Extracellular granzyme K enhances PD-L1 transcription and stability via F2RL1 activation to facilitate tumor immune evasion in lung adenocarcinoma

Background Granzyme K (GZMK) is a serine protease known for its perforin-dependent cytotoxicity. However, the non-cytotoxic role of GZMK in lung adenocarcinoma (LUAD) remains largely elusive. Methods Multiomics datasets were integrated to investigate the clinical relevance of GZMK and its association with programmed death-ligand 1 (PD-L1) in LUAD. Recombinant human GZMK (rhGzmK) was applied in tumor-CD8 + T cell co-culture systems, with its effects on PD-L1 expression and CD8 + T-cell function evaluated via flow cytometry. Key signaling proteins were analyzed by Western blotting. To evaluate the therapeutic potential of GZMK inhibition, a selective GZMK inhibitor was combined with anti-programmed cell death protein 1 (anti-PD-1) therapy in both C57BL/6 and human peripheral blood mononuclear cells (huPBMC)-reconstituted NVSG humanized mouse models. Finally, multiplex immunofluorescence analysis was conducted on paired pretreatment and post-treatment specimens from a clinical cohort of patients with LUAD receiving immunotherapy to assess the spatial dynamics of GZMK expression in response to treatment. Results GZMK upregulated PD-L1 expression on tumor cells and enhanced PD-L1/PD-1 binding. Furthermore, GZMK promoted CD8 + T-cell dysfunction through the induction of apoptosis, the promotion of CD8 + T-cell exhaustion and suppression of proliferation. Mechanistically, cleavage of F2R-like trypsin receptor 1 (F2RL1) by GZMK activated the AKT Serine/Threonine Kinase (AKT) /glycogen synthase kinase-3β/β-catenin and Janus kinase 2/signal transducer and activator of transcription 1 (JAK2/STAT1) pathways, triggering nuclear accumulation of β-catenin and phosphorylated STAT1, which ultimately drove PD-L1 transcription. Additionally, F2RL1 signaling upregulated COPS8, stabilizing PD-L1 through inhibition of its ubiquitin-mediated degradation. In vivo, pharmacological inhibition of GZMK synergized with anti-PD-1 therapy to suppress tumor growth and enhance CD8 + T-cell infiltration and function. Clinically, high baseline GZMK expression correlated with an improved response to immunotherapy, and anti-PD-1 treatment modulated the spatial distribution of GZMK within the tumor microenvironment. Conclusion In the absence of perforin, GZMK acquires an immunosuppressive function through F2RL1 activation on tumor cells, which in turn promotes the formation of an immune-suppressive niche. Accordingly, combined targeting of the GZMK/F2RL1 axis and the PD-1/PD-L1 pathway represents a promising synergistic strategy to overcome immune evasion in LUAD.