Role of hepatocyte nuclear factor-3 alpha and hepatocyte nuclear factor-3 beta in Clara cell secretory protein gene expression in the bronchiolar epithelium.

The 5' flanking region of the Clara cell secretory protein (CCSP) gene contains two cis-acting elements which bind hepatocyte nuclear factor (HNF)-3 alpha and HNF-3 beta in vitro. To determine the role of these proteins in mediating CCSP gene expression in the bronchiolar epithelium, chimeric CCSP-reporter gene constructs containing various regions of the CCSP 5' flanking region were co-transfected into H-441 cells with HNF-3 alpha or HNF-3 beta expression plasmids. These studies indicate that each of these transcription factors positively regulates CCSP gene expression and revealed that CCSP region I (-132 to -76) is sufficient to mediate this effect. Gel-mobility-shift assays with oligonucleotides corresponding to CCSP region I, nuclear extract from bronchiolar epithelial cells and HNF-3-specific antibodies indicate that HNF-3 alpha and HNF-3 beta are the only proteins in bronchiolar epithelial cells which directly interact with this region. Consistent with these observations, HNF-3 alpha and HNF-3 beta transcripts were found to be enriched in this cell population and in situ hybridization of adult lung revealed HNF-3 gene expression in non-ciliated bronchiolar epithelial cells expressing the CCSP gene. Finally, experiments with CCSP region I and a heterologous promoter indicate that this region acts in a promoter-specific context, suggesting that additional factors interacting via the minimal CCSP promoter region are essential in determining the effects of HNF-3 on cell-specific CCSP gene expression in the bronchiolar epithelium.