Differential effects of glucocorticoid on expression of surfactant proteins in a human lung adenocarcinoma cell line

Abstract

Synthesis of pulmonary surfactant-associated glycoproteins of M r 28 000–36 000 (SP-A) and M r 42 000–46 000 (proSP-B) has been identified in a continuous cell line derived from a human lung adenocarcinoma. SP-A was detected by immunoblot analysis, ELISA assay and by [ 35S]methionine labelling of the cells. SP-A was secreted into the media as an endoglycosidase F sensitive glycoprotein which co-migrated with the isoforms of SP-A identified in human lavage fluid by 2D-IEF-SDS-PAGE. Hybridization of cellular RNA with SP-A-specific cDNA identified an abundant 2.2 kb mRNA species, identical to that observed in human lung. SP-A RNA and protein content were markely inhibited by dexamethasone in a dose-dependent fashion. Under identical culture conditions, synthesis of a distinct surfactant protein, SP-B, was markedly stimulated by the glucocorticoid. The SP-B precursor was secreted into the media as heterogenous M r 42 000–46 00 protein,p I 4.6–5.1, and was sensitive to endoglycosidase F. Synthesis of proSP-B was enhanced by the glucocorticoid in a dose-dependent fashion and was associated with increased SP-B mRNA of 2.0 kb detected by Northern blot analysis. The cell line secreted proSP-B as M r 42 000–46 000 glycosylated protein and did not process the precursor to the M r 7000–8000 and secretes peptide. In summary, a human adenocarcinoma cell line has been identified which synthesized and secretes two surfactant-associated proteins, SP-A and proSP-B. Glucocorticoid enhanced SP-B but inhibited SP-A expression in this cell line. The identification of a continuous cell line secreting surfactant proteins may be useful in the study of synthesis and secretion of these important proteins and for production of the proteins for clinical uses.