Pim-1 induced polyploidy but did not affect megakaryocytic differentiation of K562 cells and CD34+ cells from cord blood

In a previous study, we determined the gene expression profile of both megakaryocytic and non-megakaryocytic lineage cells via serial analysis of gene expression and microarray methods, and demonstrated that Pim-1 was expressed more abundantly in megakaryocytic lineage cells. In this study, we knocked down Pim-1 in K562 cells, as well as in CD34+ cells from cord blood, via RNA interference, in order to analyze the effects of Pim-1 expression on the megakaryocytic differentiation of these cells. We then additionally overexpressed the Pim-1 genes in K562 cells, and conducted a comparison of these effects with those of RNAi cells on the course of megakaryocytic differentiation. The results of this study revealed that Pim-1 knockdown exerted no effects on commitment or differentiation toward megakaryocytic lineage, as evidenced by the detected CD41+ or CD61+ cells, or on the number of megakaryocytic colony forming units. However, Pim-1 knockdown was found to elicit a reduction in CD41+ cells with >4n DNA content, and a concomitant increase in the fraction of cells achieving a ploidy of >4n in the Pim-1 overexpressing population of K562 cells. Collectively, the findings of these studies indicate that the expression of Pim-1 expression is both necessary and sufficient for polyploidization, but is not critical to cytoplasmic differentiation on megakaryopoiesis.