Intracellular Signal Transduction and Topological Change of Intranuclear DNA in the Differentiation of Human Leukemic HL-60 Cells.

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Human myelogenous HL-60 leukemia cells can be induced to differentiate into either monocyte/macrophage-like cells or into granulocytes by various chemical agents. These include 1,25-dihydroxyvitamin D_3(1,25-(OH)_2D_3) and 12-o-tetra-decanoylphorbol 13-acetate(TPA), which mediate monocytic differentiation, and all-trans retinoic acid(ATRA) for granulocytic differentiation. The activation, translocation and subsequent down-regulation of protein kinase C(PKC) appears to be essential for TPA-induced differentiation of HL-60 cells into macrophage-like cells. This is evidenced by pharmacological methods using PKC inhibitors such as H-7 and sphinganine, and investigations with TPA-resistant HL-60 variant(HL-60R) cells. Among PKC isozymes, PKC-beta may be crucial signal in the regulation of TPA-induced HL-60 cell differentiation, and the resistance of HL-60R cells to TPA induction may be due to the selective depression of cytosolic PKC-beta. The levels of both PKC activity and the expression … More of PKC-alpha, -beta, -gamma isoforms have been shown to increase during HL-60 differentiation induced by DMSO and ATRA. 1,25-(OH)_2D_3 induced monocytic differentiation is also associated with an in- crease in both PKC activity and the expression of PKC-alpha and -beta. These results suggest that PKC activation and/or modulation of its isoenzyme expression play key roles in regulating the responses of hematopoietic cells to both growth factors and non-physiological inducers of cell growth and differentiation.The regulation of protein function by phosphorylation necessarily requires protein phosphatases(PPs) in addition to protein kinases. It is conceivable that PPs may also be involved in the process of HL-60 cell differentiation. Potent inhibitors of PP1 and PP2A, calyculin-A(CAL-A) and okadaic acid could augment ATRA-induced granulocytic differentiation, whereas the differentiation toward macrophage lineage by TPA was unchanged in the presence of CAL-A. Treatment of HL-60 cells with ATRA led to a dramatic decrease in the activity of PP and PP2A protein expression. The mRNA level of PP2A was markedly decreased within 3 hrs after addition of ATRA. Thus, down regulation of PP2A may be involved in differentiation events of HL-60 cells induced by ATRA.We are now examining the modulation/expression of topoisomerase II induced by differentiation inducers in order to know the regulatory roles of protein phosphorylation in the topological changes of nuclear DNAs during HL-60 cell differentiation. Less