Lactate Dehydrogenase C4 Accelerates Triple-Negative Breast Cancer Progression by Promoting Acetyl-CoA Acyltransferase 2 Lactylation to Increase Free Fatty Acid Accumulation.

Lactate-induced protein lysine (K) lactylation is inherently connected to cellular metabolism and is implicated in oncogenesis. As a crucial glycolytic enzyme in lactate metabolism, lactate dehydrogenase C4 (LDHC4) has undefined yet potentially significant biological functions and mechanistic roles in triple-negative breast cancer (TNBC) that warrant further investigation. This study aims to determine whether and how LDHC4 affects TNBC progression by regulating protein lactylation. LDHC4 expression in human TNBC tissues and adjacent nontumor tissues is analyzed through immunoblotting and immunohistochemistry (IHC). Functional experiments verified the biological features of LDHC4 in human TNBC cells both in vitro and in vivo (subcutaneous, orthotopic, and pulmonary metastatic mouse models). 4D label-free lactylproteome expression analysis (4D-LFQP-LA), immunoblotting, and immunoprecipitation are utilized to confirm lactylation at specific lysine sites in acetyl-CoA acyltransferase 2 (ACAA2) following LDHC4 induction. Targeted lipidomic analysis is performed to characterize ACAA2-induced metabolite alterations. Immunoblotting, immunofluorescence, and transmission electron microscopy are performed to investigate the mechanisms underlying LDHC4-induced ACAA2 lactylation and tumor progression in TNBC. LDHC4 expression is upregulated in TNBC, and LDHC4 is an independent predictive factor for prognosis. Both in vitro and in vivo experiments demonstrated that LDHC4 promotes TNBC progression. Subsequent mechanistic investigation revealed that LDHC4 enhances the lactylation of ACAA2 at K214, resulting in increased ACAA2 catalytic activity. This increase in ACAA2 activity accelerates fatty acid (FA) metabolism, promotes TNBC progression both in vitro and in vivo, and leads to increased free fatty acid (FFA) generation and accumulation. The increase in FFAs in turn induces autophagy and promotes cell cycle activity in TNBC cells, thereby promoting TNBC progression. The findings reveal a novel pathway through which LDHC4 induces ACAA2 lactylation to regulate FA metabolism in TNBC cells, thus promoting TNBC progression, highlighting the critical role of LDHC4 in TNBC progression.