Specific association of increased cyclin-dependent kinase 5 expression with monocytic lineage of differentiation of human leukemia HL60 cells.

: Hematopoietic cell differentiation takes place in phenotypically recognizable stages characterized by morphology as well as by the expression of enzymes and surface markers. It is recognized that differentiation results from an interaction of environmental cues, such as cytokines and hormones, with internal cellular programs, but the precise mechanisms are not entirely clear. HL60 cells, a human acute myeloid leukemia (AML) cell line with promyelocytic features, provide a model for such studies because they behave like stem cells, which can differentiate into two different lineages, granulocytic or monocytic/macrophage, depending on the inducer. Protein levels and kinase activity of cyclin-dependent kinase 5 (Cdk5) were reported [F. Chen and G. P. Studzinski (1999) Exp. Cell Res. 249, 422, 1999] to increase in HL60 cells induced to monocytic differentiation by 1alpha,25-dihydroxyvitamin D3 (1,25D3), but the specificity of the association of Cdk5 with the monocytic phenotype has not been established. We show here that up-regulation of Cdk5 does not occur in granulocytic differentiation, whereas inhibition of Cdk5 activity by olomoucine, or its expression by a plasmid construct expressing antisense Cdk5, switches the 1,25D3-induced monocytic phenotype (a combination of positive nonspecific esterase reaction, expression of the CD14 marker, and morphology) to general myeloid phenotype (positive nitro-blue tetrazolium reaction, CD11b marker and morphology). The transcriptional up-regulation of Cdk5 by 1,25D3 was not inhibited by olomoucine. These findings show that in human myeloid cells up-regulation of Cdk5 is specifically associated with the monocytic phenotype.