Journal Article

Epidermal Transit of Replication-Arrested, Undifferentiated Keratinocytes in UV-Exposed XPC Mice: An Alternative to in situ Apoptosis

Dennis M. Calkhoven, Olaf Pijper, Claude M. P. Backendorf, Rein Willemze, Gerdine J. Stout, Daniel Westdijk, Leon H. F. Mullenders, de Gruijl, Frank R.

2005

Overview

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.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Animals / Apoptosis / Biological Sciences / Bromodeoxyuridine - pharmacology / Cell Differentiation / Cell Transformation, Neoplastic / Cells / Cellular biology / Cellular differentiation / Cephalopelvic disproportion / Deoxyribonucleic acid / DNA / DNA - chemistry / DNA Damage / DNA Repair / DNA-Binding Proteins - genetics / DNA-Binding Proteins - physiology / Epidermal cells / Epidermis / Epidermis - metabolism / Flow Cytometry / Heterozygote / Immunohistochemistry / Keratinocytes / Keratinocytes - cytology / Keratinocytes - radiation effects / Keratins - metabolism / Mice / Mice, Transgenic / Models, Biological / Mutation / Rodents / Skin / Time Factors / Transgenes / Ultraviolet radiation / Ultraviolet Rays