Expression of P62, A Putative Collagen Receptor, on Human Megakaryocytic Leukemia Cells

The expression of glycoprotein (GP)/Ia/Ila and that of P62, a putative collagen receptor defined by IgG in a patient with idiopathic thrombocytopenic purpura (Blood, 69, 1712), was demonstrated on a human megakaryocytic cell line (CMK) using flow-cytometric analysis and Western blotting. Immunological reaction to GPIa/IIa and P62 antigen was detected in about 80% and 50% of CMK cells, respectively. On stimulation with 12-0-tetradecanoylphorbol-13-acetate, the expression of P62 antigen increased markedly, in contrast to that of GPIa/IIa. Immunoblot studies revealed that CMK cells had P62 antigens with molecular weights of 48 kDa and 43 kDa under both reduced and non-reduced conditions. In contrast to the effect of thrombin stimulation, the addition of collagen caused no increase in cytosolic free Ca²⁺ in CMK cells. We conclude that the lack of response of CMK cells to collagen may result from the presence of dysfunctional collagen receptors.