Lysine lactylation regulates ATF4-mediated stress responses under glucose starvation in canine hemangiosarcoma

Hemangiosarcoma (HSA) is a malignant endothelial tumor that occurs frequently in dogs but is rare in other species including humans. Due to its aggressive behavior and limited therapeutic options, patient prognosis is generally poor. Tumor cells produce excess lactate via anerobic glycolysis, and it regulate gene expressions through histone lactylation in response to cellular metabolic conditions. However, how histone lactylation affects biological behavior under glucose-limited conditions in HSA remains unknown. Here, we established canine HSA cell lines and patient-derived xenograft models and investigated the role of histone lactylation during glucose deprivation. HSA cells exhibited higher global histone lactylation levels than normal endothelial cells. Although glucose restriction reduced global histone lactylation levels, Cleavage Under Targets and Tagmentation (CUT&Tag) analysis revealed enrichment of lactylation peaks at transcription-start sites (TSSs) of ATF4-regulated stress-response, asparagine biosynthesis and immune-related genes. TSSs of stress-response genes were co-occupied with RNA polymerase II phosphorylated at serine 5 and showed increased gene expressions, suggesting that lactylation at TSSs activated transcription under glucose-deprived conditions. [U- ¹³ C]glutamine tracing indicated that HSA cells synthesized asparagine from glutamine when glucose was scarce. Asparagine supplementation modestly activated cell proliferation. In HSA patient tissues, H3K18la levels were heterogeneous, and M2-like macrophages preferentially infiltrated tumor regions showing low histone lactylation levels. Consistently, glucose-starved HSA cells attracted macrophages and induced M2-like polarization in vitro . These findings demonstrate that lysine lactylation, possibly histone lactylation, persists even under glucose-deprived conditions and regulate transcription that supports tumor cell survival and fosters a pro-tumor microenvironment.