AMPK-independent down-regulation of cFLIP and sensitization to TRAIL-induced apoptosis by AMPK activators

Abstract

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a TNF superfamily member that is being considered as a new strategy in anticancer therapy because of its ability to induce apoptosis, alone or in combination with other stimuli, in many cancer cells. AMPactivated protein kinase (AMPK) is an evolutionarily conserved key regulator of cellular energy homeostasis that protects the cell from energy depletion and stress by activating several biochemical pathways that lead to the conservation, as well as generation, of ATP.Here we report that a number of AMPK activators, including the small molecule activator A-769662, markedly sensitize TRAIL-resistant breast cancer cells to TRAIL-induced apoptosis.However, silencing AMPKα1 expression with siRNA or over-expression of DN-AMPKα1 does not inhibit AICAR, glucose deprivation, phenformin or A-769662-induced sensitization to TRAIL. Furthermore, the expression of constitutively active AMPK subunits does not sensitize resistant breast cancer cells to TRAIL-induced apoptosis. The cellular FLICEinhibitory proteins (cFLIP L and cFLIP S ) were significantly down-regulated following exposure to AMPK activators through an AMPK-independent mechanism. Furthermore, in cells over-expressing cFLIP L , sensitization to TRAIL by AMPK activators was markedly reduced. In summary, our results indicate that AMPK activators facilitate the activation by TRAIL of an apoptotic cell death program through a mechanism independent of AMPK and dependent on the down-regulation of cFLIP levels.

Compound C sensitizes Caki renal cancer cells to TRAIL-induced apoptosis through reactive oxygen species-mediated down-regulation of c-FLIPL and Mcl-1

“…This view is supported by our findings: (a) suppression of AMPK expression with its siRNA did not increase compound C-induced sensitization to TRAIL-mediated apoptosis; (b) transduction of DN-AMPK failed to increase in TRAIL-induced apoptosis through the AMPK inhibition. Recently, it have been reported that potent AMPK activator such as AICAR or the small molecule activator A-769662, enhances death receptor-triggered formation of death-inducing signaling complex and markedly sensitizes tumor cells to death receptor-mediated apoptosis [10,23]. Contrastingly with their reports, we demonstrate that pretreatment of human renal cancer cells with AMPK inhibitor compound C promotes the activation by TRAIL.…”

Goniothalamin enhances TRAIL-induced apoptosis in colorectal cancer cells through DR5 upregulation and cFLIP downregulation

“…Another mechanism which is involved in sensitization to TRAIL-induced apoptosis is downregulation of cFLIP and Mcl1. cFLIP is the major protein that prevents caspase-8 from activation by death receptors through binding to FADD and/or caspase-8 and TRAIL receptor DR5 in a ligand-dependent and -independent manner and forms an apoptosis inhibitory complex (AIC), then prevents death-inducing signaling complex (DISC) formation and subsequently suppress the activation of caspase cascade (46)(47)(48)(49)(50)(51)(52)(53). Mcl1 is an antiapoptotic protein involved in death receptor mediated pathway crosslink to mitochondrial mediated pathway by interacting with truncated Bid (tBid) and then strongly inhibits tBid-induced cytochrome c release in mitochondrial mediated apoptosis pathway (54)(55)(56)(57).…”

XIAP Inhibition and Generation of Reactive Oxygen Species Enhances TRAIL Sensitivity in Inflammatory Breast Cancer Cells

“…In addition to XIAP, the antiapoptotic caspase-8 homolog cFLIP has previously been reported to block apoptosis induced by ligand binding to Fas, TRAIL, TNF, and CD95 receptors (14,32,33). Inhibition or downregulation of cFLIP in certain contexts is able to sensitize resistant cells to TRAIL-induced apoptosis (34)(35)(36)(37)(38)(39). In the current study, although cFLIP protein levels decreased significantly in TRAIL-or embelin þ TRAIL-treated parental SUM149 cells undergoing cell death, cFLIP levels remained unchanged in embelin þ TRAIL-treated XIAP-overexpressing cells that were also undergoing apoptosis.…”