title: The total amount of DNA damage determines ultraviolet-radiation-induced cytotoxicity after uniformor localized irradiation of human cells.
abstract: We have recently developed a micropore ultraviolet irradiation technique. An isopore membrane filter with 3 microm diameter pores shields ultraviolet C radiation from cultured human fibroblasts, leading to partial irradiation within the cells with an average of about three exposed areas per nucleus. This study addressed the question of whether the spatial distribution of DNA damage within a cell nucleus is important in triggering ultraviolet-induced cytotoxicity. We have examined whether there are differences in cytotoxicity between partially ultraviolet-irradiated cells and uniformly irradiated cells after equal amounts of DNA damage were induced in the cell nuclei. We first determined DNA damage formation in normal human fibroblasts using an enzyme-linked immunosorbent assay. We found that 5 J per m2 ultraviolet irradiation produced an equivalent amount of cyclobutane pyrimidine dimers and (6-4) photoproducts per cell as 100 J per m2 with the membrane filter shield. At those doses, we found that both types of ultraviolet irradiation induced similar levels of cytotoxicity as assessed by a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay. Both types of ultraviolet-irradiated cells also had similar cell-cycle distribution and apoptosis as measured by flow cytometry. Moreover, no significant differences in repair kinetics for either type of photolesion were observed between the two different ultraviolet treatments. Similar results were obtained in Cockayne syndrome cells that are defective in transcription-coupled nucleotide excision repair. Present results indicate that in the range of photoproducts studied, the spatial distribution of DNA damage within a cell is less important than the amount of damage in triggering ultraviolet-induced cytotoxicity.
authors.affiliation: Radioisotope Research Center Departments of Dermatology Public Health Medical Genetics Research Center, Nara Medical University, Kashihara, Japan.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Imoto
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Kobayashi
authors.forename: Sachiko
authors.initials: S
authors.lastname: Katsumi
authors.forename: Yoko
authors.initials: Y
authors.lastname: Nishiwaki
authors.forename: Taka-aki
authors.initials: TA
authors.lastname: Iwamoto
authors.forename: Aya
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Yukio
authors.initials: Y
authors.lastname: Yamashina
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Shirai
authors.forename: Sachiko
authors.initials: S
authors.lastname: Miyagawa
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Dohi
authors.forename: Shigeki
authors.initials: S
authors.lastname: Sugiura
authors.forename: Toshio
authors.initials: T
authors.lastname: Mori
mesh_terms: D017209:Apoptosis / Q000528:radiation effects; D002453:Cell Cycle / Q000528:radiation effects; D002467:Cell Nucleus; D002478:Cells, Cultured; D004249:DNA Damage; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000166:cytology / Q000528:radiation effects*; D006801:Humans; D014466:Ultraviolet Rays