The genomic aberration profile of chromosome 20q in distal CIN colon carcinomas was analysed using allelotyping and CGH arrays. Allelotyping revealed carcinomas with allelic imbalance along the full long arm, and carcinomas with fully non-aberrant 20q. Oligonucleotide-based CGH showed that among the carcinomas without allelic imbalance, 47% had in fact a gain. In this subgroup, quantitative PCR for the TOPI gene (20q12) confirmed this gain, and fluorescence in situ hybridization showed that the chromosome 20q gain resulted from tetra/polysomy instead of aneusomy. The 20q gain correlated with a high frequency of aberrations, with allelic imbalance at TP53 locus but not at APC locus, and carcinomas with a disomic 20q showed low frequency of genomic aberrations and were significantly associated to mucinous phenotype. The prognostic value of 20q amplification was not demonstrated in this study. These results indicate that on the basis of aberration frequency, chromosome 20q and TP53/APC locus status, distal CIN carcinomas harbor a high degree of genetic heterogeneity suggesting several pathways for carcinogenesis. This study also indicates that allelotyping needs to be carried out with a complementary technique, such as quantitative PCR.

TATA Box Bergmann Etienne, Bergmann EtienneSearch for more papers by this authorJean-Marc Egly, Jean-Marc Egly Parc d'Innovation, Illkirch, FranceSearch for more papers by this author Bergmann Etienne, Bergmann EtienneSearch for more papers by this authorJean-Marc Egly, Jean-Marc Egly Parc d'Innovation, Illkirch, FranceSearch for more papers by this author First published: 15 January 2002 https://doi.org/10.1002/047120918X.emb1518 Read the full textAbout ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Encyclopedia of Molecular BiologyBrowse other articles of this reference work:BROWSE BY TOPICBROWSE A-Z RelatedInformation

P210BCR-ABL counteracted against the complementary effect of XPB on DNA repair when ultraviolet (UV)-sensitive 27-1 cells were treated with UV or cisplatin but not with hydrogen peroxide. Wortmannin, an inhibitor of PI3 kinase did not affect its anti-repair effect. Enhanced recruitment of p44 with TFIIH after cisplatin treatment is inhibited by the expression of P210BCR-ABL in a kinase activity-dependent manner. Although purified TFIIH from P210BCR-ABL expressor and non-expressor showed almost no difference in molar ratio of each component, the in vitro activity of TFIIH was decreased by 5–10% in repair assay but was increased by more than two-fold in transcription assay.

Trichothiodystrophy (TTD) is a rare genetic disorder characterized by a hair dysplasia and associated with numerous symptoms affecting mainly organs derived from the neuroectoderm. About half of TTD patients exhibit photosensitivity because their nucleotide-excision repair pathway (NER) does not remove UV-induced DNA lesions efficiently. However, they do not present the skin cancer susceptibility expected from such an NER disorder. Their deficiencies result from phenotype-specific mutations in either XPB or XPD. These genes encode the helicase subunits of TFIIH, a DNA repair factor that is also required for transcription of class II genes. Thus, time- and tissue-specific impairments of transcription might explain the developmental and neurological symptoms of TTD. In a third group of photosensitive patients, TTD-A, no mutation has been identified, although TFIIH amount is reduced.

In order to unravel the mechanism that regulates transcription of protein-coding genes, we investigated the function of the p44 subunit of TFIIH, a basal transcription factor that is also involved in DNA repair. We have shown previously that mutations in the C terminus of the XPD helicase, another subunit of TFIIH, prevent its regulation by p44 (Coin, F., Bergmann, E,, Tremeau-Bravard, A, and Egly, J. M. (1999) EMBO 18, 1357-1366). By using a site-directed mutagenesis approach within the p44 region from amino acids 66 to 200, we indicate how a decrease in the interaction between p44 and XPD results in a decrease of the XPD helicase activity and leads to a defect in the first steps of the transcription reaction, namely the first phosphodiester bond formation and promoter clearance. We thus provide some explanation for the transcriptional defect found in SSL1 mutated yeast (Wang, Z,, Buratowski, S., Svejstrup, J. Q,, Feaver, W. J.. Wu, X., Kornberg, R. D., Donahue, T, F., and Friedberg, E. C, (1995) Mol. Cell. Biol. 15, 2288-2293). Moreover, this study shows how the activity of the the cyclin-dependent kinase-activating kinase associated with TFIIH complex in stimulating transcription is mediated in part by p44/XPD interaction.

The repair-deficient form of trichothiodystrophy (TTD) most often results from mutations in the genes XPB or XPD, encoding helicases of the transcription/repair factor TFIIH. The genetic defect in a third group, TTD-A, is unknown, but is also caused by dysfunctioning TFIIH. None of the TFIIH subunits carry a mutation and TFIIH from TTD-A cells is active in both transcription and repair. Instead, immunoblot and immunofluorescence analyses reveal a strong reduction in the TFIIH concentration. Thus, the phenotype of TTD-A appears to result from sublimiting amounts of TFIIH, probably due to a mutation in a gene determining the complex stability. The reduction of TFIIH mainly affects its repair function and hardly influences transcription.

TFIIH (transcription factor IIH) is a multiprotein complex consisting of nine subunits initially characterized as a basal transcription factor required for initiation of protein-coding RNA synthesis. TFIIH was the first transcription factor shown to harbor several enzymatic activities, likely indicative of functional complexity. This intricacy was further emphasized with the cloning of the genes encoding the different subunits which disclosed direct connections between transcription, DNA repair and cell cycle regulation. In this review, we emphasize those functions of TFIIH involved in DNA repair, as well as their relationship to TFIIH's roles in transcription, cell cycle control and apoptosis. These connections may prove to be essential for the cellular response to DNA damage.

As part of TFIIH, XPB and XPD helicases have been shown to play a role in nucleotide excision repair (NER). Mutations in these subunits are associated with three genetic disorders: xeroderma pigmentosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD). The strong heterogeneous clinical features observed in these patients cannot be explained by defects in NER alone. We decided to look at the transcriptional activity of TFIIH from cell lines of XP individuals. We set up an immunopurification procedure to isolate purified TFIIH from patient cell extracts. We demonstrated that mutations in two XP‐B/CS patients decrease the transcriptional activity of the corresponding TFIIH by preventing promoter opening. The defect of XPB in transcription can be circumvented by artificial opening of the promoter. Western blot analysis and enzymatic assays indicate that XPD mutations affect the stoichiometric composition of TFIIH due to a weakness in the interaction between XPD–CAK complex and the core TFIIH, resulting in a partial reduction of transcription activity. This work, in addition to clarifying the role of the various TFIIH subunits, supports the current hypothesis that XP‐B/D patients are more likely to suffer from transcription repair syndromes rather than DNA repair disorders alone.