Metformin Targets Clusterin To Control Lipogenesis And The Growth Of Bladder Cancer Through SREBP-1c/FASN Axis

PURPOSE: Activation of fatty acid metabolism is essential for bladder tumorigenesis which is a frequent feature of bladder cancer.Metformin is a broadly prescribed drug for type 2 diabetes that exerts antitumor activity,yet the underlying mechanisms of antitumor activity remain incompletely understood.In this study,we evaluated Clusterin as a potential target of metformin in bladder cancer,and investigated its contribution in lipogenesis.METHODS: Clusterin expression was analyzed in bladder cancer tissues by tissue microarray.High-throughput protein chip was used to screen differential proteins with metformin treatment.Cells proliferation,colony formation,migration and apoptosis were evaluated after metformin treatment and investigated the efficacy of metformin under circumstances that Clusterin was knock-down or over-expressed.Finally,the mechanisms mediated by Clusterin were explored using CO-IP and Cytosolic/nuclear fractionation.RESULTS:(1)Clusterin is overexpressed in bladder cancer and the level of Clusterin was positively correlates with tumor progression and differentiation grade.(2)Clusterin was screened as one of targeted proteins with metformin treatment,Metformin treatment is associated with down-regulation of Clusterin expression.(3)Bladder cancer cells characterized by high Clusterin expression are more sensitive to metformin.(4)Clusterin knockdown led to inhibition of proliferation,colony formation,migration and induction of apoptosis in bladder cancer cells which would insensitize bladder cancer cells to metformin treatment.Clusterin overexpression leads to increased the abilities of proliferation,colony formation and migration which were characterized by higher metformin induced inhibition of colony formation as well as migration.(5)Clusterin silencing inhibited both the precursor and mature forms of SREBP-1c,and decreased FASN levels.CONCLUSION: Our study proved that the susceptibility to the growth inhibitory effects of metformin in bladder cancer depends on the level of Clusterin expression.Further,metformin down-regulated SREBP-1c/FASN signaling axis to inhibit bladder cancer growth by inhibiting lipogenesis.The study provides a novel potential approach for individualized treatment with metformin in cancer patients with differential expression of Clusterin.