Visit our Expo - Redox and Inflammation signaling 2012

Session II : Receptor signaling and G proteins Poster II, 44
UVB-induced EGFR-Signaling is mediated via the AhR
Claudia Schäfer1, Ulrike Hübenthal1, Jason Cline1, Melanie Wurm2, Christian Calles1,
Peter Schroeder1, Lars-Oliver Klotz3, Helmut Hanenberg2, Jean Krutmann1, Josef
Abel1 and Ellen Fritsche1
Institut für umweltmedizinische Forschung, Auf’m Hennekamp 50; 2Department of
Paediatric Oncology, 3Institute of Biochem. and Mol. Biol., University of Düsseldorf,
Universitätsstrasse 1, 40225 Düsseldorf, Germany; e-mail: claudia.schaefer@uniduesseldorf.de
The aryl hydrocarbon receptor (AhR) is a ligand-dependend transcription factor that rests in
its inactive form as a multiprotein complex in the cytoplasm of most cells. AhR ligands
include polycyclic aromatic hydrocarbons (PAH) and halogenated PAH. Ligand binding leads
to dissociation of the interacting proteins, AhR nuclear translocation, heterodimerization with
the AhR nuclear translocator (ARNT) and activation of AhR-dependent genes like
cytochrome P450 (CYP) 1A1. CYP1A1 induction by UVB irradiation was recently described
and the formation of an endogenous AhR ligand by UVB was proposed. Epidermal growth
factor receptor (EGFR)-signaling is also initiated by UVB irradiation. Considering that the
AhR ligand TCDD causes EGFR-activation in human mammary carcinoma cells, we
investigated whether UVB-initiated EGFR-signaling is mediated by activation of the AhR
pathway.
Signaling was studied in the immortalized keratinocyte cell line HaCaT. Irradiation of cells
was carried out with 100 J/m2 UVB. Irradiation led to an AhR-dependent increase in
CYP1A1 and COX-2 mRNA as determined by quantitative real-time PCR. Because COX-2
expression can be modulated by EGFR activation, we performed immunocytochemical
analyses of the EGFR. These experiments revealed that clustering and internalization of the
EGFR after UVB irradiation are also –at least partially- AhR dependent. Further EGFR
downstream targets which are activated after UVB irradiation are Erk1/2 phosphorylation and
COX-2 protein expression. We determined by Western blotting that Erk1/2 phosphorylation
and COX-2 expression are partially dependent on AhR signaling. Involvement of the AhR in
UVB-induced signaling was verified by utilization of the AhR antagonist MNF and by AhR
gene knockdown. In summary we found that the AhR is involved in UVB-induced activation
of the EGFR signaling pathway. Therefore we conclude that the AhR serves as a photosensor
in the cytoplasm of keratinocytes mediating UVB-induced signal transduction.
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