Self-renewal and commitment to differentiation of human leukemic promyelocytic cells (HL-60)

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Abstract
More than 80% of cells from a human promyelocytic leukemic cell line (HL-60) possess the capacity for self-renewal as evidenced by their ability to form large primary colonies in semisolid medium and the presence within these colonies of cells capable of subsequent colony formation. Colony development is independent of the normal regulator-the myeloid colony stimulating factor. The observed autostimulation suggests the production of specific growth promoters by the cells. Differentiation either to mature granulocytes or macrophages, induced by various agents, was associated with reduced cloning potential. Nevertheless, colonies containing differentiated cells could be developed either by cloning cells in the presence of suboptimal concentrations of inducer or by adding inducers over colonies developed in its absence. Upon differentiation, there was a morphological change from compact to diffused colony morphology due to cell mobility in the semisolid medium. Even at suboptimal concentrations of inducer more than 95% of the colonies became diffused, indicating clonaI homogeneity of the population with respect to differentiation capacity. The loss of self-renewal was found to be one of the early properties which changed following the initiation of differentiation. The loss preceded not only the overt expression of maturation-specific functions but also cellular commitment to terminal differentiation; shorter contact with the inducer was required to cause loss of self-renewal than to induce an irreversible transition to differentiation. This resulted in cells that lost their self-renewal potential without being able to complete their program of differentiation.