The proximal STAT6 and NF-kappaB sites are responsible for IL-13- and TNF-alpha-induced RhoA transcriptions in human bronchial smooth muscle cells.

RhoA protein is involved in the Ca(2+) sensitization of bronchial smooth muscle (BSM) contraction, and an upregulation of RhoA in BSMs has been suggested in allergic bronchial asthma. However, the mechanism of upregulation of RhoA remains poorly understood. In the present study, the transcriptional regulation of human RhoA gene was investigated in cultured human BSM cells stimulated with IL-13 and TNF-alpha, both of which have an ability to upregulate RhoA protein. Luciferase-based assay showed that the RhoA promoter activity was augmented by both IL-13 and TNF-alpha. The deletion studies revealed a significant level of promoter activity between the 112 bp upstream and the transcription start site, which contains the STAT6 (78-70 bp upstream) and NF-kappaB (84-74 bp upstream) binding regions. The promoter activity was also decreased significantly by the mutations of these regions. Thus, the current study for the first time characterized the transcriptional regulation of the human RhoA gene. The findings also suggest that STAT6 and NF-kappaB are important for the upregulation of RhoA in human BSM induced by IL-13 and TNF-alpha, both of which are major cytokines in the pathogenesis of allergic bronchial asthma.