PGLYRP4 sensitizes oral squamous cell carcinoma to ferroptosis by targeting GPX4: A novel molecular mechanism for overcoming therapeutic resistance

Oral squamous cell carcinoma (OSCC) remains challenging due to therapeutic resistance and high recurrence, underscoring the need for novel therapeutic targets and prognostic biomarkers. Peptidoglycan recognition protein 4 (PGLYRP4), an innate immune molecule, has been correlated with improved prognosis in head and neck cancer, yet its functional role in OSCC remains undefined. Here, we characterized the expression pattern, clinical significance, biological function, and mechanism of PGLYRP4 in OSCC, focusing on its role in ferroptosis regulation. PGLYRP4 expression was analyzed using the TCGA database, single-cell RNA sequencing data, and immunohistochemistry on tissue microarrays comprising 133 OSCC and 39 normal oral mucosa samples. Functional roles in proliferation, cell death, and ferroptosis were examined in CAL27 and HN6 cells using pharmacological inducers (RSL3, Erastin, ML162) and immune-derived ferroptotic signals (IFN-γ plus arachidonic acid). Mechanistic studies, including RT-qPCR, cycloheximide chase assays, and pharmacological inhibition of degradation pathways and palmitoylation, were performed to elucidate PGLYRP4-mediated regulation of GPX4. PGLYRP4 transcript and PGLYRP4 protein are markedly elevated in OSCC specimens, with expression predominantly confined to malignant cells by scRNA-seq. High PGLYRP4 expression correlates with favorable overall survival in head and neck squamous cell carcinoma (HNSCC) patients. Functionally, PGLYRP4 knockdown promotes proliferation and colony formation while reducing cell death; conversely, overexpression suppresses growth and enhances cell death. PGLYRP4 overexpression leads to elevated intracellular Fe 2+ levels and enhances cellular sensitivity to ferroptosis-inducing agents as well as immune-derived ferroptotic signals, rescued by ferrostatin-1. Mechanistically, PGLYRP4 selectively downregulates GPX4 protein with no impact on its mRNA or on other ferroptosis regulators. Genetic rescue confirms that GPX4 depletion abolishes PGLYRP4 knockdown-mediated ferroptosis resistance. Pharmacological studies reveal that PGLYRP4 promotes GPX4 degradation via the lysosome rather than the proteasome, and this process is linked to GPX4 palmitoylation status. This study identifies PGLYRP4 as a novel favorable prognostic biomarker and a positive regulator of ferroptosis in OSCC. PGLYRP4 sensitizes OSCC cells to ferroptosis by promoting lysosomal degradation of GPX4 in a palmitoylation-associated manner, establishing a previously unrecognized PGLYRP4-GPX4 regulatory axis that links innate immunity to ferroptosis execution. PGLYRP4 expression carries dual translational promise, serving as both a prognostic marker and a predictive indicator for guiding ferroptosis-based therapies. Assessing PGLYRP4 levels may help stratify OSCC patients, particularly those with HPV-negative or TP53 -mutant tumors, eligible for ferroptosis-inducing agents. Intervening in this regulatory axis provides a viable approach for modulating ferroptosis sensitivity and circumventing treatment refractoriness in OSCC. • PGLYRP4 is a novel favorable prognostic biomarker in OSCC. • PGLYRP4 sensitizes OSCC cells to ferroptosis by targeting GPX4. • PGLYRP4 promotes GPX4 lysosomal degradation in a palmitoylation-dependent manner. • PGLYRP4-GPX4 axis links innate immunity to therapy resistance.