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Maturation of human megakaryocytic cell line (CMK-7) on the human umbilical vein endothelial cell (EC) monolayer.

Human umbilical vein endothelial cells (EC) were studied to determine whether they were capable of stimulating the maturation of a human megakaryocytic cell line CMK-7. CMK-7 overlaid on EC monolayers in direct contact conditions (CMK-7EC1) and in non-contact conditions (CMK-7EC2), were compared with unstimulated CMK-7 (CMK-7US) and CMK-7 treated with 10(-8) M phorbol ester (CMK-7TPA). The increases in cell-size, CD41b and CD42 positivity, adenosine triphosphate (ATP) and serotonin (5-HT), platelet factor 4 (PF4), beta-thromboglobulin (beta-TG), and DNA contents, indicated both stimulated endomitosis and cytoplasmic maturation in the CMK-7TPA. In contrast, CMK-7EC1 increased in size, in ATP and 5-HT contents and in PF4 and beta-TG contents, without an increase in DNA content, indicating that only cytoplasmic maturation occurred. These findings showed that EC was able to stimulate the cytoplasmic maturation of CMK-7 only under direct contact conditions. Furthermore, the CMK-7EC1 on the EC monolayer developed long cytoplasmic processes that resembled those of megakaryocytes in the terminal stage.