Identification of a platelet-aggregating factor of murine colon adenocarcinoma 26: Mr 44,000 membrane protein as determined by monoclonal antibodies.

The interaction between platelets and tumor cells plays an important role in the hematogenous spread of certain malignant cancers. We found that metastatic clones of murine colon adenocarcinoma 26 induced platelet aggregation in a membrane protein-dependent manner. Two monoclonal antibodies (mAbs) of IgG2a class were generated against a highly metastatic colon 26 clone, NL-17. These two mAbs, designated 8F11 and 20A11, showed a two-fold higher level of NL-17 binding than a low metastatic clone, NL-14, which possesses low platelet-aggregating ability. Both mAbs retarded platelet aggregation induced by NL-17. Western blot analysis showed that both mAbs recognized the same Mr 44,000 membrane protein as antigen under reducing conditions. Trypsin treatment of NL-17 diminished the ability of the cells to induce platelet-aggregation and resulted in a decrease in the reactivity of the cells to 8F11. These results suggest that the Mr 44,000 membrane protein recognized by the two mAbs is a platelet-aggregating factor of colon 26 cells.