title: Epidermal transit of replication-arrested, undifferentiated keratinocytes in UV-exposed XPC mice: an alternative to in situ apoptosis.
abstract: The interplay among nucleotide excision repair, cell-cycle regulation, and apoptosis in the UV-exposed epidermis is extremely important to avoid mutations and malignant transformation. In Xpc(-/-) mice deficient in global genome nucleotide excision repair (GGR), a cell-cycle arrest of epidermal cells in late S-phase [with near-double normal diploid (4N) DNA content] was observed 48-72 h after UV exposure. This arrest resolved without apoptosis (96-168 h). We surmised that these arrested keratinocytes with persistent DNA damage were removed by epidermal turnover. In vivo BrdUrd pulse-chase labeling (>17 h after UV exposure) showed that DNA replication after UV exposure was resumed in Xpc(-/-) mice, but it did not reveal any evidence of retained BrdUrd-labeled S-phase cells in the basal layer of the epidermis at 72 h. Interestingly, by this time a maximum number of cytokeratin 10-negative and cytokeratin 5-positive cells had appeared in the suprabasal epidermal cell layers of UV-exposed Xpc(-/-) mice. Accumulation of these "basal cell"-like keratinocytes in the suprabasal layers was clearly aberrant and was not observed in WT and heterozygous mice. Flow cytometric analyses of single-cell suspensions from UV-exposed Xpc(-/-) epidermis further showed that the "near-4N" arrested cells retained cytokeratin 5 and lacked cytokeratin 10. Hence, we conclude that the arrested near-4N cells became detached from the basal layer without entering a proper differentiation program and were indeed subsequently lost through the epidermal turnover. This expulsion apparently constitutes an alternative route, different from in situ apoptosis, to eliminate DNA-damaged arrested cells from the epidermis.
authors.affiliation: Department of Dermatology, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands.
authors.forename: Gerdine J
authors.initials: GJ
authors.lastname: Stout
authors.forename: Daniel
authors.initials: D
authors.lastname: Westdijk
authors.forename: Dennis M
authors.initials: DM
authors.lastname: Calkhoven
authors.forename: Olaf
authors.initials: O
authors.lastname: Pijper
authors.forename: Claude M P
authors.initials: CM
authors.lastname: Backendorf
authors.forename: Rein
authors.initials: R
authors.lastname: Willemze
authors.forename: Leon H F
authors.initials: LH
authors.lastname: Mullenders
authors.forename: Frank R
authors.initials: FR
authors.lastname: de Gruijl
mesh_terms: D000818:Animals; D017209:Apoptosis; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002454:Cell Differentiation; D002471:Cell Transformation, Neoplastic; D004247:DNA / Q000737:chemistry; D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000502:physiology; D004817:Epidermis / Q000378:metabolism; D005434:Flow Cytometry; D006579:Heterozygote; D007150:Immunohistochemistry; D015603:Keratinocytes / Q000166:cytology* / Q000528:radiation effects; D007633:Keratins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D009154:Mutation; D013997:Time Factors; D019076:Transgenes; D014466:Ultraviolet Rays
chemical_list: D004268:DNA-Binding Proteins; C501002:Xpc protein, mouse; D007633:Keratins; D004247:DNA; D001973:Bromodeoxyuridine