GATA-6 activates transcription of surfactant protein A

Surfactant protein A (SP-A) is a member of the collectin family of innate h ost defense molecules expressed primarily in respiratory epithelial cells o f the lung. SP-A concentrations are influenced by both cell-specific and ub iquitous nuclear proteins that regulate SP-A gene transcription in a cell-s elective and temporally regulated manner. In this work, a consensus GATA-bi nding site (GBS) was identified at positions -69 to -64 of the mouse SP-A g ene. The transcriptional activity of wildtype SP-A reporter constructs in H eLa cells was increased 5-10-fold when cotransfected with a GATA-6 expressi on plasmid, Deletion of the GBS completely blocked transactivation by GATA- 6, Transfection of a construct expressing GATA-6-engrailed fusion protein i nhibited basal expression of the SP-A/chloramphenicol acetyltransferase con struct in MLE-15 cells. Nuclear extract proteins from MLE-15 cells bound to the GBS in the mouse SP-A gene, and a supershifted band was detected with a GATA-6-specific antibody. Transactivation of the wild-type SP-A construct s by GATA-6 increased transcriptional activity 7-10-fold, whereas thyroid t ranscription factor-1 (TTF-1) increased the activity of these constructs 12 -18-fold. The effects of cotransactivating with both GATA-6 and TTF-1 expre ssion constructs were additive. However, mutation of the TTF-1-binding site s alone or in combination decreased GATA-6 transactivation. Likewise, mutat ion of the GBS blocked TTF-1 activation of the SP-A promoter. In situ hybri dization demonstrated GATA-6 mRNA in the peripheral epithelial cells of fet al mouse lung, consistent with the sites of SP-A expression. GATA-6 is expr essed in respiratory epithelial cells and binds to a cis-acting element in the SP-A gene promoter, activating the transcriptional activity of the gene .