Nutrient sensor O-GlcNAc transferase regulates breast cancer tumorigenesis through targeting of the oncogenic transcription factor FoxM1

Abstract

Cancer cells upregulate glycolysis, increasing glucose uptake to meet energy needs. A small fraction of a cell's glucose enters the hexosamine biosynthetic pathway (HBP), which regulates levels of O-linked b-N-acetylglucosamine (O-GlcNAc), a carbohydrate posttranslational modification of diverse nuclear and cytosolic proteins. We discovered that breast cancer cells upregulate the HBP, including increased O-GlcNAcation and elevated expression of O-GlcNAc transferase (OGT), which is the enzyme catalyzing the addition of O-GlcNAc to proteins. Reduction of O-GlcNAcation through RNA interference of OGT in breast cancer cells leads to inhibition of tumor growth both in vitro and in vivo and is associated with decreased cell-cycle progression and increased expression of the cellcycle inhibitor p27 Kip1 . Elevation of p27Kip1 was associated with decreased expression and activity of the oncogenic transcription factor FoxM1, a known regulator of p27 Kip1 stability through transcriptional control of Skp2. Reducing O-GlcNAc levels in breast cancer cells decreased levels of FoxM1 protein and caused a decrease in multiple FoxM1-specific targets, including Skp2. Moreover, reducing O-GlcNAcation decreased cancer cell invasion and was associated with the downregulation of matrix metalloproteinase-2, a known FoxM1 target. Finally, pharmacological inhibition of OGT in breast cancer cells had similar anti-growth and anti-invasion effects. These findings identify O-GlcNAc as a novel mechanism through which alterations in glucose metabolism regulate cancer growth and invasion and suggest that OGT may represent novel therapeutic targets for breast cancer.

Global Analysis of O-GlcNAc Glycoproteins in Activated Human T Cells

“…Our observation of higher O-GlcNAc levels in activated T cells, which undergo rapid division, suggests that O-GlcNAc levels are positively correlated with cell proliferation. Indeed, elevated O-GlcNAc levels also were reported in cancer (31,66,67). Consistent with previous work using genetic approaches (25,38), we show in this study with a specific inhibitor that OGT is important for T cell function, because blocking its activity suppressed IL-2 production and cell proliferation.…”

Dynamic O-GlcNAcylation and its roles in the cellular stress response and homeostasis

“…Several OGT inhibitors have also been isolated that work well in vitro (Gross et al 2005), and thus far these have been useful in isolated neonatal cardiomyocytes (5 μM; ) and breast cancer cells (200 μM;Caldwell et al 2010). A more recent study has focused on synthesizing novel OGT inhibitors with structural analogues to UDPGlcNAc/UDP (Dorfmueller et al 2011).…”

O-Linked β-N-Acetylglucosaminylation (O-GlcNAcylation) in Primary and Metastatic Colorectal Cancer Clones and Effect of N-Acetyl-β-d-glucosaminidase Silencing on Cell Phenotype and Transcriptome

“…(22), and alterations in O-GlcNAcylation were found to contribute to tumorigenesis (7). In human colon cancer cell lines, increased UDP-GlcNAc levels led to disruptions of cell growth and differentiation (8).…”

“…Overexpression of both OGT and OGA disrupted mitosis (possibly by disrupting cyclin expression), and in the case of OGT, overexpression also increased polyploidy, a characteristic of cancer cells (9). Increased OGlcNAcylation and OGT levels were reported in various types of cancer, including colon, lung, and breast cancers (7,10,11), and were found to correlate with the progression of tumorigenesis (10 -12). O-GlcNAcylation was also found to directly affect key proteins involved in tumorigenesis.…”

“…colon, breast, lung, and liver), O-GlcNAcylation was found to be enhanced, especially in advanced tumors, and in some cases it was linked to cellular features relevant to metastasis, e.g. invasion and migration (7,10,11,19).…”