scholarly journals Evidence from mutation spectra that the UV hypermutability of xeroderma pigmentosum variant cells reflects abnormal, error-prone replication on a template containing photoproducts.

1993 ◽  
Vol 13 (7) ◽  
pp. 4276-4283 ◽  
Author(s):  
Y C Wang ◽  
V M Maher ◽  
D L Mitchell ◽  
J J McCormick
Keyword(s):  
Xeroderma Pigmentosum ◽  
Excision Repair ◽  
Mutagenic Effect ◽  
S Phase ◽  
G1 Phase ◽  
Coding Region ◽  
Normal Cells ◽  
Pyrimidine Dimers ◽  
Hypoxanthine Guanine Phosphoribosyltransferase ◽  
Mutation Spectra

Xeroderma pigmentosum (XP) variant patients are genetically predisposed to sunlight-induced skin cancer. Fibroblasts derived from these patients are extremely sensitive to the mutagenic effect of UV radiation and are abnormally slow in replicating DNA containing UV-induced photoproducts. However, unlike cells from the majority of XP patients, XP variant cells have a normal or nearly normal rate of nucleotide excision repair of such damage. To determine whether their UV hypermutability reflected a slower rate of excision of photoproducts specifically during early S phase when the target gene for mutations, i.e., the hypoxanthine (guanine) phosphoribosyltransferase gene (HPRT), is replicated, we synchronized diploid populations of normal and XP variant fibroblasts, irradiated them in early S phase, and compared the rate of loss of cyclobutane pyrimidine dimers and 6-4 pyrimidine-pyrimidones from DNA during S phase. There was no difference. Both removed 94% of the 6-4 pyrimidine-pyrimidones within 8 h and 40% of the dimers within 11 h. There was also no difference between the two cell lines in the rate of repair during G1 phase. To determine whether the hypermutability resulted from abnormal error-prone replication of DNA containing photoproducts, we determined the spectra of mutations induced in the coding region of the HPRT gene of XP variant cells irradiated in early S and G1 phases and compared with those found in normal cells. The majority of the mutations in both types of cells were base substitutions, but the two types of cells differed significantly from each other in the kinds of substitutions, but the two types differed significantly from each other in the kinds of substitutions observed either in mutants from S phase (P < 0.01) or from G1 phase (P = 0.03). In the variant cells, the substitutions were mainly transversions (58% in S, 73% in G1). In the normal cells irradiated in S, the majority of the substitutions were G.C --> A.T, and most involved CC photoproducts in the transcribed strand. In the variant cells irradiated in S, substitutions involving cytosine in the transcribed strand were G.C --> T.A transversions exclusively. G.C --> A.T transitions made up a much smaller fraction of the substitutions than in normal cells (P < 0.02), and all of them involved photoproducts located in the nontranscribed strand. The data strongly suggest that XP variant cells are much less likely than normal cells to incorporate either dAMP or dGMP opposite the pyrimidines involved in photoproducts. This would account for their significantly higher frequency of mutants and might explain their abnormal delay in replicating a UV-damaged template.

Evidence from mutation spectra that the UV hypermutability of xeroderma pigmentosum variant cells reflects abnormal, error-prone replication on a template containing photoproducts

1993 ◽  
Vol 13 (7) ◽  
pp. 4276-4283
Author(s):  
Y C Wang ◽  
V M Maher ◽  
D L Mitchell ◽  
J J McCormick
Keyword(s):  
Xeroderma Pigmentosum ◽  
Excision Repair ◽  
Mutagenic Effect ◽  
S Phase ◽  
G1 Phase ◽  
Coding Region ◽  
Normal Cells ◽  
Pyrimidine Dimers ◽  
Hypoxanthine Guanine Phosphoribosyltransferase ◽  
Mutation Spectra

Xeroderma pigmentosum (XP) variant patients are genetically predisposed to sunlight-induced skin cancer. Fibroblasts derived from these patients are extremely sensitive to the mutagenic effect of UV radiation and are abnormally slow in replicating DNA containing UV-induced photoproducts. However, unlike cells from the majority of XP patients, XP variant cells have a normal or nearly normal rate of nucleotide excision repair of such damage. To determine whether their UV hypermutability reflected a slower rate of excision of photoproducts specifically during early S phase when the target gene for mutations, i.e., the hypoxanthine (guanine) phosphoribosyltransferase gene (HPRT), is replicated, we synchronized diploid populations of normal and XP variant fibroblasts, irradiated them in early S phase, and compared the rate of loss of cyclobutane pyrimidine dimers and 6-4 pyrimidine-pyrimidones from DNA during S phase. There was no difference. Both removed 94% of the 6-4 pyrimidine-pyrimidones within 8 h and 40% of the dimers within 11 h. There was also no difference between the two cell lines in the rate of repair during G1 phase. To determine whether the hypermutability resulted from abnormal error-prone replication of DNA containing photoproducts, we determined the spectra of mutations induced in the coding region of the HPRT gene of XP variant cells irradiated in early S and G1 phases and compared with those found in normal cells. The majority of the mutations in both types of cells were base substitutions, but the two types of cells differed significantly from each other in the kinds of substitutions, but the two types differed significantly from each other in the kinds of substitutions observed either in mutants from S phase (P < 0.01) or from G1 phase (P = 0.03). In the variant cells, the substitutions were mainly transversions (58% in S, 73% in G1). In the normal cells irradiated in S, the majority of the substitutions were G.C --> A.T, and most involved CC photoproducts in the transcribed strand. In the variant cells irradiated in S, substitutions involving cytosine in the transcribed strand were G.C --> T.A transversions exclusively. G.C --> A.T transitions made up a much smaller fraction of the substitutions than in normal cells (P < 0.02), and all of them involved photoproducts located in the nontranscribed strand. The data strongly suggest that XP variant cells are much less likely than normal cells to incorporate either dAMP or dGMP opposite the pyrimidines involved in photoproducts. This would account for their significantly higher frequency of mutants and might explain their abnormal delay in replicating a UV-damaged template.

Xeroderma pigmentosum complementation group C cells remove pyrimidine dimers selectively from the transcribed strand of active genes

1991 ◽  
Vol 11 (8) ◽  
pp. 4128-4134
Author(s):  
J Venema ◽  
A van Hoffen ◽  
V Karcagi ◽  
A T Natarajan ◽  
A A van Zeeland ◽  
...  
Keyword(s):  
Xeroderma Pigmentosum ◽  
Mammalian Cells ◽  
Excision Repair ◽  
Complementation Group ◽  
C Cells ◽  
Dhfr Gene ◽  
Normal Cells ◽  
Pyrimidine Dimers ◽  
Normal Human ◽  
Active Genes

We have measured the removal of UV-induced pyrimidine dimers from DNA fragments of the adenosine deaminase (ADA) and dihydrofolate reductase (DHFR) genes in primary normal human and xeroderma pigmentosum complementation group C (XP-C) cells. Using strand-specific probes, we show that in normal cells, preferential repair of the 5' part of the ADA gene is due to the rapid and efficient repair of the transcribed strand. Within 8 h after irradiation with UV at 10 J m-2, 70% of the pyrimidine dimers in this strand are removed. The nontranscribed strand is repaired at a much slower rate, with 30% dimers removed after 8 h. Repair of the transcribed strand in XP-C cells occurs at a rate indistinguishable from that in normal cells, but the nontranscribed strand is not repaired significantly in these cells. Similar results were obtained for the DHFR gene. In the 3' part of the ADA gene, however, both normal and XP-C cells perform fast and efficient repair of either strand, which is likely to be caused by the presence of transcription units on both strands. The factor defective in XP-C cells is apparently involved in the processing of DNA damage in inactive parts of the genome, including nontranscribed strands of active genes. These findings have important implications for the understanding of the mechanism of UV-induced excision repair and mutagenesis in mammalian cells.

scholarly journals Xeroderma pigmentosum complementation group C cells remove pyrimidine dimers selectively from the transcribed strand of active genes.

1991 ◽  
Vol 11 (8) ◽  
pp. 4128-4134 ◽  
Author(s):  
J Venema ◽  
A van Hoffen ◽  
V Karcagi ◽  
A T Natarajan ◽  
A A van Zeeland ◽  
...  
Keyword(s):  
Xeroderma Pigmentosum ◽  
Mammalian Cells ◽  
Excision Repair ◽  
Complementation Group ◽  
C Cells ◽  
Dhfr Gene ◽  
Normal Cells ◽  
Pyrimidine Dimers ◽  
Normal Human ◽  
Active Genes

We have measured the removal of UV-induced pyrimidine dimers from DNA fragments of the adenosine deaminase (ADA) and dihydrofolate reductase (DHFR) genes in primary normal human and xeroderma pigmentosum complementation group C (XP-C) cells. Using strand-specific probes, we show that in normal cells, preferential repair of the 5' part of the ADA gene is due to the rapid and efficient repair of the transcribed strand. Within 8 h after irradiation with UV at 10 J m-2, 70% of the pyrimidine dimers in this strand are removed. The nontranscribed strand is repaired at a much slower rate, with 30% dimers removed after 8 h. Repair of the transcribed strand in XP-C cells occurs at a rate indistinguishable from that in normal cells, but the nontranscribed strand is not repaired significantly in these cells. Similar results were obtained for the DHFR gene. In the 3' part of the ADA gene, however, both normal and XP-C cells perform fast and efficient repair of either strand, which is likely to be caused by the presence of transcription units on both strands. The factor defective in XP-C cells is apparently involved in the processing of DNA damage in inactive parts of the genome, including nontranscribed strands of active genes. These findings have important implications for the understanding of the mechanism of UV-induced excision repair and mutagenesis in mammalian cells.

scholarly journals DNA repair synthesis in human heterokaryons. III. The rapid and slow complementing varieties of xeroderma pigmentosum

1976 ◽  
Vol 20 (1) ◽  
pp. 207-213
Author(s):  
F. Giannelli ◽  
S.A. Pawsey
Keyword(s):  
Protein Synthesis ◽  
Xeroderma Pigmentosum ◽  
Excision Repair ◽  
Dependent Manner ◽  
Repair Synthesis ◽  
Normal Cells ◽  
Complementation Groups ◽  
Dna Repair Synthesis ◽  
And Control ◽  
The Relationship

Patients with Xeroderma pigmentosum and defective DNA excision repair can be distinguished as a rapid (r-XP) and slow (s-XP) complementing variety. When fused with normal cells, fibroblasts from the r-XP are complemented rapidly and in the absence of protein synthesis while those from the s-XP are complemented slowly by a process partly, but not entirely, dependent on protein synthesis. Heterokaryons with different ratios of r-XP to s-XP nuclei (i.e. 1:1-5 and 1-5:1) and control heterokaryons containing one normal and 1-5 r- or s-XP nuclei show that if cell fusion and incubation is conducted in medium preventing protein synthesis, the rXP cells do not complement the s-XP partner at all and, conversely, that the latter is not as effective as normal cells at complementing the rXP partner. On the contrary, if protein synthesis is permitted, the 2 types of XP cells complement each other in a gene dose-dependent manner and to an extent similar to that observed in the control heterokaryons. These findings indicate that the r- and s-XP varieties are caused by mutations at different loci and suggest that the products of these loci interact to produce a functional unit which is present in normal control cells but absent in the XP strains. The relationship between the complementation groups described here and those already reported in the literature being investigated.

Non-specific elongation of cell cycle phases by cycloheximide in rat 3Y1 cells, and specific reduction of G1 phase elongation by simian virus 40 large T antigen

1988 ◽  
Vol 91 (2) ◽  
pp. 295-302
Author(s):  
A. Okuda ◽  
G. Kimura
Keyword(s):  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
S Phase ◽  
G1 Phase ◽  
Protein Accumulation ◽  
Large T Antigen ◽  
Coding Region ◽  
Sv40 Large T Antigen ◽  
In Cells

Partial inhibition of protein synthesis by cycloheximide caused prolongation of G1, S and G2 phases in rat 3Y1 fibroblasts. In cells expressing simian virus 40 (SV40) large T antigen, by infection with SV40 in the previous generation, the prolongation of G1 phase in the presence of cycloheximide was suppressed. However, the prolongation of S and G2 phases in the presence of cycloheximide was not suppressed in cells expressing large T antigen, by infection with SV40 in the current generation. Similarly, when density-arrested cells (cells in G0 phase) were infected with SV40 (either wild-type strain or a mutant deleted in the unique coding region for small t antigen) and reseeded sparsely in the presence of cycloheximide, the cycloheximide-induced delay of entry into S phase was suppressed. In this case, the reduction in [35S]methionine incorporation, that in protein accumulation and that in cell volume increase, were not surmounted by SV40 infection. In T-antigen-negative cells, all the regions in G1 phase seemed to be sensitive to cycloheximide, i.e. they suffered elongation. These results suggest that, in comparison with cells that enter S phase by the action of growth factors, cells expressing large T antigen can enter S phase more efficiently through a quite different process.

scholarly journals Evidence that xeroderma pigmentosum cells from complementation group E are deficient in a homolog of yeast photolyase.

1989 ◽  
Vol 9 (11) ◽  
pp. 5105-5112 ◽  
Author(s):  
M Patterson ◽  
G Chu
Keyword(s):  
Xeroderma Pigmentosum ◽  
Excision Repair ◽  
Complementation Group ◽  
Binding Activity ◽  
Multiple Forms ◽  
Yeast Saccharomyces Cerevisiae ◽  
Dna Lesion ◽  
Pyrimidine Dimers ◽  
Binding Factor ◽  
Damaged Dna

Xeroderma pigmentosum (XP) patients are deficient in the excision repair of damaged DNA. Recognition of the DNA lesion appears to involve a nuclear factor that is defective in complementation group E (XPE binding factor). We have now identified a factor in the yeast Saccharomyces cerevisiae that shares many properties with XPE binding factor, including cellular location, abundance, magnesium dependence, and relative affinities for multiple forms of damaged DNA. Yeast binding activity is dependent on photolyase, which catalyzes the photoreactivation of pyrimidine dimers. These results suggest that yeast photolyase may also function as an auxiliary protein in excision repair. Furthermore, XPE binding factor appears to be the human homolog of yeast photolyase.

scholarly journals Abnormal, Error-Prone Bypass of Photoproducts by Xeroderma Pigmentosum Variant Cell Extracts Results in Extreme Strand Bias for the Kinds of Mutations Induced by UV Light

1999 ◽  
Vol 19 (1) ◽  
pp. 147-154 ◽  
Author(s):  
W. Glenn McGregor ◽  
Dong Wei ◽  
Veronica M. Maher ◽  
J. Justin McCormick
Keyword(s):  
Xeroderma Pigmentosum ◽  
Excision Repair ◽  
Uv Light ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
Induced Mutations ◽  
Coding Region ◽  
Cell Extracts ◽  
Variant Cell ◽  
Leading Strand

ABSTRACT Xeroderma pigmentosum (XP) is a rare genetic disease characterized by a greatly increased susceptibility to sunlight-induced skin cancer. Cells from the majority of patients are defective in nucleotide excision repair. However, cells from one set of patients, XP variants, exhibit normal repair but are abnormally slow in replicating DNA containing UV photoproducts. The frequency of UV radiation-induced mutations in the XP variant cells is significantly higher than that in normal human cells. Furthermore, the kinds of UV-induced mutations differ very significantly from normal. Instead of transitions, mainly C→T, 30% of the base substitutions consist of C→A transversions, all arising from photoproducts located in one strand. Mutations involving cytosine in the other strand are almost all C→T transitions. Forty-five percent of the substitutions involve thymine, and the majority are transversions. To test the hypothesis that the UV hypermutability and the abnormal spectrum of mutations result from abnormal bypass of photoproducts in DNA, we compared extracts from XP variant cells with those from HeLa cells and a fibroblast cell strain, MSU-1.2, for the ability to replicate a UV-irradiated form I M13 phage. The M13 template contains a simian virus 40 origin of replication located directly to the left or to the right of the target gene,lacZα, so that the template for the leading and lagging strands of DNA replication is defined. Reduction of replication to ∼37% of the control value required only 1 photoproduct per template for XP variant cell extracts, but ∼2.2 photoproducts for HeLa or MSU-1.2 cell extracts. The frequency of mutants induced was four times higher with XP variant cell extracts than with HeLa or MSU-1.2 cell extracts. With XP variant cell extracts, the proportion of C→A transversions reached as high as 43% with either M13 template and arose from photoproducts located in the template for leading-strand synthesis; with HeLa or MSU-1.2 cell extracts, this value was only 5%, and these arose from photoproducts in either strand. With the XP variant extracts, 26% of the substitutions involved thymine, and virtually all were T→A transversions. Sequence analysis of the coding region of the catalytic subunit of DNA polymerase delta in XP variant cell lines revealed two polymorphisms, but these do not account for the reduced bypass fidelity. Our data indicate that the UV hypermutability of XP variant cells results from reduced bypass fidelity and that unlike for normal cells, bypass of photoproducts involving cytosine in the template for the leading strand differs significantly from that of photoproducts in the lagging strand.

scholarly journals Xeroderma Pigmentosum: Gene Variants and Splice Variants

Genes ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1173
Author(s):  
Marie Christine Martens ◽  
Steffen Emmert ◽  
Lars Boeckmann
Keyword(s):  
Dna Damage ◽  
Xeroderma Pigmentosum ◽  
Splice Variants ◽  
Excision Repair ◽  
Genetic Disorder ◽  
Cyclobutane Pyrimidine Dimers ◽  
Pyrimidine Dimers ◽  
Damage Repair ◽  
Nucleotide Excision ◽  
Functional Relevance

The nucleotide excision repair (NER) is essential for the repair of ultraviolet (UV)-induced DNA damage, such as cyclobutane pyrimidine dimers (CPDs) and 6,4-pyrimidine-pyrimidone dimers (6,4-PPs). Alterations in genes of the NER can lead to DNA damage repair disorders such as Xeroderma pigmentosum (XP). XP is a rare autosomal recessive genetic disorder associated with UV-sensitivity and early onset of skin cancer. Recently, extensive research has been conducted on the functional relevance of splice variants and their relation to cancer. Here, we focus on the functional relevance of alternative splice variants of XP genes.

Cell cycle-dependent strand bias for UV-induced mutations in the transcribed strand of excision repair-proficient human fibroblasts but not in repair-deficient cells

1991 ◽  
Vol 11 (4) ◽  
pp. 1927-1934
Author(s):  
W G McGregor ◽  
R H Chen ◽  
L Lukash ◽  
V M Maher ◽  
J J McCormick
Keyword(s):  
Nucleotide Excision Repair ◽  
Excision Repair ◽  
Uv Light ◽  
Human Fibroblasts ◽  
S Phase ◽  
G1 Phase ◽  
Strand Bias ◽  
Hprt Gene ◽  
Significant Difference ◽  
Nucleotide Excision

To study the effect of nucleotide excision repair on the spectrum of mutations induced in diploid human fibroblasts by UV light (wavelength, 254 nm), we synchronized repair-proficient cells and irradiated them when the HPRT gene was about to be replicated (early S phase) so that there would be no time for repair in that gene before replication, or in G1 phase 6 h prior to S, and determined the kinds and location of mutations in that gene. As a control, we also compared the spectra of mutations induced in synchronized populations of xeroderma pigmentosum cells (XP12BE cells, which are unable to excise UV-induced DNA damage). Among the 84 mutants sequenced, base substitutions predominated. Of the XP mutants from S or G1 and the repair-proficient mutants from S, approximately 62% were G.C----A.T. In the repair-proficient mutants from G1, 47% were. In mutants from the repair-proficient cells irradiated in S, 71% (10 of 14) of the premutagenic lesions were located in the transcribed strand; with mutants from such cells irradiated in G1, only 20% (3 of 15) were. In contrast, there was no statistically significant difference in the fraction of premutagenic lesions located in the transcribed strand of the XP12BE cells; approximately 75% (24 of 32) of the premutagenic lesions were located in that strand, i.e., 15 of 19 (79%) in the S-phase cells and 9 of 13 (69%) in the G1-phase cells. The switch in strand bias supports preferential nucleotide excision repair of UV-induced damage in the transcribed strand of the HPRT gene.

scholarly journals Cell cycle-dependent strand bias for UV-induced mutations in the transcribed strand of excision repair-proficient human fibroblasts but not in repair-deficient cells.

1991 ◽  
Vol 11 (4) ◽  
pp. 1927-1934 ◽  
Author(s):  
W G McGregor ◽  
R H Chen ◽  
L Lukash ◽  
V M Maher ◽  
J J McCormick
Keyword(s):  
Nucleotide Excision Repair ◽  
Excision Repair ◽  
Uv Light ◽  
Human Fibroblasts ◽  
S Phase ◽  
G1 Phase ◽  
Strand Bias ◽  
Hprt Gene ◽  
Significant Difference ◽  
Nucleotide Excision

To study the effect of nucleotide excision repair on the spectrum of mutations induced in diploid human fibroblasts by UV light (wavelength, 254 nm), we synchronized repair-proficient cells and irradiated them when the HPRT gene was about to be replicated (early S phase) so that there would be no time for repair in that gene before replication, or in G1 phase 6 h prior to S, and determined the kinds and location of mutations in that gene. As a control, we also compared the spectra of mutations induced in synchronized populations of xeroderma pigmentosum cells (XP12BE cells, which are unable to excise UV-induced DNA damage). Among the 84 mutants sequenced, base substitutions predominated. Of the XP mutants from S or G1 and the repair-proficient mutants from S, approximately 62% were G.C----A.T. In the repair-proficient mutants from G1, 47% were. In mutants from the repair-proficient cells irradiated in S, 71% (10 of 14) of the premutagenic lesions were located in the transcribed strand; with mutants from such cells irradiated in G1, only 20% (3 of 15) were. In contrast, there was no statistically significant difference in the fraction of premutagenic lesions located in the transcribed strand of the XP12BE cells; approximately 75% (24 of 32) of the premutagenic lesions were located in that strand, i.e., 15 of 19 (79%) in the S-phase cells and 9 of 13 (69%) in the G1-phase cells. The switch in strand bias supports preferential nucleotide excision repair of UV-induced damage in the transcribed strand of the HPRT gene.

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