Ganglioneuromas and renal anomalies are induced by activated RETMEN2B in transgenic mice

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Abstract
Multiple endocrine neoplasia type 2B (MEN2B) is an autosomal dominant syndrome characterized by the development of medullary thyroid carcinoma, pheochromocytomas, musculoskeletal anomalies and mucosal ganglioneuromas. MEN2B is caused by a specific mutation (Met918→Thr) in the RET receptor tyrosine kinase. Different mutations of RET lead to other conditions including MEN2A, familial medullary thyroid carcinoma and intestinal aganglionosis (Hirschsprung disease). Transgenic mice were created using the dopamine β-hydroxylase promoter to direct expression of RETMEN2B in the developing sympathetic and enteric nervous systems and the adrenal medulla. DβH-RETMEN2B transgenic mice developed benign neuroglial tumors, histologically identical to human ganglioneuromas, in their sympathetic nervous systems and adrenal glands. The enteric nervous system was not affected. The neoplasms in DβH-RETMEN2B mice were similar to benign neuroglial tumors induced in transgenic mice by activated Ras expression under control of the same promoter. Levels of phoshorylated MAP kinase were not increased in the RETMEN2B-induced neurolgial proliferations, suggesting that alternative pathways may play a role in the pathogenesis of these lesions. Transgenic mice with the highest levels of DβH-RETMEN2B expression, unexpectedly developed renal malformations analogous to those reported with loss of function mutations in the Ret gene.