Analysis of novel disease-related genes in bronchial asthma.

Bronchial asthma is a complex disease characterized by airway inflammation involving interleukin (IL)-4 and IL-13. We have applied microarray analyses to human bronchial epithelial cultures to probe for genes regulated by these cytokines and have identified a subset of disease-relevant genes by comparison with cDNA libraries derived from normal and asthmatic bronchial biopsies. Squamous cell carcinoma antigen-1 (SCCA1) and SCCA2, the cysteine and serine protease inhibitors, respectively, showed the highest expression by IL-4 and IL-13, and particularly, SCCA1 was significantly increased in the asthmatic cDNA library. STAT6 was shown to be involved in expression of SCCA1 and SCCA2 in vitro. Furthermore, serum levels of SCCA were also elevated in asthmatic patients. Taken together, it was supposed that SCCA may play some role in the pathogenesis of bronchia asthma, and measuring its serum level may be relevant for diagnosing or monitoring the status of bronchial asthma. In a complex disorder such as asthma, this combination of in vitro and in vivo genomic approaches is a powerful discriminatory method enabling identification of novel disease-related genes and their mechanisms of regulation.

Identification of an alternative splicing variant of cathepsin C/dipeptidyl-peptidase I.

Cathepsin C/dipeptidyl-peptidase I is a papain-like lysosomal cysteine proteinase implicated in the processing of various proenzymes to their active forms. In this study, we identified an alternative splicing variant of cathepsin C in both human and mouse species for the first time. The variant messenger RNA (mRNA) encodes 137 amino acids corresponding to the first and second exons, followed by additional 31 amino acids. The two newly recognized exons are located in the former intron 2. The variant mRNA is distributed ubiquitously, but predominantly in kidney, placenta, and lymph nodes. Furthermore, both interleukin 4 (IL-4) and IL-13, but not a range of cytokines induce expression of the variant in bronchial epithelial cells. These results indicate that the variant may play a role in regulating the biological activities of cathepsin C, involved in the pathogenesis of bronchial asthma.

Upregulation of IL-13 concentration in vivo by the IL13 variant associated with bronchial asthma.

BACKGROUND: A substantial body of evidence exists to support the pivotal role of IL-13 in the pathogenesis of bronchial asthma. We recently found that a variant of the IL13 gene (Arg110Gln) is genetically associated with bronchial asthma, which is concordant with animal experiments using IL-13 in the development of asthma. OBJECTIVE: To address whether the Gln110 variant of IL13 influences IL-13 function, contributing to the pathogenesis of bronchial asthma, we studied the functional properties of the variant. METHODS: We generated 2 types of recombinant IL-13 proteins, the amino acids of which at 110 were arginine or glutamine, and analyzed the binding affinities with the IL-13 receptors, as well as the stability of the proteins. We further compared the relationship between the genotype and serum levels of IL-13. RESULTS: The variant showed a lower affinity with the IL-13 receptor alpha2 chain, a decoy receptor, causing less clearance. The variant also demonstrated an enhanced stability in both human and mouse plasma. We further identified that asthmatic patients homozygous for the Gln110 variant have higher serum levels of IL-13 than those without the variant. CONCLUSION: These results suggested that the variant might act as a functional genetic factor of bronchial asthma with a unique mechanism to upregulate local and systemic IL-13 concentration in vivo.