Transcription of the Lung-specific Surfactant Protein C Gene Is Mediated by Thyroid Transcription Factor 1 (*)

Surfactant protein C (SP-C) is expressed in alveolar Type II epithelial cells of the lung. In order to determine the mechanism(s) that regulate gene transcription, we have analyzed the activation of the murine SP-C promoter in mouse lung epithelial cells (MLE cells) and in HeLa cells after co-transfection with a vector expressing rat thyroid transcription factor-1 (TTF-1). TTF-1 transactivated SP-C-chloramphenicol acetyltransferase constructs containing −13 kilobase pairs to −320 base pairs (bp) of the 5′ flanking region of the SP-C gene. Essential cis-acting elements were functionally localized to between −320 and −180 bp from the start of transcription by transfection analysis. Five DNase-protected regions, indicating multiple protein-DNA interactions within the −320 bp TTF-1-responsive region of the SP-C gene, were identified by DNase footprint analysis. A 40-bp segment of SP-C DNA from −197 to −158 linked to a heterologous promoter-chloramphenicol acetyltransferase construct activated expression after co-transfection with CMV-TTF-1 in HeLa and MLE cells. The −197 to −158 segment contained two consensus TTF-1 sites, which were specifically identified as TTF-1 binding sites by gel retardation and antibody supershift with MLE cell nuclear extracts and purified TTF-1 homeodomain protein. Site-specific mutagenesis of either of the TTF-1 binding sites completely blocked activation by TTF-1, indicating both sites are required for TTF stimulation of SP-C transcription.

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