Elevation of the epidermal growth factor receptor and dependent signaling in human papillomavirus-infected laryngeal papillomas

Laryngeal papillomas are benign tumors caused by human papillomaviruses types 6 and 11. This study addressed alterations in levels of signal transduction from the epidermal growth factor receptor (EGFR) in papillomas and cultured papilloma cells compared to normal tissue and cells. Mitogen- activated protein kinase (MAPK) was activated to a greater extent, phosphotyrosine was more abundant, and EGFR was overexpressed in laryngeal papillomas compared to normal laryngeal epithelium by Western blot analysis. The EGFR was 3 times more abundant in cultured papilloma cells than in normal laryngeal cells by Scatchard analysis and Western blot, without gene amplification or an increase in steady-state levels of mRNA. Following stimulation with EGF, a significant portion of the EGFR was recycled to the surface in papilloma cells, whereas in normal cells, it was not. Tyrosine kinase activity and activation of MAPK was more responsive to epidermal growth factor stimulation in papilloma cells than in uninfected primary laryngeal cells. PD153035, a specific inhibitor of the EGFR, and an EGFR- specific antibody that blocks ligand binding completely abrogated basal MAPK activation by endogenous ligands in laryngeal papilloma cells. These results demonstrated that infection of laryngeal epithelium by low-risk human papillomaviruses elevates the EGFR by posttranslational mechanisms, increasing its responsiveness to ligand-mediated activation. They also showed that MAPK activation in laryngeal papillomas depends upon ligand-mediated EGFR stimulation.