Signal transducer and activator of transcription 6 (STAT-6) expression andfunction in asthmatic bronchial epithelium

Background: Asthma is associated with increased production of IL-4 and IL-1 3. Objective: Because many of the effects of these cytokines are mediated by a ctivation of signal transducer and activator of transcription 6 (STAT-6), w e investigated expression and function of this transcription factor in the airways. Methods: STAT-6 expression was investigated through use of immunohistochemi stry or RT-PCR applied to bronchial biopsy specimens or brushings from norm al control or asthmatic subjects. STAT-6 function was investigated by means of Western blotting and ELISA applied to primary epithelial cell cultures. Results: Immunohistochemistry revealed that the bronchial epithelium was th e major site of STAT-6 expression, both cytoplasmic and nuclear staining be ing observed. The level of STAT-6 expression in subjects with mild asthma ( median [range] percent epithelial staining, 3.4% [0% to 16.0%]; n = 14) did not differ significantly from that in normal controls (4.7% [0.0% to 20.0% ]; n = 11); however, in subjects with severe asthma, epithelial STAT-6 expr ession (13.7% [4.8% to 25.7%]; n = 9) was increased in comparison with subj ects with mild asthma and normal controls (P < .05). RT-PCR analysis showed that epithelial STAT-6 expression was heterogeneous and comprised both ful l-length STAT-6 and the dominant-negative variant that lacks the SH2 domain . Treatment of primary cultures of bronchial epithelial cells with IL-4 res ulted in STAT-6 phosphorylation and stimulation of IL-8 secretion; however, no difference in the responses of epithelial cells was observed between no rmal (n = 12) and asthmatic (n = 14) donors. Conclusion: These data demonstrate expression and activation of STAT-6 in n ormal and asthmatic bronchial epithelium. The activity of this transcriptio n factor is likely to play a key role in mediating the responses of the bro nchial epithelium to T(H)2 cytokines that are characteristic of the asthmat ic phenotype.