Down-regulation of proliferation-inhibiting factor EGR1 in brain metastatic cancer cells on a soft matrix

Metastasis of cancer cells to the brain leads to a poor prognosis in patients with cancer. The brain environment is characterized by cell types, extracellular matrices (ECMs), and mechanical properties that differ from those of the primary tumors. A previous study using human melanoma cells (WM266.4 cells) and its highly brain-metastatic subline cells (WM266.4-BrM3 cells) revealed that WM266.4-BrM3 cells showed enhanced proliferation in brain tissues after cardiac injection in mice compared with WM266.4 cells. However, the effects of mechanical properties such as ECM stiffness on growth and gene expression in WM266.4-BrM3 cells remain to be clarified. In this study, we cultured these cells on ECMs of different stiffnesses. On a soft ECM, WM266.4-BrM3 cells showed significantly higher proliferation and lower expression of early growth response 1 (EGR1) and TP53 than WM266.4 cells. In contrast, on a stiff ECM, the proliferation and EGR1 expression of WM266.4 and WM266.4-BrM3 cells were not significantly different. Additionally, EGR1 knockdown by siRNA transfection in WM266.4 cells results in promoted cell proliferation and downregulated TP53 on a soft ECM. These results suggest that brain metastatic WM266.4 cells decrease EGR1 expression, thereby promoting cell proliferation via TP53 downregulation on a soft ECM.Key words: EGR1, ECM stiffness, metastasis, cancer, growth.