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Nonsteroidal Anti-inflammatory Drug-Activated Gene-1 Expression Inhibits Urethane-Induced Pulmonary Tumorigenesis in Transgenic Mice

Authors' Affiliations: ¹ Department of Pathobiology, College of Veterinary Medicine, The University of Tennessee, Knoxville, Tennessee; ² Laboratory of Molecular Carcinogenesis, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, North Carolina; and ³ Department of Carcinogenesis, Science Park-Research Division, The University of Texas M. D. Anderson Cancer Center, Smithville, Texas

Requests for reprints: Seung Joon Baek, Department of Pathobiology, College of Veterinary Medicine, The University of Tennessee, Knoxville, TN 37996. Phone: 865-974-8216; Fax: 865-974-5616; E-mail: sbaek2{at}utk.edu.

The expression of nonsteroidal anti-inflammatory drug-activated gene-1 (NAG-1) inhibits gastrointestinal tumorigenesis in NAG-1 transgenic mice (C57/BL6 background). In the present study, we investigated whether the NAG-1 protein would alter urethane-induced pulmonary lesions in NAG-1 transgenic mice on an FVB background (NAG-1^Tg+/FVB). NAG-1^Tg+/FVB mice had both decreased number and size of urethane-induced tumors, compared with control littermates (NAG-1^Tg+/FVB = 16 ± 4 per mouse versus control = 20 ± 7 per mouse, P < 0.05). Urethane-induced pulmonary adenomas and adenocarcinomas were observed in control mice; however, only pulmonary adenomas were observed in NAG-1^Tg+/FVB mice. Urethane-induced tumors from control littermates and NAG-1^Tg+/FVB mice highly expressed proteins in the arachidonic acid pathway (cyclooxygenases 1/2, prostaglandin E synthase, and prostaglandin E₂ receptor) and highly activated several kinases (phospho-Raf-1 and phosphorylated extracellular signal-regulated kinase 1/2). However, only urethane-induced p38 mitogen-activated protein kinase (MAPK) phosphorylation was decreased in NAG-1^Tg+/FVB mice. Furthermore, significantly increased apoptosis in tumors of NAG-1^Tg+/FVB mice compared with control mice was observed as assessed by caspase-3/7 activity. In addition, fewer inflammatory cells were observed in the lung tissue isolated from urethane-treated NAG-1^Tg+/FVB mice compared with control mice. These results paralleled in vitro assays using human A549 pulmonary carcinoma cells. Less phosphorylated p38 MAPK was observed in cells overexpressing NAG-1 compared with control cells. Overall, our study revealed for the first time that the NAG-1 protein inhibits urethane-induced tumor formation, probably mediated by the p38 MAPK pathway, and is a possible new target for lung cancer chemoprevention.

Key Words: NAG-1 • lung tumorigenesis • p38 MAPK • apoptosis • inflammation