HnRNP A2/B1 proteins in nontumorous alveolar cells.

The overexpression of heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1, especially of B1, had been reported to detect preclinical lung cancer for early detection. In order to examine whether the expression of the protein is specific for lung cancer, we investigated the expression of the protein in human nonmalignant alveolar cells. Human airway cells obtained by bronchoalveolar lavage (BAL) were analyzed by immunostaining and Western blotting using monoclonal antibodies 4G8 (specifically reacts to A2) and 2B2 (specific to B1). In alveolar cells obtained by BAL, hnRNP A2/B1 proteins were localized primarily in the nucleus, excluding the nucleolus, although the expression of A2 protein was weaker than that of B1 protein. Staining pattern of these cells was similar to those observed in cancer cells. Western blotting with 4G8 and 2B2 demonstrated expression of A2 and B1 proteins in the airway cells. HnRNP A2/B1 proteins were apparently expressed in nonmalignant alveolar cells as well as cancer cells, although the expression in alveolar cells was weaker than that of cancer cells. More quantitative determination of A2/B1 is required to elucidate their significance in early lung cancer detection.