Oncogenic activation of the ret protooncogene in thyroid cancer.
Recent studies have established that the ret protooncogene is involved in the development of thyroid tumors, including medullary and papillary thyroid carcinomas. Germ line mutations of the ret protooncogene were identified in multiple endocrine neoplasia (MEN) types 2A and 2B that share the clinical feature of medullary thyroid carcinoma and pheochromocytoma. MEN 2A mutations involved cysteine residues in the extracellular domain and induced disulfide-linked homodimerization of the Ret protein on the cell surface, leading to activation of its intrinsic tyrosine kinase. On the other hand, a single point mutation in the tyrosine kinase domain was found in MEN 2B, as well as in 30 to 40% of sporadic medullary carcinoma. This mutation also resulted in activation of Ret tyrosine kinase without the formation of its covalent homodimerization. Differences in the mechanisms of ret activation might account for the different phenotypes observed in MEN 2A and MEN 2B. In addition, somatic rearrangement of the ret protooncogene was frequently detected in papillary thyroid carcinoma, particularly from adult Europeans. A recent report demonstrated that the same rearrangement was observed in approximately 60% of papillary carcinomas of children from areas contaminated by the Chernobyl accident, suggesting that ret rearrangement was induced as a direct consequence of radiation exposure. In this review, I focus on the ret mutations detected in thyroid cancer and discuss the mechanisms of its oncogenic activation.
Takahashi
M
M
Department of Pathology, Nagoya University School of Medicine, Japan.
D002291:Carcinoma, Papillary / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins; D015972:Gene Expression Regulation, Neoplastic; D018095:Germ-Line Mutation; D006801:Humans; D018813:Multiple Endocrine Neoplasia Type 2a / Q000235:genetics; D018814:Multiple Endocrine Neoplasia Type 2b / Q000235:genetics; D009381:Neoplasms, Radiation-Induced / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D051096:Proto-Oncogene Proteins c-ret; D011519:Proto-Oncogenes; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D013964:Thyroid Neoplasms / Q000235:genetics* / Q000378:metabolism
D029721:Drosophila Proteins; D011518:Proto-Oncogene Proteins; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila