Background: Human rhinovirus (HRV) triggers exacerbations of asthma and chronic obstructive pulmonary disease\r\n(COPD). Cigarette smoking is the leading risk factor for the development of COPD and 25% of asthmatics smoke.\r\nSmoking asthmatics have worse symptoms and more frequent hospitalizations compared to non-smoking\r\nasthmatics. The degree of neutrophil recruitment to the airways correlates with disease severity in COPD and\r\nduring viral exacerbations of asthma. We have previously shown that HRV and cigarette smoke, in the form of\r\ncigarette smoke extract (CSE), each induce expression of the neutrophil chemoattractant and activator, CXCL8, in\r\nhuman airway epithelial cells. Additionally, we demonstrated that the combination of HRV and CSE induces\r\nexpression of levels of CXCL8 that are at least additive relative to induction by each stimulus alone, and that\r\nenhancement of CXCL8 expression by HRV+CSE is regulated, at least in part, via mRNA stabilization. Here we further\r\ninvestigate the mechanisms by which HRV+CSE enhances CXCL8 expression.\r\nMethods: Primary human bronchial epithelial cells were cultured and treated with CSE alone, HRV alone or the\r\ncombination of the two stimuli. Stabilizing/destabilizing proteins adenine/uridine-rich factor-1 (AUF-1), KH-type\r\nsplicing regulatory protein (KHSRP) and human antigen R (HuR) were measured in cell lysates to determine\r\nexpression levels following treatment. siRNA knockdown of each protein was used to assess their contribution to\r\nthe induction of CXCL8 expression following treatment of cells with HRV and CSE.\r\nResults: We show that total expression of stabilizing/de-stabilizing proteins linked to CXCL8 regulation, including\r\nAUF-1, KHSRP and HuR, are not altered by CSE, HRV or the combination of the two stimuli. Importantly, however,\r\nsiRNA-mediated knock-down of HuR, but not AUF-1 or KHSRP, abolishes the enhancement of CXCL8 by HRV+CSE.\r\nData were analyzed using one-way ANOVA with student Newman-Keuls post hoc analysis and values of p= 0.05\r\nwere considered significant.\r\nConclusions: Induction of CXCL8 by the combination of HRV and CSE is regulated by mRNA stabilization\r\ninvolving HuR. Thus, targeting the HuR pathway may be an effective method of dampening CXCL8 production\r\nduring HRV-induced exacerbations of lower airway disease, particularly in COPD patients and asthmatic patients\r\nwho smoke.
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