LUNG CELL-SPECIFIC EXPRESSION OF THE MURINE SURFACTANT PROTEIN-A (SP-A) GENE IS MEDIATED BY INTERACTIONS BETWEEN THE SP-A PROMOTER AND THYROID TRANSCRIPTION FACTOR-I

Cis-acting elements determining lung epithelial cell-selective transcr iption of the murine surfactant protein A (SP-A) gene were identified between nucleotide positions -255 and -57. This region of the murine S P-A gene contained nucleotide sequences consistent with thyroid transc ription factor-1 (TTF-1) binding motifs. An SP-A-CAT plasmid containin g the TTF-1 binding sites was transcriptionally active in mouse lung e pithelial (MLE-15) cells but not in HeLa, 3T3, or H441 cells. However, transcription of the SP-A-CAT construct was activated after cotransfe ction of HeLa cells with a vector expressing recombinant TTF-1, pCMV-T TF-1. Recombinant TTF-1 homeodomain protein bound to four distinct bin ding sites located between nucleotides -231 to -168. Proteins in nucle ar extracts of MLE-15 cells bound TTF-1 binding sites and were supersh ifted by TTF-1 antibody. Mutations of three of the TTF-1 binding sites in this region reduced expression of the SP-A-CAT construct in transf ected MLE-IB cells and reduced transactivation in HeLa cells. TTF-1 in teracts with complex protein/DNA binding sites located in the 5'-flank ing region of the murine SP-A gene enhancing lung epithelial cell-spec ific expression in vitro.