Expression of the epidermal growth factor system in human middle ear cholesteatoma

Abstract

Conclusion: The detection of the HER4 receptor in 50% of cholesteatomas but never in the reference tissue, and the increased expression of its activating ligand EPI, suggest that EPI-mediated activation of HER4 might play a role in cholesteatoma growth. Objective: To investigate the expression of the epidermal growth factor (EGF) system in human middle ear cholesteatoma. Methods: Forty-seven patients referred for surgery due to cholesteatoma were included in the study. Clinical data were collected. Biopsies of cholesteatoma and skin from the external ear canal were obtained during surgery. mRNA expression was quantified with real-time PCR. The corresponding proteins were visualized using immunohistochemistry. Results: A systematic investigation of all four receptors, HER1, HER2, HER3, and HER4, and the ligands EGF, transforming growth factor (TGF)-α, amphiregulin (AR), heparin-binding EGF-like growth factor (HB-EGF), and epiregulin (EPI) of the EGF system is presented. At the mRNA level, the study demonstrates an up-regulation of mRNA encoding EPI and AR. In contrast HER1 and EGF were down-regulated. HER4 mRNA could be detected in 50% of cholesteatoma and 20% of reference tissues, and the HER4 protein was detectable only in cholesteatoma tissue. HER1 and HER2 were also visualized by immunohistochemistry, whereas the ligands EPI, AR, and EGF were undetectable with our methods.

Keywords::

• Epiregulin
• amphiregulin
• HER1
• HER4
• EGF
• Q-PCR

Acknowledgments

The authors are grateful to the patients who donated tissue samples to the present study. We wish to thank Lars Vendelbo Johansen MD DMSc and Kjell Tveterås MD for helping with the sampling procedure. Expert technical assistance provided by laboratory technicians Birgit Mortensen, Birgit Westh Mortensen, Lene Dabelstein, Alice Willemoes, and Jette Shousboe is greatly appreciated. Professor Michael Væth MSci PhD is thanked for help with statistical analysis. We thank the Oticon Foundation, the Oda Pedersen Research Foundation, and the Institute of Clinical Medicine for financial support.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.