Modulation of ornithine decarboxylase gene transcript levels by differentiation inducers in human promyelocytic leukemia HL60 cells.

We have analyzed the changes in the steady-state levels of ornithine decarboxylase (ODC) mRNA during differentiation of HL60 cells, a human promyelocytic leukemia cell line. Induction of differentiation with either retinoic acid, dimethylsulfoxide, dibutyryl cAMP or dihydroxy-vitamin D3 resulted in a decrease of the cellular content of ODC RNA. Such a decrease occurred late after induction and coincided with the slowing of cell growth activity and with the expression of a cell surface differentiation marker (CD11b antigen). In contrast, the inducers provoked a rapid reduction of c-myc RNA levels, which preceded both the slowing of cell growth and the expression of the differentiation marker. When the cells were treated with a phorbol ester (TPA), the down-regulation of ODC was preceded by a transient increase in the steady-state levels of this RNA. However, such an increase was not observed with other inducers. The possible significance of these results in relation to the control of HL60 cell differentiation is discussed.