Lactylation of HMGB1 at K177 Drives Nuclear Export of TIAR to Promote Hypoxia-Induced Stress Granule Formation.

HMGB1, one of the most abundant nuclear non-histone proteins, also performs extracellular functions, and its nuclear export mechanisms have been extensively studied. Here, a novel mechanism of nuclear export for HMGB1 driven by lactylation is proposed. In addition, it is revealed that hypoxia-induced lactylation of HMGB1 facilitates its nuclear export in a complex with TIAR, promoting stress granule (SG) formation in the cytosol. Mass spectrometry revealed 12 lysine residues in HMGB1 undergoing lactylation, with K172 and K177 being the most susceptible. Functional studies using lysine-to-arginine mutants (K→R) demonstrated that lactylation at K177 is crucial for HMGB1-TIAR complex export, as K177R mutation completely blocked this export and subsequent SG formation. Notably, this lactylation-mediated mechanism is specific to hypoxic stress, while other stressors, such as sodium arsenite exposure and heat shock, triggered TIAR nuclear export and SG assembly independently of HMGB1. These findings reveal a previously unrecognized role of HMGB1 lactylation in mediating nuclear export and SG formation under hypoxia.