Aberrant O-GlcNAcylation impairs progestin-therapy in endometrial cancer cells by reducing progesterone receptor expression

In the endometrium, progesterone (P4) opposes estrogen-driven growth and is dependent upon adequate expression of progesterone receptors (PR). Cell surface expression of PR and estrogen receptor (ER) in endometrial cancer cells (ECCs) are among determinant factors in predicting the clinical outcome of progestin therapy in patients with endometrial cancer (EC). While the incidence and mortality rates have been decreasing for other cancer, EC rates are on the rise. In particular, higher rates of obesity, a significant risk factor for EC in younger populations, have raised the alarm for the reducing efficacy of fertility-sparing progestin therapy. In obese patients, global β-N-acetylglucosaminylation (O-GlcNAcylation), which naturally plays important roles in regulating protein O-phosphorylation and metabolic status of the cell, is substantially increased. Previous studies have demonstrated the influences of aberrant O-GlcNAcylation on ECC proliferation and metastasis, suggesting a relationship between O-GlcNAcylation and PR expression. This study utilizes the O-GlcNAcase (OGA) inhibitor, Thiamet-G, to augment O-GlcNAcylation in the endometrial cell line, Ishikawa cells. Immunoblotting of whole-cell lysates preliminarily demonstrates decreases in both PR A and PR B concentrations in Thiamet-G treated cells, even in the presence of P4 (p < 0.05, n=3). Additionally, normal cell proliferation is inhibited by P4, and under hyper-O-GlcNAcylation, cell proliferation was returned to normal with or without P4 treatment (p < 0.05, n=4). Further work will analyze the cell cycle progression by flow cytometry and immunocytochemistry for both PR and ER expressions. The outcomes of this study will inform the medical community of the potential benefits of metabolic therapy to maximize the clinical outcome of progestin treatment.

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