Modulation of gene expression in the acute promyelocytic leukemia cell line NB4

The human leukemic cell line NB4 was derived from a patient with acute promyelocytic leukemia and is characterized by a specific 15;17 chromosomal translocation. We analyzed the response of NB4 and HL-60 cells to the biomodulators all-transretinoic acid (ATRA), vitamin D3 (Vit D3) and the protein kinase C agonists bryostatin 1 (Bryo 1) and phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). HL-60 cells were used for comparison being arrested at the myeloblastic-promyelocytic stage, but lacking the t(15;17) abnormality. In most experiments Vit D3 was only weakly or not at all effective. The other three reagents effectively slowed or stopped the proliferation of the cells in suspension. Associated with this proliferation arrest was the cell differentiation along the myeloid cell lineages: ATRA modulated morphological features indicative of granulocytic differentiation; Bryo 1 and TPA caused also distinct morphological changes. The inducers up-regulated the expression of CD11b (without changing the surface expression of other markers, e.g. CD13, CD14, CD15, CD33, CD68, HLA-DR) and completely down-regulated the originally strong expression of myeloperoxidase and c-myc at the mRNA level. Thus, ATRA- or protein kinase C activator-induced differentiation involved changes associated with maturational processes. Induction of terminal differentiation of leukemic cells by physiological or pharmacological modulators may be able to control the growth of the malignant cells and has therapeutic implications.