Dokument: Role of the aryl hydrocarbon receptor in ultraviolet radiation-induced DNA damage responses of the skin
| Titel: | Role of the aryl hydrocarbon receptor in ultraviolet radiation-induced DNA damage responses of the skin | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=45535 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20180406-090415-9 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Shaik, Siraz [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Krutmann, Jean [Gutachter] Prof. Dr. Proksch, Peter [Gutachter] | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 570 Biowissenschaften; Biologie | |||||||
| Beschreibungen: | Exposure to ultraviolet (UV) radiation, particularly its UVB component, is one of the most important risk factors for the development of skin cancer, such as non-melanoma skin cancer (NMSC). When solar light penetrates the skin, high-energy UVB rays are absorbed by the DNA of epidermal keratinocytes (KC) leading to the formation of mutagenic DNA photoproducts, especially cyclobutane pyrimidine dimers (CPDs). To prevent UVB-induced mutagenesis, which may give rise to skin cancer, damaged KC undergo cell cycle arrest and initiate DNA repair. Thus, an increase of DNA repair activity, in most cases, protects the cells from DNA damage and thus counteracts tumorigenesis. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor, which is expressed in KC and is activated in response to UVB-irradiation. UVB-radiation is known to cause DNA-damage-dependent and DNA-damage-independent responses in KC. So far it was well-established that AhR is a crucial mediator of the DNA-damage-independent stress responses, for instance triggering the UVB-mediated induction of pro-inflammatory enzymes. In contrast, if and to which extent AhR signaling affects DNA-damage responses in UVB-exposed KC is quite enigmatic.
Therefore, the aim of the present work was to assess the role of AhR in UVB-irradiated DNA damage responses in KC. For this purpose HaCaT cells, AhR knockdown (HaCaT-shAhR) cells and cutaneous squamous cell carcinoma (SCC) cell-lines have been investigated. Both shRNA-mediated and chemical inhibition of AhR signaling in HaCaT cells resulted in a significantly improved removal of UVB-induced CPDs as shown by southwestern slot blot technique. Further RNAi-based studies targeting the expression of the nucleotide excision repair (NER) enzymes xeroderma pigmentosum complementation group A (XPA), XPC, and Cockayne syndrome protein B (CSB) revealed that AhR specifically regulates the global genome repair (GGR) sub-pathway of NER in HaCaT cells. However, instead of rescuing damaged KC from apoptosis, AhR inhibition enhanced UVB-induced apoptosis at later time points upon irradiation. Interestingly the enhanced apoptosis susceptibility of the KC positively correlated with increased DNA double-strand breaks as evidenced by neutral comet assay analyses and gamma-H2AX quantification. Thus, AhR inhibition contributes to both improved CPD removal and increased apoptosis, and thus may be suitable target for chemoprevention of UVB-induced skin malignancies. However, as apoptosis is triggered by DNA double-strand breaks, which may not only initiate cell death but also genomic alterations, this option should be further validated. Since an enhancement of apoptosis susceptibility may be of interest with regards to cancer cell killing, AhR antagonism may foster chemotherapeutic measures. Indeed, genetic, Abstract IV and chemical AhR inhibition in the two human SCC cell-lines A431 and SCL-1 resulted in elevated apoptotic cell death in response to UVB exposure. Thus, AhR antagonism may present a suitable strategy to improve the therapeutic effect of genotoxic anti-cancer drugs. These results indicate that the AhR plays a central role in regulating genomic integrity: Whereas AhR inhibits NER and thus fosters skin photocarcinogenesis, it seems to be critical for the proper repair of mitosis-related DNA double-strand breaks.Exposure to ultraviolet (UV) radiation, particularly its UVB component, is one of the most important risk factors for the development of skin cancer, such as non-melanoma skin cancer (NMSC). When solar light penetrates the skin, high-energy UVB rays are absorbed by the DNA of epidermal keratinocytes (KC) leading to the formation of mutagenic DNA photoproducts, especially cyclobutane pyrimidine dimers (CPDs). To prevent UVB-induced mutagenesis, which may give rise to skin cancer, damaged KC undergo cell cycle arrest and initiate DNA repair. Thus, an increase of DNA repair activity, in most cases, protects the cells from DNA damage and thus counteracts tumorigenesis. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor, which is expressed in KC and is activated in response to UVB-irradiation. UVB-radiation is known to cause DNA-damage-dependent and DNA-damage-independent responses in KC. So far it was well-established that AhR is a crucial mediator of the DNA-damage-independent stress responses, for instance triggering the UVB-mediated induction of pro-inflammatory enzymes. In contrast, if and to which extent AhR signaling affects DNA-damage responses in UVB-exposed KC is quite enigmatic. Therefore, the aim of the present work was to assess the role of AhR in UVB-irradiated DNA damage responses in KC. For this purpose HaCaT cells, AhR knockdown (HaCaT-shAhR) cells and cutaneous squamous cell carcinoma (SCC) cell-lines have been investigated. Both shRNA-mediated and chemical inhibition of AhR signaling in HaCaT cells resulted in a significantly improved removal of UVB-induced CPDs as shown by southwestern slot blot technique. Further RNAi-based studies targeting the expression of the nucleotide excision repair (NER) enzymes xeroderma pigmentosum complementation group A (XPA), XPC, and Cockayne syndrome protein B (CSB) revealed that AhR specifically regulates the global genome repair (GGR) sub-pathway of NER in HaCaT cells. However, instead of rescuing damaged KC from apoptosis, AhR inhibition enhanced UVB-induced apoptosis at later time points upon irradiation. Interestingly the enhanced apoptosis susceptibility of the KC positively correlated with increased DNA double-strand breaks as evidenced by neutral comet assay analyses and gamma-H2AX quantification. Thus, AhR inhibition contributes to both improved CPD removal and increased apoptosis, and thus may be suitable target for chemoprevention of UVB-induced skin malignancies. However, as apoptosis is triggered by DNA double-strand breaks, which may not only initiate cell death but also genomic alterations, this option should be further validated. Since an enhancement of apoptosis susceptibility may be of interest with regards to cancer cell killing, AhR antagonism may foster chemotherapeutic measures. Indeed, genetic, Abstract IV and chemical AhR inhibition in the two human SCC cell-lines A431 and SCL-1 resulted in elevated apoptotic cell death in response to UVB exposure. Thus, AhR antagonism may present a suitable strategy to improve the therapeutic effect of genotoxic anti-cancer drugs. These results indicate that the AhR plays a central role in regulating genomic integrity: Whereas AhR inhibits NER and thus fosters skin photocarcinogenesis, it seems to be critical for the proper repair of mitosis-related DNA double-strand breaks. | |||||||
| Lizenz: |  Urheberrechtsschutz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät | |||||||
| Dokument erstellt am: | 06.04.2018 | |||||||
| Dateien geändert am: | 06.04.2018 | |||||||
| Datum der Promotion: | 28.03.2017 |
