RESUMO
Mutations of the neurofibromatosis 2 (NF2) tumor suppressor gene have frequently been detected not only in schwannomas and other central nervous system tumors of NF2 patients but also in their sporadic counterparts and malignant tumors unrelated to the NF2 syndrome such as malignant mesothelioma, indicating a broader role for the NF2 gene in human tumorigenesis. However, the mechanisms by which the NF2 product, merlin or schwannomin, is regulated and controls cell proliferation remain elusive. Here, we identify a novel GTP-binding protein, dubbed NGB (referring to NF2-associated GTP binding protein), which binds to merlin. NGB is highly conserved between Saccharomyces cerevisiae, Caenorhabditis elegans, and human cells, and its GTP-binding region is very similar to those found in R-ras and Rap2. However, ectopic expression of NGB inhibits cell growth, cell aggregation, and tumorigenicity in tumorigenic schwanomma cells. Down-regulation and infrequent mutation of NGB were detected in human glioma cell lines and primary tumors. The interaction of NGB with merlin impairs the turnover of merlin, yet merlin does not affect the GTPase nor GTP-binding activity of NGB. Finally, the tumor suppressor functions of NGB require merlin and are linked to its ability to suppress cyclin D1 expression. Collectively, these findings indicate that NGB is a tumor suppressor that regulates and requires merlin to suppress cell proliferation.
Assuntos
Proteínas de Ligação ao GTP/metabolismo , Neurofibromina 2/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Sequência de Aminoácidos , Animais , Sequência de Bases , Adesão Celular , Movimento Celular , Proliferação de Células , Sequência Conservada , Ciclina D1/metabolismo , Regulação para Baixo , Proteínas de Ligação ao GTP/química , Proteínas de Ligação ao GTP/genética , Proteínas de Ligação ao GTP/isolamento & purificação , Regulação Neoplásica da Expressão Gênica , Humanos , Camundongos , Dados de Sequência Molecular , Neoplasias/genética , Neoplasias/metabolismo , Neoplasias/patologia , Neurofibromina 2/genética , Ligação Proteica , Ratos , Alinhamento de Sequência , Proteínas Supressoras de Tumor/química , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/isolamento & purificação , Técnicas do Sistema de Duplo-Híbrido , Ubiquitina/metabolismoRESUMO
Previous studies have demonstrated amplification of the centrosome serine/threonine kinase BTAK/Aurora-A in 10-25% of ovarian cancers. However, alterations of BTAK/Aurora-A at kinase and protein levels and its role in ovarian cancer progression have not been well documented. In this study, we examined the kinase activity and protein levels of BTAK/Aurora-A in 92 patients with primary ovarian tumors. In vitro kinase analyses revealed elevated BTAK/Aurora-A kinase activity in 44 cases (48%). Increased BTAK/Aurora-A protein levels were detected in 52 (57%) specimens. High protein levels of BTAK/Aurora-A correlated well with elevated kinase activity. Activation and overexpression of BTAK/Aurora-A were more frequently detected in early stage/low-grade ovarian tumors, although there was no statistic significance at the kinase level between early stage/low-grade and late stage/high-grade tumors. Moreover, BTAK/Aurora-A was preferentially expressed in noninvasive tumors, as revealed by immunohistochemical staining, suggesting that alterations of BTAK/Aurora-A could be an early event in human ovarian oncogenesis. To our knowledge, this is the first demonstration of recurrent activation and overexpression of BTAK/Aurora-A in human ovarian cancer, which may play a critical role in development of this malignancy.
