Abstract
RGS10 regulates ovarian cancer cell growth and survival, and RGS10 expression is suppressed in cell models of ovarian cancer chemoresistance. However, the mechanisms governing RGS10 expression in ovarian cancer are poorly understood. Here we report RGS10 suppression in primary ovarian cancer and CAOV-3 ovarian cancer cells compared to immortalized ovarian surface epithelial (IOSE) cells, and in A2780-AD chemoresistant cells compared to parental A2780 cells. RGS10-1 and RGS10-2 transcripts are expressed in ovarian cancer cells, but only RGS10-1 is suppressed in A2780-AD and CAOV-3 cells, and the RGS10-1 promoter is uniquely enriched in CpG dinucleotides. Pharmacological inhibition of DNA methyl-transferases (DNMTs) increased RGS10 expression, suggesting potential regulation by DNA methylation. Bisulfite sequencing analysis identified a region of the RGS10-1 promoter with significantly enhanced DNA methylation in chemoresistant A2780-AD cells relative to parental A2780 cells. DNA methylation in CAOV-3 and IOSE cells was similar to A2780 cells. More marked differences were observed in histone acetylation of the RGS10-1 promoter. Acetylated histone H3 associated with the RGS10-1 promoter was significantly lower in A2780-AD cells compared to parental cells, with a corresponding increase in histone deacetylase (HDAC) enzyme association. Similarly, acetylated histone levels at the RGS10-1 promoter were markedly lower in CAOV-3 cells compared to IOSE cells, and HDAC1 binding was doubled in CAOV-3 cells. Finally, we show that pharmacological inhibition of DNMT or HDAC enzymes in chemoresistant A2780-AD cells increases RGS10 expression and enhances cisplatin toxicity. These data suggest that histone de-acetylation and DNA methylation correlate with RGS10 suppression and chemoresistance in ovarian cancer. Markers for loss of RGS10 expression may identify cancer cells with unique response to therapeutics.
Highlights
Cancer cells exploit multiple receptor-mediated growth and survival signaling pathways to evade normal quiescence and cell death responses
To determine if Regulator of G-Protein Signaling 10 (RGS10) is downregulated in primary ovarian cancer cells, we immunoblotted lysates from the benign, immortalized immortalized ovarian surface epithelial (IOSE) cell and from six primary epithelial ovarian cancer cell samples isolated from patient ascites (Figure 1A)
RGS10 protein expression was markedly lower in cells from each patient, suggesting that RGS10 expression is suppressed in clinical ovarian cancer
Summary
Cancer cells exploit multiple receptor-mediated growth and survival signaling pathways to evade normal quiescence and cell death responses. RGS10 transcript expression is downregulated in multiple models of acquired chemoresistance in ovarian cancer, and RGS10 expression levels alter ovarian cancer cell sensitivity to cisplatin and taxane cytotoxicity [10] These observations suggest that suppression of RGS10 expression may contribute to ovarian cancer progression and the development of chemoresistance by amplifying GPCR-mediated growth and survival signaling pathways. DNA methylation and DNMT expression increase in ovarian cancer progression [22], and histone deacetylases (HDACs) are overexpressed in ovarian cancer tissues [23] This suggests that epigenetic regulation of RGS genes may contribute to their dynamic expression in cancer progression. Our results suggest that epigenetic histone modifications may contribute to the loss of RGS10 expression in ovarian cancer cells, and that DNA methylation may contribute to further loss of expression during acquired chemoresistance
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