Permissive Effects of Oxygen on Cyclic AMP and Interleukin-1 Stimulation of Surfactant Protein A Gene Expression Are Mediated by Epigenetic Mechanisms

Abstract

Surfactant protein A (SP-ATo define mechanisms involved in lung cell-specific, developmental, and hormonal regulation of pulmonary surfactant synthesis, we have focused on surfactant protein A (SP-A), the major surfactant protein, which is lung specific and synthesized in type II cells. SP-A, a member of the collectin subfamily of C-type lectins, plays an important role in immune defense within the lung alveolus by binding to a variety of bacterial, viral, and fungal pathogens to facilitate their uptake by alveolar macrophages and to enhance macrophage migration and cytokine production (see reference 53 for a review). SP-A is an excellent marker of type II cell differentiation and surfactant synthesis in the fetal lung, since it is developmentally regulated with surfactant phospholipid synthesis (see reference 36 for a review). Recently, we obtained compelling evidence that SP-A secreted by the fetal lung into amniotic fluid acts as a hormone that stimulates the migration of amniotic fluid macrophages to the uterus, where they initiate an inflammatory response leading to parturition (13).In studies using midgestation human fetal lung explants cultured in a 20% O 2 environment, we found that type II cell differentiation and SP-A gene expression were enhanced by hormones and factors that increase cyclic AMP (cAMP) (43). Interestingly, cAMP stimulation of type II cell differentiation and SP-A expression are dependent upon a critical atmospheric O 2 tension (1). When fetal lung explants were cultured in a 1 to 2% O 2 -containing environment, type II cells failed to differentiate, and no stimulatory effects of cAMP on SP-A expression were apparent. These findings led us to postulate that increased vascularization of the fetal lung during the third trimester of gestation and enhanced O 2 availability to type II cell precursors may facilitate cAMP induction of type II cell differentiation and surfactant protein gene expression (1).To define genomic regions and response elements involved in lung cell-specific, developmental, and hormonal regulation of SP-A expression, we have utilized transgenic mice and transfected type II cells. In transgenic mice, we found that as little as ϳ400 bp of DNA flanking the 5Ј end of the rabbit SP-A gene directed appropriate lung cell-specific and developmental regulation of expression (3). This region contains four response elements that are individually required for basal and cAMP stimulation of SP-A promoter activity in transfected type II cells (2,17,32,39,56,57). The finding that mutagenesis of any one of these elements markedly reduced basal and cAMP induction of SP-A promoter activity suggests a cooperative interaction of transcription factors binding to these sites. One of these response elements, termed thyroid transcription factor 1 (TTF-1)-binding element (TBE), at Ϫ170 bp binds the homeodomain factor, thyroid transcription factor 1 (TTF-1/Nkx2

Hypoxic Repression of Endothelial Nitric-oxide Synthase Transcription Is Coupled with Eviction of Promoter Histones

“…Hypoxia inhibits this hyperacetylation through the concerted up-regulation of HDACs and the down-regulation of the HAT, CREB-binding protein. Hypoxia also increased H3K9Me at the SPA promoter, preventing its induction (22). Increases in promoter-associated and global levels of H3K9Me2 and H3K9Me3 in hypoxic cells have also been reported by others (23).…”

“…Additionally, the cAMP-mediated transcriptional induction of surfactant protein A is also compromised under hypoxic conditions. Reduced histone acetylation and increased lysine 9 methylation of histone H3 (H3K9Me) at the promoter of this gene have been suggested to be important in this hypoxic repression (22). Similar hypoxia-dependent global and gene-specific increases in H3K9Me (23) and decreases in global levels of histone H4 acetylation (24) have also been described by others.…”

“…Other studies have suggested a potential role for HDACs in repressing genes under hypoxic conditions (20,21), but these studies did not measure the effects of hypoxia on promoter acetylation or on the transcription of the regulated genes. A role for histone acetylation has also been implicated in the cAMP induction of surfactant protein A (SPA) in normoxic cells (22). Hypoxia inhibits this hyperacetylation through the concerted up-regulation of HDACs and the down-regulation of the HAT, CREB-binding protein.…”

Hypoxia-induced and stress-specific changes in chromatin structure and function

“…Analysis by immunoblotting revealed a global reduction of acetylated H3-K9 in response to hypoxia, as well as decreased CBP protein levels and increased expression of HDACs 1,2,4 and 11 [60]. If histone deacetylation contributes to regulation of transcription under hypoxia, one would expect to find hypoacetylated histones at the promoters of hypoxia-repressed genes.…”

Involvement of Nuclear Factor κB (NF-κB) Signaling Pathway in Regulation of Cardiac G Protein-coupled Receptor Kinase 5 (GRK5) Expression

“…ChIP-NRVMs were cultured for 24 h in complete medium and then changed to 5% FBS containing medium for another 24 h. Cells in 5% medium were then maintained in serum-free medium in the presence or absence of PMA for 24 h. ChIP was performed as described in detail previously (20). The soluble chromatin (500 l) was incubated with antibodies for p50 and p65 (Santa Cruz) at 4°C overnight.…”