RESUMO
The proto-oncogene tyrosine kinase c-ROS is an orphan receptor whose normal expression pattern is tightly spatio-temporally restricted during development. In glioma, c-ROS mRNA expression is frequently ectopically up-regulated. In this study, we determined by immunohistochemical means that c-ROS receptor protein is present in 25% of low-grade and 30% of malignant glioma tumor samples from tissue microarrays. We then explored the molecular basis for the up-regulation of c-ROS expression in these tumors. We identified and characterized the c-ROS gene promoter region and report that the ectopic expression of c-ROS in tumors is tied to hypomethylation of a CpG island in the c-ROS promoter. Bisulfite sequencing analysis in glioma tumor samples revealed that demethylation of the CpG island (-384 to -132 bp) correlated with c-ROS expression. Moreover, c-ROS expression could be activated by treatment of c-ROS-negative cells with the demethylating agent 5-aza-2'-deoxycytidine. These results establish a strong link between c-ROS promoter demethylation and gain of c-ROS expression and function in glioma. Our data suggest that epigenetic activation of c-ROS represents an important oncogenic mechanism for glioma initiation and progression and suggest that cautionary measures in the clinical use of 5-aza-dC for the treatment of glioma be taken into consideration. [Cancer Res 2009;69(6):2180-4].
Assuntos
Astrocitoma/enzimologia , Astrocitoma/genética , Receptores Proteína Tirosina Quinases/biossíntese , Receptores Proteína Tirosina Quinases/genética , Astrocitoma/tratamento farmacológico , Astrocitoma/patologia , Azacitidina/análogos & derivados , Azacitidina/farmacologia , Metilação de DNA , Decitabina , Progressão da Doença , Epigênese Genética , Regulação Neoplásica da Expressão Gênica , Humanos , Imuno-Histoquímica , Análise em Microsséries , Regiões Promotoras Genéticas , Proto-Oncogene Mas , RNA Mensageiro/biossíntese , RNA Mensageiro/genética , Células Tumorais Cultivadas , Regulação para CimaAssuntos
Transformação Celular Neoplásica/metabolismo , Receptores Proteína Tirosina Quinases/metabolismo , Animais , Anticorpos Monoclonais/imunologia , Anticorpos Monoclonais/metabolismo , Transformação Celular Neoplásica/genética , Transformação Celular Neoplásica/imunologia , Humanos , Receptores Proteína Tirosina Quinases/genética , Receptores Proteína Tirosina Quinases/imunologia , Transdução de SinaisRESUMO
Activating oncogenic mutations of receptor tyrosine kinases (RTKs) have been reported in several types of cancers. In many cases, genomic rearrangements lead to the fusion of unrelated genes to the DNA coding for the kinase domain of RTKs. All RTK-derived fusion proteins reported so far display oligomerization sequences within the 5' fusion partners that are responsible for oncogenic activation. Here, we report a mechanism by which an altered RTK gains oncogenic potential in a glioblastoma cell line. A microdeletion on 6q21 results in the fusion of FIG, a gene coding for a Golgi apparatus-associated protein, to the kinase domain of the protooncogene c-ROS. The fused protein product FIG-ROS is a potent oncogene, and its transforming potential resides in its ability to interact with and become localized to the Golgi apparatus. Thus we have found a RTK fusion protein whose subcellular location leads to constitutive kinase activation and results in oncogenic transformation.