Induction of differentiation in erythroleukemic K562 cells by gamma-irradiation.

Various agents have been shown to induce differentiation in neoplastic cells. The present study aimed at investigating comparable phenomena induced by high doses of gamma-irradiation in the presence of physiological factors. The erythroleukemic K562 cells were gamma-irradiated or treated with cytosine-arabinoside (Ara-C), and examined for cell size, protein content, acetylcholinesterase (AChE)-activity and hemoglobin synthesis in relation to mitotic activity. At doses above 10 Gy, differentiation was induced, as recognized by elevated AChE-activity, accompanied by an increase in cell size and protein content and cessation of cell proliferation. Moreover, irradiation, as well as Ara-C, induced hemoglobin synthesis when cultures were supplemented with hemin prior to treatment. It is suggested that the basic mechanisms of differentiation induction are similar for ionizing radiation and certain chemical agents and are related to continued growth of essential cytoplasmic constituents during inhibition of mitotic activity.