In susceptible individuals, RV infection of the pulmonary epithelia triggers airway hyperresponsiveness and asthma development or exacerbation. After infection, epithelial cells secrete IL-8, a potent CXC chemokine that elicits neutrophil, lymphocyte and macrophage influx into the lung. Once there, immune cells destroy RV infected epithelia as well as recruit additional immune cells. Thus, understanding the regulation of IL-8 production by infected pulmonary epithelia is critical for understanding the initial pathophysiology of RV induced asthma as well as providing a potential target for therapy. While the contribution of IL-8 gene transcription to chemokine production after infection has been investigated, the role of post-transcriptional events remains largely unknown. The 3' untranslated region (UTR) of IL-8 mRNA contains multiple copies of AUUUA repeats. These elements are found in a variety of cytokine, chemokine and proto-oncogene mRNAs where they cause rapid decay in resting cells. However, after cell activation, the effects of the AUUUA motifs are nullified, leading to mRNA stabilization and accumulation. Herein we show that IL-8 mRNA is very unstable in quiescent pulmonary epithelia. Within several hours after RV infection, IL-8 mRNA is significantly stabilized, and this processes requires mitogen activated protein kinase (MAPK) signaling. We also demonstrate that IL-8 mRNA specifically interacts in vitro with several, known AUUUA specific mRNA binding proteins including HuR, AUF-1 and YB-1. Based on these data, we hypothesize that RV infection of epithelia triggers IL-8 production by stabilizing IL-8 mRNA. Stabilization is accomplished by increasing interactions between AUUUA binding proteins and IL-8 mRNA. Thus, our aims are to determine: (1) which AUUUA RNA binding protein(s) interacts with IL-8 mRNA and mediates RV induced stabilization; (2) which region(s) of IL-8 mRNA is/are required for RV induced stabilization; and (3) which components of the MAP kinase cascade are activated by RV and required for IL-8 mRNA stabilization.
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