Suppression of Epithelial Signal Transducer and Activator of Transcription 1 Activation by Extracts of Aspergillus fumigatus

Bhushan, B.; Homma, T.; Norton, J. E.; Sha, Q.; Siebert, J.; Gupta, D. S.; Schroeder, J. W., Jr.; Schleimer, R. P.

Am J Respir Cell Mol Biol. 2014 Dec 5; 53(1):87-95

Abstract

Aspergillus fumigatus (AF) is often pathogenic in immune-deficient individuals and can cause life-threatening infections such as invasive aspergillosis. The pulmonary epithelial response to AF infection and the signaling pathways associated with it have not been completely studied. BEAS-2B cells or primary human bronchial epithelial cells were exposed to extracts of AF and challenged with IFN-beta or the Toll-like receptor 3 agonist double-stranded RNA (dsRNA). Cytokine release (B-cell activating factor of the TNF family [BAFF], IFN-gamma-induced protein-10 [IP-10], etc.) was assessed. AF extract was separated into low-molecular-weight (LMW) and high-molecular-weight (HMW) fractions using ultra 4 centrifugal force filters to characterize the activity. Real-time PCR was performed with a TaqMan method, and protein estimation was performed using ELISA techniques. Western blot was performed to assess phosphorylation of signal transducer and activator of transcription 1 (STAT1). IFN-beta and dsRNA induced messenger RNA (mRNA) expression of BAFF (350- and 452-fold, respectively [n = 3]) and IP-10 (1,081- and 3,044-fold, respectively [n = 3]) in BEAS-2B cells. When cells were pretreated with AF extract for 1 hour and then stimulated with IFN-beta or dsRNA for 6 hours, induction of BAFF and IP-10 mRNA was strongly suppressed relative to levels produced by IFN-beta and dsRNA alone. When compared with control, soluble BAFF and IP-10 protein levels were maximally suppressed in dsRNA-stimulated wells treated with 1:320 wt/vol AF extract (P < 0.005). Upon molecular size fractionation, a LMW fraction of AF extract had no measurable suppressive effect on IP-10 mRNA expression. However, a HMW fraction of the AF extract significantly suppressed IP-10 expression in BEAS-2B cells that were stimulated with dsRNA or IFN-beta. When BEAS-2B cells were pretreated with AF extract and then stimulated with IFN-beta, reduced levels of pSTAT1 were observed, with maximum suppression at 4 and 6 hours. Our results show that AF extracts suppressed expression of inflammatory cytokines in association with inhibition of the IFN-beta signaling pathway and suppression of the formation of pSTAT1.

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