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Abstract

The molecular mechanism underlying degenerative joint disease, also known as osteoarthritis (OA), is not fully understood. Disruption of mitogen inducible gene 6 (Mig-6) in mice by homologous recombination (KO mice) led to early onset OA as revealed by simultaneous enlargement and deformity of multiple joints, degradation of articular cartilage and the development of bony outgrowths or osteophytes within the joint space. The latter appeared to be derived from proliferation of mesenchymal progenitor cells followed by differentiation into chondrocytes. Because of the striking similarity to human OA, Mig-6 KO mice arc a useful animal model for studying the mechanism of this disease and for testing new drugs or therapies for treating OA. These KO mice also developed epithelial hyperplasia, adenoma, and adenocarcinoma in organs such as lung, gallbladder, and bile duct. Mig-6 is therefore a tumor suppressor gene and is a candidate gene for the frequent Ip36 genetic alterations found in lung cancer. It can be used as a tumor biomarker as well as a target for cancer therapy. Mig-6 is located in human chromosome Ip36, a locus frequently associated with human lung cancer. Mig-6 is a negative regulator of EGF signaling, and like EGF, was induced by HGF/SF in human lung cancer cell lines. Frequently the receptors EGFR and Met were co-expressed, and Mig-6 was induced by both EGF and HGF/SF in a MAPK-dependent fashion. Not all tumor lines express Mig-6 in response to either EGF or HGF/SF. In these cases, missense and nonsense mutations in the Mig-6 coding region were found, as was evidence for Mig-6 transcriptional silencing.

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