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BackgroundThe loss of tumor suppressor gene expression is involved in the carcinogenesis of gastric cancer (GC). Klotho is a recently identified tumor suppressor gene that epigenetically inactivated in gastric cancer. However, the signaling pathways involved in the suppressive role of klotho have rarely been reported in gastric cancer. In this study, we investigated the involvement of klotho in gastric cancer cell proliferation, apoptosis, and autophagy as well as the associated signaling.MethodsMethylation of klotho gene promoter in GC-7901, MNK-45 and AGS gastric cancer cells as well as GES-1 normal gastric epithelial cells was detected by bisulfate-based PCR. Restoration of klotho gene expression was established by applying a demethylating agent and delivering aklotho gene expression vector into GC-7901 cells. Cell viability was measured by CCK-8 assay. Cell apoptosis and cycling were analyzed by flow cytometry. Autophagy was measured by detecting LC3-I and LC3-II expression. Protein levels and phosphorylation were measured by Western blot assay.ResultsMethylation of klotho gene promoter and expression of the klotho gene were detected in GC cells. Restoration of klotho gene expression significantly inhibited cell proliferation, induced cell apoptosis, and increased LC3-I/LC3-II expression in GC cells. Restoration of klotho gene expression downregulated the phosphorylation levels of IGF-1 receptor, IRS-1, PI3K, Akt, and mTOR proteins. Both apoptosis and autophagy inhibitors blocked klotho-induced apoptosis and autophagy.ConclusionKlotho is a tumor suppressor in gastric cancer, which regulates IGF-1R phosphorylation and the subsequent activation of IRS-1/PI3K/Akt/mTOR signaling, tumor cell proliferation, apoptosis, and autophagy.

The klotho gene is a classical "aging suppressor" gene. Its roles in the pathology of chronic kidney diseases have been well documented. However, the role of Klotho in tumorigenesis, cancer progression, and prognosis is attracting more and more attention. Recent studies have shown that Klotho participates in the progression of several types of human cancers. Klotho functions as a tumor suppressor by inhibiting insulin/IGF1, p53/p21, and Wnt signaling. Silencing klotho gene expression is mainly mediated through promoter hypermethylation and histone deacetylation in cancer. Klotho has been proposed to take part in cell proliferation, survival, autophagy, and resistance to anti-cancer therapies.