Role of AMP-activated protein kinase in cross-talk between apoptosis and autophagy in human colon cancer

Abstract

Unresectable colorectal liver metastases remain a major unresolved issue and more effective novel regimens are urgently needed. While screening synergistic drug combinations for colon cancer therapy, we identified a novel multidrug treatment for colon cancer: chemotherapeutic agent melphalan in combination with proteasome inhibitor bortezomib and mTOR (mammalian target of rapamycin) inhibitor rapamycin. We investigated the mechanisms of synergistic antitumor efficacy during the multidrug treatment. All experiments were performed with highly metastatic human colon cancer CX-1 and HCT116 cells, and selected critical experiments were repeated with human colon cancer stem Tu-22 cells and mouse embryo fibroblast (MEF) cells. We used immunochemical techniques to investigate a cross-talk between apoptosis and autophagy during the multidrug treatment. We observed that melphalan triggered apoptosis, bortezomib induced apoptosis and autophagy, rapamycin caused autophagy and the combinatorial treatment-induced synergistic apoptosis, which was mediated through an increase in caspase activation. We also observed that mitochondrial dysfunction induced by the combination was linked with altered cellular metabolism, which induced adenosine monophosphate-activated protein kinase (AMPK) activation, resulting in Beclin-1 phosphorylated at Ser 93/96. Interestingly, Beclin-1 phosphorylated at Ser 93/96 is sufficient to induce Beclin-1 cleavage by caspase-8, which switches off autophagy to achieve the synergistic induction of apoptosis. Similar results were observed with the essential autophagy gene, autophagy-related protein 7, -deficient MEF cells. The multidrug treatment-induced Beclin-1 cleavage was abolished in Beclin-1 double-mutant (D133A/D146A) knock-in HCT116 cells, restoring the autophagy-promoting function of Beclin-1 and suppressing the apoptosis induced by the combination therapy. These observations identify a novel mechanism for AMPK-induced apoptosis through interplay between autophagy and apoptosis.

Proteasome inhibitors induce AMPK activation via CaMKKβ in human breast cancer cells

“…It has been reported that AMPK has three major upstream kinases: LKB1, CaMKKb, and TAK1, each of which is activated by different stimuli and in various tissues resulting in diverse outcomes [1,7]. Furthermore, the possibility of crosstalk between AMPK and UPS adds another layer of complexity to the system [29][30][31][32][33]. Considering the importance of AMPK and UPS signaling as two major anticancer strategies, it is important to understand their crosstalk.…”

Creatine maintains intestinal homeostasis and protects against colitis

“…The mTOR pathway has been shown to be critical in epithelial regeneration in response to colitis (24,25). Additionally, it is well established that AMPK activation inhibits proliferation as well as increases colonic epithelium cell death susceptibility in vitro (23,(38)(39)(40). Although some of creatine's effects are AMPK-dependent, the link between creatine and colitis is less established due to the profound and diverse effects of AMPK signaling, including its antiinflammatory functions within macrophage populations (41)(42)(43).…”

“…AMPK opposes the activation of the mammalian target of rapamycin (mTOR) signaling pathway and is up-regulated in skeletal muscle of creatine-deficient animals (22). In colonic epithelial cells, activation of AMPK leads to increased susceptibility to apoptotic stimuli (23). We examined whether DSS-induced colitis induces AMPK phosphorylation in isolated colonic epithelium from Gatm c/c mice.…”

Isogambogenic Acid Inhibits the Growth of Glioma Through Activation of the AMPK-mTOR Pathway

“…Moreover, they found that inhibition of the early stage of autophagy reduced the activation of caspase-8 and caspase-3, while the effect of late autophagy inhibition was the opposite [42]. In addition to autophagy, several studies have shown that the activation of AMPK and inhibition of mTOR is closely related to apoptosis [44-47]. In our study, activation of the AMPK-mTOR pathway led to a higher amount of apoptosis, which suggests that the AMPK-mTOR pathway may also contribute to isogambogenic acid-induced apoptosis in glioma cells.…”