Jianhai Jiang

N-acetylneuraminate pyruvate lyase (NPL) is a key enzyme in sialic acid catabolism that links sialylation to cellular metabolism, but its role in cancer cell metabolic adaptation is poorly defined. In particular, it remains unclear whether NPL contributes to ATP maintenance in hepatocellular carcinoma (HCC) under nutrient stress through its role in sialic acid catabolism. HCC is a highly lethal malignancy characterized by extensive metabolic reprogramming. Here, we investigated whether NPL links sialic acid catabolism to ATP maintenance in HCC cells under glucose deprivation. Glucose deprivation induced NPL expression in Huh7 and PLC/PRF/5 cells, which is consistent with an adaptive response to energetic stress. Stable NPL knockdown reduced intracellular ATP levels. Consistently, cell growth was significantly reduced, as assessed by Cell Counting Kit-8 (CCK-8) and colony formation assays. These effects were more pronounced in the absence of glucose. Exogenous pyruvate partially restored ATP levels and the growth inhibition caused by NPL knockdown, particularly in the absence of glucose. This rescue further suggests that NPL may support ATP maintenance under glucose deprivation partly through pyruvate metabolism. Together, these findings indicate that NPL contributes to maintaining intracellular ATP levels during glucose deprivation, thereby supporting HCC cell adaptation to metabolic stress. To extend these biological findings to potential therapeutic exploration, we performed virtual screening and molecular docking using a U.S. Food and Drug Administration (FDA)-approved drug library. Candidate compounds predicted to bind NPL were identified, providing a basis for further validation and optimization.

Targeting the niche components surrounding glioblastoma stem cells (GSCs) helps to develop more effective glioblastoma treatments. However, the mechanisms underlying the crosstalk between GSCs and microenvironment remain largely unknown. Clarifying the extracellular molecules binding to GSCs marker CD133 helps to elucidate the mechanism of the communication between GSCs and the microenvironment. Here, it is found that the extracellular domain of high mannose type CD133 physically interacts with Collagen 1 (COL1) in GSCs. COL1, mainly secreted by cancer‐associated fibroblasts, is a niche component for GSCs. COL1 enhances the interaction between CD133 and p85 and activates Akt phosphorylation. Activation of Akt pathway increases transcription factor ATF4 protein level, subsequently enhances SLC1A5‐dependent glutamine uptake and glutathione synthesis. The inhibition of CD133‐COL1 interaction or down‐regulation of SLC1A5 reduces COL1‐accelerated GSCs self‐renewal and tumorigenesis. Analysis of glioma samples reveals that the level of COL1 is correlated with histopathological grade of glioma and the expression of SLC1A5. Collectively, COL1, a niche component for GSCs, enhances the tumorigenesis of GSCs partially through CD133‐Akt‐SLC1A5 signaling axis, providing a new mechanism underlying the cross‐talk between GSCs and extracellular matrix (ECM) microenvironment.

Purpose: Sialic acid-bound immunoglobulin-like lectin 15 (Siglec15) has emerged as a novel therapeutic target in tumor immunotherapy. This study is designed to investigate the function and mechanism of Siglec15 in thyroid carcinoma (THCA). Materials and methods: The information on patients with THCA from TGCA and GEO database were used to analyze the expression of Siglec15 in THCA. THCA cells were treated with Siglec15-mFc, a recombinant fusion protein consisting of the extracellular domain of human Siglec15 and murine IgG Fc. THP-1 cells expressing human Siglec15 and its mutant were co-cultured with THCA cells to mimic the contact between Siglec15-expressing tumor-associated macrophages and THCA cells. Wound-healing assay and transwell migration assay were used to examine the migration abilities of BCPAP and C643 cells. Pull-down assay was performed to examine the interaction between Siglec15 and epidermal growth factor receptor (EGFR) on the cancer cells. Cycloheximide (CHX) assay was used to evaluate the stability of the protein. Results: The expression of Siglec15 in thyroid carcinoma tissues is higher than in normal tissues. Siglec15 promotes the migration of THCA cells by binding to EGFR in a sialic acid-dependent manner and increases EGFR protein expression. Inhibition of the EGFR pathway blocks the effect of Siglec15 on the migration of THCA cells. Conclusions: Our findings reveals that Siglec15 promotes the migration of thyroid carcinoma cells by enhancing the EGFR protein stability.

The monocyte adhesion to endothelial cells is an early step in chronic inflammation. Interferon-γ (IFN-γ) is regarded as a master regulator of inflammation development. However, the significance and mechanisms of IFN-γ in the monocyte adhesion to endothelial cells remains largely unknown. IFN-γ up-regulates PD-L1 on various types of cells. Here, we performed flow cytometry to examine the contribution of IFN-γ-induced PD-L1 expression on monocyte adhesion to endothelial cells. Up-regulation of PD-L1 by IFN-γ enhanced the adhesion of monocytes to endothelial cells. By immunoprecipitation and lectin blot, PD-L1 in endothelial cells interacted with CD169/Siglec 1 in monocytes depending on the α2,3-sialylation of PD-L1. ST3Gal family (ST3β-galactoside α-2,3-sialyltransferase) was the major glycosyltransferase responsible for the α2,3-sialylation of membrane proteins. Down-regulation of ST3Gal4 by RNAinterference partially reduced the α2,3-sialylation of PD-L1 and the PD-L1-CD169 interaction. Finally, purified PD-L1 protein with α2,3-sialylation, but not PD-L1 protein without α2,3-sialylation, partially reduced IFN-γ-induced monocyte adhesion to endothelial cells. These findings provide evidence that the interaction between PD-L1 and CD169 promoted monocyte adhesion to endothelial cells and might elucidate a new mechanism of monocyte adhesion to endothelial cells.

The quiescent/slow‐cycling state preserves the self‐renewal capacity of cancer stem cells (CSCs) and leads to the therapy resistance of CSCs. The mechanisms maintaining CSCs quiescence remain largely unknown. Here, it is demonstrated that lower expression of MAN1A1 in glioma stem cell (GSC) resulted in the formation of high‐mannose type N‐glycan on CD133. Furthermore, the high‐mannose type N‐glycan of CD133 is necessary for its interaction with DNMT1. Activation of p21 and p27 by the CD133–DNMT1 interaction maintains the slow‐cycling state of GSC, and promotes chemotherapy resistance and tumorigenesis of GSCs. Elimination of the CD133–DNMT1 interaction by a cell‐penetrating peptide or MAN1A1 overexpression inhibits the tumorigenesis of GSCs and increases the sensitivity of GSCs to temozolomide. Analysis of glioma samples reveals that the levels of high‐mannose type N‐glycan are correlated with glioma recurrence. Collectively, the high mannose CD133–DNMT1 interaction maintains the slow‐cycling state and tumorigenic potential of GSC, providing a potential strategy to eliminate quiescent GSCs.