M2 isoform of pyruvate kinase rewires glucose metabolism during radiation therapy to promote an antioxidant response and glioblastoma radioresistance

BACKGROUND

Resistance to existing therapies is a significant challenge in improving outcomes for glioblastoma (GBM) patients. Metabolic plasticity has emerged as an important contributor to therapy resistance, including radiation therapy (RT). Here, we investigated how GBM cells reprogram their glucose metabolism in response to RT to promote radiation resistance.

METHODS

Effects of radiation on glucose metabolism of human GBM specimens were examined in vitro and in vivo with the use of metabolic and enzymatic assays, targeted metabolomics, and FDG-PET. Radiosensitization potential of interfering with M2 isoform of pyruvate kinase (PKM2) activity was tested via gliomasphere formation assays and in vivo human GBM models.

RESULTS

Here, we show that RT induces increased glucose utilization by GBM cells, and this is accompanied with translocation of GLUT3 transporters to the cell membrane. Irradiated GBM cells route glucose carbons through the pentose phosphate pathway (PPP) to harness the antioxidant power of the PPP and support survival after radiation. This response is regulated in part by the PKM2. Activators of PKM2 can antagonize the radiation-induced rewiring of glucose metabolism and radiosensitize GBM cells in vitro and in vivo.

CONCLUSIONS

These findings open the possibility that interventions designed to target cancer-specific regulators of metabolic plasticity, such as PKM2, rather than specific metabolic pathways, have the potential to improve the radiotherapeutic outcomes in GBM patients.

MetaFlux: Meta-learning global carbon fluxes from sparse spatiotemporal observations

We provide a global, long-term carbon flux dataset of gross primary production and ecosystem respiration generated using meta-learning, called MetaFlux. The idea behind meta-learning stems from the need to learn efficiently given sparse data by learning how to learn broad features across tasks to better infer other poorly sampled ones. Using meta-trained ensemble of deep models, we generate global carbon products on daily and monthly timescales at a 0.25-degree spatial resolution from 2001 to 2021, through a combination of reanalysis and remote-sensing products. Site-level validation finds that MetaFlux ensembles have lower validation error by 5-7% compared to their non-meta-trained counterparts. In addition, they are more robust to extreme observations, with 4-24% lower errors. We also checked for seasonality, interannual variability, and correlation to solar-induced fluorescence of the upscaled product and found that MetaFlux outperformed other machine-learning based carbon product, especially in the tropics and semi-arids by 10-40%. Overall, MetaFlux can be used to study a wide range of biogeochemical processes.

Abstract PO-020: The NRF2-redox-metabolism axis protects pancreatic cancer cells from radiation toxicity

More than 90% of pancreatic ductal adenocarcinomas (PDAC) are driven by activating KRAS mutations (mKRAS), which promote a remarkable resistance to all non-surgical therapies, including radiation therapy (RT). Unfortunately, mKRAS remains undruggable for the vast majority of PDAC tumors. This necessitates the discovery of downstream targets, which most likely govern the oxidative stress response and promote the acquisition of radiation resistance. Notably, the master orchestrator of oxidative stress response, the transcription factor NRF2, is upregulated by mKRAS and in some models, NRF2 is activated by irradiation (IR). This suggests that IR may amplify the already heightened, mKRAS-driven activation of NRF2 in PDAC. NRF2 targets include genes involved in restoring redox balance, likely promoting survival during RT. However, the involvement of NRF2 in PDAC radioresistance remains unknown. To fill this knowledge gap, we have systematically investigated the role of the NRF2 pathway in regulating radiation response in PDAC tumors. Our studies show that depletion of NRF2 via CRISPR/Cas9 targeted gene deletion (NRF2-ko) results in the accumulation of significantly higher levels of reactive oxygen species in irradiated PDAC cells. Importantly, this correlates with increased radiosensitivity of NRF2-ko cells in vitro, compared to NRF2-wt controls. Interestingly, irradiation of PDAC cells upregulates the expression of metabolic genes that drive the generation of various antioxidant species, in a NRF2-dependent manner. At the metabolite level, IR induces re-routing of glycolytic metabolites towards the antioxidant pentose phosphate pathway and the depletion of NRF2 abrogates these changes. Together, these findings suggest that part of the mechanism via which NRF2 promotes radiation survival of PDAC cells is by reprogramming cellular metabolism to drive a metabolic antioxidant response. Altogether, these findings support a crucial role for the NRF2-redox-metabolism axis in driving RT resistance in PDAC. This further suggests that inhibition of the NRF2 pathway would be followed by a failure to resist IR-induced oxidative stress, and subsequently sensitize mKRAS pancreatic cancer to RT.

Citation Format: Justine Bailleul, Taha Yazal, David Sung, Juan Nathaniel, Daisy Palomera, Anahita Sehgal, Rachel Ruan, Erina Vlashi. The NRF2-redox-metabolism axis protects pancreatic cancer cells from radiation toxicity [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-020.

Intragenic suppressor mutations of the COQ8 protein kinase homolog restore coenzyme Q biosynthesis and function in Saccharomyces cerevisiae

Saccharomyces cerevisiae Coq8 is a member of the ancient UbiB atypical protein kinase family. Coq8, and its orthologs UbiB, ABC1, ADCK3, and ADCK4, are required for the biosynthesis of coenzyme Q in yeast, E. coli, A. thaliana, and humans. Each Coq8 ortholog retains nine highly conserved protein kinase-like motifs, yet its functional role in coenzyme Q biosynthesis remains mysterious. Coq8 may function as an ATPase whose activity is stimulated by coenzyme Q intermediates and phospholipids. A key yeast point mutant expressing Coq8-A197V was previously shown to result in a coenzyme Q-less, respiratory deficient phenotype. The A197V substitution occurs in the crucial Ala-rich protein kinase-like motif I of yeast Coq8. Here we show that long-term cultures of mutants expressing Coq8-A197V produce spontaneous revertants with the ability to grow on medium containing a non-fermentable carbon source. Each revertant is shown to harbor a secondary intragenic suppressor mutation within the COQ8 gene. The intragenic suppressors restore the synthesis of coenzyme Q. One class of the suppressors fully restores the levels of coenzyme Q and key Coq polypeptides necessary for the maintenance and integrity of the high-molecular mass CoQ synthome (also termed complex Q), while the other class provides only a partial rescue. Mutants harboring the first class of suppressors grow robustly under respiratory conditions, while mutants containing the second class grow more slowly under these conditions. Our work provides insight into the function of this important yet still enigmatic Coq8 family.