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Published on: December 16, 2022
Divergent roles of PKM2 in regulating PD-L1 and PD-L2 expression and their implications in human and mouse cancer
Shuo He1,2, Shujuan Luo1,2, Bangwu Cai1,2
1State Key Laboratory of Pathogenesis, Prevention, Treatment of Central Asian High Incidence Diseases, Clinical Medical Research Institute, First Affiliated Hospital of Xinjiang Medical University, Xinjiang Uygur Autonomous Region, Urumqi 830011, China.
Abstract:
Cancer cells evade immune detection through checkpoint molecules like PD-L1 and PD-L2 which suppress T-cell activation. While PD-L1 is well-studied, the role of PD-L2 remains unclear. Pyruvate kinase M2 (PKM2), a metabolic enzyme, influences immune checkpoint regulation, but its role in PD-L1 and PD-L2 modulation is not well defined. Here, we investigate the role of pyruvate kinase M2 (PKM2) in modulating the immune checkpoint molecules PD-L1 and PD-L2 via GATA3 in cancer cells, with insights from both human and mouse models. We find that PKM2 enhances PD-L1 expression while inhibiting PD-L2, a dual regulatory mechanism that facilitates immune evasion. Knockdown and overexpression experiments revealed GATA3 as a key mediator. PKM2 knockout reduced GATA3 level, leading to decreased PD-L1 and increased PD-L2 expression. Chromatin immunoprecipitation (ChIP)-qPCR demonstrates that GATA3 functions as a direct transcription factor capable of binding to the promoters of PD-L1 and PD-L2. In silico analyses of 81 esophageal squamous cell carcinoma (ESCC) cases from the TCGA database demonstrate that PKM2 mRNA is unrelated to PD-L1 and PD-L2 expression but is negatively correlated with CD8 + T-cell infiltration in ESCC. To further validate these findings, we establish a xenograft model using immune-competent C57/BL6N mice, where knockdown of PKM2 results in significant downregulation of both PD-L1 and PD-L2 expression. Collectively, these findings underscore the divergent roles of PKM2 in regulating immune checkpoint expression in human and mouse cancer models and suggest that targeting the PKM2-GATA3 axis could enhance cancer immunotherapy by fine-tuning PD-L1 and PD-L2 levels.
Insights
Pyruvate kinase M2 (PKM2) differentially regulates immune checkpoints PD-L1 and PD-L2 via GATA3, impacting cancer immune evasion. Targeting this PKM2-GATA3 axis may improve cancer immunotherapy outcomes.
Area of Science:
- Immunology
- Molecular Biology
- Cancer Research
Background:
- Immune checkpoints like PD-L1 and PD-L2 are crucial for cancer cells to evade immune detection by suppressing T-cell activity.
- While PD-L1's role is established, PD-L2's function in immune evasion is less understood.
- Pyruvate kinase M2 (PKM2), a metabolic enzyme, is implicated in immune checkpoint regulation, but its specific influence on PD-L1 and PD-L2 is not well-defined.
Purpose of the Study:
- To investigate the role of pyruvate kinase M2 (PKM2) in modulating the expression of immune checkpoint molecules PD-L1 and PD-L2.
- To elucidate the involvement of the transcription factor GATA3 in the PKM2-mediated regulation of PD-L1 and PD-L2.
- To explore the implications of the PKM2-GATA3 axis in cancer immune evasion using human and mouse models.
Main Methods:
- Utilized knockdown and overexpression experiments to assess the function of PKM2 and GATA3.
- Employed Chromatin Immunoprecipitation (ChIP)-qPCR to determine GATA3's direct binding to PD-L1 and PD-L2 gene promoters.
- Conducted in silico analyses on esophageal squamous cell carcinoma (ESCC) patient data (TCGA database) and established a mouse xenograft model.
Main Results:
- PKM2 was found to enhance PD-L1 expression while simultaneously inhibiting PD-L2 expression, a dual mechanism promoting immune evasion.
- PKM2 knockout led to reduced GATA3 levels, resulting in decreased PD-L1 and increased PD-L2 expression.
- GATA3 acts as a direct transcription factor binding to the promoters of both PD-L1 and PD-L2.
- In ESCC, PKM2 mRNA levels did not correlate with PD-L1/PD-L2 but negatively correlated with CD8+ T-cell infiltration.
- PKM2 knockdown in a mouse xenograft model significantly downregulated both PD-L1 and PD-L2 expression.
Conclusions:
- PKM2 exhibits divergent roles in regulating PD-L1 and PD-L2 expression across human and mouse cancer models.
- The PKM2-GATA3 signaling pathway is a key regulator of immune checkpoint molecules PD-L1 and PD-L2.
- Targeting the PKM2-GATA3 axis presents a potential therapeutic strategy to enhance cancer immunotherapy by modulating PD-L1 and PD-L2 levels.
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