Aphidicolin , an Inhibitor of DNA Replication , Blocks the TPA - Induced Differentiation of a Human Megakaryoblastic Cell Line , M E G - 0 1

The commitment process of a human megakaryoblastic cell line (MEG-01) induced with phorbol ester, TPA, was investigated with special reference to glycoprotein (GP) Ilb/ llla expression, multinuclear formation, and DNA replication. TPA (lo-’ mol/L) completely inhibited cellular division in MEG-01. but did not suppress de novo DNA synthesis. Two days’ culture with lo-’ mol/L TPA was sufficient for MEG-01 cells to initiate an irreversible commitment process. These cells could not resume cell growth and expressed GP Ilb/llla antigen; some of them showed multinuclear form and DNA polyploidy even after removal of TPA from the culture medium. DNA histogram analysis showed that, upon treatment with TPA, the percentage of cells whose DNA ploidy was more than 8N was 5 to 10 times higher than that of control cells. Precise analysis using cell size fractionation by centrifugal elutriation method showed that there was strong correlation between the percentage of multinuclear cells and DNA polyploidy in TPA-treated cells. The percentage and staining intensity of GP Ilb/llla and other megakaryocytic