Lactylation increases the stability of <scp>RBM15</scp> to drives <scp>m6A</scp> modification in non‐small‐cell lung cancer cells

Emerging evidence supports the involvement of N6-Methyladenosine (m6A) modification in the etiology and progression of lung adenocarcinoma (LUAD), highlighting its potential as a therapeutic target. RNA-binding protein 15 (RBM15) is a well-known m6A writer protein that enhances global m6A methylation levels by associating with the METTL3-WTAP complex. Previous studies have demonstrated that RBM15 is upregulated and exerts an oncogenic role in LUAD by promoting the N6-methyladenosine-mediated mRNA stability. However, the regulatory mechanisms of RBM15 remain elusive. In this study, we observed that L-lactate upregulates RBM15 protein levels in non-small-cell lung cancer cell lines A549 and H23 in a time- and dosage-dependent manner. Furthermore, we discovered that lactate uptake mediated by Monocarboxylate transporter 1 (MCT1) is essential for RBM15 induction. Subsequent investigations revealed that L-lactate promotes lactylation of RBM15 majorly at Lys850 (K850), while histone deacetylase 3 (HDAC3) acts as the delactylase for RBM15. Importantly, lactylation of RBM15 stabilizes itself by inhibiting proteasome-mediated ubiquitin degradation. Mutation of the lactylation site K850R disrupts the association between RBM15 and METTL3, leading to a reduction in global m6A levels. Moreover, K850R significantly abrogated RBM15-mediated cell proliferation and migration in LUAD cells. Collectively, these findings unveil lactylation as a novel regulatory mechanism affecting both stability and m6A methylation activity of RBM15 in LUAD cells.