Multiple endocrine neoplasia type 2B mutation in human RET oncogene induces medullary thyroid carcinoma in transgenic mice

Multiple endocrine neoplasia type 2B (MEN 2B) is a familial cancer syndrome, in which the cardinal feature is medullary thyroid carcinoma (MTC), a malignant tumor arising from the calcitonin producing thyroid C-cells. MEN 2B is associated with a germline point mutation in the RET proto-oncogene, leading to a Met-->Thr substitution at codon 918 in the kinase domain, which alters the substrate specificity of the protein. We used the human calcitonin gene (CALC-I) promoter to generate transgenic mice expressing either the human RET oncogene with the MEN2B-specific 918 Met-->Thr mutation (CALC-MEN2B-RET) or the human non-mutated RET proto-oncogene (CALC-WT-RET) in the C-cells. At 20 - 22 months of age three out of eight CALC-MEN2B-RET transgenic founders presented with macroscopic bilateral MTC. In two founders nodular C-cell hyperplasia (CCH) was observed. Thyroid abnormalities were never observed in CALC-WT-RET transgenic mice or control non-transgenic mice analysed at this age. In some mice from established CALC-MEN2B-RET transgenic lines nodular CCH was observed from 8 months on whereas MTC was detected in 13% of mice from one CALC-MEN2B-RET line, from the age of 11 months on. These results show for the first time that the MEN2B mutation in the RET oncogene predisposes mice for MTC.