Mechanisms in the Regulation of SP-A Gene Expression

Ut Southwestern Medical Center, Dallas TX

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Abstract

DESCRIPTION (provided by applicant): Surfactant protein A (SP-A) is developmentally regulated in fetal lung type II cells in concert with surfactant phospholipid synthesis and, thus, serves as an excellent marker of type II cell differentiation and surfactant production. SP-A, a C-type lectin, plays an important role in immune defense within the lung alveolus and may serve as a fetal signal in the initiation of labor. SP-A expression in cultured human fetal type II cells is markedly stimulated by cAMP and by interleukin-1 (IL-1), and is inhibited by glucocorticoids. cAMP stimulation of SP-A expression is O2-dependent and mediated by binding of estrogen-related receptor ( (ERR(), a complex of thyroid transcription factor-1 (TTF-1/Nkx2.1) and nuclear factor (B (NF-(B), upstream stimulatory factors (USFs) 1 and 2, and Sp1 to critical response elements upstream of the SP-A gene. The stimulatory effects of cAMP and IL-1, permissive effects of O2 and inhibitory effects of glucocorticoids on SP-A expression are associated with changes in phosphorylation, DNA-binding and transcriptional activity of TTF-1 and NF-(B. Increased TTF-1/NF-(B binding alters recruitment to the SP-A promoter of coactivators and corepressors eliciting modifications in histone phosphorylation, acetylation and methylation that likely cause profound changes in chromatin structure. In the proposed research, we will utilize fetal lung tissues from humans and mice to further define the underlying biochemical and molecular mechanisms for epigenetic and genetic changes associated with developmental, hormonal and O2 regulation of SP-A gene expression in fetal lung. Using chromatin immunoprecipitation, we will analyze temporal changes in in vivo recruitment of key transcription factors and coregulators to the SP-A promoter in lung tissues and cells of fetal and neonatal mice and in human fetal lung explants and epithelial cells during type II cell differentiation in culture. This will be correlated with local changes in histone modification, DNA methylation, and DNaseI hypersensitive sites, to assess changes in chromatin structure. The histone- and DNA-modifying enzymes that bind to the SP-A promoter in type II cells and mediate developmental-, hormonal- and O2-regulated changes in chromatin structure also will be defined; their functional importance will be assessed using RNAi-mediated knockdown. The potential roles of hypoxia-induced transcription factors as mediators of the effects of O2 tension on SP-A expression also will be considered.