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 transie nt increase in adhesion, The adhesion to tissue culture plastic occurred wi thin 4 h and could be reversed by treatment with RGDS-peptide suggesting th e involvement of one or more RGD-binding integrins, Ligand-binding adhesion assays suggested that PMA-induced CHRF 288-11 cells had very little affini ty for fibrinogen, a low affinity for vitronectin and a much higher affinit y for fibronectin. Further adhesion assays performed in the presence of var ious integrin antagonists or inhibiting monoclonal antibodies demonstrated that the fibronectin-mediated cell adhesion is via the alpha(5)beta(1), fib ronectin receptor, integrin, Flow cytometrical investigations showed that t his 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)-integr in expression and inferred that increased adhesion is achieved by an increa se in alpha(5)beta(1) ligand-binding function. These findings confirm other reports using different cells that the expression and function of integrin s may play an important role in megakaryocytopoiesis. Modulation of integri n function may facilitate the migration of maturing megakaryoblasts in the bone marrow stroma before their movement through the sinus wall and into th e blood stream. The report demonstrates that the CHRF 288-11 megakaryoblast ic cell line is a useful model for investigating some aspects of these phen omena.