Dataset Information

Cigarette smoking induces overexpression of a fat-depleting gene AZGP1 in the human.

ABSTRACT:

Background

Smokers weigh less and have less body fat than nonsmokers. Increased body fat and weight gain are observed following smoking cessation. To assess a possible molecular mechanism underlying the inverse association between smoking and body weight, we hypothesized that smoking may induce the expression of a fat-depleting gene in the airway epithelium, the cell population that takes the brunt of the stress of cigarette smoke.

Methods

To assess whether smoking up-regulates expression in the airway epithelium of genes associated with weight loss, microarray analysis was used to evaluate genes associated with fat depletion in large airway epithelial samples obtained by fiberoptic bronchoscopy from healthy smokers and healthy nonsmokers. As a candidate gene we further evaluated the expression of alpha(2)-zinc-glycoprotein 1 (AZGP1), a soluble protein that stimulates lipolysis, induces a reduction in body fat in mice, is associated with the cachexia related to cancer, and is known to be expressed in secretory cells of lung epithelium. AZGP1 protein expression was assessed by Western analysis and localization in the large airway epithelium by immunohistochemistry.

Results

Both microarray and TaqMan analysis demonstrated that AZGP1 messenger RNA levels were higher in the large airway epithelium of healthy smokers compared to healthy nonsmokers (p < 0.05, all comparisons). Western analysis of airway biopsy specimens from smokers compared with those from nonsmokers demonstrated up-regulation of AZGP1 at the protein level, and immunohistochemical analysis demonstrated up-regulation of AZGP1 in secretory as well as neuroendocrine cells of smokers.

Conclusions

In the context that AZGP1 is involved in lipolysis and fat loss, its overexpression in the airway epithelium of chronic smokers may represent one mechanism for the weight difference in smokers vs nonsmokers.

SUBMITTER: Vanni H

PROVIDER: S-EPMC2679098 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND: Exposure to cigarette smoke is a major risk factor for lung cancer, but how it induces cancer is unclear. The overexpressed in lung cancer 1 (OLC1) gene is one of 50 candidate lung cancer genes identified by suppression subtractive hybridization as having higher expression in squamous cell carcinoma (SCC) than normal lung epithelia. METHODS: We used immunohistochemistry (IHC) to measure OLC1 protein levels in primary lung cancer samples from 559 patients and used fluorescence in situ hybridization to measure OLC1 copy number in primary SCC samples from 23 patients. We compared OLC1 protein expression in SCC samples of 371 patients with and without a smoking history using the Pearson chi(2) test. We assayed OLC1 protein levels by immunoblotting in H1299 human lung cancer cells, immortalized human bronchial epithelial cells, and primary cultured normal human bronchial epithelial cells that were treated with cigarette smoke condensate. We assayed tumor formation in athymic mice using NIH3T3 mouse fibroblast cells transfected with OLC1 (eight mice) and analyzed apoptosis and colony formation of H1299 and H520 lung cancer cells transfected with scrambled (negative) or OLC1 small interfering RNAs (siRNAs) (s1). RESULTS: OLC1 protein was overexpressed in 387 of 464 (83.4%) of primary lung cancers, as detected by IHC, and OLC1 was amplified in 14 of 23 (60%) of SCC samples. OLC1 protein overexpression was more common in SCC patients with a smoking history than those without (77.1% vs 45.8%, P < .001). In addition, cigarette smoke condensate increased OLC1 protein levels in H1299 cells, immortalized human bronchial epithelial cells, and primary cultured normal human bronchial epithelial cells. Overexpression of OLC1 induced tumor formation in athymic mice (control vs OLC1, 0% vs 100%). Knockdown of OLC1 increased apoptosis (mean percentage of apoptotic H1299 cells, s1 vs negative: 30.3% vs 6.4%, difference = 23.9%, 95% confidence interval [CI] = 19.1% to 28.5%, P = .002; mean percentage of apoptotic H520 cells, s1 vs negative: 21.6% vs 4.9%, difference = 16.7%, 95% CI = 10.6% to 22.8%, P = .007) and decreased colony formation (mean no. of colonies of H1299 cells transfected with siRNAs, negative vs s1: 84 vs 4, difference = 80, 95% CI = 71 to 88, P < .001; mean no. of colonies of H520 cells transfected with siRNAs, negative vs s1: 103 vs 24, difference = 79, 95% CI = 40 to 116, P = .005). CONCLUSIONS: OLC1 is a candidate oncogene in lung cancer whose expression may be regulated by exposure to cigarette smoke.