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1 Departments of Pulmonary and Critical Care Medicine, 2 Cancer Biology, and 3 Cell Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195
Respiratory epithelium
expresses nitric oxide synthase 2 (NOS2) continuously in vivo; however,
mechanisms responsible for its expression are only partially
understood. We definitively identify an autocrine mechanism of
induction and maintenance of NOS2 in human airway epithelial cells
through the synthesis and secretion of a soluble mediator. Short
exposure of human airway cells to interferon (IFN)-
leads to
prolonged NOS2 expression. Transfer of the overlying culture medium
(conditioned medium) induces NOS2 expression in other airway epithelial
cells, suggesting the presence of an intermediary substance regulating
NOS2 expression in an autocrine loop. Characterization of the soluble
mediator reveals that it is stable and transferable in conditioned
medium for up to 7 days. However, soluble mediator does not induce NOS2 mRNA in human alveolar macrophages, indicating that the response to
soluble mediator is unique to human respiratory epithelium. Soluble
mediator is heat labile but is not inactivated by acid treatment,
unlike IFN-
itself. Importantly, IFN regulatory factor-1, which is
critical for murine NOS2 expression, is expressed and activated by
soluble mediator through the signal transducer and activator of
transcription-1-dependent pathway. Based on these findings, we propose
novel regulatory mechanisms for NOS2 expression in human airway epithelium.
lung; nitric oxide; inflammatory mediators; gene regulation; signal transduction
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