Localization of keratin mRNA in human tracheobronchial epithelium and bronchogenic carcinomas by in situ hybridization

Abstract

An in situ hybridization technique was applied to detect expression of keratin mRNAs in xenotransplanted human tracheobronchial epithelium and lung carcinomas. Tissues from eight tracheas repopulated with cells from five different noncancerous donors and 15 squamous cell carcinomas were used. Using a K6 (56 kd) human keratin cDNA (KA-1) and a K14 (50 kd) cDNA (KB-2) as probes, radiolabeled by nick-translation with 3H-dATP/TTP, the specificity and significant differences in the levels of silver grains on various epithelial lesions in formalin-fixed, paraffin-embedded tissue sections were demonstrated. In situ hybridization with either KA-1 or KB-2 probe showed similar localization of silver grains in all histologic types in consecutive tissue sections. In xenotransplanted tracheobronchial epithelia, very few grains were seen over cells of simple, pseudostratified, or stratified epithelia two to three cell layers thick. Nonkeratinizing stratified hyperplastic epithelia of more than three cell layers showed uniform localization of numerous grains throughout the lesions. In contrast, epidermoid metaplasias exhibited a dense and localized pattern of grains on the basal and parabasal cell layers with a decrease in grain density toward the surface layers. Carcinoma cells from bronchogenic squamous cell carcinomas showed a higher density and more uniform localization of grains. Well-differentiated carcinoma cells contained more keratin mRNAs than moderately to poorly differentiated carcinoma cells. This evidence obtained with the KA-1 and KB-2 probes demonstrates the different localization patterns of keratin mRNAs in different epithelial lesions. In addition, the levels of mRNA expressed show a positive correlation with the degree of squamous differentiation. It was of particular interest that an ordered program of keratin mRNA expression proportional to the level of cellular differentiation was observed in epidermoid metaplasias. Both of these probes serve as keratinization markers of human tracheobronchial epithelial lesions.