BuHyun Youn

Primary solid tumors often exhibit accelerated glucose metabolism yet generate limited ATP due to reduced flux through the tricarboxylic acid (TCA) cycle. However, how these distinct metabolic alterations contribute to therapeutic resistance—and whether they represent targetable metabolic vulnerabilities—remains unclear. Here, we identify adenylate kinase 4 (AK4), a mitochondrial regulator of adenylate homeostasis, as a key mediator of radioresistance in glioblastoma (GBM) cells. We found that AK4 is upregulated in radioresistant GBM cells, where it suppresses mitochondrial oxidative phosphorylation to maintain redox homeostasis and promote cell survival following ionizing radiation (IR). Moreover, AK4 maintains elevated intracellular AMP, leading to the activation of AMP-activated protein kinase (AMPK), a master regulator of energy metabolism. AMPK activation subsequently inhibits acetyl-CoA carboxylase (ACC), suppressing cellular lipid synthesis. Through these mechanisms, AK4 limits IR-induced ferroptosis and contributes to radioresistance. Notably, we demonstrate that entinostat, a class I histone deacetylase (HDAC) inhibitor, downregulates AK4 expression and enhances the sensitivity of GBM cells to IR both in vitro and in vivo. In conclusion, our study reveals that AK4 promotes radioresistance in GBM by coordinating mitochondrial redox regulation and AMPK-mediated lipid metabolism, highlighting AK4 as a promising therapeutic target for overcoming GBM radioresistance. Graphical abstract

Protein-protein interactions (PPIs) are critical regulators of cellular processes and represent promising therapeutic targets. However, existing drug discovery approaches for PPI targeting, such as surface plasmon resonance, have inherent limitations, including their inability to fully recapitulate the cellular environment. To address these challenges, we developed a NanoBRET-based RAB11A activation biosensor that utilizes bioluminescence resonance energy transfer (BRET) to detect PPIs in live cells while preserving native protein function. Using this platform, we screened a library of 7040 small molecules and identified potent inhibitors that significantly disrupted RAB11A binding to its effector proteins, as indicated by a reduction in the BRET ratio. RAB11A is a key regulator of recycling endosomes, particularly in glucose transporter (GLUT) trafficking, making it an attractive target for metabolic intervention. Given that RAB11 family interacting protein 2 (FIP2) binding is essential for RAB11A activation, disrupting this interaction impairs GLUT3 trafficking and reduces glucose uptake, a critical metabolic process driving glioblastoma progression. We found that inhibition of the RAB11A-FIP2 axis attenuates GLUT3 trafficking, thereby impairing glucose metabolism in glioblastoma. Among the identified small molecules, three candidates were further validated to interfere with both RAB11A activation and GLUT3 trafficking, highlighting their potential as metabolic regulators. Our NanoBRET-based biosensor provides a robust and scalable platform for high-throughput screening of PPI inhibitors, offering a promising strategy for developing novel therapeutics targeting PPIs.

Background: Neuroplasticity and synaptic homeostasis are essential in regulating neuronal activity and behavioral functions within the hippocampus. Alzheimer’s disease (AD) is characterized by progressive cognitive decline, pathological accumulation of amyloid β (Aβ) plaques and tau neurofibrillary tangles, neuroinflammation, and synaptic dysfunction. However, the temporal progression of neuroplasticity-related impairments in the hippocampus, a region particularly vulnerable to AD pathology, is not completely understood. Methods: This study examined age-dependent changes in behavioral performance and hippocampal structural plasticity in the 5×FAD (five familial Alzheimer’s disease) mouse model at 3, 6, and 12 months of age. Results: The 5×FAD mice exhibited progressive impairments in fine motor coordination and hippocampal-dependent working memory compared to control. Corresponding increases were observed in the accumulation of Aβ and phosphorylated tau, glial activation, and inflammatory cytokine production in the hippocampus across all time points. Golgi staining revealed significant age-related reductions in dendritic complexity, including fiber crossing counts, total dendritic length, and branch points in the cornu ammonis 1 (CA1) and dentate gyrus (DG) hippocampal subregions. Dendritic spine density and morphology exhibited significant alterations in the CA1 apical/basal and DG subregions with advancing age. Furthermore, the expression of synaptic proteins, including activity-regulated cytoskeleton-associated protein (Arc) and postsynaptic density protein-95 (PSD-95), significantly declined at 6 and 12 months of age. Conclusions: Our findings suggest a potential relationship between AD-related protein pathology, neuroinflammation, and structural plasticity impairments in the hippocampus. Collectively, these changes may contribute to disrupted synaptic transmission and behavioral deficits associated with AD pathology.

Background Glioblastoma (GBM) is an aggressive brain tumor characterized by a poor prognosis and resistance to radiotherapy. Although multiple mechanisms of radioresistance have been proposed, the contribution of membrane-driven metabolic adaptations to radioresistance remains poorly understood. Methods The role of UDP-glucose ceramide glucosyltransferase (UGCG) was investigated using radioresistant GBM cell lines and in vivo xenograft models. After inhibiting UGCG function through genetic or pharmacological (miglustat) approaches, we assessed the effects on lipid raft integrity, localization of the ASCT2 transporter, glutamine uptake, oxidative stress, and radiosensitivity. Results UGCG was upregulated in radioresistant GBM cells and promoted lipid raft stabilization. This facilitated the membrane recruitment of the glutamine transporter ASCT2 (SLC1A5), thereby sustaining redox homeostasis under radiation stress. Genetic or pharmacological inhibition of UGCG disrupted lipid raft integrity, impaired ASCT2 localization, reduced glutamine uptake, and increased oxidative stress, leading to enhanced radiosensitivity. In GBM xenograft models, UGCG inhibition combined with radiotherapy significantly suppressed tumor growth and extended survival. Conclusions These findings reveal a previously underexplored, membrane-centric mechanism of radioresistance in which UGCG orchestrates lipid raft remodeling to facilitate glutamine-dependent redox balance. This highlights UGCG as a potential therapeutic target to enhance the efficacy of radiotherapy in GBM.

Background/Aim: Glioblastoma multiforme (GBM) is a highly aggressive, treatment-resistant brain tumor with a dismal prognosis, and identifying key molecules involved in its therapeutic resistance is essential to improve patient outcomes. This study was undertaken to identify hub genes associated with the radioresistance and temozolomide (TMZ) resistance of GBM using bioinformatics analysis. Materials and Methods: RNA-seq and microarray datasets from the GEO database were analyzed to identify differentially expressed genes (DEGs). GO and KEGG pathway enrichment analyses were performed using Enrichr. A protein-protein interaction (PPI) network was constructed using STRING and visualized with Cytoscape, and hub genes were identified by MCODE analysis. Expression and survival analyses were conducted on TCGA and GTEx datasets using GEPIA2. Results: Twenty-four DEGs were considered linked to radioresistance and 122 to TMZ resistance. Functional enrichment and PPI network analyses highlighted key therapeutic resistance pathways, including cytokine-mediated signaling and inflammatory response pathways. Notably, CXCL8, IL1A, and IL1B were identified as key hub genes significantly enriched in these pathways. Expression analysis confirmed their up-regulation in GBM, and survival analysis indicated their association with prognosis. Conclusion: This study identifies CXCL8, IL1A, and IL1B as potential therapeutic targets for overcoming the resistance of GBM to radiotherapy and chemotherapy. In addition, these genes might serve as prognostic biomarkers and key regulators of GBM malignancy. Future studies are warranted to explore their functional roles in vivo and assess their potential use as therapeutic intervention targets.