Characterization of rabbit SP-B promoter region responsive to downregulation by tumor necrosis factor-α

Abstract

Surfactant protein B (SP-B) is essential for the maintenance of biophysical properties and physiological function of pulmonary surfactant. Tumor necrosis factor-α (TNF-α), an important mediator of lung inflammation, inhibits surfactant phospholipid and surfactant protein synthesis in the lung. In the present study, we investigated the TNF-α inhibition of rabbit SP-B promoter activity in a human lung adenocarcinoma cell line (NCI-H441). Deletion experiments indicated that the TNF-α response elements are located within −236 bp of SP-B 5′-flanking DNA. The TNF-α response region contained binding sites for nuclear factor-κB (NF-κB), Sp1/Sp3, thyroid transcription factor (TTF)-1, and hepatocyte nuclear factor (HNF)-3 transcription factors. Inhibitors of NF-κB activation such as dexamethasone and N-tosyl-l-phenylalanine chloromethyl ketone and mutation of the NF-κB element did not reverse TNF-α inhibition of SP-B promoter, indicating that TNF-α inhibition of SP-B promoter activity occurs independently of NF-κB activation. TNF-α treatment decreased the binding activities of TTF-1 and HNF-3 elements without altering the nuclear levels of TTF-1 and HNF-3α proteins. Pretreatment of cells with okadaic acid reversed TNF-α inhibition of SP-B promoter activity. Taken together these data indicated that in NCI-H441 cells 1) TNF-α inhibition of SP-B promoter activity may be caused by decreased binding activities of TTF-1 and HNF-3 elements, 2) the decreased binding activities of TTF-1 and HNF-3α are not due to decreased nuclear levels of the proteins, and 3) okadaic acid-sensitive phosphatases may be involved in mediating TNF-α inhibition of SP-B promoter activity.