三阴性乳腺癌中乳酸代谢与免疫逃逸的调控机制研究

This study systematically investigates the regulatory network of lactate metabolism, histone lactylation, and programmed death-ligand 1 (PD-L1) glycosylation in triple-negative breast cancer (TNBC) from the perspective of metabolic-epigenetic interactions, as well as the synergistic effects of these three factors in promoting tumor immune evasion. The study found that monocarboxylate transporter 4 (MCT4) can directly interact with PD-L1 and maintain intracellular lactate levels by exporting lactate, thereby driving histone H3 lysine 18 lactylation (H3K18la). Notably, H3K18la, an important epigenetic modification, further promotes PD-L1 glycosylation, ultimately driving immune evasion in TNBC. Mechanistic studies have shown that lactate can activate the WNT/β-catenin signaling pathway, which synergistically upregulates H3K18la levels and PD-L1 glycosylation levels. Inhibitors of this pathway, such as XAV939, can effectively reverse this process. In summary, this study not only reveals the critical role of the MCT4/lactate/H3K18la/PD-L1 glycosylation axis in TNBC immune suppression but also demonstrates that targeting this axis through genetic means (silencing MCT4) or pharmacological interventions (using 2-deoxy-D-glucose (2-DG), XAV939) can effectively inhibit the stability and function of PD-L1, providing a potential combination therapy strategy to overcome resistance to immunotherapy in TNBC. Triple-negative breast cancer (TNBC) is a highly heterogeneous subtype of breast cancer with limited treatment options. Prior to 2019, chemotherapy was the primary treatment; in recent years, the combination of immunotherapy and chemotherapy has been applied clinically. Immune checkpoint blockade (ICB) therapy, which restores antitumor immune function by inhibiting negative immune regulatory factors, has shown some potential, but the clinical response rate remains low. Therefore, elucidating the mechanisms of immune evasion is crucial for developing effective treatment strategies [1]. The main factors contributing to this challenge are twofold: first, PD-L1 on the surface of TNBC cells is often highly glycosylated, and glycosylation-mediated PD-L1 stability is a key mechanism for suppressing T-cell activity [32], helping tumor cells achieve immune evasion; second, the immunosuppressive effect of the tumor microenvironment (TME)—TNBC utilizes the Warburg effect to metabolize glucose into lactate, leading to a significant increase in lactate concentration in the TME (normal tissue lactate concentration is approximately 0.5-2 mmol/L, while in the TME of TNBC, it can reach 10-40 mmol/L). Acidification of the TME directly impairs the function and proliferation of cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, while promoting the infiltration of regulatory T cells (Tregs) [12]. Lactate is closely associated with tumor-mediated immune suppression and can regulate the immune microenvironment through multiple pathways, thereby inhibiting T-cell activation. Specifically, lactate can bind to the GPR81 receptor on the surface of macrophages, inducing polarization of macrophages towards the pro-tumor M2 type; M2-type macrophages secrete immunosuppressive factors such as interleukin-10 (IL-10) and transforming growth factor-β (TGF-β), which impair T-cell function and promote tumor angiogenesis. Additionally, lactate can upregulate the expression of chemokine CCL28, recruiting Tregs to the TME, and enhance their immunosuppressive activity by activating the Foxp3 protein within Tregs. Studies have shown that lactate produced by lactate dehydrogenase A (LDHA) can directly act on T cells and NK cells, weakening the body's tumor immune surveillance function [13]. Our research found that LDHA is significantly upregulated in TNBC and negatively correlates with T-cell infiltration; serum lactate levels in TNBC patients are higher than those in non-TNBC patients, suggesting that lactate regulation plays a key role in TNBC immune evasion. Glycolysis is a core component of tumor metabolic reprogramming. It not only shapes the TME through lactate accumulation but also provides substrates for lysine lactylation (Kla). Lysine lactylation, a novel post-translational modification (PTM) discovered by Professor Yingming Zhao's team in 2019, directly links cellular metabolism with epigenetic regulation. Among numerous lactylation sites, histone H3 lysine 18 lactylation (H3K18la) is a key modification form regulating gene expression [14][31]. This metabolic-epigenetic association further influences PD-L1: lactylation can promote PD-L1 stability, membrane localization, and immunosuppressive function by regulating glycosylation-related molecules, ultimately exacerbating tumor immune evasion. The "glycolysis-PD-L1" metabolic-immune axis is a core mechanism in the field of tumor metabolism and immunity. Studies have explored the combined use of glycolysis inhibitors and immune checkpoint blockers: 2-deoxy-D-glucose can mediate PD-L1 deglycosylation, reversing the immunosuppressive state of TNBC [26]; D-mannose can interfere with PD-L1 glycosylation and stability by activating AMP-activated protein kinase (AMPK), thereby enhancing the efficacy of immunotherapy [1]. To further clarify how tumor cells utilize the "metabolic reprogramming-immunosuppression" dual strategy to drive PD-L1 expression and construct an immune evasion system centered on PD-L1, we regulated tumor cell metabolism and reshaped the TME using glucose, 2-DG, and sodium lactate. Results confirmed that lactate not only promotes the proliferation and migration of TNBC but also upregulates PD-L1 glycosylation by increasing H3K18la levels. Under hypoxic conditions, tumor cells maintain metabolic homeostasis through lactate shuttling mediated by monocarboxylate transporters (MCTs). MCT1, MCT2, and MCT4 are the core subtypes involved in lactate transport. Among them, MCT4 is highly expressed on the surface of tumor cells, exporting lactate to the TME to promote tumor proliferation and invasion; it also participates in lactate metabolism regulation in ischemic diseases. Due to its role as a "key metabolic hub" in tumors and other pathological processes, MCT4 has become a research hotspot. In anti-tumor therapy, inhibiting MCT4 (e.g., using small molecule inhibitors such as AZD3965, α-cyano-4-hydroxycinnamic acid (CHC)) can block lactate efflux from tumor cells, leading to intracellular acidosis and energy depletion, thereby inhibiting tumor growth. Our study revealed that MCT4 regulates histone lactylation and PD-L1 glycosylation in TNBC: knocking down MCT4 reduces lactylation-induced PD-L1 glycosylation levels, decreases PD-L1 stability, and inhibits TNBC growth. The study also confirmed that the Wnt pathway, as an upstream signal, can regulate MCT4 expression; inhibiting the Wnt signal reduces lactate production, lowers lactylation levels, and PD-L1 glycosylation levels, thus weakening the tumor's proliferation, invasion, stemness maintenance, and immunosuppressive capabilities. In summary, MCT4 plays a key role in TNBC progression by regulating histone lactylation and influencing PD-L1 glycosylation. Additionally, the Wnt pathway can also regulate histone lactylation. This study elucidates a complex positive feedback loop among MCT4, the Wnt pathway, and histone lactylation, collectively driving the malignant progression of TNBC. These findings provide new strategies for TNBC treatment. Limitations of the Study Although this study confirms the critical role of MCT4 in mediating histone lactylation and regulating PD-L1 glycosylation stability, several questions remain to be investigated: Do other histone lysine sites (such as H4K12la) lactylate and co-regulate PD-L1 expression? Can lactylation at these sites indirectly regulate PD-L1 transcription through other transcription factors? Furthermore, future research needs to employ glycomics analysis and glycosyltransferase activity assays to clarify the specific molecular mechanisms by which lactylation affects PD-L1 glycosylation.