Photoproducts in transcriptionally active DNA induce signal transduction to the delayed U.V.-responsive genes for collagenase and metallothionein

Abstract

Mammalian cells in culture react to ultraviolet irradiation with the massive transcriptional activation of several genes and with the stabilization of the p53 protein. While U.V.-induced transcription of several immediate-response genes depends on U.V.-induced activation of signal transduction generated by non-nuclear mechanisms, stabilization of p53 and the transcription of several delayed-response genes are triggered by U.V.-induced DNA damage. By comparing dose responses for the activation by U.V. of delayed-responsive genes (collagenase 1, metallothionein IIA) in cells from patients with dierent DNA repair de®ciencies (complementation groups of Xeroderma pigmentosum, Cockayne's syndrome and Trichothiodystrophy), we show here that U.V.-induced transcription of these genes does depend on pyrimidine dimers in transcribed regions of the genome (but not on damage in its silent part). Since all cells with defects in DNA repair that had been tested and which lack dierent enzymes, respond to U.V. with expression of these same genes, functional repair does not appear to be required for the induction of expression, and repair intermediates (which would not be identical in cells of dierent repair de®ciency) cannot be responsible for signal generation.

Proneness to UV-induced apoptosis in human fibroblasts defective in transcription coupled repair is associated with the lack of Mdm2 transactivation

“…In agreement with other observations in similar cell systems and comparable UV doses (Li et al, 1996;Ljungman and Zhang, 1996;Blattner et al, 1998;McKay et al, 1998), normal ®broblasts showed fast stabilization of p53 protein, rapid activation of bax and p21 (whose kinetics of induction closely follow p53) and late activation of Mdm2 (that rises markedly 24 h after irradiation). In XP-A ®broblasts the fast increase in p53 and activation of bax and p21 were not followed by Mdm2 activation.…”

“…Accumulating experimental evidence suggests that the induction of the p53 response by UV is not triggered by DNA strand breaks but rather, is linked to inhibition of transcription due to persistent DNA damage (Ljungman et al, 1999). Among the various photoproducts, the major trigger for UV-induced apoptosis may be the presence of CPDs (Dumaz et al, 1997(Dumaz et al, , 1998Blattner et al, 1998). This is further supported by our results in CS cells which normally remove (6-4)P from the transcribed strand of active genes whereas they are speci®cally defective in CPD removal (Barrett et al, 1991;Parris and Kraemer, 1993;Evans and Bohr, 1994).…”

“…Only a few studies have analysed the responses to UV irradiation of primary ®broblasts from patients with inborn defects in NER (Yamaizumi and Sugano, 1994;Li et al, 1996;Ljungman and Zhang, 1996;Dumaz et al, 1997Dumaz et al, , 1998Blattner et al, 1998;McKay et al, 1998). In line with previous reports, we have shown that an enhancement in the UV-induced apoptosis is associated with defective TCR but, in addition, we provide the ®rst evidence that the lack of Mdm2 activation plays a crucial role in the cascade of events leading to apoptosis.…”

Enzyme plus light therapy to repair DNA damage in ultraviolet-B-irradiated human skin

“…A possible explanation for this discrepancy might be that not all dimers are equal, but that repair of a fraction of dimers might have disproportionate effects on biological responses. This hypothesis is supported by the recent observation that only photoproducts in actively transcribed DNA, which are preferentially repaired (30) and constitute only a small fraction of the total DNA, are important in signal transduction (31). Perhaps DNA regions involved in the transcriptional regulation of the human ICAM-1 gene may be repaired more rapidly than others may.…”

The Transcription Stress Response

“…4,5 In addition, less distorting but highly mutagenic lesions, such as O 6 -methyl guanine, can be converted from non-blocking lesions into blocking lesions by the binding of mismatch repair proteins to the lesions. 6 Using human cell lines or mouse models with specific defects in nucleotide excision repair, it has been shown that the induction of p53 [7][8][9][10][11][12] and apoptosis 8 following UV-irradiation depends on persistent lesions localized in the transcribed strand of active genes. Furthermore, a number of agents that interfere with RNA polymerase II-mediated transcription have been shown to induce p53 and apoptosis suggesting that blockage of transcription may act as a trigger for stress response activation.…”