LINE-1 HYPERMETHYLATION IN BREAST CANCER STROMAL CELLS

Abstract

Change in methylation level of genes containing Long Interspersed Element-1 (LINE-1) alters host genes regulation. Here we demonstrated paracrine signalling of breast cancer influents the epigenetic regulation of stromal cells. First, we proved by an increased level of genome-wide LINE-1 methylation of laser-captured lymphocytes of metastatic breast cancer lymph nodes. To demonstrate paracrine signaling, in vitro co-cultures between breast cancer cell lines and male or female peripheral blood mononuclear cells (PBMCs) of normal individuals, female fibroblasts or the cervical cancer cell line (HeLa) were set up. Interestingly, LINE-1 hypermethylation occurred exclusively in female PBMCs (P values = 0.0044) or fibroblasts (P values = 0.0288) after co-culture at 4-8 h. No LINE-1 methylation change was observed in co-cultured male PBMCs or HeLa cells. Next, genes containing LINE-1 of breast cancer stromal cells were upregulated. Finally, one of the genes, MUC-1, was validated to have expression in plasma cells from lymph nodes of patients with lymph node metastasis or micrometastasis. In conclusion, breast cancer sends a paracrine signal in stroma cells causing LINE-1 epigenetic regulation. Moreover, the regulated genes in stroma cells are potential biomarkers for detecting breast cancer micrometastasis.