Cellular DNA damage responses (DDRs) are induced by unrepaired DNA lesions and constitute a protective back-up system that prevents the expansion of damaged cells. These cellular signaling pathways trigger either growth arrest or cell death and are believed to be major components of an early anti-cancer barrier. Cultures of C57BL/6J keratinocytes with various defects in NER sub-pathways allowed us to follow the kinetics of DDRs in an isogenic background and in the proper (physiologically relevant) target cells, supplementing earlier studies in heterogenic human fibroblasts. In a series of well-controlled parallel experiments we have shown that, depending on the NER deficiency, murine keratinocytes elicited highly selective DDRs. After a dose of UV-B that did not affect wild-type keratinocytes, Xpa-/- keratinocytes (complete NER deficiency) showed a rapid depletion of DNA replicating S-phase cells, a transient increase in quiescent S-phase cells (not replicating DNA), followed by massive apoptosis. Csb-/- keratinocytes (TC-NER deficient) responded by a more sustained increase in QS-phase cells and appeared more resistant to UV-B induced apoptosis than Xpa-/-. In irradiated Xpc-/- keratinocytes (GG-NER deficient) the loss of replicating S-phase cells was associated with a gradual build-up of both QS-phase cells and cells arrested in late-S phase, in complete absence of apoptosis. Our analysis complements and extends previous in vivo investigations and highlights both similarities and differences with earlier fibroblast studies. In vitro cultures of murine keratinocytes provide a new tool to unravel the molecular mechanisms of UV-induced cellular stress responses in great detail and in a physiologically relevant background. This will be essential to fully appreciate the implications of DDRs in tumor suppression and cancer prevention.

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Keywords Apoptosis, Cell cycle arrest, Global genome repair (GG-NER), Mouse keratinocytes, Nucleotide excision repair (NER), Transcription-coupled repair (TC-NER), Ultraviolet light
Persistent URL dx.doi.org/10.1016/j.dnarep.2005.07.012, hdl.handle.net/1765/60506
Journal D N A Repair
Stout, G.J, van Oosten, M, Acherrat, F.Z, de Wit, J, Vermeij, W.P, Mullenders, L.H.F, … Backendorf, C.M.P. (2005). Selective DNA damage responses in murine Xpa-/-, Xpc -/- and Csb-/- keratinocyte cultures. D N A Repair, 4(11), 1337–1344. doi:10.1016/j.dnarep.2005.07.012