Figure 2.

Diagrammatic representation of the formation of αIISp, XPF, and FANCD2 foci in the nuclei of normal human cells after damage with a DNA ICL agent. (a) In undamaged cells, αIISp, XPF, FANCD2 are localized diffusely in the nucleus; 16 h after damage with either 8-MOP plus UVA light or mitomycin C (MMC), αIISp and XPF are co-localize in nuclear foci at sites of ICLs.¹³ FANCD2 has also formed nuclear foci; however, these foci do no colocalize with αIISp foci and it is inferred from this that they do not co-localize with XPF foci.⁶⁴ Since, after DNA ICL damage, FANCD2 foci form before those of αIISp or XPF foci (at 2 h vs. 8 h) and follow a different time course for formation, we have proposed that FANCD2 acts upstream of αIISp and XPF.⁶⁴ Thus, at the same point in time after ICL damage, FANCD2 do not localize on the same sites on DNA as αIISp and XPF, hence the different localization of FANCD2 foci compared to those of αIISp and XPF. (b) In normal human cells in which αIISp has been knocked-down by siRNA, XPF and FANCD2 are localized diffusely in the nucleus; however, levels of αIISp are only ∼30% of those found in non-treated cells; 16 h after ICL damage, FANCD2 is localized in nuclear foci; however, XPF does not form nuclear foci.^13,64 Thus, αIISp is needed for formation of XPF nuclear foci and localization of XPF to sites of DNA ICLs, but it is not needed for the localization of FANCD2 to sites of damage.⁶⁴