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Molecular cancer research : MCR

mTOR/MYC Axis Regulates O-GlcNAc Transferase Expression and O-GlcNAcylation in Breast Cancer.


PMID 25636967

Abstract

Cancers exhibit altered metabolism characterized by increased glucose and glutamine uptake. The hexosamine biosynthetic pathway (HBP) uses glucose and glutamine, and directly contributes to O-linked-β-N-acetylglucosamine (O-GlcNAc) modifications on intracellular proteins. Multiple tumor types contain elevated total O-GlcNAcylation, in part, by increasing O-GlcNAc transferase (OGT) levels, the enzyme that catalyzes this modification. Although cancer cells require OGT for oncogenesis, it is not clear how tumor cells regulate OGT expression and O-GlcNAcylation. Here, it is shown that the PI3K-mTOR-MYC signaling pathway is required for elevation of OGT and O-GlcNAcylation in breast cancer cells. Treatment with PI3K and mTOR inhibitors reduced OGT protein expression and decreased levels of overall O-GlcNAcylation. In addition, both AKT and mTOR activation is sufficient to elevate OGT/O-GlcNAcylation. Downstream of mTOR, the oncogenic transcription factor c-MYC is required and sufficient for increased OGT protein expression in an RNA-independent manner and c-MYC regulation of OGT mechanistically requires the expression of c-MYC transcriptional target HSP90A. Finally, mammary tumor epithelial cells derived from MMTV-c-myc transgenic mice contain elevated OGT and O-GlcNAcylation and OGT inhibition in this model induces apoptosis. Thus, OGT and O-GlcNAcylation levels are elevated via activation of an mTOR/MYC cascade. Evidence indicates OGT as a therapeutic target in c-MYC-amplified cancers.