TGF-alpha protein and receptor localization in laryngotracheal tissue

Both normal cell turnover and healing of laryngeal and tracheal injuries involve cell migration and mitosis. The proteins that regulate normal cell turnover and wound healing in the larynx and trachea have not been established. It is possible that peptide growth factors, such as transforming growth factor-alpha (TGF alpha) acting through its receptor (EGF/TGF alpha-R), participate in the regulation of these processes. To investigate this hypothesis, we analyzed laryngotracheal cells for TGF alpha protein and receptor in normal and postwounding conditions. TGF alpha protein was detected by immunohistochemical analysis in normal ferret laryngeal and tracheal mucosa. Specific binding to the EGF/TGF alpha receptor in membrane homogenates of ferret larynx and trachea reached saturation after 60 minutes at 37 degrees C, and was effectively displaced by unlabeled epidermal growth factor (EGF) or TGF alpha, but not by unlabeled insulin, angiotensin II, or basic fibroblast growth factor. Scatchard analysis of the specific binding indicated the presence of high-affinity (Kd = 117 pmol) and low-affinity (Kd = 40 nmol) binding sites. The maximum number of available binding sites was 73 fmol/mg protein. Localization of the EGF/TGF alpha receptor by autoradiographic analysis of 125I-EGF binding to sections of normal ferret larynx and trachea revealed EGF/TGF alpha receptors throughout the epithelium, with the highest grain density in the basal layers. Quantitative analysis of autoradiographic grain density between normal, intubated, and extubated animals revealed no significant differences. The presence of TGF alpha protein and its receptor in normal and wounded larynx and trachea supports the hypothesis that these proteins are involved in regulating physiologic responses of laryngotracheal cells.