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Metformin sensitizes human bladder cancer cells to TRAIL-induced apoptosis through mTOR/S6K1-mediated downregulation of c-FLIP.

Abstract：

:Metformin, an oral antidiabetic agent, has been reported to potentiate chemotherapeutic-induced cytotoxicity. In this study, we investigated the effects and molecular mechanisms of metformin in sensitizing tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in human bladder cancer cells. Metformin alone did not induce apoptosis, but markedly potentiated TRAIL-induced apoptosis in 253J and RT4 bladder cancer cells. To elucidate the underlying mechanism, we examined the modulatory effects of metformin on the key components of the TRAIL signaling pathway and found that metformin did not alter the expression levels of death receptor 4 (DR4) and death receptor 5 (DR5), but significantly reduced the cellular Fas-associated death domain (FADD)-like interleukin-1β-converting enzyme (FLICE) inhibitory protein (c-FLIP) levels, contributing toward the sensitization to TRAIL. Further experiments showed that metformin did not affect the mRNA level, proteasomal degradation, and protein stability of c-FLIPL. However, metformin inhibited the mTOR/S6K1 pathway in 253J and RT4 cells, which usually regulates protein translation; moreover, knockdown of S6K1 effectively reduced the levels of c-FLIPL, indicating that metformin downregulates c-FLIP through inhibition of the mTOR/S6K1 pathway. In addition, AMP-activated protein kinase (AMPK) inhibitor compound C did not prevent the inhibitory effects of metformin on the mTOR/S6K1 pathway and metformin-mediated sensitization to TRAIL. Taken together, our results indicate that metformin sensitizes human bladder cancer cells to TRAIL-induced apoptosis through downregulation of c-FLIP, which is mediated by the mTOR/S6K1 pathway, but independent of AMPK; furthermore, these findings provide a rationale for the combined application of metformin with TRAIL in the treatment of bladder cancer.

journal_name

Anticancer Drugs

journal_title

Anti-cancer drugs

authors

Zhang T,Wang X,He D,Jin X,Guo P

doi

10.1097/CAD.0000000000000116

subject

Has Abstract

pub_date

2014-09-01 00:00:00

pages

887-97

issue

eissn

0959-4973

issn

1473-5741

journal_volume

pub_type

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Metformin sensitizes human bladder cancer cells to TRAIL-induced apoptosis through mTOR/S6K1-mediated downregulation of c-FLIP.