Differential regulation by hematopoietic growth factors of apoptosis and mitosis in acute myeloblastic leukemia cells

We evaluated the effects of various hematopoietic growth factors (HGFs) on the prevention of apoptosis in blasts from 19 patients with acute myeloblastic leukemia (AML) by assessing DNA ladder formation. After incubation without HGF, apoptosis was noted in all but two patients. HGFs prevented, did not affect, or enhanced apoptosis in 39 (60%), 14 (22%), or 12 (18%) of 65 suspension cultures, respectively. HGFs that prevented apoptosis also stimulated and/or synergized blast colony formation in 35 of 39 corresponding methylcellulose cultures. HGFs that alone stimulated colony formation also prevented apoptosis in all but two of 28 corresponding suspension cultures. In contrast, HGFs that did not prevent apoptosis also failed to stimulate growth in 17 of 26 corresponding methylcellulose cultures. HGFs that enhanced apoptosis alone never stimulated colony formation. After incubation, we noted enhanced c-fos and cjun genes as well as induction of p21 protein. An appropriate dose of HGF elevated c-fos, reduced c-jun and p21, induced G1/S transition, and inhibited apoptosis. In two patients, apoptosis was not induced after incubation. Cells not treated with HGF expressed no c-fos, c-jun, or c-myc, and remained in G0/G1. Taken together, our results support the conclusion that not only c-fos, cjun, and c-myc, but also p53 and p21 are required for blast apoptosis. HGF differentially prevents apoptosis and induces mitosis, and both events seem to be integral to the self-renewal of AML clonogenic cells.