Cannabinoid action induces autophagy-mediated cell death through stimulation of ER stress in human glioma cells

Abstract

Autophagy can promote cell survival or cell death, but the molecular basis underlying its dual role in cancer remains obscure. Here we demonstrate that Δ 9 -tetrahydrocannabinol (THC), the main active component of marijuana, induces human glioma cell death through stimulation of autophagy. Our data indicate that THC induced ceramide accumulation and eukaryotic translation initiation factor 2α (eIF2α) phosphorylation and thereby activated an ER stress response that promoted autophagy via tribbles homolog 3-dependent (TRB3-dependent) inhibition of the Akt/mammalian target of rapamycin complex 1 (mTORC1) axis. We also showed that autophagy is upstream of apoptosis in cannabinoid-induced human and mouse cancer cell death and that activation of this pathway was necessary for the antitumor action of cannabinoids in vivo. These findings describe a mechanism by which THC can promote the autophagic death of human and mouse cancer cells and provide evidence that cannabinoid administration may be an effective therapeutic strategy for targeting human cancers. IntroductionMacro-autophagy, hereafter referred to as "autophagy," is a highly conserved cellular process in which cytoplasmic materials - including organelles - are sequestered into double-membrane vesicles called autophagosomes and delivered to lysosomes for degradation or recycling (1). In many cellular settings, triggering of autophagy relies on the inhibition of mammalian target of rapamycin complex 1 (mTORC1), an event that promotes the activation (de-inhibition) of several autophagy proteins (Atgs) involved in the initial phase of membrane isolation (1). Enlargement of this complex to form the autophagosome requires the participation of 2 ubiquitin-like conjugation systems. One involves the conjugation of ATG12 to ATG5 and the other of phosphatidylethanolamine to LC3/ATG8 (1). The final outcome of the activation of the autophagy program is highly dependent on the cellular context and the strength and duration of the stress-inducing signals (2-5). Thus, besides its role in cellular homeostasis, autophagy can be a form of programmed cell death, designated "type II programmed cell death," or play a cytoprotective role, for example in situations

Oncogenic BRAF induces chronic ER stress condition resulting in increased basal autophagy and apoptotic resistance of cutaneous melanoma

“…As ER stress-induced upregulation of TRB3 induces autophagy and the inhibition of the Akt/mTORC1 axis, 41 we investigated the contribution of TRB3 to BRAF V600E -induced basal autophagy. RNAi-mediated knockdown of TRB3 was carried out in A375 cells (Figure 6c) and the effect on basal autophagy rate analysed in the presence or absence of bafilomycin.…”

Loss of Tribbles pseudokinase-3 promotes Akt-driven tumorigenesis via FOXO inactivation

“…In line with this observation and with the notion that TRIB3 participates in the regulation of AKT phosphorylation by mTORC2, we found that genetic inactivation of TRIB3 leads to an enhanced phosphorylation of FOXO and BAD but not of GSK3or PRAS 40. Moreover, we recently found that treatment with D 9 -tetrahydrocannabinol (a compound derived from the plant Cannabis sativa that exerts antitumor effects in mouse models of cancer 14,15,35 ) triggers AKT inhibition via an enhanced interaction of TRIB3 with AKT and a subsequent decrease in the interaction of AKT and TRIB3 with the mTORC2 complex. 19 Our data also show that Trib3 interacts more strongly with WT AKT, or with AKT mutants in which Thr 308 and Ser 473 have been mutated to Ala, than with AKT mutants in which these two phosphorylatable residues have been mutated to Asp to mimic the negative charge associated with their phosphorylation (author's unpublished observations).…”

“…11,12 In addition, administration of different anticancer agents promotes cancer cell death via TRIB3 upregulation and the subsequent inhibition of Akt. [13][14][15][16][17][18][19] However, the precise molecular basis of the regulation of Akt by TRIB3 and whether loss of this pseudokinase may contribute to cancer initiation and progression remains to be clarified.In this study, we investigated the effect of the genetic inactivation of TRIB3 in several cellular and animal models of cancer. Our findings indicate that genetic inhibition of TRIB3 enhances tumorigenesis and that this effect is due -at least primarily -to a selective inactivation of the transcription factor FOXO by the mammalian target of rapamycin complex 2 (mTORC2)/AKT axis.…”

Developmental roles of tribbles protein family members

“…While knockdown suppresses the effect of GMCSF withdrawal, overexpression of Trib2 stimulates apoptosis by means of a caspase, not the proteosome (Lin et al, 2007). Trib3 also promotes apoptosis in macrophages (Shang et al, 2009), gliomas (Salazar et al, 2009), pancreatic b-cells (Humphrey et al, 2010), and chondrocytes (Cravero et al, 2009). …”