Ets-1 regulates intracellular glutathione levels: key target for resistant ovarian cancer.
BACKGROUND
Ovarian cancer is characterized by high rates of metastasis and therapeutic resistance. Many chemotherapeutic agents rely on the induction of oxidative stress to cause cancer cell death, thus targeting redox regulation is a promising strategy to overcome drug resistance.


METHODS
We have used a tetracycline-inducible Ets-1 overexpression model derived from 2008 ovarian cancer cells in the present study. To examine the role of Ets-1 in glutathione regulation we have measured intracellular reactive oxygen species and glutathione levels, as well as glutathione peroxidase enzyme activity. Glutathione synthesis was limited using transsulfuration or Sx(c)- pathway blocking agents, and glutamate release was measured to confirm Sx(c)- blockade. Cell viability following drug treatment was assessed via crystal violet assay. Oxidative stress was induced through glucose oxidase treatment, which produces hydrogen peroxide by glucose oxidation. The protein expressions of redox-related factors were measured through western blotting.


RESULTS
Overexpression of Ets-1 was associated with decreased intracellular ROS, concomitantly with increased intracellular GSH, GPX antioxidant activity, and Sx(c)- transporter activity. Under basal conditions, inhibition of the transsulfuration pathway resulted in decreased GSH levels and GPX activity in all cell lines, whereas inhibition of Sx(c)- by sulfasalazine decreased GPX activity in Ets-1-expressing cells only. However, under oxidative stress the intracellular GSH levels decreased significantly in correlation with increased Ets-1 expression following sulfasalazine treatment.


CONCLUSIONS
In this study we have identified a role for proto-oncogene Ets-1 in the regulation of intracellular glutathione levels, and examined the effects of the anti-inflammatory drug sulfasalazine on glutathione depletion using an ovarian cancer cell model. The findings from this study show that Ets-1 mediates enhanced Sx(c)- activity to increase glutathione levels under oxidative stress, suggesting that Ets-1 could be a promising putative target to enhance conventional therapeutic strategies.
Meghan L
ML
Verschoor
Department of Pathology and Molecular Medicine, McMaster University, 1280 Main Street W, Hamilton, Ontario 12943, Canada. singhg@mcmaster.ca.
Gurmit
G
Singh
D027182:Amino Acid Transport System y+ / Q000378:metabolism; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D005260:Female; D015870:Gene Expression; D005978:Glutathione / Q000378:metabolism*; D005979:Glutathione Peroxidase / Q000378:metabolism; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D018384:Oxidative Stress; D000090063:Proto-Oncogene Mas; D050784:Proto-Oncogene Protein c-ets-1 / Q000502:physiology*; D012460:Sulfasalazine / Q000494:pharmacology; D000094765:Glutathione Peroxidase GPX1
D027182:Amino Acid Transport System y+; D000894:Anti-Inflammatory Agents, Non-Steroidal; C494041:ETS1 protein, human; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D050784:Proto-Oncogene Protein c-ets-1; C118895:SLC7A11 protein, human; D012460:Sulfasalazine; C117436:GPX2 protein, human; D005979:Glutathione Peroxidase; D005978:Glutathione; D000094765:Glutathione Peroxidase GPX1; C000722067:GPX1 protein, human