PROLIFERATION KINETICS AND PCNA EXPRESSION OF HL-60 CELLS FOLLOWING IONIZING IRRADIATION AND GRANULOCYTIC DIFFERENTIATION

The human promyelocytic leukaemia cell line, HL-60, was investigated w ith regard to proliferation and terminal differentiation following irr adiation. The cells were X-irradiated and induced with 1.25% dimethyl sulfoxide (DMSO) towards the granulocytic lineage. Proliferation was m easured via cell growth, clonogenicity and the bromodeoxyuridine/DNA i ncorporation assay. Immunohistochemical detection of proliferating cel l nuclear antigen (PCNA) expression was used to discriminate cycling f rom non-cycling cells. The differentiation obtained was proved by test ing for the immune function of the respiratory burst (NBT reduction te st). The HL-60 cells studied revealed a high radiosensitivity (D-0 = 0 .63 Gy). After induction with DMSO, declines in cell growth, clonogeni city and PCNA positivity of the cells indicated a decrease in prolifer ation and an increase in differentiation. Starting on day 2 in culture , irradiation after seeding with 1 Gy accelerated the loss of the PCNA expression in induced cells (46% v. 3% PCNA-negative control cells on day 3). Induced cells gained the capability of exerting the respirato ry burst, which was found to be dose-dependent radiosensitive (42% and 12% NBT-positive cells after 1 and 2 Gy, respectively, v. 53% NBT-pos itive control cells on day 8). Subpopulations in the cell line were ev ident in all parameters investigated. We discuss the HL-60 cell, not o nly as a model comparable to human progenitor cells, but also as a sui table tool in radiobiological research with regard to proliferation an d differentiation following ionizing irradiation.