Role of the aryl hydrocarbon receptor in ultraviolet-B radiation-induced DNA damage responses and skin carcinogenesis

• Applicant: Privatdozent Dr. Thomas Haarmann-Stemmann
• Subject Area: Dermatology ; Public Health, Healthcare Research, Social and Occupational Medicine
• Term: from 2016 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 322588062

• Final Report Year: 2024

Final Report Abstract

The aryl hydrocarbon receptor (AHR) is a transcription factor that is activated by UVB radiation in keratinocytes (KC) and contributes to photocarcinogenesis by dampening both nucleotide excision repair (NER) and apoptosis. Active AHR induces the proteolysis of the cell-cycle inhibitor p27KIP1 (p27), thereby differentially affecting NER and homologous recombination repair (HRR). The latter fixes DNA double-strand breaks (DSBs), which are an important trigger for KC apoptosis. Based on these findings, we aimed to unravel the molecular mechanism by which p27 affects NER, assess if an exposure of UVB-irradiated KC to AHR agonists attenuates NER and increases skin tumorigenesis, clarify if p27 affects the initiation of HRR, and investigate if AHR antagonism enhances the susceptibility of SCC cells to apoptosis induced by genotoxic drugs. To unravel how p27 affects NER in UVB-irradiated KC, we immunoprecipitated proteins from sham- and UVB-irradiated AHR-proficient and AHR-knockdown KC by using antibodies against p27 and the NER enzyme Xeroderma pigmentosum C and subsequently identified the interactome by mass spectrometry. Although the functional validation is still pending, the results so far suggest an involvement of certain ribosomal proteins and executor proteins of the interferon response. Irrespectively of the precise mechanism, inhibition of AHR accelerates whereas activation by exogenous AHR agonists attenuated the repair of UVB-induced DNA photoproducts in KC. This prompted us to design a skin carcinogenesis study using AHR+/+ and AHR-/- hairless mice. Briefly, the mice were exposed to UVB and then topically treated with the AHR agonist β-naphthoflavone (bNF). After ten cycles of treatment (initiation phase), tumor growth was promoted by phorbol ester application. Irrespectively of the treatment, AHR- /- mice developed 40%-50% less SCCs than the solvent-treated AHR+/+ mice, thus confirming AHR’s previously reported oncogenic function in UVB-exposed skin. However, in contrast to our hypothesis, AHR+/+ mice treated with UVB/bNF developed clearly less SCCs than solventtreated AHR+/+ mice. This group also contained the most tumor-free mice, implying that bNF rather reduces than enhances tumor initiation. Irradiation studies using p27-, AHR- and double-knockdown KC revealed a reduced activation of HRR and an increased occurrence of DSBs and apoptosis in AHR-silenced KC. These effects were abolished in the double-knockdown cells, a finding which for the first time identifies p27 as an important regulator of HRR that might be targeted to enhance the apoptotic death, for instance of UV-damaged KC or genotoxin-exposed cancer cells. However, targeting of AHR to enhance the susceptibility of SCC cells to genotoxin-induced apoptosis is not trivial. Our data indicate that the effects of respective co-exposures strongly depend on the chosen AHR antagonist, with MNF for instance exhibiting rather additive than synergistic effects on cell viability. Also, genetic silencing of AHR has sensitized HaCaT KC and breast cancer cells, but not A431 SCC cells, to drug-induced apoptosis by upregulating p27. Hence, the suitability of AHR inhibition to enhance the efficacy of chemotherapy depend on the chosen antagonist, the target cell/tissue (mutation status?) and probably other parameters.

Publications

• Role of the Aryl Hydrocarbon Receptor in Environmentally Induced Skin Aging and Skin Carcinogenesis. International Journal of Molecular Sciences, 20(23), 6005.
  Vogeley, Christian; Esser, Charlotte; Tüting, Thomas; Krutmann, Jean & Haarmann-Stemmann, Thomas
  
• The aryl hydrocarbon receptor as a target of environmental stressors – Implications for pollution mediated stress and inflammatory responses. Redox Biology, 34, 101530.
  Vogel, Christoph F.A.; Van Winkle, Laura S.; Esser, Charlotte & Haarmann-Stemmann, Thomas
  
• Targeting the Aryl Hydrocarbon Receptor Signaling Pathway in Breast Cancer Development. Frontiers in Immunology, 12.
  Vogel, Christoph F. A.; Lazennec, Gwendal; Kado, Sarah Y.; Dahlem, Carla; He, Yi; Castaneda, Alejandro; Ishihara, Yasuhiro; Vogeley, Christian; Rossi, Andrea; Haarmann-Stemmann, Thomas; Jugan, Juliann; Mori, Hidetoshi; Borowsky, Alexander D.; La Merrill, Michele A. & Sweeney, Colleen
  
• Aryl Hydrocarbon Receptor Signaling Synergizes with TLR/NF-κB-Signaling for Induction of IL-22 Through Canonical and Non-Canonical AhR Pathways. Frontiers in Toxicology, 3.
  Ishihara, Yasuhiro; Kado, Sarah Y.; Bein, Keith J.; He, Yi; Pouraryan, Arshia A.; Urban, Angelika; Haarmann-Stemmann, Thomas; Sweeney, Colleen & Vogel, Christoph F. A.
  
• The Aryl Hydrocarbon Receptor in the Pathogenesis of Environmentally-Induced Squamous Cell Carcinomas of the Skin. Frontiers in Oncology, 12.
  Vogeley, Christian; Rolfes, Katharina M.; Krutmann, Jean & Haarmann-Stemmann, Thomas
  
• 1153 AHR controls keratinocyte stress responses to UVB radiation: Role of the p27 tumor suppressor protein. Journal of Investigative Dermatology, 143(5), S197.
  Gilardino, V.; Rolfes, K.M.; Krutmann, J. & Haarmann-Stemmann, T.
  
• Functions of the aryl hydrocarbon receptor (AHR) beyond the canonical AHR/ARNT signaling pathway. Biochemical Pharmacology, 208, 115371.
  Sondermann, Natalie C.; Faßbender, Sonja; Hartung, Frederick; Hätälä, Anna M.; Rolfes, Katharina M.; Vogel, Christoph F.A. & Haarmann-Stemmann, Thomas
  
• Role of the aryl hydrocarbon receptor in the pathogenesis of cutaneous squamous cell carcinoma. 20th Congress of the European Society for Photobiology (ESP), Lyon, France – Invited talk (2023)
  Haarmann-Stemmann T.