Proximal Promoter of the Surfactant Protein D Gene

Abstract

Pulmonary surfactant protein D (SP-D)1 is a member of the collectin (collagenous lectin) subfamily of mammalian C-type lectins, which includes pulmonary surfactant protein A (SP-A), serum mannose-binding lectin, and at least two bovine serum lectins related to SP-D, conglutinin and CL-43 (1, 2). The genes for both lung collectins and mannose-binding lectin are encoded in close proximity on human chromosome 10q. The pulmonary collectins, like the homologous serum proteins, are believed to contribute to innate (nonclonal) immunity and the host response to microorganisms (2). In addition, both SP-A and SP-D may contribute to the regulation of surfactant lipid homeostasis under certain circumstances in vivo (3-5).SP-A and SP-D are secreted into the distal airways and pulmonary alveoli by Clara cells and type II pneumocytes. The expression of SP-A and SP-D by these cells is increased following many forms of pulmonary injury (2), and the rapid increase in SP-A and SP-D accumulation following intratracheal instillation of bacterial endotoxin suggests that they contribute to a pulmonary acute phase response (6). However, the regulation of these responses is not understood. We have previously shown that DNA sequences within 285 bp of the start site of transcription of the human SP-D promoter are able to confer glucocorticoid-responsive gene expression in H441 human lung adenocarcinoma cells but not liver HepG2 cells (7), suggesting that the proximal sequence contains information sufficient to direct lung-restricted expression. Sequence analysis of the proximal promoter suggested potential regulatory roles for a variety of ubiquitous and lung-restricted transcription factors.In considering the potential contributions of these regulatory motifs to SP-D gene regulation, we initially focused our attention on the AP-1 consensus (5Ј-TGAGTCA-3Ј) at Ϫ109 bp relative to the start site of transcription (7). Preliminary footprinting assays showed preferential protection of this motif and its contiguous flanking sequences by nuclear extracts from H441 cells. In addition, an identical AP-1 motif is spatially conserved in the rat and mouse promoters (7,8) and in the promoter of the homologous bovine conglutinin gene (9, 10) (Fig. 1). Because alterations in the composition of the AP-1 complex regulate a wide variety of transcriptional events associated with cellular differentiation and the response to environmental stimuli including cell injury, inflammation, and the systemic acute phase response, we hypothesized that the AP-1 motif plays important roles in the regulation of SP-D expression.The flanking regions of the conserved AP-1 motif also contain sequences resembling binding sites for factors known to regulate respiratory epithelial cell differentiation and the expression of various secreted lung proteins including Clara cellspecific protein (CCSP) and SP-A, -B, and -C (11). These include potential binding sites for the homeodomain-containing protein, thyroid transcription factor 1 (TTF-1), and the forkhead/winged helix transcript...

Nuclear Factor of Activated T Cells Regulates Transcription of the Surfactant Protein D Gene (Sftpd) via Direct Interaction with Thyroid Transcription Factor-1 in Lung Epithelial Cells

“…Mutation of DNA binding sites for forkhead transcription factors FoxA1 and FoxA2 decreased transcription of SFTPD. In contrast, TTF-1 did not activate its expression in H441 cells in vitro (24).…”

“…Indeed, an NFAT⅐AP-1 composite site in the Sftpd proximal promoter (Ϫ139/Ϫ125) produced DNase I footprints with nuclear proteins from lung epithelial cells and was responsive to ionomycin and PMA, a hallmark of NFAT⅐AP-1 sites that bind activated NFAT and AP-1 family of transcription factors in target genes (41). Human SFTPD is regulated by AP-1 family members (24). Because AP-1 activity isalsomodulatedbydiversesignalingpathways(63),NFAT⅐AP-1-dependent transcription may integrate responses to lung injury.…”

“…AP-1 family members regulate SFTPD promoter activity. JunB and JunD enhanced, whereas c-Jun and c-Fos inhibited, transcription (24). Mutation of DNA binding sites for forkhead transcription factors FoxA1 and FoxA2 decreased transcription of SFTPD.…”

“…Glucocorticoid treatment in utero precociously increased SP-D mRNA and accelerated lung maturation. Whereas the mechanism of SP-D induction is not known, it has been suggested that dexamethasone treatment increases promoter occupancy of CCAAT enhancer-binding protein-␤ (C/EBP-␤) (24,28). Retinoblastoma protein stimulated SFTPD activation by directly forming a complex with C/EBPs bound to the NF-IL-6 (C/ EBP-␤) consensus site in the SFTPD promoter.…”

“…Recently, a role for SP-1-like transcription factors has been implicated in regulation of the human SP-D gene (SFTPD) promoter, but the identity of these factors is unknown (24). AP-1 family members regulate SFTPD promoter activity.…”