BR22, a novel protein, interacts with thyroid transcription factor-1 and activates the human surfactant protein B promoter

Surfactant protein (SP)-B expression is restricted to type II pneumocytes a nd Clara cells in the lung. Previously, a promoter region of human SP-B gen e from -64 to -118 has been identified as critical for the tissue-specific expression of this gene. Two cis-elements for thyroid transcription factor (TTF)-1 and hepatocyte nuclear factor (HNF)-3 alpha binding were found with in this area. Using an oligonucleotide fragment, we incorporated this regio n sequence into the promoter of a HIS3 reporter gene in yeast. With this mo dified yeast a human lung complementary DNA (cDNA) library was screened for DNA-binding proteins, other than TTF-1 and HNF-3 alpha, that interacted wi th this promoter segment. A cDNA clone encoding a novel polypeptide, BR22, was identified that activated the reporter gene expression in yeast. This g ene is expressed in many tissues and encodes a protein with bipartite nucle ar localization signals. Studies using in vivo yeast two-hybrid analysis, i n vitro protein-protein interactions, and coimmunoprecipitation analyses de monstrated that BR22 formed a protein complex with TTF-1. In vivo cotransfe ction studies further indicated that BR22 could act with TTF-1 to synergist ically activate the SP-B promoter in mammalian cells. Our data suggest that BR22 is a TTF-1-associated protein. Through a protein-protein interaction with TTF-1, BR22 can form a complex and activate the human SP-B promoter in vivo.