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

Berhane, Kiflu, Ramgopal K. Margana, and Vijayakumar Boggaram. Characterization of rabbit SP-B promoter region responsive to downregulation by tumor necrosis factor-a. Am J Physiol Lung Cell Mol Physiol 279: L806–L814, 2000.—Surfactant protein B (SP-B) is essential for the maintenance of biophysical properties and physiological function of pulmonary surfactant. Tumor necrosis factor-a (TNF-a), an important mediator of lung inflammation, inhibits surfactant phospholipid and surfactant protein synthesis in the lung. In the present study, we investigated the TNF-a inhibition of rabbit SP-B promoter activity in a human lung adenocarcinoma cell line (NCI-H441). Deletion experiments indicated that the TNF-a response elements are located within 2236 bp of SP-B 59-flanking DNA. The TNF-a response region contained binding sites for nuclear factor-kB (NF-kB), Sp1/Sp3, thyroid transcription factor (TTF)-1, and hepatocyte nuclear factor (HNF)-3 transcription factors. Inhibitors of NF-kB activation such as dexamethasone and N-tosyl-L-phenylalanine chloromethyl ketone and mutation of the NF-kB element did not reverse TNF-a inhibition of SP-B promoter, indicating that TNF-a inhibition of SP-B promoter activity occurs independently of NF-kB activation. TNF-a treatment decreased the binding activities of TTF-1 and HNF-3 elements without altering the nuclear levels of TTF-1 and HNF-3a proteins. Pretreatment of cells with okadaic acid reversed TNF-a inhibition of SP-B promoter activity. Taken together these data indicated that in NCI-H441 cells 1) TNF-a 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-3a are not due to decreased nuclear levels of the proteins, and 3) okadaic acid-sensitive phosphatases may be involved in mediating TNF-a inhibition of SP-B promoter activity.