Role of CBP/p300 and SRC-1 in Transcriptional Regulation of the Pulmonary Surfactant Protein-A (SP-A) Gene by Thyroid Transcription Factor-1 (TTF-1)

Ming Yi,Guo-Xia Tong,Barbara Murry,Carole R Mendelson

doi:10.1074/jbc.m109793200

Abstract

Surfactant protein-A (SP-A) gene expression is developmentally regulated in fetal lung type II cells and is enhanced by cAMP. cAMP stimulation of SP-A gene expression is mediated by protein kinase A (PKA) phosphorylation of thyroid transcription factor 1 (TTF-1), expressed selectively in developing lung epithelium. In this study, we analyzed roles of CREB-binding protein (CBP) and steroid receptor coactivator-1 (SRC-1) in TTF-1 regulation of SP-A expression. Upon differentiation of human fetal lung in culture, nuclear localization of CBP, SRC-1, and TTF-1 increased in ductular epithelium in association with type II cell differentiation and induction of SP-A expression. In transient transfections, CBP and SRC-1 acted synergistically with TTF-1 to increase SP-A promoter activity. Overexpression of PKA catalytic subunit enhanced hSP-A promoter activation by SRC-1 plus TTF-1. Adenoviral E1A overexpression reduced TTF-1 +/- SRC-1 induction of SP-A promoter activity, suggesting a role of endogenous CBP/p300. TTF-1 interacted with SRC-1 and CBP in vitro. SRC-1 immunodepletion from type II cell nuclear extracts reduced binding to the TTF-1 binding element upstream of SP-A gene. In cultured type II cells, cAMP increased TTF-1 acetylation. This suggests that cAMP-mediated TTF-1 phosphorylation facilitates interaction with CBP and SRC-1, resulting in its hyperacetylation, further enhancing TTF-1 DNA-binding and transcriptional activity.

Highlights

Pulmonary surfactant, a developmentally regulated phospholipid-rich lipoprotein synthesized exclusively in lung type II cells, reduces surface tension, thereby preventing alveolar collapse upon exhalation of air
Surfactant protein-A (SP-A) gene expression is developmentally regulated in fetal lung type II cells and is enhanced by cAMP. cAMP stimulation of SP-A gene expression is mediated by protein kinase A (PKA) phosphorylation of thyroid transcription factor 1 (TTF-1), expressed selectively in developing lung epithelium
In contrast to our findings with the bSP-A2Ϫ255:human growth hormone (hGH) reporter construct, when the (TBE)3:hGH reporter was used, we consistently found that steroid receptor coactivator-1 (SRC-1), in the absence of cotransfected CREB-binding protein (CBP), increased bSP-A2 promoter activity ϳ2-fold as compared with the effect of TTF-1 alone

Summary

Introduction

A developmentally regulated phospholipid-rich lipoprotein synthesized exclusively in lung type II cells, reduces surface tension, thereby preventing alveolar collapse upon exhalation of air. In type II cell transfection studies, we observed that basal and cAMP-induced hSP-A2 promoter activity is critically dependent upon four regulatory elements within the proximal SP-A 5Ј-flanking region. These elements, which are highly conserved in the 5Јflanking regions of the SP-A genes of various species [16], include a putative nuclear receptor binding site [17, 18], a GT-box that binds Sp1 and related Kruppel factors [19], an E-box that binds USFs 1 [20] and 2,2 and a binding site (TBE) for thyroid transcription factor-1 (TTF-1) [21, 22]. We observed that cAMP acting through cAMP-dependent protein kinase (PKA) increased TTF-1 phosphorylation, TBE1 binding, and transcriptional activity in lung type II cells [21]

Methods

Results

Conclusion