DNA Repair and Transcriptional Effects of Mutations in TFIIH inDrosophilaDevelopment

Abstract

Mutations in XPB and XPD TFIIH helicases have been related with three hereditary human disorders: xeroderma pigmentosum, Cockayne syndrome, and trichothiodystrophy. The dual role of TFIIH in DNA repair and transcription makes it difficult to discern which of the mutant TFIIH phenotypes is due to defects in any of these different processes. We used haywire (hay), the Drosophila XPB homolog, to dissect this problem. Our results show that when hay dosage is affected, the fly shows defects in structures that require high levels of transcription. We found a genetic interaction between hay and cdk7, and we propose that some of these phenotypes are due to transcriptional deficiencies. We also found more apoptotic cells in imaginal discs and in the CNS of hay mutant flies than in wild-type flies. Because this abnormal level of apoptosis was not detected in cdk7 flies, this phenotype could be related to defects in DNA repair. In addition the apoptosis induced by p53 Drosophila homolog (Dmp53) is suppressed in heterozygous hay flies.

The genetic depletion or the triptolide inhibition of TFIIH in p53 deficient cells induce a JNK-dependent cell death in Drosophila

“…Moreover, E2F and Dp53 are involved in inducing apoptosis in an independent manner during development, but both are required for apoptosis when DNA is damaged (Moon et al, 2008). However, in previous works, it has been reported that the apoptosis that is generated by the overexpression of p53 requires the presence of a functional TFIIH (Robles et al, 1999;Merino et al, 2002). In this study, we found that when both TFIIH and Dp53 were not functional in the wing imaginal disc, apoptosis was dramatically enhanced.…”

“…Genetic interactions between TFIIH and p53 have been demonstrated in human cells derived from patients afflicted with xeroderma pigmentosum who carry mutations in XPD and XPB as well as in Drosophila XPB mutants (Robles et al, 1999;Wang et al, 2003;Merino et al, 2002). These studies were performed by overexpressing p53 to induce apoptosis in backgrounds deficient for XPD or XPB.…”

“…Genetically, it has been demonstrated that in human cells derived from patients whose XPD and XPB subunits have been mutated, the apoptotic effect caused by p53 overexpression is suppressed (Wang et al, 1996). In Drosophila, a similar result was obtained in XPB (haywire) mutant flies (Fuller et al, 1989;Merino et al, 2002). Although these results suggest that p53 requires the presence of intact TFIIH to promote apoptosis, these experiments were conducted in an artificial situation in which p53 was overexpressed.…”

Defective Hfp-dependent transcriptional repression of dMYC is fundamental to tissue overgrowth in Drosophila XPB models

“…TTDA is required for the stability of the TFIIH complex, but unlike XPB and XPD, which are implicated in all three diseases, defects in TTDA only cause the developmental disease TTD, not XP/CS and/or cancer 8,41 . Intriguingly, three different XPB families with mutations in ERCC3, the gene coding XPB, causing loss of the wild-type C terminus of XPB, all display the severe neurodegenerative progeroid disorder characteristic of CS, but have different cancer predisposition (one severe, one moderate, one with no cancer) 3,41,42 . Altogether with the knowledge that all patients in these families have reduced NER, these observations suggest that cancer phenotypes are not due to NER defects per se, but likely due to a second mutation.…”

“…Haywire (Hay) is the Drosophila XPB homologue 40,41,43,44 , and loss-of-function Hay mutants display increased cell death, consistent with DNA repair and/or transcription defects 41,42,46 . The Drosophila orthologue of FIR, Half Pint (Hfp) behaves as a tumour suppressor, as loss of Hfp results in larval overgrowth and overproliferation 43,44 .…”