Hypoxia-mediated mechanism of MUC5AC production in human nasal epithelia and its implication in rhinosinusitis.
BACKGROUND
Excessive mucus production is typical in various upper airway diseases. In sinusitis, the expression of MUC5AC, a major respiratory mucin gene, increases. However, the mechanisms leading to mucus hypersecretion in sinusitis have not been characterized. Hypoxia due to occlusion of the sinus ostium is one of the major pathologic mechanisms of sinusitis, but there have been no reports regarding the mechanism of hypoxia-induced mucus hypersecretion.


RESULTS
This study aims to identify whether hypoxia may induce mucus hypersecretion and elucidate its mechanism. Normal human nasal epithelial (NHNE) cells and human lung mucoepidermoid carcinoma cell line (NCI-H292) were used. Sinus mucosa from patients was also tested. Anoxic condition was in an anaerobic chamber with a 95% N2/5% CO2 atmosphere. The regulatory mechanism of MUC5AC by anoxia was investigated using RT-PCR, real-time PCR, western blot, ChIP, electrophoretic mobility shift, and luciferase assay. We show that levels of MUC5AC mRNA and the corresponding secreted protein increase in anoxic cultured NHNE cells. The major transcription factor for hypoxia-related signaling, HIF-1α, is induced during hypoxia, and transfection of a mammalian expression vector encoding HIF-1α results in increased MUC5AC mRNA levels under normoxic conditions. Moreover, hypoxia-induced expression of MUC5AC mRNA is down-regulated by transfected HIF-1α siRNA. We found increased MUC5AC promoter activity under anoxic conditions, as indicated by a luciferase reporter assay, and mutation of the putative hypoxia-response element in MUC5AC promoter attenuated this activity. Binding of over-expressed HIF-1α to the hypoxia-response element in the MUC5AC promoter was confirmed. In human sinusitis mucosa, which is supposed to be hypoxic, expression of MUC5AC and HIF-1α is higher than in control mucosa.


CONCLUSIONS
The results indicate that anoxia up-regulates MUC5AC by the HIF-1α signaling pathway in human nasal epithelia and suggest that hypoxia might be a pathogenic mechanism of mucus hypersecretion in sinusitis.
BK 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea; Research Center for Human Natural Defense System, Yonsei University College of Medicine, Seoul, Korea.
Yoon-Ju
YJ
Kim
Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul, Korea; The Airway Mucus Institute, Yonsei University College of Medicine, Seoul, Korea.
Hyung-Ju
HJ
Cho
Hana ENT Hospital, Seoul, Korea.
Woo-Chul
WC
Shin
Research Center for Human Natural Defense System, Yonsei University College of Medicine, Seoul, Korea.
Hyun-Ah
HA
Song
Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul, Korea; The Airway Mucus Institute, Yonsei University College of Medicine, Seoul, Korea; BK 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea; Research Center for Human Natural Defense System, Yonsei University College of Medicine, Seoul, Korea.
Joo-Heon
JH
Yoon
Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul, Korea; The Airway Mucus Institute, Yonsei University College of Medicine, Seoul, Korea.
Chang-Hoon
CH
Kim
D015153:Blotting, Western; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D024202:Electrophoretic Mobility Shift Assay; D006801:Humans; D000860:Hypoxia / Q000209:etiology / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D008156:Luciferases; D055271:Mucin 5AC / Q000378:metabolism*; D009093:Mucus / Q000378:metabolism*; D009297:Nasal Mucosa / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D012852:Sinusitis / Q000150:complications / Q000378:metabolism*
C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C524678:MUC5AC protein, human; D055271:Mucin 5AC; D008156:Luciferases