Glutamine metabolism regulates FLIP expression and sensitivity to TRAIL in triple-negative breast cancer cells

Abstract

Glutamine plays an important role in the metabolism of tumor cells through its contribution to redox homeostasis, bioenergetics, synthesis of macromolecules, and signaling. Triple-negative breast cancers (TNBC) are highly metastatic and associated with poor prognosis. TNBC cells show a marked dependence on extracellular glutamine for growth. Herein we demonstrate that TNBC cells are markedly sensitized to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis upon glutamine deprivation. Upregulation of pro-apoptotic TRAIL receptor 2 (TRAIL-R2/DR5) and downregulation of FLICE-inhibitory protein (FLIP) are observed in glutamine-deprived TNBC cells. Activation of the amino-acid-sensing kinase general control nonderepressible 2 (GCN2) upon glutamine deprivation is responsible for TRAIL-R2 upregulation through a signaling pathway involving ATF4 and CHOP transcription factors. In contrast, FLIP downregulation in glutamine-deprived TNBC occurs by a GCN2-independent mechanism. Importantly, silencing FLIP expression by RNA interference results in a marked sensitization of TNBC cells to TRAIL-induced apoptosis. In addition, pharmacological or genetic inhibition of transaminases increases TRAIL-R2 expression and downregulates FLIP levels, sensitizing TNBC cells to TRAIL. Interestingly, treatment with l-asparaginase markedly sensitizes TNBC cells to TRAIL through its glutaminase activity. Overall, our findings suggest that targeting the glutamine addiction phenotype of TNBC can be regarded as a potential antitumoral target in combination with agonists of proapoptotic TRAIL receptors.

CIB1 depletion with docetaxel or TRAIL enhances triple-negative breast cancer cell death

“…Once believed to be a safe, tumor-specific targeting therapy, TRAIL as a mono-therapy failed due to resistance driven by mutations in TRAIL receptors and dysfunctional signaling complexes at the receptor intracellular domain [10, 11, 39]. Subsequent studies have focused on combination approaches using chemotherapeutics, natural compounds and targeted agents to sensitize otherwise resistant breast cancer cells to TRAIL by upregulating TRAIL receptors and restoring TRAIL receptors’ intracellular signaling complex activity [14, 40–45]. In comparison, our approach of targeting CIB1 allowed us to use five to tenfold lower concentrations of TRAIL to induce as much or greater cytotoxicity in cultured TNBC cells.…”

Novel Apoptosis-Inducing Agents for the Treatment of Cancer, a New Arsenal in the Toolbox

“…Cell metabolism: Several reports indicate that manipulating cell metabolism, such as glutamine deprivation [314], methionine depletion [315], and metformin [316], can sensitize TNBC cells to DR agonists. A recent study suggest that mitochondrial content is a useful biomarker for the prediction of apoptotic susceptibility [317].…”

Increased expression of glutamine transporter SNAT2/SLC38A2 promotes glutamine dependence and oxidative stress resistance, and is associated with worse prognosis in triple-negative breast cancer

“…From a metabolic point of view, Gln-dependent mechanisms also can vary substantially among breast cancer subtypes. 3 Triple-negative breast cancer (TNBC), an aggressive form of breast cancer, is dependent on exogenous Gln for survival and growth 4 , 5 and inhibitors of Gln transport and metabolism have been proposed as potential anti-tumour therapies. 6 , 7 …”