Reduction in the radiation-induced late S phase and G2 blocks in HL-60 cell populations by amiloride, an efficient inhibitor of the Na+/H+ transporter

• Published in: Cancer research (Chicago, Ill.) Ill.), 1998-02, Vol.58 (3), p.413-420
• Main Authors: SAILER, B. L, BARRASSO, A. M, VALDEZ, J. G, COBO, J. M, D'ANNA, J. A, CRISSMAN, H. A
• Format: Article
• Language: English
• Subjects: Amiloride - pharmacology; Apoptosis - drug effects; Biological and medical sciences; Caffeine - pharmacology; Carcinogenesis, carcinogens and anticarcinogens; Cyclin B - biosynthesis; Cyclin B - genetics; Cyclin B1; DNA Fragmentation; DNA, Neoplasm - analysis; Enzyme Inhibitors - pharmacology; Flow Cytometry; G2 Phase - drug effects; G2 Phase - radiation effects; Gamma Rays; Gene Expression Regulation, Leukemic - drug effects; Gene Expression Regulation, Leukemic - radiation effects; HL-60 Cells - drug effects; HL-60 Cells - radiation effects; Humans; Medical sciences; Physical agents; Radiation-Protective Agents - pharmacology; S Phase - drug effects; S Phase - radiation effects; Sodium-Hydrogen Exchangers - antagonists & inhibitors; Staurosporine - pharmacology; Tumors
• ISSN: 0008-5472; 1538-7445

Recent investigations that showed that amiloride delayed or inhibited apoptosis indicated it might also attenuate cell cycle checkpoints activated by ionizing radiation. In this report, single- and dual-parameter flow cytometry were used to investigate the effects of amiloride on cell cycle progression, and the effectiveness of amiloride to attenuate the S and G2 phase checkpoint responses induced by 2.5, 5.0, and 7.5 Gy of gamma radiation. The late S-phase delay, noted at 8 h following irradiation, and a radiation-induced G2 block, which was maximum at 16 h after irradiation, were both significantly reduced in amiloride-treated samples. Attenuation of the radiation-induced late S phase and G2 blocks resulted in cell division without apparent apoptosis or necrosis over a 24-h period. Results presented indicate that amiloride reduces the radiation-induced G2 block in HL-60 cell populations almost equally well as caffeine and to a greater extent than staurosporine. Immunofluorescent detection and quantitation of cyclin B1 expression demonstrated that amiloride only significantly reduced cyclin B1 expression following 5.0 Gy, when there was a notable induction of a significant G2 delay, followed by a relatively rapid recovery in cycling potential. The results suggest that amiloride affects the radiation-triggered signaling cascades to alter the kinase activity of proteins associated with mitotic progression, particularly the cyclin B1-p34cdc2 complex. Alternatively, alterations in intracellular ion concentrations induced by amiloride may lead to changes in Ca2+-dependent signaling cascades and thereby decrease the radiation-mediated cell cycle perturbations.