Precision post-translational modification of PML defines neuroblastoma clinical behaviour

Promyelocytic leukaemia protein (PML), a key regulator of nuclear architecture and cellular homeostasis, is increasingly recognised for its tumour-suppressive functions. In neuroblastoma (NBL), a clinically heterogeneous and aggressive paediatric malignancy, the prognostic role of PML and its post-translational modifications remains largely unexplored.

We investigated the prognostic and predictive significance of PML expression and its site-specific phosphorylation at serine 518 (S⁵¹⁸) in a cohort of 121 NBL patients. Custom-synthesised antibodies and high-resolution tissue microarrays were used to quantitatively profile PML and pPML S⁵¹⁸ expression via automated immunohistochemistry and digital image analysis. Survival outcomes were assessed using Kaplan-Meier and Cox regression analyses. Mechanistic insights were obtained using reverse‑engineered phospho‑mutant models enabling selective modulation of S518 phosphorylation.

Our findings reveal a striking inverse relationship between PML abundance and S⁵¹⁸ phosphorylation, with low PML and high pPML S⁵¹⁸ strongly associated with advanced disease stage, metastasis, relapse, and therapy resistance. Survival analyses demonstrate that low PML predicts poor overall survival (OS), progression-free survival (PFS), and relapse-free survival (RFS), while elevated pPML S⁵¹⁸ correlates with significantly worse outcomes across all endpoints. Multivariate Cox regression confirms both markers as independent predictors of survival. Mechanistically, reverse-engineered phospho-mutant models that enable selective switch-on/switch-off modulation of S⁵¹⁸ phosphorylation demonstrated that phosphorylation at this site reduces PML abundance and promotes invasive cellular phenotype.

PML loss and site-specific phosphorylation of PML at S⁵¹⁸ represent robust prognostic and predictive biomarkers with potential utility in risk stratification. Targeting PML phosphorylation may offer a promising translational strategy to improve therapeutic efficacy in high‑risk NBL.

PML depletion is a defining feature of aggressive neuroblastoma and is associated with advanced stage, metastasis and relapse. S⁵¹⁸ phosphorylation emerges as the dominant post translational trigger committing PML to ubiquitin mediated degradation. High pPML S⁵¹⁸ and low PML form a powerful prognostic axis that independently predicts OS, PFS, and RFS in neuroblastoma. PML loss and S⁵¹⁸ phosphorylation define a molecular framework of heightened cellular plasticity underlying aggressive clinical behavior.