Nitric oxide synthase 2 through an autocrine loop via respiratory epithelial cell-derived mediator.
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)-gamma 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-gamma 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.
Uetani
K
K
Department of Pulmonary and Critical Care Medicine, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, OH 44195, USA.
Thomassen
M J
MJ
Erzurum
S C
SC
D019898:Autocrine Communication / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000378:metabolism* / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000187:drug effects; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D050856:Interferon Regulatory Factor-1; D007371:Interferon-gamma / Q000494:pharmacology; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000096:biosynthesis* / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D010750:Phosphoproteins / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D050794:STAT1 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015534:Trans-Activators / Q000378:metabolism
D017077:Culture Media, Conditioned; D004268:DNA-Binding Proteins; C494257:IRF1 protein, human; D050856:Interferon Regulatory Factor-1; D010750:Phosphoproteins; D012333:RNA, Messenger; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; D007371:Interferon-gamma; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II