Far-infrared irradiation inhibits breast cancer cell proliferation independently of DNA damage through increased nuclear Ca2+/calmodulin binding modulated-activation of checkpoint kinase 2.
Far-infrared (FIR) irradiation is reported to inhibit cell proliferation in various types of cancer cells; the underlying mechanism, however, remains unclear. We explored the molecular mechanisms using MDA-MB-231 human breast cancer cells. FIR irradiation significantly inhibited cell proliferation and colony formation compared to hyperthermal stimulus, with no alteration in cell viability. No increase in DNA fragmentation or phosphorylation of DNA damage kinases including ataxia-telangiectasia mutated kinase, ataxia telangiectasia and Rad3-related kinase, and DNA-dependent protein kinase indicated no DNA damage. FIR irradiation increased the phosphorylation of checkpoint kinase 2 (Chk2) at Thr68 (p-Chk2-Thr68) but not that of checkpoint kinase 1 at Ser345. Increased nuclear p-Chk2-Thr68 and Ca2+/CaM accumulations were found in FIR-irradiated cells, as observed in confocal microscopic analyses and cell fractionation assays. In silico analysis predicted that Chk2 possesses a Ca2+/calmodulin (CaM) binding motif ahead of its kinase domain. Indeed, Chk2 physically interacted with CaM in the presence of Ca2+, with their binding markedly pronounced in FIR-irradiated cells. Pre-treatment with a Ca2+ chelator significantly reversed FIR irradiation-increased p-Chk2-Thr68 expression. In addition, a CaM antagonist or small interfering RNA-mediated knockdown of the CaM gene expression significantly attenuated FIR irradiation-increased p-Chk2-Thr68 expression. Finally, pre-treatment with a potent Chk2 inhibitor significantly reversed both FIR irradiation-stimulated p-Chk2-Thr68 expression and irradiation-repressed cell proliferation. In conclusion, our results demonstrate that FIR irradiation inhibited breast cancer cell proliferation, independently of DNA damage, by activating the Ca2+/CaM/Chk2 signaling pathway in the nucleus. These results demonstrate a novel Chk2 activation mechanism that functions irrespective of DNA damage.
['Cho|Du-Hyong|DH|', 'Lee|Hyeon-Ju|HJ|', 'Lee|Jee Young|JY|', 'Park|Jung-Hyun|JH|', 'Jo|Inho|I|']
D001943:Breast Neoplasms D002118:Calcium D002147:Calmodulin D045744:Cell Line, Tumor D002467:Cell Nucleus D049109:Cell Proliferation D002470:Cell Survival D064447:Checkpoint Kinase 2 D004249:DNA Damage D005260:Female D006801:Humans D007259:Infrared Rays D010766:Phosphorylation D011485:Protein Binding D034622:RNA Interference D034741:RNA, Small Interfering D015854:Up-Regulation
Far-infrared irradiation Cancer cell proliferation Checkpoint kinase 2 Calcium Calmodulin