Selectins and
fibrin(
ogen) play key roles in the hematogenous dissemination of
tumor cells, and especially of colon
carcinomas. However, the
fibrin(
ogen) receptor(s) on colon
carcinoma cells has yet to be defined along with its relative capacity to bind
fibrinogen versus
fibrin under flow. Moreover, the functional
P-selectin ligand has yet to be validated using intact platelets rather than purified
selectin substrates. Using human CD44-knockdown and control LS174T cells, we demonstrate the pivotal involvement of CD44 in the
P-selectin-mediated binding to platelets in shear flow. Quantitative comparisons of the binding kinetics of LS174T versus
P-selectin glycoprotein ligand-1 (PSGL-1)-expressing THP-1 cells to activated platelets reveal that the relative avidity of P-selectin-CD44 binding is more than sevenfold lower than that of P-selectin-PSGL-1 interaction. Using CD44-knockdown LS174T cells and
microspheres coated with CD44 immunoprecipitated from control LS174T cells, and purified
fibrin(
ogen) as substrate, we provide the first direct evidence that CD44 also acts as the major
fibrin, but not
fibrinogen, receptor on LS174T colon
carcinoma cells. Interestingly, binding of plasma
fibrin to CD44 on the colon
carcinoma cell surface interferes with the P-selectin-CD44 molecular interaction and diminishes platelet-LS174T heteroaggregation in the high shear regime. Cumulatively, our data offer a novel perspective on the apparent metastatic potential associated with CD44 overexpression on colon
carcinoma cells and the critical roles of
P-selectin and
fibrin(
ogen) in metastatic spread and provide a rational basis for the design of new therapeutic strategies to impede
metastasis.