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. 2016 Sep 20;7(38):60940-60953.
doi: 10.18632/oncotarget.10902.

Repair of UVB-induced DNA damage is reduced in melanoma due to low XPC and global genome repair

Timothy Budden  1 , Ryan J Davey  1 , Ricardo E Vilain  1   2   3   4 , Katie A Ashton  1 , Stephen G Braye  4 , Natalie J Beveridge  1 , Nikola A Bowden  1
Affiliations

Repair of UVB-induced DNA damage is reduced in melanoma due to low XPC and global genome repair

Timothy Budden et al. Oncotarget. .

Abstract

UVB exposure leads to DNA damage, which when unrepaired induces C>T transitions. These mutations are found throughout the melanoma genome, particularly in non-transcribed regions. The global genome repair (GGR) branch of nucleotide excision repair (NER) is responsible for repairing UV-induced DNA damage across non-transcribed and silent regions of the genome. This study aimed to examine the relationship between UVB and GGR in melanoma. DNA repair capacity and relative expression of NER in melanocytes and melanoma cell lines before and after treatment with UVB was quantified. Transcript expression from 196 melanomas was compared to clinical parameters including solar elastosis and whole transcriptome data collected. Melanoma cell lines showed significantly reduced DNA repair when compared to melanocytes, most significantly in the S phase of the cell cycle. Expression of GGR components XPC, DDB1 and DDB2 was significantly lower in melanoma after UVB. In the melanoma tumours, XPC expression correlated with age of diagnosis and low XPC conferred significantly poorer survival. The same trend was seen in the TCGA melanoma dataset. Reduced GGR in melanoma may contribute to the UV mutation spectrum of the melanoma genome and adds further to the growing evidence of the link between UV, NER and melanoma.

Keywords: UVB; XPC; global genome repair; melanoma; nucleotide excision repair.

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Conflict of interest statement

The authors state no conflict of interest.

Figures

Figure 1
Figure 1. Repair of 6-4 photoproducts in melanoma and melanocyte cell lines after 650J/m2 UVB: Geometric mean fluorescence (FITC) was normalized to baseline to calculate the percentage of 6-4 PPs remaining at each timepoint
Points are mean of triplicates of three individual experiments, bars = SE.
Figure 2
Figure 2. Repair of 6-4 photoproducts in melanoma and melanocytes in individual phases of the cell cycle: Bivariate distributions of 6-4 PPs versus DNA content (PI) in
a. melanocytes (HEMn-MP) and b. melanoma cell line (Mel-RM) immediately (red dots) and 12 hours post-UVB (blue dots). c. All cell lines were divided into individual cell cycle phases, and repair of 6-4 PPs was measured in each individual phase. Points are mean of triplicates of three individual experiments, bars = SE.
Figure 3
Figure 3. Repair of CPDs in melanoma and melanocytes in individual phases of the cell cycle: All cell lines were divided into individual cell cycle phases, using propidium iodide staining and the repair of CPDs was measured in each individual phase
Significance was calculated between levels of CPDs in melanocytes and melanoma at each time point. Points are mean of triplicates of three individual experiments, bars = SE.
Figure 4
Figure 4. Expression of GGR and p53 in melanocytes and melanoma cell lines after treatment with 650J/m UVB
a.-c. relative expression (RE) GGR transcripts XPC, DDB1, and DDB2 in melanocytes and melanoma cell lines. Points are mean of triplicates of three individual experiments, bars = SE, d. Western blot of XPC and p53 for all cell lines before and after UVB. Blots are representative of duplicate blots run for all proteins and cell lines.
Figure 5
Figure 5. Kaplin-Meier survival plot for XPC high melanomas (green line) and XPC low melanomas (blue line)
Survival for XPC high melanomas was significantly longer (733.5 weeks, 95% CI 456.8 - 1010.3) than XPC low melanomas (454.7 weeks, 95% CI 262.2 - 647.2) *p = 0.037.
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