Abstract
Epidermal growth factor receptor (EGFR) is a critical mediator of several types of epithelial cancers. Skin cancer arising from exposure to ultraviolet B irradiation (UVB) from the sun is a prominent form of human cancer. Recent data indicate that in addition to cognate ligands, EGFR is activated by UVB irradiation. We used pharmacological and genetic approaches to investigate the function of EGFR in mediating UVB-induced signal transduction in human skin keratinocyte HaCaT cells. Pharmacological inhibition of EGFR tyrosine kinase significantly inhibited UVB-mediated induction of ERK, p38, and JNK MAP kinases, and their effectors, transcription factors c-Fos and c-Jun. Inhibition of UVB activation of EGFR also suppressed activation of AKT-, PKC-, and PKA-dependent signal transduction pathways. B82 mouse L cells devoid of EGFR were used to further investigate EGFR dependence of UVB-induced signal transduction. UVB failed to induce ERK, and JNK activation was reduced 60% in B82 cells compared to B82K+ cells, which express EGFR. In addition, UVB induced both c-Fos and c-Jun proteins in B82K+ cells, whereas neither were induced in B82 cells. Taken together, these data demonstrate that EGFR is required for UVB-mediated induction of multiple signaling pathways that are known to mediate tumor formation in skin.
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