Lithium and hydrocortisone interactions on cell growth and gene expression in human promyelocytic leukemia (HL60)

Lithium (Li) and hydrocortisone (HC) modify gene expression as well as stimulate human hematopoiesis in vivo and in vitro. The responses of blood-forming tissues, to these natural substances individually, are closely similar. However, clonogenic co-culture experiments, using normal human bone marrow cells, have revealed that the effects of Li and HC are not additive but rather mutually inhibitory. Studies of HL-60 cells in suspension indicate that growth of this human promyelocytic leukemic line is enhanced by HC at 10(-6) M, a "therapeutic" plasma concentration. This phenomenon is abrogated by the co-addition of Li at 3 x 10(-4) M, likewise a "therapeutic" plasma concentration. Neither substrate exerts any influence on the morphological or cytochemical features of differentiation which accompany exposure of HL-60 cells to dimethyl sulphoxide (DMSO), retinoic acid (RA), tetradecanoyl phorbol acetate (TPA) or sodium butyrate. In contrast, the expression of c-fms, a cellular proto-oncogene which codes for the CSF-1 (monocyte-macrophage colony-stimulating factor) surface membrane receptor, is modified by Li in the presence of the differentiation induction agents DMSO and RA which promote the development of mature granulocytes from HL-60 cells. These observations afford further insights into the humoral mechanisms which modulate the expression of genes involved in the regulation of hematopoiesis.