GATA-6 activates transcription of thyroid transcription factor-1

Thyroid transcription factor-1 (TTF-1) is expressed in respiratory epithelial cells, where it regulates the transcription of target genes expressed in a cell-selective manner. GATA-5 and -6, members of the zinc finger family of transcription factors, are also expressed in various cell types within in the developing lung. In the present work, GATA-6 mRNA was detected in adult mouse lung, purified mouse type II epithelial cells, and differentiated mouse pulmonary adenocarcinoma cells (MLE-15 cells), being co-expressed with TTF-1 mRNA. In order to test whether GATA factors regulated TTF-1 gene transcription, GATA-5 and -6 expression vectors were co-transfected with TTF-1 luciferase expression vector. GATA-6, but not GATA-5, markedly activated TTF-1 gene transcription in HeLa cells. EMSA and supershift analysis with GATA-6 antiserum demonstrated that GATA-6 in MLE-15 cell nuclear extracts bound to an element located 96-101 base pairs from major start of TTF-1 gene transcription. Site directed mutagenesis of the GATA element in the TTF-1 promoter region inhibited transactivation by GATA-6 in HeLa cells. GATA-6 is co-expressed with TTF-1 in the respiratory epithelium in vivo and respiratory epithelial cells in vitro. GATA-6 strongly enhanced activity of the human TTF-1 gene promoter in vitro. These findings support the concept that GATA-6 may play an important role in lung cell differentiation and gene expression, at least in part by altering the expression of TTF-1 and its potential targets.