Different regulation of p53 stability in UV-irradiated normal and DNA repair deficient human cells

The stabilization of p53 protein was studied after UV exposure of normal human skin fibroblasts and cells derived from patients suffering from xeroderma pigmentosum (XP) and trichothiodystrophy (TTD). The data show that p53 is transiently stabilized both in UV-irradiated normal and repair deficient cells. However, particularly at later times after UV irradiation, stabilization of p53 persists much longer in repair deficient XP and TTD cells than in normal cells. The stabilization of p53 was found to be dose-dependent in normal and XP cells. These results indicate that unremoved DNA damage could possibly be responsible for the induction of transient stabilization of p53.     

Xeroderma pigmentosum group F protein binds to Eg5 and is required for proper mitosis: implications for XP-F and XFE

The xeroderma pigmentosum group F-cross-complementing rodent repair deficiency group 1 (XPF-ERCC1) complex is a structure-specific endonuclease involved in nucleotide excision repair (NER) and interstrand cross-link (ICL) repair. Patients with XPF mutations may suffer from two forms of xeroderma pigmentosum (XP): XP-F patients show mild photosensitivity and proneness to skin cancer but rarely show any neurological abnormalities, whereas XFE patients display symptoms of severe XP symptoms, growth retardation and accelerated aging. Xpf knockout mice display accelerated aging and die before weaning. These results suggest that the XPF-ERCC1 complex has additional functions besides NER and ICL repair and is essential for development and growth. In this study, we show a partial colocalization of XPF with mitotic spindles and Eg5. XPF knockdown in cells led to an increase in the frequency of abnormal nuclear morphology and mitosis. Similarly, the frequency of abnormal nuclei and mitosis was increased in XP-F and XFE cells. In addition, we showed that Eg5 enhances the action of XPF-ERCC1 nuclease activity. Taken together, these results suggest that the interaction between XPF and Eg5 plays a role in mitosis and DNA repair and offer new insights into the pathogenesis of XP-F and XFE.