Oxidative stress induced by UVA photoactivation of the tryptophan UVB photoproduct 6-formylindolo[3,2-b]carbazole (FICZ) inhibits nucleotide excision repair in human cells

Reto Brem,Peter Macpherson,Melisa Guven,Peter Karran

doi:10.1038/s41598-017-04614-8

Reto Brem, Peter Macpherson + Show 2 more

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https://doi.org/10.1038/s41598-017-04614-8

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Journal: Scientific Reports	Publication Date: Jun 27, 2017
Citations: 34	License type: open-access

Affiliation: The Francis Crick Institute

Abstract

Potentially mutagenic DNA lesions induced by UVB (wavelengths 280–320 nm) are important risk factors for solar ultraviolet (UV) radiation-induced skin cancer. The carcinogenicity of the more abundant UVA (320–400 nm) is less well understood but is generally regarded to reflect its interaction with cellular chromophores that act as photosensitisers. The arylhydrocarbon receptor agonist 6-formylindolo[3,2-b] carbazole (FICZ), is a UVB photoproduct of tryptophan and a powerful UVA chromophore. Combined with UVA, FICZ generates reactive oxygen species (ROS) and induces oxidative DNA damage. Here we demonstrate that ROS generated by FICZ/UVA combinations also cause extensive protein damage in HaCaT human keratinocytes. We show that FICZ/UVA-induced oxidation significantly inhibits the removal of potentially mutagenic UVB-induced DNA photolesions by nucleotide excision repair (NER). DNA repair inhibition is due to FICZ/UVA-induced oxidation damage to the NER proteome and DNA excision repair is impaired in extracts prepared from FICZ/UVA-treated cells. NER protects against skin cancer. As a likely UVB photoproduct of intracellular tryptophan, FICZ represents a de facto endogenous UVA photosensitiser in sun-exposed skin. FICZ formation may increase the risk of solar UV-induced skin cancer by promoting photochemical damage to the NER proteome and thereby preventing the removal of UVB-induced DNA lesions.

Highlights

Tryptophan is an essential amino acid and is present in human serum at around 50–100 μM4, 5
In order to determine whether UVA photoactivation of FICZ poses a threat to DNA repair and might thereby increase skin cancer risk, we have examined the effects of UVA/FICZ on nucleotide excision repair (NER) and base excision repair (BER) in vivo in cultured HaCaT keratinocytes and in vitro by biochemical assays
Our findings demonstrate that the NER system that provides important protection against skin cancer is compromised in cells treated with UVA and the UVA/visible photosensitiser FICZ

Summary

Introduction

Tryptophan is an essential amino acid and is present in human serum at around 50–100 μM4, 5. Carbazole (FICZ) is a major UVB photoproduct of tryptophan both in vitro and in irradiated human cells[6] It is a potent agonist of the arylhydrocarbon receptor (AhR), a transcriptional activator that upregulates a number of stress-related genes[7] including members of the MAPK signalling cascade[8]. Consistent with the generation of oxidative stress, the combination of FICZ and UVA triggers the production of ROS (including singlet oxygen, 1O2) and induces the formation DNA 8-oxo-7,8-dihydroguanine (8-oxoG)[9]. This potentially mutagenic DNA lesion can be excised by the base excision repair (BER) system initiated by the hOGG-1 DNA glycosylase. In order to determine whether UVA photoactivation of FICZ poses a threat to DNA repair and might thereby increase skin cancer risk, we have examined the effects of UVA/FICZ on NER and BER in vivo in cultured HaCaT keratinocytes and in vitro by biochemical assays

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