TPA induces differentiation of purified human myeloblasts in the absence of proliferation.

Normal granulocyte-monocyte progenitor cells have an absolute requirement for colony-stimulating factor (CSF) for proliferation and differentiation in vitro. In contrast, cells derived from acute myeloblastic leukemia patients are often defective in their response to CSF, but can be induced to undergo terminal differentiation by exposure to 12-o-tetradecanoyl phorbol-13-acetate (TPA) by a process that does not require cell proliferation. To investigate the relationship between TPA-induced leukemic cell differentiation and CSF-induced myeloid cell differentiation we investigated the effects of TPA on myeloblasts highly enriched from normal bone marrow and stable-phase chronic myeloid leukemia peripheral blood. TPA (10(-6)-10(-9) M) induced the rapid appearance of macrophage characteristics in the majority of myeloblasts in the absence of proliferation. The mechanisms of TPA- and CSF-induced myeloblast differentiation were compared by examining the requirement for DNA synthesis. Exposure of myeloblasts to CSF induced increased triatiated thymidine (3H-TdR) incorporation within a few hours, while TPA did not induce 3H-TdR incorporation by itself and was inhibitory to CSF-induced 3H-TdR uptake. This requirement for DNA synthesis was further investigated by reversibly inhibiting DNA synthesis by depleting intracellular polyamines with difluoromethylorinithine (DFMO). DFMO inhibited both CSF-induced proliferation and differentiation of myeloblasts, but had no effect on TPA-induced differentiation. These results demonstrate that the process of differentiation of myeloblasts induced by TPA is distinct from CSF-induced differentiation.