The role of SCCA1 in asthma related physiological events in the airway epithelium and the effect of promoter variants on asthma and gene function

Abstract

Even though the systemic level of SCCA1, a serine protease inhibitor, was shown to be elevated in asthma, its physiological role is unknown. We sought to determine the effect of SCCA1 on apoptosis, cytokine expression and mucus production by A549 cells and define the effect of promoter variants on gene expression and association with asthma. SCCA levels were measured by ELISA. Promoter variants were determined by direct sequencing. 442 asthmatic children and 191 controls were genotyped by RFLP. The functional effect of the polymorphisms was assessed in transient transfection experiments using reporter constructs. A transcription factor ELISA was used for differential binding of GATA proteins to the variant region. The effects of SCCA1 on cytokine synthesis, mucus production and apoptosis were determined in A549 cells transfected with SCCA1 pcDNA vector. MUC5AC expression in A549 cells was determined with RT-PCR. SCCA1 protein level was significantly higher in asthmatic children compared to healthy controls. Four polymorphisms SCCA1 promoter that were in linkage disequilibrium were associated with skin test positivity in asthmatic children and showed higher promoter activity and higher binding of GATA-2 and GATA-3 after IL-4+IL-13 stimulation. IL-6, IL-8 levels were significantly higher in cells transfected with SCCA1 whereas RANTES increased only after IL-4 stimulation. Transfection of A549 cells with SCCA1 resulted in decreased MUC5AC expression and conferred protection against apoptosis. Our results showed that SCCA1 has diverse effects on many of the cellular events that characterize asthma and its role extends beyond protease inhibition.