Neutrophil elastase stimulatesMUC1gene expression through increased Sp1 binding to theMUC1promoter

Abstract

We previously reported MUC1 was a cell surface receptor for Pseudomonas aeruginosa, and binding of bacteria to cells was significantly reduced by pretreatment with neutrophil elastase (NE) (Lillehoj EP, Hyun SW, Kim BT, Zhang XG, Lee DI, Rowland S, and Kim KC. Am J Physiol Lung Cell Mol Physiol 280: L181-L187, 2001). The current study was conducted to ascertain NE effects on MUC1 gene transcription, and MUC1 protein synthesis and degradation. A549 human lung carcinoma cells treated with NE exhibited significantly higher MUC1 protein levels in detergent lysates compared with cells treated with vehicle alone. Also, MUC1 protein shed into cell-conditioned medium was rapidly and completely degraded by NE. Actinomycin D blocked NE-stimulated increase in MUC1 protein expression, suggesting a mechanism of increased gene transcription that was confirmed by measurement of quantitatively greater MUC1 mRNA levels in NE-treated cells compared with controls. However, NE did not alter MUC1 mRNA stability, implying increased de novo transcription induced by the protease. NE increased promoter activity in A549 cells transfected with MUC1 gene promoter-luciferase reporter plasmid. This effect of NE was completely blocked by mithramycin A, an inhibitor of Sp1, as well as mutation of one of the putative Sp1 binding sites in MUC1 promoter located at -99/-90 relative to transcription initiation site. EMSA revealed NE enhanced binding of Sp1 to this 10-bp segment in a time-dependent manner. These results indicate the increase in MUC1 gene transcription by NE is mediated through increase in Sp1 binding to -99/-90 segment of MUC1 promoter.

Sputum mucin 1 is increased during the acute phase of chronic obstructive pulmonary disease exacerbation

“…The mucus with bacterial burden will be cleared from the mucosal surface by cilia beating (26). Under inflammatory environment, the sputum EC fragments came from a neutrophil elastase mediated degradation of EC MUC1 on the surface of airway epithelial cells (11). However, excessive mucus production will contribute to airway blockage and lung functions decline, a situation consistent with positive correlation between sputum MUC1 EC fragment level and obstruction (determined by FEV 1 /FVC value reduction) revealed by linear regression analysis (Table 4).…”

“…An indispensable antiinflammatory role of Muc1 has been found in the airway during Pseudomonas aeruginosa and respiratory syncytial virus infection (8,9). Muc1 levels in bronchoalveolar lavage (BAL) fluid were increased during the acute phase of lung inflammation and positively correlated with TNF-α level increase (8,10) and neutrophil elastase levels upregulation (11). Chronic airway inflammation is one of characteristics of COPD.…”

Proteases and cystic fibrosis

“…We have recently reported that NE upregulates a cytoplasmic oxidoreductase, NADPH quinone oxidoreductase 1 that is required for NE-induced lipid peroxidation and for NE-regulated MUC5AC mRNA expression . NE also upregulates two membrane-associated mucins, MUC4 (Fischer, 2003) and MUC1 (Kuwahara et al, 2005), in airway epithelial cells. MUC1 and MUC4 regulate intracellular signaling via the ErbB family of receptor tyrosine kinases in cancer cells (Hollingsworth and Swanson, 2004) and may have similar functions in the lung.…”

Regulation of Airway Mucin Gene Expression

“…Signaling through these pathways may affect the apoptotic state of the cell, which may explain the greater expression of MUC1 in neoplastic cells (126). MUC1's expression in airway epithelial cells can be induced by NE and CpG DNA from bacteria (127,128). Otherwise, it is regulated by inflammatory mediators in noncancerous airway cells.…”