevilla, Spain.
María Inés
MI
Carmona-López
Manuel
M
De Miguel
Hugo
H
Galera-Ruiz
María José
MJ
Ríos-Moreno
Ana
A
Fernández
Hugo
H
Galera-Davidson
D018263:Adenocarcinoma, Follicular / Q000139:chemically induced / Q000235:genetics* / Q000473:pathology*; D000818:Animals; D001483:Base Sequence; D005091:Exons; D005260:Female; D011905:Genes, ras; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010472:Perchlorates / Q000633:toxicity; D017680:Potassium Compounds / Q000633:toxicity; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics*; D013964:Thyroid Neoplasms / Q000139:chemically induced / Q000235:genetics* / Q000473:pathology
D010472:Perchlorates; D017680:Potassium Compounds; C009006:potassium perchlorate; C482123:Braf protein, rat; D048493:Proto-Oncogene Proteins B-raf