O-GlcNAcylation of Keratin 18 coordinates TCA cycle to promote cholangiocarcinoma progression

Abstract

Glycosylation in human cholangiocarcinoma (CCA) actively contributes to pathophysiological steps of tumor progression. Of note is the dynamic modification of proteins by O-linked {beta}-N-acetyl-glucosamine (O-GlcNAcylation) that modulates various tumor-associated biological activities. By using a cutting-edge chemical proteomic methodology for intact glycopeptide analysis, we show herein that O-GlcNAcylation of Keratin 18 (K18) coordinates the tricarboxylic acid (TCA) cycle enzymes, namely isocitrate dehydrogenases (IDHs), to promote CCA progression. Mechanistically, site-specific O-GlcNAcylation of K18 on Ser 30 stabilizes K18, which benefits the expression of cell cycle checkpoints to enhance cell cycle progression and cell growth. Interaction with IDHs down-regulates the level of citrate and isocitrate, while up-regulates the level of -ketoglutarate (-KG). Our study thus expands the current understanding of protein O-GlcNAcylation, and adds another dimension of complexity to post-translational control over metabolism and tumorigenesis.