कैंसर विज्ञान एवं चिकित्सा

Thorough Methylation Analysis of CpG Island Region outside the Putative Promoter of CXCL12 Gene in Breast Cancer Cell Lines

Abstract

Liliane M. B. Klassen, Edneia A. S. Ramos, Karin Braun-Prado, Graciele C. M. Manica and Giseli Klassen

Metastasis contributes to 90% of all breast cancer death. Several studies have highlighted the role of epigenetic events such as DNA methylation in promoter regions of genes as an important event in the process of metastasis in breast cancer. The promoter of the CXCL12 gene, encoding a chemokine, is silenced by methylation in gastric, colon as well as in the breast cancer. The aim of this work was to map methylated regions flanking the promoter of CXCL12 by cloning bisulfite treated DNA containing the distinct CpG regions and also correlate methylation pattern with the gene expression in different breast tumor cell lines. The results showed that the CpG islands 1, 3, 5 as well as the middle end of CpG 2 were more than 80% methylated in the cell lines that expressed the gene CXCL12 (HB4a, PMC42 and MCF7). Expression analysis indicates strongly that these regions do not regulate this gene expression. However, CpG island 4 (CGI 4) located approximately 1550 bp away from the transcription start region and outside the putative promoter region, was differentially methylated and it seems to promote CXCL12 gene silencing. In conclusion the CGI 4 is probably the last region to be methylated for silencing of CXCL12 gene and could be a suitable DNA region for the diagnostic and prognostic to breast cancer studies.