S100A8 lactylation at K23/K36 reduces RNF5-dependent degradation and promotes colorectal cancer progression.

Colorectal cancer (CRC) progression is deeply influenced by the acidic, lactate-rich tumor microenvironment. While the calcium-binding protein S100A8 is a known oncogenic driver and prognostic biomarker in CRC, the mechanisms governing its protein stability remain incompletely understood. This study investigated the competitive interplay between lactate-induced lactylation and RNF5-mediated ubiquitination of S100A8. Reanalysis of clinical lactylomic datasets and survival analyses revealed that S100A8 is heavily lactylated in colon cancer tissues and its elevated expression correlates with poor patient prognosis. Through immunoprecipitation and mutagenesis studies in HCT116 and HT-29 colon cancer cells, this study identified lysine residues K23 and K36 as the primary lactylation sites on S100A8. Lactate stimulation significantly enhanced S100A8 lactylation, which consequently increased its protein stability. Mechanistically, lactylation at K23 and K36 impaired the interaction between S100A8 and the E3 ubiquitin ligase RNF5, thereby suppressing RNF5-mediated ubiquitination and subsequent proteasomal degradation. To validate this crosstalk, an S100A8 K23R/K36R mutant was generated. This mutant exhibited enhanced intrinsic stability by evading ubiquitination, robustly promoted CRC cell proliferation, and effectively reversed the tumor-suppressive effects of RNF5 both in vitro and in murine xenograft models. Collectively, findings of this study uncover a novel metabolic-post-translational modification crosstalk in which tumor-derived lactate stabilizes S100A8 via lactylation, shielding it from RNF5-mediated degradation and ultimately driving CRC pathogenesis.