PD-L1 up-regulation in cancer contributes to immune evasion by tumor cells. Here, we show that Wnt ligand and activated EGFR induce the binding of the β-catenin/TCF/LEF complex to the CD274 gene promoter region to induce PD-L1 expression, in which AKT activation plays an important role. β-Catenin depletion, AKT inhibition, or PTEN expression reduces PD-L1 expression in tumor cells, enhances activation and tumor infiltration of CD8+ T cells, and reduces tumor growth, accompanied by prolonged mouse survival. Combined treatment with a clinically available AKT inhibitor and an anti–PD-1 antibody overcomes tumor immune evasion and greatly inhibits tumor growth. In addition, AKT-mediated β-catenin S552 phosphorylation and nuclear β-catenin are positively correlated with PD-L1 expression and inversely correlated with the tumor infiltration of CD8+ T cells in human glioblastoma specimens, highlighting the clinical significance of β-catenin activation in tumor immune evasion.

Background: Cancer cells undergo cellular adaptation through metabolic reprogramming to sustain survival and rapid growth under various stress conditions. However, how brain tumors modulate their metabolic flexibility in the naturally serine/glycine (S/G)-deficient brain microenvironment remain unknown. Methods: We used a range of primary/stem-like and established glioblastoma (GBM) cell models in vitro and in vivo. To identify the regulatory mechanisms of S/G deprivation-induced metabolic flexibility, we employed high-throughput RNA-sequencing, transcriptomic analysis, metabolic flux analysis, metabolites analysis, chromatin immunoprecipitation (ChIP), luciferase reporter, nuclear fractionation, cycloheximide-chase, and glucose consumption. The clinical significances were analyzed in the genomic database (GSE4290) and in human GBM specimens. Results: The high-throughput RNA-sequencing and transcriptomic analysis demonstrate that the de novo serine synthesis pathway (SSP) and glycolysis are highly activated in GBM cells under S/G deprivation conditions. Mechanistically, S/G deprivation rapidly induces reactive oxygen species (ROS)-mediated AMP-activated protein kinase (AMPK) activation and AMPK-dependent hypoxia-inducible factor (HIF)-1α stabilization and transactivation. Activated HIF-1α in turn promotes the expression of SSP enzymes phosphoglycerate dehydrogenase (PHGDH), phosphoserine aminotransferase 1 (PSAT1), and phosphoserine phosphatase (PSPH). In addition, the HIF-1α-induced expression of glycolytic genes (GLUT1, GLUT3, HK2, and PFKFB2) promotes glucose uptake, glycolysis, and glycolytic flux to fuel SSP, leading to elevated de novo serine and glycine biosynthesis, NADPH/NADP⁺ ratio, and the proliferation and survival of GBM cells. Analyses of human GBM specimens reveal that the levels of overexpressed PHGDH, PSAT1, and PSPH are positively correlated with levels of AMPK T172 phosphorylation and HIF-1α expression and the poor prognosis of GBM patients. Conclusion: Our findings reveal that metabolic stress-enhanced glucose-derived de novo serine biosynthesis is a critical metabolic feature of GBM cells, and highlight the potential to target SSP for treating human GBM.

Tumor cells often overexpress immune checkpoint proteins, including CD47, for immune evasion. However, whether or how oncogenic activation of receptor tyrosine kinases, which are crucial drivers in tumor development, regulates CD47 expression is unknown. Here, it is demonstrated that epidermal growth factor receptor (EGFR) activation induces CD47 expression by increasing the binding of c‐Src to CD47, leading to c‐Src‐mediated CD47 Y288 phosphorylation. This phosphorylation inhibits the interaction between the ubiquitin E3 ligase TRIM21 and CD47, thereby abrogating TRIM21‐mediated CD47 K99/102 polyubiquitylation and CD47 degradation. Knock‐in expression of CD47 Y288F reduces CD47 expression, increases macrophage phagocytosis of tumor cells, and inhibits brain tumor growth in mice. In contrast, knock‐in expression of CD47 K99/102R elicits the opposite effects compared to CD47 Y288F expression. Importantly, CD47‐SIRPα blockade with an anti‐CD47 antibody treatment significantly enhances EGFR‐targeted cancer therapy. In addition, CD47 expression levels in human glioblastoma (GBM) specimens correlate with EGFR and c‐Src activation and aggravation of human GBM. These findings elucidate a novel mechanism underlying CD47 upregulation in EGFR‐activated tumor cells and underscore the role of the EGFR‐c‐Src‐TRIM21‐CD47 signaling axis in tumor evasion and the potential to improve the current cancer therapy with a combination of CD47 blockade with EGFR‐targeted remedy.

N⁶-adenosine methylation (m⁶A) is critical for controlling cancer cell growth and tumorigenesis. However, the function and detailed mechanism of how m⁶A methyltransferases modulate m⁶A levels on specific targets remain unknown. In the current study, we identified significantly elevated levels of RBM15, an m⁶A writer, in basal-like breast cancer (BC) patients compared to nonbasal-like BC patients and linked this increase to worse clinical outcomes. Gene expression profiling revealed correlations between RBM15 and serine and glycine metabolic genes, including PHGDH, PSAT1, PSPH, and SHMT2. RBM15 influences m⁶A levels and, specifically, the m⁶A levels of serine and glycine metabolic genes via direct binding to target RNA. The effects of RBM15 on cell growth were largely dependent on serine and glycine metabolism. Thus, RBM15 coordinates cancer cell growth through altered serine and glycine metabolism, suggesting that RBM15 is a new therapeutic target in BC.

Su Hwan Park, M.S., Juheon Lee, M.S., Hye Jin Yun, B.S., Seok-Ho Kim, Ph.D., and Jong-Ho Lee, Ph.D.. Ann Lab Med -0001;0:. https://doi.org/10.3343/alm.2023.0443

DNA repair defects are important factors in cancer development. High DNA repair activity can affect cancer progression and chemoresistance. DNA double-strand breaks in cancer cells caused by anticancer agents can be restored by non-homologous end joining (NHEJ) and homologous recombination repair (HRR). Our previous study has identified E2F1 as a key gene in bladder cancer progression. In this study, DNA repair genes related to E2F1 were analyzed, and RAD54L involved in HRR was identified. In gene expression analysis of bladder cancer patients, the survival of patients with high RAD54L expression was shorter with cancer progression than in patients with low RAD54L expression. This study also revealed that E2F1 directly binds to the promoter region of RAD54L and regulates the transcription of RAD54L related to the HRR pathway. This study also confirmed that DNA breaks are repaired by RAD54L induced by E2F1 in bladder cancer cells treated with MMC. In summary, RAD54L was identified as a new target directly regulated by E2F1. Our results suggest that, E2F1 and RAD54L could be used as diagnostic markers for bladder cancer progression and represent potential therapeutic targets.