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 recognizab le stages characterized by morphology as well as by the expression of enzym es 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 cle ar, HL60 cells, a human acute myeloid leukemia (AML) cell line with promyel ocytic features, provide a model for such studies because they behave like stem cells, which can differentiate into two different lineages, granulocyt ic or monocytic/macrophage, depending on the inducer, Protein levels and ki nase activity of cyclin-dependent kinase 5 (Cdk5) were reported [F, Chen an d G, P. Studzinski (1999) Exp, Cell Res. 249, 422, 1999] to increase in HL6 0 cells induced to monocytic differentiation by 1 alpha,25-dihydroxyvitamin D-3 (1,25D(3)), but the specificity of the association of Cdk5 with the mo nocytic 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 e xpressing antisense Cdk5, switches the 1,25D(3)-induced monocytic phenotype (a combination of positive nonspecific esterase reaction, expression of th e CD14 marker, and morphology) to general myeloid phenotype (positive nitro -blue tetrazolium reaction, CD11b marker and morphology), The transcription al up-regulation of Cdk5 by 1,25D(3) was not inhibited by olomoucine, These findings show that iu human myeloid cells up-regulation of Cdk5 is specifi cally associated with the monocytic phenotype.