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Peter W. Chen, Leila Sadegh, Jerry Y. Niederkorn; Epigenetic Regulation of CXCR4 Expression by the Ocular Environment. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1454.
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Expression of the chemokine CXCR4 by uveal melanoma favors metastatic tumor growth in the liver. Downregulating CXCR4 expression may reduce the capacity of uveal melanomas to form liver metastasis. This study examined the whether epigenetic gene regulation by the ocular environment downregulates CXCR4 gene expression.
LS174T colon cancer cells were injected in the anterior chamber (AC), a subcutaneous space in the flank (SC) or in the spleen of immune deficient NOD-SCID mice. LS174T tumor cells from intraocular tumors, subcutaneous tumors or liver metastasis from splenic injections were collected and used for immunohistochemistry (IHC), flow cytometry, and to generate total RNA, or protein lysates. CXCR4 gene transcription was analyzed by RT-PCR using CXCR4 specific primers. CXCR4 protein expression was visualized by IHC and quantitated by flow cytometry. Global methylation, DNA methyltransferase activity and global histone methylation was determined by methylation ELISA assays. Treatment with 5 Aza 2-deoxycytidine (5 Aza) was used to induce global demethylation of the tumor cells.
AC-derived LS174T tumor cells downregulated CXCR4 gene expression compared to wild type tumor cells. Expression of CXCR4 by subcutaneous-, and liver-derived LS174T cells was unchanged compared to wild type cells. AC-derived LS174T tumor cells upregulated DNA methyltransferase activity while methyltransferase activity of subcutaneous-, and liver-derived LS174T cells remained unchanged compared to wild type tumor cells. Global methylation of histones was elevated in AC-derived tumor cells compared to SC-derived, liver-derived or wild type tumor cells. Treatment of AC-derived tumor cells with 5 Aza upregulated CXCR4 gene and protein expression.
Factors in the ocular microenvironment epigenetically regulate CXCR4 gene expression. DNA and histone methylation is necessary to induce the downregulation of tumor CXCR4 expression. Previously reported studies demonstrated that downregulation of uveal melanoma CXCR4 expression produced fewer liver metastasis in a murine model. Strategies using epigenetic gene regulation may provide a novel modality to mitigate uveal melanoma liver metastasis.
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