Heterogeneous nuclear ribonucleoprotein B1 as early cancer biomarker for occult cancer of human lungs and bronchial dysplasia

Heterogeneous nuclear ribonucleoprotein (hnRNP) B1 is a RNA-binding protein of M-r 37,000. We previously reported that hnRNP B1 was specifically overe xpressed in the nuclei of human lung cancer cells, particularly in squamous cell carcinoma (E, Sueoka et al., Cancer Res., 59: 1404-1407, 1999), We ex tended this study to determine whether hnRNP B1 was overexpressed in roentg enographically occult cancers of the lungs and premalignant lesions of squa mous cell carcinomas, such as bronchial dysplasia. The additional object of our study was to examine the usefulness of hnRNP B1 as a potential diagnos tic marker for squamous cell carcinoma of various organs, such as the oral cavity and esophagus in humans. Surgically resected specimens of bronchial dysplasia, lung cancers, and various human squamous cell carcinomas, collec ted at two hospitals in Japan, were subjected to immunohistochemical staini ng with anti-hnRNP B1 antibody. Overexpression of hnRNP B1 protein was obse rved in 100% of stage I lung cancer tissues, but it was not found in normal bronchial epithelium, Squamous cell carcinoma of the lungs showed stronger staining than other histological types, and elevation of hnRNP B1 was foun d in both roentgenographically occult lung cancers and bronchial dysplasia. Furthermore, cytological examination with anti-hnRNP B1 antibody detected cancer cells in sputum, suggesting the potential of hnRNP B1 protein as a n ew biomarker for the very early stage of lung cancer in humans. Because str ong staining of hnRNP B1 was also observed in various squamous cell carcino mas of oral and esophageal tissues as shown in our recent reports, overexpr ession of hnRNP B1 seems to be a common event in the carcinogenic processes of squamous cell carcinoma. These results suggest that hnRNP Bt protein co uld be a useful diagnostic biomarker For both the very early stages of lung cancer and various squamous cell carcinomas in humans.