Human SP-C gene sequences that confer lung epithelium-specific expression in transgenic mice

We used transgenic mice to identify cis-active regions of the human pulmona ry surfactant protein C (SP-C) gene that impart tissue- and cell-specific e xpression in vivo in the lung. Approximately 3.7 kb of genomic SP-C DNA ups tream of the transcription start site was sufficient to direct chlorampheni col acetyltransferase (CAT) reporter gene expression specifically in bronch iolar and alveolar epithelial cells of the lung. To further define cis-acti ve regulatory elements that mediate cell-specific expression, we tested del etions of the parental 3.7-kb human SP-C sequence in transgenic mice. Tissu e CAT assays of mice generated with truncations or overlapping internal del etions of the 3.7-kb construct functionally map alveolar cell-specific regu latory elements to within -215 bp of the SP-C promoter. Analysis of SP-C pr omoter deletions demonstrate that sequences between -3.7 kb and -1.9 kb con tain enhancer sequences that stimulate SP-C transgene expression. In situ h ybridization studies demonstrate that deletion of the -1,910- to -215-bp re gion abolishes the ectopic bronchiolar expression seen with the original 3. 7-kb SP-C promoter construct. Comparison of sequences from -215 to +1 bp id entified consensus binding sites for the homeodomain transcription factor t hyroid transcription factor-1 (TTF-1). Cotransfection assays of the human 3 .7-kb SP-C: or -1,910- to -215-bp SP-C deletion construct with a TTF-1 expr ession plasmid demonstrates that TTF-1 transactivates the human SP-C gene. These results suggest that the TTF-1 cis-active sites are important in dire cting cell-specific expression of the SP-C gene in vivo.