432 The epidermal growth factor receptor is critical for the Staphylococcus aureus-mediated induction of human beta-defensin-3 in keratinocytes

Abstract

Antimicrobial peptides (AMP) contribute to cutaneous defense due to their potent antimicrobial activity. A feature of many AMP expressed by keratinocytes is their inducibility by cytokines and microbial factors. There is increasing evidence that several skin infections may be associated with a dysregulation of AMP. Patients receiving anti-EGFR (epidermal growth factor receptor) therapy often suffer from cutaneous infection caused by Staphylococcus (S.) aureus. This is in line with recent studies indicating a pivotal role of the EGFR to mediate the expression of various AMP in keratinocytes. Human beta-defensin-3 (hBD-3) is an important AMP expressed by keratinocytes to control the growth of S. aureus. Since S. aureus is able to induce the expression of hBD-3 in keratinocytes we analyzed if the EGFR is involved in this induction. To this end we stimulated human primary keratinocytes with S. aureus in the presence of the anti-EGFR antibody cetuximab. Inactivation of the EGFR by cetuximab already resulted in a decreased constitutive hBD-3 gene expression as measured by real-time PCR. Simulation of the keratinocytes with living S. aureus or their culture supernatants resulted in an increased hBD-3 gene expression which was abrogated in the presence of cetuximab. Accordingly, the EGFR inhibitor AG1478 also inhibited the S. aureus-mediated hBD-3 induction. Induction of hBD-3 in keratinocytes treated with the EGFR ligand TGF-alpha confirmed the EGFR-dependent induction of hBD-3. Treatment of a 3D skin equivalent with living S. aureus also resulted in an increased expression of hBD-3. This S. aureus-mediated hBD-3 induction was decreased in skin equivalents treated with cetuximab. Together, these data further highlight the importance of the EGFR-pathway in cutaneous defense against S. aureus. Our data suggest that a failure of S. aureus-mediated hBD-3 induction in patients receiving anti-EGFR therapy may contribute to the increased S. aureus infection rate seen in these patients.