Identification of functional TTF-1 and Sp1/Sp3 sites in the upstream promoter region of rabbit SP-B gene.

Surfactant protein B (SP-B) is essential for the maintenance of biophysical properties and physiological function of pulmonary surfactant. SP-B mRNA is expressed in a cell type-restricted manner in alveolar type II and bronchiolar (Clara) epithelial cells of the lung and is developmentally induced. In NCI-H441 cells, a lung cell line with characteristics of Clara cells, a minimal promoter region comprising -236 to +39 nucleotides supports high-level expression of chloramphenicol acetyltransferase reporter activity. In the present investigation, we characterized the upstream promoter region, -236 to -140 nucleotides, that is essential for promoter activity. Deletion mapping identified two segments, -236 to -170 and -170 to -140 nucleotides, that are important for promoter activity. Mutational analysis and gel mobility shift experiments identified thyroid transcription factor-1, Sp1, and Sp3 as important trans-acting factors that bind to sequences in the upstream promoter region. Our data suggest that SP-B promoter activity is dependent on interactions between factors bound to upstream and downstream regions of the promoter.