Persistence of repair proteins at unrepaired DNA damage distinguishes diseases withERCC2(XPD) mutations: cancer-prone xeroderma pigmentosum vs. non-cancer-prone trichothiodystrophy

Abstract

Patients with xeroderma pigmentosum (XP) have a 1,000-fold increase in ultraviolet (UV)-induced skin cancers while trichothiodystrophy (TTD) patients, despite mutations in the same genes, ERCC2 (XPD) or ERCC3 (XPB), are cancer-free. Unlike XP cells, TTD cells have a nearly normal rate of removal of UV-induced 6-4 photoproducts (6-4PP) in their DNA and low levels of the basal transcription factor, TFIIH. We examined seven XP, TTD, and XP/TTD complex patients and identified mutations in the XPD gene. We discovered large differences in nucleotide excision repair (NER) protein recruitment to sites of localized UV damage in TTD cells compared to XP or normal cells. XPC protein was rapidly localized in all cells. XPC was redistributed in TTD, and normal cells by 3 hr postirradiation, but remained localized in XP cells at 24-hr postirradiation. In XP cells recruitment of other NER proteins (XPB, XPD, XPG, XPA, and XPF) was also delayed and persisted at 24 hr (p < 0.001). In TTD cells with defects in the XPD, XPB, or GTF2H5 (TTDA) genes, in contrast, recruitment of these NER proteins was reduced compared to normals at early time points (p < 0.001) and remained low at 24 hr postirradiation. These data indicate that in XP persistence of NER proteins at sites of unrepaired DNA damage is associated with greatly increased skin cancer risk possibly by blockage of translesion DNA synthesis. In contrast, in TTD, low levels of unstable TFIIH proteins do not accumulate at sites of unrepaired photoproducts and may permit normal translesion DNA synthesis without increased skin cancer.

Effect of mutations in XPD(ERCC2) on pregnancy and prenatal development in mothers of patients with trichothiodystrophy or xeroderma pigmentosum

“…2,5,6 In the TTD patients, the mutations involve the C-terminal region (p.A725T in TTD421BE, p.E731Rfs*14 in TTD355BE and p.R722W in TTD351BE) as well as other locations in the XPD protein. 2,22 The pregnancies yielding patients TTD421BE and TTD355BE had pre-eclampsia, but the pregnancy yielding patient TTD351BE did not have pre-eclampsia. 16 Thus, mutations in the C-terminal region of the XPD protein are not always associated with pre-eclampsia.…”

“…Mutations are spread out along the 761 amino-acid structure of XPD in both disorders 1,5,[8][9][10][11] The mutations may affect nucleotide-excision repair and/or transcription to different extents. 2,3 In addition, some mutations are found in both XP and TTD patients. As XPD is an essential part of the basal transcription factor TFIIH, complete absence of this protein is not compatible with life.…”

A Japanese trichothiodystrophy patient with XPD mutations

“…The R722W substitution has been reported in nine TTD patients; one was homozygous and the others were compound heterozygous for the mutation. [9][10][11][12][13][14] Patients with R722W normally exhibit severe physical and mental impairments. However, one patient (TTD24PV) has been found with a mutation at the 3¢ end of intron 10 that results in production of a small amount of normal XPD transcripts, and exhibits a relatively mild TTD phenotype.…”

Abnormal XPD-induced nuclear receptor transactivation in DNA repair disorders: trichothiodystrophy and xeroderma pigmentosum

“…8 TTD and XP have an incidence of about 1 per million live births in the United States and Western Europe. 9 Very rare XP/TTD patients have clinical features of both XP and TTD 10,11 and carry an increased cancer risk.…”

“…[12][13][14][15] XP and TTD patients may have different, although overlapping, XPD mutations, suggesting that the site of mutation influences the clinical phenotype. 10,[16][17][18][19][20] Cells from XP and TTD patients with XPD mutations differ in the rate of repair of ultraviolet-induced DNA photoproducts and in the time course of localization and removal of nucleotide excision repair proteins to sites of UV damage. 10 Nuclear receptors are hormone-dependent transcription factors that play essential roles in development, differentiation, and metabolism by controlling the expression of specific networks of genes.…”