Tumors utilize aerobic glycolysis to support growth and invasion. However, the molecular mechanisms that link metabolism with invasion are not well understood. The nutrient sensor O-linked-β-N-acetylglucosamine (O-GlcNAc) transferase (OGT) modifies intracellular proteins with N-acetylglucosamine. Cancers display elevated O-GlcNAcylation and suppression of O-GlcNAcylation inhibits cancer invasion and metastasis. Here, we show that the regulation of cancer invasion by OGT is dependent on the NAD+-dependent deacetylase SIRT1. Reducing O-GlcNAcylation elevates SIRT1 levels and activity in an AMPK-dependent manner. Reduced O-GlcNAcylation in cancer cells leads to SIRT1-mediated proteasomal degradation of oncogenic transcription factor FOXM1 in a MEK/ERK-dependent manner. SIRT1 is critical for OGT-mediated regulation of FOXM1 ubiquitination and reducing SIRT1 activity reverses OGT-mediated regulation of FOXM1. Moreover, we show that SIRT1 levels are required for OGT-mediated regulation of invasion and metastasis in breast cancer cells. Thus, O-GlcNAcylation is a central component linking metabolism to invasion and metastasis via a SIRT1/ /FOXM1 axis.

Elevated O-GlcNAcylation is associated with disease states such as diabetes and cancer. O-GlcNAc transferase (OGT) is elevated in multiple cancers and inhibition of this enzyme genetically or pharmacologically inhibits oncogenesis. Here we show that O-GlcNAcylation modulates lipid metabolism in cancer cells. OGT regulates expression of the master lipid regulator the transcription factor sterol regulatory element binding protein 1 (SREBP-1) and its transcriptional targets both in cancer and lipogenic tissue. OGT regulates SREBP-1 protein expression via AMP Activated protein kinase (AMPK). SREBP-1 is critical for OGT-mediated regulation of cell survival and of lipid synthesis, as overexpression of SREBP-1 rescues lipogenic defects associated with OGT suppression, and tumor growth in vitro and in vivo. These results unravel a previously unidentified link between O-GlcNAcylation, lipid metabolism and the regulation of SREBP-1 in cancer and suggests a crucial role for O-GlcNAc signaling in transducing nutritional state to regulate lipid metabolism.

Breast tumors are heterogeneous and composed of different subpopulation of cells, each with dynamic roles that can change with stage, site, and microenvironment. Cellular heterogeneity is, in part, due to cancer stem-like cells (CSC) that share properties with stem cells and are associated with treatment resistance. CSCs rewire metabolism to meet energy demands of increased growth and biosynthesis. O-GlcNAc transferase enzyme (OGT) uses UDP-GlcNAc as a substrate for adding O-GlcNAc moieties to nuclear and cytoplasmic proteins. OGT/O-GlcNAc levels are elevated in multiple cancers and reducing OGT in cancer cells blocks tumor growth. Here, we report that breast CSCs enriched in mammosphere cultures contain elevated OGT/O-GlcNAcylation. Inhibition of OGT genetically or pharmacologically reduced mammosphere forming efficiency, the CD44 H /CD24 L , NANOGþ, and ALDHþ CSC population in breast cancer cells. Conversely, breast cancer cells overexpressing OGT increased mammosphere formation, CSC populations in vitro, and also increased tumor initiation and CSC frequency in vivo. Furthermore, OGT regulates expression of a number of epithelial-to-mesenchymal transition and CSC markers including CD44, NANOG, and c-Myc. In addition, we identify Kr€ uppel-like factor 8 (KLF8) as a novel regulator of breast cancer mammosphere formation and a critical target of OGT in regulating CSCs.Implications: These findings demonstrate that OGT plays a key role in the regulation of breast CSCs in vitro and tumor initiation in vivo, in part, via regulation of KLF8, and thus inhibition of OGT may serve as a therapeutic strategy to regulate tumor-initiating activity.

Elevated O-GlcNAcylation is emerging as a general characteristic of most cancers. Although O-GlcNAcylation can regulate many cell biological pathways, recent evidence suggests that it is a key regulator of metabolic pathways including glycolysis in cancer cells. This review summarizes our current understanding of how O-GlcNAcylation regulates glycolytic pathways and contributes to alterations in cancer cell metabolism.

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