Pharmacological inhibition of DNA repair enzymes differentially modulates telomerase activity and apoptosis in two human leukaemia cell lines

Abstract

Purpose: To investigate the effect of wortmannin and 3‐aminobenzamide (3‐AB) on telomerase activity and apoptosis in two human leukaemia cells.

Materials and methods: MOLT‐4 (p53‐wild type) and KG1a (p53‐null) cells were irradiated with γ‐rays (3 Gy at 1.57 Gy min⁻¹) and the effects of wortmannin and 3‐AB were evaluated. Telomerase activity was measured by polymerase chain reaction and the expression of human telomerase reverse transcriptase, human telomerase RNA and telomerase‐associated protein 1 was assessed by reverse transcriptase‐polymerase chain reaction. Apoptosis was evaluated by fluorescence microscopy and flow cytometry.

Results: A radiation‐induced up‐regulation of telomerase activity was observed from 4 h post‐irradiation in both cell lines. This up‐regulation was abrogated by wortmannin and 3‐AB. Telomerase activity was maximal 24 h post‐irradiation, coinciding with an accumulation of human telomerase reverse transcriptase mRNA. Apoptosis and G2/M arrest were evident from 4 h post‐irradiation in MOLT‐4 cells. KG1a cells exhibited a G2/M block at 24 h post‐irradiation and apoptosis increased between 24 and 48 h post‐irradiation. 3‐AB abolished G2/M blockage and enhanced radiation‐induced apoptosis in both cell lines, while wortmannin increased apoptosis only in MOLT‐4 cells.

Conclusions: 3‐AB inhibits the radiation‐associated telomerase activity increase and enhances apoptosis in MOLT‐4 and KG1a cells. Wortmannin, which also inhibits the radiation‐associated telomerase activity increase in both cell lines, does not modify radiation‐induced apoptosis in KG1a cells. DNA repair enzymes might be selective targets for enhancing radiosensitivity in certain tumour cells.