ESTABLISHMENT AND CHARACTERIZATION OF AN IMMATURE HUMAN MEGAKARYOBLASTIC CELL-LINE, MEG-A2

We have established a novel human megakaryoblastic cell line, designat ed as MEG-A2, from a patient with megakaryoblastic crisis of Philadelp hia (Ph) chromosome positive chronic myelogenous leukemia. MEG-A2 cell s showed positive phenotypes for periodic acid Schiff and alpha-naphth yl buthylate esterase reactions, but were negative for myeloperoxidase and naphthol ASD chloroacetate esterase reactions. Flow cytometric an alyses of cell surface markers revealed that MEG-A2 cells had a low le vel of GP IIb/IIIa expression as well as apparent expressions of CD4, CD7, CD13, CD33 and CD34 antigens, but no expression of GP Ib nor glyc ophorin A. Stimulation with phorbol 12-myristate 13-acetate (PMA) dram atically increased the expression of megakaryocyte-related markers suc h as HPL-3, J15, Plt-1, Y2/51 and AN51 in MEG-A2 cells. The PMA-stimul ation also induced expression of platelet peroxidase (PPO) in MEG-A2 c ells on electromicroscopic observation. Proliferative responses to gra nulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3) or erythropoietin were observed, and the expression of GP IIb/I IIa was increased by stimulation with GM-CSF, IL-3, erythropoietin and interleukin-6 (IL-6). Protein S mRNA expression was seen in cultured cells on Northern blot analysis. Expression of platelet factor 4 mRNA was induced in PMA-stimulated cells, and a marked accumulation of prot ein was observed in the culture medium. In conclusion, a new cell line , MEG-A2, belongs to the relatively immature megakaryocytic lineage an d has markedly increased megakaryocytic characteristics with PMA stimu lation.