UVC-induced apoptosis in human epithelial tumor A431 cells: sequence of apoptotic changes and involvement of caspase (-8 and -3) cascade

• Published in: Journal of radiation research 2000-09, Vol.41 (3), p.243-258
• Main Authors: Choi, K H, Hama-Inaba, H, Wang, B, Haginoya, K, Odaka, T, Yamada, T, Hayata, I, Ohyama, H
• Format: Article
• Language: English
• Subjects: Apoptosis; Apoptosis - radiation effects; Caspase 3; Caspase 8; Caspase 9; Caspases - metabolism; Cells; Chromatin; Humans; Neoplasms, Glandular and Epithelial - metabolism; Neoplasms, Glandular and Epithelial - pathology; Neoplasms, Glandular and Epithelial - radiotherapy; Signal Transduction - radiation effects; Tumor Cells, Cultured; Tumors; Ultraviolet Rays
• ISSN: 0449-3060
• DOI: 10.1269/jrr.41.243

Human epidermoid tumor A431 cells underwent apoptosis following exposure to ultraviolet C (UVC). The apoptosis was of the interphase death type, and mostly occurred within one cell cycle, independent of the cell-cycle phases. We further examined the detailed sequential order of apoptotic changes in cells after UVC exposure and the involvement of caspases using six caspase inhibitors. The loss of mitochondrial transmembrane potential (delta psi m) appeared in the earliest phase; subsequently, the chromatin condensation and DNA-fragmentation occurred. Cell shrinkage and loss of the plasma-membrane integrity, judged by propidium iodide (PI) staining, were observed in the later phase. A broad-spectrum caspase inhibitor, z-VAD-fmk, completely prevented all apoptotic changes, except for the depletion of delta psi m. Both Ac-DEVD-CHO and Ac-IETD-CHO, inhibitors of caspase -3 and -8, respectively, effectively inhibited typical chromatin condensation to almost the same extent. However, the nuclei still showed partial condensation. A caspase -9 inhibitor, Ac-LEHD-CHO, did not prevent chromatin condensation, though it partially inhibited cell-size reduction and PI-stainability. None of the caspase inhibitors could inhibit the delta psi m reduction. These results strongly suggest that the collapse of delta psi m is not a part of the central apoptotic machinery, and that caspase cascade(s), especially caspase-8 to -3, play an important role in UVC-induced apoptosis in A431.