Article

Ceramide decreases surfactant protein B gene expression via downregulation of TTF-1 DNA binding activity

University of Texas Health Science Center at Tyler, Tyler, Texas, United States
AJP Lung Cellular and Molecular Physiology (Impact Factor: 4.08). 03/2006; 290(2):L351-8. DOI: 10.1152/ajplung.00275.2005
Source: PubMed

ABSTRACT

Ceramide, a sphingolipid, is an important signaling molecule in the inflammatory response. Mediators of acute lung injury such as TNF-alpha, platelet-activating factor, and Fas/Apo ligand stimulate sphingomyelin hydrolysis to increase intracellular ceramide levels. Surfactant protein B (SP-B), a hydrophobic protein of pulmonary surfactant, is essential for surfactant function and lung stability. In this study we investigated the effects of ceramide on SP-B gene expression in H441 lung epithelial cells. Ceramide decreased SP-B mRNA levels in control and dexamethasone-treated cells after 24-h incubation and inhibition of SP-B mRNA was associated with inhibition of immunoreactive SP-B. In transient transfections assays, ceramide inhibited SP-B promoter activity, indicating that the inhibitory effects are exerted at the transcriptional level. Deletion mapping experiments showed that the ceramide-responsive region is located within the -233/-80-bp region of human SP-B promoter. Electrophoretic mobility shift and reporter assays showed that ceramide reduced the DNA binding activity and transactivation capability of thyroid transcription factor 1 (TTF-1/Nkx2.1), a key factor for SP-B promoter activity. Collectively these data showed that ceramide inhibits SP-B gene expression by reducing the DNA biding activity of TTF-1/Nkx2.1 transcription factor. Protein kinase C inhibitor bisindolylmaleimide and the protein tyrosine kinase inhibitor genistein partially reversed ceramide inhibition, indicating that protein kinases play important roles in the ceramide inhibition of SP-B gene expression. Chemical inhibitors of de novo ceramide synthesis and sphingomyelin hydrolysis had no effect on TNF-alpha inhibition of SP-B promoter activity and mRNA levels, suggesting that ceramide does not play a role in the inhibition.

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Available from: Vijayakumar Boggaram
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    • "Ceramide binding was shown to reduce the transactivation capability of thyroid transcription factor 1 (TTF-1/Nkx2.1), a key factor for SP-B promoter activity [66]. An overall view of sphingolipid interaction with other lipids and of their inflammatory and anti-inflammatory activities is provided in Figures 1(a) and 1(b). "
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    • "Ceramide has been shown to trigger apoptosis in an experimental mouse model of emphysema [22], and increased levels of apoptosis have been found in the lungs of patients with severe cigarette-induced emphysema [23]. Increased ceramide levels have also been shown to influence surfactant production [24] and activity [25]. Since ceramide levels are increased in the lungs of patients with smoke-induced emphysema [22] ceramide upregulation might be an important pathogenetic element in emphysema development. "
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    • "These results suggest that there may be a decrease in phospholipase A2 activity that would degrade both cell membranes and surfactant to increase levels of these lipid species [35]. High levels of these lipids are known to increase the sensitivity to protein inhibition that decreases surfactant bioactivity and is observed in respiratory distress syndromes and lung injury [34], [35], [36]. "
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