Chemokine CCL2 facilitates ICAM-1-mediated interactions of cancer cells and lymphatic endothelial cells in sentinel lymph nodes.

We examined the effects of CCL1, CCL2, CCL12 and CCL21 on the expression of adhesion molecules in cultured human lymphatic endothelial cells using immunohistochemical staining or Western blot analysis. In addition, we investigated whether the expressed adhesion molecule was able to facilitate the attachment of carcinoma cells to the lymphatic endothelial cells as an in vitro micrometastatic model. CCL2 caused a selective and significant expression of ICAM-1 on human lymphatic endothelial cells but CCL1, CCL12 and CCL21 did not. By increasing the stimulation time from 4 to 18 and 48 h, the intensity of immunoreactivity for ICAM-1 was significantly increased in a time-dependent manner up to 18 h. The ICAM-1 mRNA levels were also elevated significantly up to 18 h. The CCL2-mediated immunohistochemical expression of ICAM-1 was dose-dependently increased from 10 pg/mL to 1 ng/mL. The CCL2-mediated expression of ICAM-1 was significantly reduced by neutralization of CCL2 using a specific CCL2 antibody. The 18-h treatment with CCL2 caused a significant facilitation of in vitro attachment of MDA-MB-231 and MCF-7 cells to the lymphatic endothelial cells (LECs). The CCL2-mediated response in the attachment assay was also significantly reduced either by the neutralization of CCL2 or by additional treatment with anti-ICAM-1 antibody. Immunohistochemical expression of ICAM-1, but not E-selectin, was strongly observed around and within the metastatic region of sentinel lymph node isolated from breast cancer patients. These findings suggest that CCL2 induces selective and significant expression of ICAM-1 on cultured human lymphatic endothelial cells and then facilitates the attachment of carcinoma cells to the lymphatic endothelial cells, thus providing an in vitro micrometastatic model via the overexpression of ICAM-1.