RESUMO
The neurofibromatosis 1 (NF1) gene has been implicated in astrocyte growth regulation in several studies. To determine whether loss of NF1 expression is associated with progression towards malignancy in sporadic astrocytomas from individuals without NF1, twenty-eight fresh astrocytoma operative specimens (low and high grade tumors) and seven primary human astrocytoma cell lines were examined for NF1 mRNA and protein expression. In all astrocytomas examined, increased NF1 expression was observed in the tumors relative to normal resting astrocytes. This increased neurofibromin expression correlated with elevated levels of activated p21-ras measured in both the fresh tumor specimens and the primary cell lines. Furthermore, when levels of activated p21 ras were decreased in astrocytoma cells expressing the ras inhibitory Asn-17 dominant-negative mutant, levels of neurofibromin expression decreased. In addition, fibroblasts induced to express oncogenic activated p21-ras(val12) had increased expression of NF1. These results suggested that neurofibromin expression is increased in human astrocytic tumors as a result of positive feedback regulation by increased levels of activated p21-ras.
Assuntos
Astrocitoma/genética , Regulação Neoplásica da Expressão Gênica/fisiologia , Genes da Neurofibromatose 1 , Proteínas Proto-Oncogênicas p21(ras)/fisiologia , Animais , Astrocitoma/metabolismo , Sequência de Bases , Expressão Gênica , Glioma/genética , Glioma/metabolismo , Glioma/patologia , Humanos , Camundongos , Dados de Sequência Molecular , Neurofibromina 1 , Reação em Cadeia da Polimerase , Biossíntese de Proteínas , Transcrição GênicaRESUMO
Tumor suppressor genes encode proteins involved in growth regulation in differentiating and proliferating cells. Previous work from our laboratory has demonstrated that the neurofibromatosis 1 (NF1) tumor suppressor gene is dramatically upregulated in astrocytes stimulated with dibutyryl cyclic AMP and proinflammatory cytokines. To explore the possibility that the NF1 gene product, neurofibromin, plays a role in the reactive gliosis seen in response to cerebral ischemia, expression of NF1 was examined in both focal and global models of rat cerebral ischemia. In this report, we demonstrate the increased expression of both neurofibromin and glial fibrillary acidic protein (GFAP) in astrocytes surrounding areas of focal ischemia. Similar increases in neurofibromin and GFAP immunoreactivity were also observed in reactive astrocytes in the hippocampal region in a global model of ischemia. These results suggest a novel role for the NF1 tumor suppressor gene in growth regulatory pathways involved in cellular remodeling and in response to injury.
Assuntos
Astrócitos/metabolismo , Isquemia Encefálica/metabolismo , Genes da Neurofibromatose 1/genética , Biossíntese de Proteínas , Animais , Sequência de Bases , Western Blotting , Química Encefálica/fisiologia , Isquemia Encefálica/patologia , Proteína Glial Fibrilar Ácida/biossíntese , Imuno-Histoquímica , Ataque Isquêmico Transitório/metabolismo , Ataque Isquêmico Transitório/patologia , Masculino , Dados de Sequência Molecular , Neurofibromina 1 , Reação em Cadeia da Polimerase , Proteínas/genética , Ratos , Tubulina (Proteína)/biossíntese , Regulação para CimaRESUMO
The neurofibromatosis 1 (NF1) gene product, neurofibromin, is a tumor suppressor gene product capable of inhibiting the growth of cells in culture. If neurofibromin suppresses cell growth by arresting cells in G0 or G1, its expression might be regulated in a cell cycle-dependent fashion. In this study, we demonstrate that RAT-1A fibroblasts arrested in G0/G1 by serum starvation and then released to progress through the cell cycle do not demonstrate significant changes in NF1 expression. However, when arrested in G0/G1 by contact inhibition, NF1 expression in these cells is reversibly upregulated within 72 h, suggesting that NF1 expression is a late event associated with cell growth arrest which may contribute to the maintenance of the differentiated state.
