Absence of activating mutations of the genes encoding the α-subunits of G₁₁ and G(q) in thyroid neoplasia

Activating mutations of the TSH receptor and α-subunit of G(s) (Gα(s)) that increase adenylyl cyclase activity have been identified in a subset of hyperfunctioning benign thyroid follicular adenomas and, less commonly, in hypofunctioning adenomas and carcinomas. In addition, some thyroid tumors exhibit inappropriate activation of phospholipase C (PLC), a signaling pathway that has been implicated in the growth and dedifferentiation of thyroid cells. We therefore hypothesized that some thyroid tumors might be caused by somatic mutations in the genes encoding the α-chain of G(q) or G₁₁ that result in constitutive activation of the PLC pathway. We amplified regions of the α(q) and α₁₁ genes that encode amine acids, Q209 and R183, and we screened the DNA for mutations by sequence analysis and denaturing gradient gel electrophoresis. No mutations were identified after analysis of DNA from 38 thyroid tumors and 2 poorly differentiated thyroid carcinoma cell lines, including: 13 follicular adenomas, 10 follicular carcinomas, 5 papillary carcinomas, and 10 hyperplastic nodules from multinodular goiters. We conclude that activating mutations of α(q) and α₁₁ are absent or rare in hypofunctioning thyroid neoplasms and that other mechanisms must explain the elevated PLC activity reported in thyroid carcinoma.