Surfactant protein B (SP-B) is a 79-amino acid peptide produced in pulmonary non-ciliated bronchiolar epithelial cells (Clara cells) and alveolar type II epithelial cells. The SP-B peptide is stored in lamellar bodies and secreted with phospholipids into the airway lumen to facilitate the stability and rapid spreading of surfactant phospholipids during respiratory cycles. Null mutations in the SP-B gene cause lethal respiratory distress in newborn infants and in SP-B deficient mice produced by gene targeting. SP-B is essential for postnatal alveolar maturation and respiratory adaptation in newborns. The long-term goals of this work are to identify cis-acting DNA elements and trans-acting protein factors that control SP-B gene temporal/spatial expression in developing and mature lungs. During the last several years of study, it has been identified that retinoic acid receptor heterodimer (RAR/RXR), thyroid transcription factor 1 (TTF-1), nuclear receptor co-activators (CBP/p300 and p160 co-activators, including SRC-1, TIF2 and ACTR) and signal transducers and activators of transcription 3 (STAT3) cooperatively stimulate hSP-B transcription through an enhancer region (-500 to -331 bp). To extend the study, we will 1): characterize functional domains and amino acid residues that are involved in the interaction between RARalpha and STAT3; 2) characterize RARE and TTF-1 cis-acting sites in the hSP-B enhancer region (-500 to -331 bp) that determine hSP-B gene temporal/spatial expression in bronchiolar epithelial cells using LacZ transgenic mice; 3) characterize cis-acting elements that determine hSP-B gene temporal/spatial expression in alveolar type II epithelial cells using LacZ transgenic mice. These studies along with previous findings will lead to a better understanding of molecular basis for SP-B homeostasis in lung biology. Knowing this will help to design strategies to combat congenital and acquired respiratory diseases such as emphysema, respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD), the leading causes of mortality and morbidity in preterm infants.
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