The Aryl Hydrocarbon Receptor in the Pathogenesis of Environmentally-Induced Squamous Cell Carcinomas of the Skin

Abstract

Cutaneous squamous cell carcinoma (SCC) is one of the most frequent malignancies in humans and academia as well as public authorities expect a further increase of its incidence in the next years. The major risk factor for the development of SCC of the general population is the repeated and unprotected exposure to ultraviolet (UV) radiation. Another important risk factor, in particular with regards to occupational settings, is the chronic exposure to polycyclic aromatic hydrocarbons (PAH) which are formed during incomplete combustion of organic material and thus can be found in coal tar, creosote, bitumen and related working materials. Importantly, both exposomal factors unleash their carcinogenic potential, at least to some extent, by activating the aryl hydrocarbon receptor (AHR). The AHR is a ligand-dependent transcription factor and key regulator in xenobiotic metabolism and immunity. The AHR is expressed in all cutaneous cell-types investigated so far and maintains skin integrity. We and others have reported that in response to a chronic exposure to environmental stressors, in particular UV radiation and PAHs, an activation of AHR and downstream signaling pathways critically contributes to the development of SCC. Here, we summarize the current knowledge about AHR’s role in skin carcinogenesis and focus on its impact on defense mechanisms, such as DNA repair, apoptosis and anti-tumor immune responses. In addition, we discuss the possible consequences of a simultaneous exposure to different AHR-stimulating environmental factors for the development of cutaneous SCC.

Road‐traffic‐related air pollution contributes to skin barrier alteration and growth defect of sensory neurons

“…The chronic exposure to PAHs and their subsequent accumulation in tissues may have potential carcinogenic effects and might be involved in premature skin aging, and pro-inflammatory effects. [31][32][33] Dose-dependent CYP1A1 up-regulation, as in our experiment, is indicative for oxidative stress promotion after air pollution exposure.…”

Targeting aryl hydrocarbon receptor to prevent cancer in barrier organs

“…AhR is expressed in all cutaneous cell types and contributes toward multiple physiological and pathophysiological processes of the skin [ 43 ]. Comprehensive reviews on AhR and skin cancer have been published [ 7 , 46 , 47 ]. AhR ligands, which can originate from both exogenously and endogenously are found in high concentrations within the skin.…”

Environmental Air Pollutants Affecting Skin Functions with Systemic Implications

“…Chronic exposure of the skin to PAHs and/or UVR may activate the AhR transcription factor and promote downstream epidermal targets, contributing to skin cancerogenesis [ 179 , 180 ]. Other AhR ligands have the potential to increase PAH toxicity through the induction of the CYP1A1 gene.…”