Molecular study of signaling-pathway genes in experimental rat thyroid carcinoma.

ABSTRACT

INTRODUCTION: 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. MATERIAL AND 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.