Pharmacological Inhibition of O-GlcNAcase Does Not Increase Sensitivity of Glucocorticoid Receptor-Mediated Transrepression.

Glucocorticoid signaling regulates target genes by multiple mechanisms, including the repression of transcriptional activities of nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) though direct protein-protein interactions and subsequent O-GlcNAcylation of RNA polymerase II (pol II). Recent studies have shown that overexpression of O-linked β-N-acetylglucosamine transferase (OGT), which adds an O-linked β-N-acetylglucosamine (O-GlcNAc) group to the C-terminal domain of RNA pol II, increases the transrepression effects of glucocorticoids (GC). As O-GlcNAcase (OGA) is an enzyme that removes O-GlcNAc from O-GlcNAcylated proteins, we hypothesized that the potentiation of GC effects following OGT overexpression could be similarly observed via the direct inhibition of OGA, inhibiting O-GlcNAc removal from pol II. Here we show that despite pharmacological evidence of target engagement by a selective small molecule inhibitor of OGA, there is no evidence for a sensitizing effect on glucocorticoid-mediated effects on TNF-α promoter activity, or gene expression generally, in human cells. Furthermore, inhibition of OGA did not potentiate glucocorticoid-induced apoptosis in several cancer cell lines. Thus, despite evidence for O-GlcNAc modification of RNA pol II in GR-mediated transrepression, our data indicate that pharmacological inhibition of OGA does not potentiate or enhance glucocorticoid-mediated transrepression

Average potency and efficacy of prednisolone are unchanged in the presence of thiamet -G in hPBMCs.

<p>Upper Panels: IC50 and EC50 values were calculated for transrepressed and transactivated genes for each OGA inhibitor dose at 1 μg/mL LPS. Average IC/EC 50 is indicated by the line in box. Thus, a lower IC50 with increasing thiamet-G dose would indicate potentiated transpression by the OGA inhibitor. Lower Panels: Efficacy was determined by taking the difference between top and bottom signals of a prednisolone dose titration curve, and the efficacy ratio represents the effect with OGA inhibitor vs the effect with OGA vehicle control. Thus, a ratio greater than 1 would indicate potentiated transpression by the OGA inhibitor. These values are plotted for all (a) transrepressed (CXCL2, IFIH1, IFIT2, IFIT3, IL1A, IL6, IL1RN, NFKBIZ, SOCS3, TRAF1, PTGS2, CD274, CD40, TNF-α, TNFSF15, IFN-γ, LTA, TRAF4) and (b) transactivated genes (FKBP5, PER1, TSC22D3, ZBTB16, GRASP, IRS2, LPL). Error bars represent standard deviation. IC50/ EC50 datapoints represent n = 1 for each gene.</p

Thiamet-G does not alter potency of prednisolone in transactivated or transrepressed inflammatory genes in hPBMCs.

<p>PBMCs were incubated with a 10 point half- log titration of prednisolone starting at 3 μM and varying concentrations of OGA inhibitor for 30 min at 37°C. Cells were then stimulated with LPS for 2 hr, prior to lysis and shipment to CGL for analysis. Above is representative transrepressed genes (a) PTGS2 (c) TNF-α (e) IFN-γ (f) IFIT3 and transactivated genes (b) FKBP5 (d) TSC22D3 (h) PER1. MGEA5 has no response to prednisolone. Error of magnitude for the IC50 is represented as a 95% confidence interval. Dotted lines are the no-treatment control values. Data points represent n = 1</p

Prednisolone inhibits inflammatory genes that are upregulated by LPS in PBMCs.

<p>Human PBMCs were incubated with varying concentrations of prednisolone (10 nM, 100 nM, 10 μM or DMSO control) with LPS concentrations of 0.01 μg/mL, 1 μg/mL or vehicle. PBMCs were incubated with prednisolone for 30 min at 37°C. Cells were then stimulated with LPS for 2 hr at 37°C. Cell lysate was sent to Covance Genetis Lab (Seattle, WA) for analysis. Gene expression was analyzed in cell lysates with the NanoString nCounter system. Representative genes are used in this figure: transrepressed genes IFN-γ (a) and IFIT3 (b), transactivated gene PER1 (d) and MGEA5 as a negative control (c). Y-axis: Background correction (2) positive control correction and (3) housekeeping gene correction. The housekeeping genes were GAPDH, TUBB, GUSB, HPRT1, and PGK1. Positive control is undisclosed by nanostring. Data points represent n = 3. Error bars represent standard deviation.</p

Inhibition of O-GlcNAcase by thiamet -G increases O-GlcNAcylated protein levels in CD3+ T-cells, CD14+ monocytes and HTS-43 cells.

<p>(a). HTS-32 cells (CD14+) were incubated overnight at varying concentrations of thiamet-G. The cells were then stained with a custom Alexa-fluor 647 RL2 antibody to detect O-GlcNAac levels via flow cytometry, with units being representative as median fluorescent intensity. (b,c) PBMCs were incubated with varying concentrations of thiamet-G overnight. The cells were stained for monocytes (CD14+/CD3-) and T-lymphocytes (CD3+/CD14-) and then stained with the RL2 antibody for O-GlcNAc detection. Units were measured as mean fluorescence intensity. Data points represent n = 3. Error bars represent standard deviation.</p

TNF-α secretion is inhibited in LPS-stimulated PBMCs treated with prednisolone.

<p>PBMCs were treated with increasing concentrations of prednisolone 30 min at 37°C. Cells were then treated with two concentrations (a) 0.01 μg/mL (b) 1 μg/mL of LPS for for four hours 37°C. Supernatant was tested for PBMC TNF-α cytokine release using a mesoscale kit. Data points represent n = 1</p

Thiamet-G does not change the potency of prednisolone in HTS-43 cells expressing a TNF-α promoter.

<p>HTS-43 reporter cells were cultured with increasing concentrations of prednisolone and/or 10 μM thiamet-G for 30 min at 37°C. The cells were then stimulated with both TPA and LPS at concentrations of 5 ng/mL and 0.1 μg/mL respectively, for 20–24 hr. Activity was measured in a beta-lactamase assay as a blue/green ratio. High ratio value indicates increased TNF-α activity. Data points represent n = 2. Error bars represent standard deviation.</p

Thiamet-G does not potentiate the effect of dexamethasone-induced cell apoptosis in steroid resistant cell lines.

<p>Cancer cell lines were exposed to either only dexamethasone, or in addition to 1 μM OGA inhibitor or 50 nM ridaforolimus for 72 hr. Cell lysates were then tested using Cell Titer-Glo for a luminescent signal proportional to ATP presence. Data is represented as a percent viability from cell count from untreated cells. Error bars represent standard deviation. The calculated IC50 and 95% confidence interval are shown. Data points represent n = 3.</p