MODULATION OF SECRETORY LEUKOPROTEASE INHIBITOR GENE-EXPRESSION IN HUMAN BRONCHIAL EPITHELIAL-CELLS BY PHORBOL EATER

Secretory leukoprotease inhibitor (SLPI), a 12-kD nonglycosylated seri ne antiprotease, helps to protect the epithelial surface of the airway s from the destructive capacity of neutrophil elastase. Based on the r ecognition that SLPI levels can increase in the presence of airway inf lammation, we hypothesized that inflammatory stimuli should modulate t he expression of the SLPI gene in airway epithelial cells. To evaluate this, the modulation of SLPI gene expression with various inflammator y stimuli was evaluated in the HS-24 human bronchial epithelial cell l ine. After preliminary studies showed that several inflammatory mediat ors enhanced SLPI messenger RNA (mRNA) levels, PMA was used as a model inflammatory stimulus. PMA significantly increased the level of 0.7-k b SLPI mRNA transcripts in HS-24 cells in a dose- and time-dependent f ashion and increased the amount of SLPI protein in the culture superna tant. Nuclear run-on analyses showed that the SLPI gene transcription rate increased approximately twofold after PMA stimulation. Transfecti on studies using fusion genes composed of fragments of up to 1.2 kb of the 5' flanking sequence of the SLPI gene and a luciferase reporter g ene demonstrated potent promoter activity in the 131-bp segment (-115 to +16 relative to the transcription start site), and all longer segme nts up to 1.2 kb, whereas smaller segments showed low promoter activit y. An 18-bp element (-98 to -115), in a region with homology to PMA-re sponsive regions in the Moloney murine leukemia virus enhancer and the IL-8 gene, was shown to be of importance in the level of transcriptio n of the SLPI gene. However, this element was not responsible for the upregulation of SLPI gene expression by PMA. Evaluation of HS-24 cells in the presence of actinomycin D demonstrated that SLPI mRNA transcri pts were very stable and became more so in the presence of PMA. Thus, SLPI gene expression in airway epithelial cells can be upregulated by an inflammatory stimulus, and this modulation is regulated at both the transcriptional and posttranscriptional levels. These mechanisms of S LPI upregulation likely play a role in defending the epithelial surfac e in the local milieu of inflammatory lung disease.