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Epigenetic Regulation of c-ROS Receptor Tyrosine Kinase Expression in Malignant Gliomas

¹ Molecular Oncology Research Institute and ² Department of Neurosurgery, Tufts University School of Medicine, Tufts Medical Center, Boston, Massachusetts; ³ The David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts; and ⁴ Department of Biomedical Sciences, Tufts University Veterinary School, North Grafton, Massachusetts

Requests for reprints: Al Charest, Tufts University School of Medicine, 800 Washington Street, Tufts Medical Center Box 5609, Boston, MA 02111. Phone: 617-636-8876; Fax: 617-636-5277; E-mail: alain.charest{at}tufts.edu.

Key Words: c-ROS • glioblastoma • CpG island • methylation • epigenetic

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]