RESUMO
Medullary thyroid carcinoma (MTC) is a malignancy derived from the calcitonin-producing C-cells of the thyroid gland. Oncogenic mutations of the Ret proto-oncogene are found in all heritable forms of MTC and roughly one half of the sporadic cases. However, several lines of evidence argue for the existence of additional genetic lesions necessary for the development of MTC. Sprouty (Spry) family of genes is composed of four members in mammals (Spry1-4). Some Spry family members have been proposed as candidate tumor-suppressor genes in a variety of cancerous pathologies. In this work, we show that targeted deletion of Spry1 causes C-cell hyperplasia, a precancerous lesion preceding MTC, in young adult mice. Expression of Spry1 restrains proliferation of the MTC-derived cell line, TT. Finally, we found that the Spry1 promoter is frequently methylated in MTC and that Spry1 expression is consequently decreased. These findings identify Spry1 as a candidate tumor-suppressor gene in MTC.
Assuntos
Carcinoma Medular/genética , Metilação de DNA , Genes Supressores de Tumor , Proteínas de Membrana/genética , Fosfoproteínas/genética , Regiões Promotoras Genéticas , Neoplasias da Glândula Tireoide/genética , Proteínas Adaptadoras de Transdução de Sinal , Animais , Carcinoma Medular/patologia , Carcinoma Neuroendócrino , Linhagem Celular Tumoral , Proliferação de Células , Feminino , Humanos , Hiperplasia , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Knockout , Camundongos SCID , Fosfoproteínas/metabolismo , Lesões Pré-Cancerosas/patologia , Proto-Oncogene Mas , Proteínas Proto-Oncogênicas c-ret/genética , Interferência de RNA , RNA Interferente Pequeno , Deleção de Sequência , Glândula Tireoide/metabolismo , Glândula Tireoide/patologia , Neoplasias da Glândula Tireoide/patologiaRESUMO
Hereditary susceptibility to pheochromocytoma (PCC) and paraganglioma (PGL) represents a very complex genetic scenario. It has been reported that the absence of familial antecedents of the disease does not preclude the existence of a mutation affecting any of the five major susceptibility genes. In fact, 11-24% of apparently sporadic cases (without familial or syndromic antecedents) harbor an unexpected germline mutation, but we do not know what is happening in "truly apparently" sporadic patients (i.e., apparently sporadic cases diagnosed with only one tumor). In the present study, we have analyzed 135 apparently sporadic patients developing a single tumor for the five major susceptibility genes: VHL, RET, SDHB, SDHC, and SDHD. Fourteen percent of cases were found to harbor a germline mutation, and only 2.2% of patients were older than 45 years at onset. By taking into account the tumor location and a threshold age at onset of 45 years, we propose a rational scheme for genetic testing. Analyzing VHL and RET genes would be recommended only in young patients developing a single PCC. On the other hand, genetic testing of SDHD should be done in all patients developing an extra-adrenal tumor before the age of 45, and SDHC could be the responsible gene in cases developing a single head and neck tumor, independently of age. Finally, the analysis of SDHB should always be performed because of its association to malignancy and the low penetrance of mutations affecting this gene.
