We examined the effects of supernatants of culture media of MDA-MB-231 and MCF-7 cells on the expression of adhesion molecules on human lymphatic endothelial cells (LECs) and evaluated whether the overexpression of adhesion molecules facilitated the attachment of carcinoma cells to LECs. The 48-h stimulation of MDA-MB-231, but not MCF-7, supernatant produced a significant expression of ICAM-1 on human LECs but little or no expression of E-selectin. Chemical treatment with dialyzed substances of <1,000 molecular weight (MW) caused a complete reduction of the supernatant-mediated response. In contrast, pretreatment with heating, digestion with protease, or chemical treatment with dialyzed substances of <500 MW produced no significant effect on the supernatant-mediated response. ATP (10(-7) M) caused overexpression of ICAM-1 on human LECs similar to that produced by the supernatant of MDA-MB-231. The ATP- and MDA-MB-231 supernatant-mediated responses were significantly reduced by treatment with 10(-6) M suramin (a purinergic P2X and P2Y receptor antagonist). In attachment assays, 10(-7) M ATP or MDA-MB-231 supernatant produced a significant increase in the attachment of carcinoma cells to human LECs. The treatment with 10(-6) M suramin caused a significant reduction of ATP- and supernatant-mediated facilitation of the attachment responses. Additional treatment with anti-ICAM-1 antibody also caused a significant reduction of ATP- and supernatant-mediated facilitation of the attachment responses. The experimental findings suggest that MDA-MB-231 may release or leak ATP, which produces the overexpression of ICAM-1 on human LECs through activation of purinergic P2X and/or P2Y receptors and then facilitates ICAM-1-mediated attachment of carcinoma cells to LECs.