Regulation of Human MUC7 Mucin Gene Expression by Cigarette Smoke Extract or Cigarette Smoke and Pseudomonas aeruginosa Lipopolysaccharide in Human Airway Epithelial Cells and in MUC7 Transgenic Mice

The human MUC7 gene encodes a low-molecular-weight mucin glycoprotein that functions in lubrication/protection of epithelial surfaces of the oral cavity and respiratory tract. This study was designed to evaluate the effect of cigarette smoke extract (CSE), cigarette smoke (CS), and Pseudomonas aeruginosa lipopolysaccharide (LPS), either alone or in the combination, on MUC7 expression in vitro and in vivo.

qRT-PCR was used to determine the levels of mucin gene transcription in the human lung carcinoma cell line NCI-H292 (in vitro) and MUC7 transgenic mouse tissues (in vivo). ELISA was used to assess mucin glycoprotein levels in the cell line, and immunohistochemistry to assess mucins in lung and trachea sections.

In vitro treatment of cells with LPS (10 (µg/ml) or CSE (0.5, 1, 2.5 and 5%) alone, resulted in a statistically significant increase of MUC7 transcripts only with 1%CSE (3.2-fold). The combined CSE/LPS treatment resulted in a synergistic increase of MUC7 with 0.5%CSE/LPS (4.4 fold). MUC7 glycoprotein levels increased only minimally, the highest increase was seen with the 0.5%CSE/LPS combination treatment (1.3-fold). In vivo exposure of MUC7 transgenic mice to CS, LPS or CS/LPS combination resulted in significant increase in MUC7 transcripts only with LPS treatment (in both trachea and lung). Immunohistochemistry indicated variable increase in MUC7 glycoprotein with CS and LPS treatment, both in the trachea and lungs, but CS/LPS exposure appeared to yield the highest increase.

In vitro, CSE and a combination of CSE/LPS treatment upregulated MUC7 gene transcription. In vivo, LPS upregulated MUC7 transcription, and a combination of CS/LPS appeared to increase MUC7 glycoprotein.