Monoglyceride lipase gene knockout in mice leads to increased incidence of lung adenocarcinoma

Monoglyceride lipase (MGL) is a recently discovered cancer-related protein. The role of MGL in tumorigenesis remains to be fully elucidated. We have previously shown that MGL expression was reduced or absent in multiple human malignancies, and overexpression of MGL inhibited cancer cell growth. Here, we have generated the MGL knockout mice to further investigate the role of MGL in tumorigenesis in vivo. Our results indicate that MGL-deficient (MGL+/−, MGL−/−) mice exhibited a higher incidence of neoplasia in multiple organs, including the lung, spleen, liver and lymphoid tissues. Interestingly, lung neoplasms were the most common neoplastic changes in the MGL-deficient mice. Importantly, MGL-deficient animals developed premalignant high-grade dysplasia and adenocarcinomas in their lungs. Investigation of the MGL expression status in lung cancer specimens from patients also revealed that MGL expression was significantly reduced in the majority of primary human lung cancers when compared to corresponding matched normal tissues. Furthermore, mouse embryonic fibroblasts (MEFs) from MGL-deficient animals showed characteristics of cellular transformation including increased cell proliferation, foci formation and anchorage-independent growth. Our results also indicate that MGL deficiency was associated with activation of EGFR and ERK. In addition, pro-inflammatory molecules COX-2 and TNF-α were also activated in the MGL-deficient lung tissues. Thus, our results provide new insights into the novel role of MGL as an important negative regulator of EGFR, COX-2 and TNF-α. Accordingly, EGFR and COX-2/TNF-α activation/induction is expected to play important roles in MGL deficiency-driven lung tumors. Collectively, our results implicate the tumor suppressive role of MGL in preventing tumor development in vivo, particularly in context to the lung cancer, and highlight its role as a potential tumor suppressor.