Phorbol ester induces a transient increase in alpha(5)beta(1)-mediated adhesion of the megakaryoblastic cell line CHRF 288-11.

This study investigated the mechanism by which treatment of the CHRF 288-11 megakaryoblastic cell line with phorbol myristate acetate caused a transient increase in adhesion. The adhesion to tissue culture plastic occurred within 4 h and could be reversed by treatment with RGDS-peptide suggesting the involvement of one or more RGD-binding integrins. Ligand-binding adhesion assays suggested that PMA-induced CHRF 288-11 cells had very little affinity for fibrinogen, a low affinity for vitronectin and a much higher affinity for fibronectin. Further adhesion assays performed in the presence of various integrin antagonists or inhibiting monoclonal antibodies demonstrated that the fibronectin-mediated cell adhesion is via the alpha beta , fibronectin receptor, integrin. Flow cytometrical investigations showed that this increase in alpha(5)beta(1)-adhesion on CHRF 288-11 cells following PMA stimulation was not brought about by an increase in alpha(5)beta(1)-integrin expression and inferred that increased adhesion is achieved by an increase in alpha(5)beta(1) ligand-binding function. These findings confirm other reports using different cells that the expression and function of integrins may play an important role in megakaryocytopoiesis. Modulation of integrin function may facilitate the migration of maturing megakaryoblasts in the bone marrow stroma before their movement through the sinus wall and into the blood stream. The report demonstrates that the CHRF 288-11 megakaryoblastic cell line is a useful model for investigating some aspects of these phenomena.