Supplementary Material for: The IRE1α-endonuclease plays a dual role in regulating the XBP1/miRNA-34a axis and PD-1 expression within Natural Killer cells in Hodgkin Lymphoma

Introduction: Hodgkin Lymphoma (HL) is deficient in Major Histocompatibility Complex-class I, rendering it susceptible to anti-tumoral immunity by Natural Killer (NK)-cells. Despite the functional impairment of PD-1+ NK-cells in HL, the underlying mechanisms of NK-cell dysfunction remain unclear. Methods: This study involved 14 HL patients and SNK10/KHYG-1 cell lines to assess NK-cell activation against cancer cells. Activation was measured through transcript (PCR) and protein expression (flow cytometry). Regulatory mechanisms associated with IRE1α activation were validated through knock-down and luciferase reporter assays. Results: Our findings reveal a novel role for IRE1α-endonuclease in fine-tuning NK-cell effector functions by orchestrating the XBP1s/microRNA-34a-5p/PD-1 axis. When NK-cells encounter cancer cells, IRE1α-endonuclease activates the decay of microRNA-34a-5p, resulting in increased expression of XBP1s and PD-1. IRE1α-endonuclease activation enhances NK-cells function while promoting PD-1 expression. In turn, PD-1 is directly regulated by microRNA-34a-5p, which binds to the 3’UTR of PD-1 transcript to repress PD-1 protein on the NK-cell surface. Importantly, IRE1α-pathway activation is impaired in NK-cells from HL patients. Conclusion: The IRE1α-endonuclease emerges as a key player, simultaneously regulating the XBP1s/microRNA-34a-5p/PD-1 axis in NK-cells, a process disrupted in HL. Targeting the IRE1α-pathway holds promise as a therapeutic strategy to optimise NK-cell functions in Hodgkin Lymphoma treatments.