NDRG4 promoter hypermethylation is a mechanistic biomarker associated with metastatic progression in breast cancer patients

Abstract

The risk of developing metastatic disease in breast cancer patients is traditionally predictable based on the number of positive axillary lymph nodes, complemented with additional clinicopathological factors. However, since lymph node-negative patients have a 20–30% probability of developing metastatic disease, lymph node information alone is insufficient to accurately assess individual risk. Molecular approaches, such as multigene expression panels, analyze a set of cancer-related genes that more accurately predict the early risk of metastasis and the treatment response. Here, we present N-Myc downstream-regulated gene 4 (NDRG4) epigenetic silencing as a mechanistic biomarker of metastasis in ductal invasive breast tumors. While aberrant NDRG4 DNA hypermethylation is significantly associated with the development of metastatic disease, downregulation of NDRG4 transcription and protein expression is functionally associated with enhanced lymph node adhesion and cell mobility. Here, we show that epigenetic silencing of NDRG4 modulates integrin signaling by assembling β1-integrins into large punctate clusters at the leading edge of tumor cells to promote an “adhesive switch,” decreasing cell adhesion to fibronectin and increasing cell adhesion and migration towards vitronectin, an important component of human lymph nodes. Taken together, our functional and clinical observations suggest that NDRG4 is a potential mechanistic biomarker in breast cancer that is functionally associated with metastatic disease.

Biomarker: Methylated gene promoter increases risk of metastatic disease

Epigenetic silencing of a putative tumor suppressor protein confers a metastatic advantage to breast cancer cells and could serve as a mechanistic biomarker of likely disease spread. Researchers in São Paulo, Brazil, led by Érico Costa from the Molecular Oncology Center of the Hospital Sírio-Libanês, showed that NDRG4 (short for N-Myc downstream-regulated gene 4) is actively expressed in normal breast tissue. But in breast tumors and in tumor cell lines, methyl tags cover the promoter region of the NDRG4-encoding gene, resulting in reduced protein expression, increased tumor size, elevated cell mobility and other molecular features indicative of a more aggressive disease state. The researchers experimentally silenced NDRG4 expression in two non-metastatic breast cancer cell lines and observed changes in the adhesive and migratory properties of cells that promote tumor invasiveness and spread.