It is known that Src-family protein kinases inhibit cellular proliferation and megakaryocytes (Mks) differentiation. Src kinases are proto-onconogenes that play key role in cell morphology, motility, proliferation, and survival. Six of Src kinases are present in primary Mks. We used SU6656, a selective inhibitor of Src kinases, as differentiation–inducing agent for Mks. Megakaryocytopoiesis is a complex multistep process involving stem cell commitment, mitotic amplification of committed progenitors, nuclear polyploidization, and cytoplasmic maturation leading to the production of platelets. The earliest marker of megakaryocytopoiesis, appearing as early as the CFU-Mk stage, is the GpIIb/IIIa complex (CD41a). The enzyme a 1,6-fucosyltransferase (6FucT) is involved in GpIIb/IIIa synthesis. Previously we reported that the activity of 6FucT could be a useful marker of the commitment of cultured hematopoietic stem cells into the megakaryocytic lineage. The aim of this study was to analyse the differentiation and maturation of Mk progenitor cells in ex vivo culture of hematopoietic stem cells and megakaryblastic cell line Meg-01 (CML, Ph⁺) after exposure to SU6656. CD34⁺ cells were isolated from human umbilical cord blood and cultured in serum-free medium supplemented with cytokines promoting Mks development. SU6656 diminished the growth rate of cells and induced the changes in morphology, phenotype, ploidy and the activity of 6FucT, confirming the maturation of Mk progenitor cells. Inhibitor also blocked proliferation and simultaneously induced differentiation of Meg-01 cells. It was concluded that the addition of SU6656 to the culture system of megakaryocytic progenitors from CD34⁺ cells and cells of Meg-01 line induced their maturation towards later stages of Mk differentiation with increased activity of 6FucT. The analysis of the activity of 6FucT in culture of Mks after exposure to SU6656 additionally confirmed special status of the enzyme in the process of megakaryocytopoiesis.

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