Expression And Antioxidant Function Of PARP1 In Human Ovarian Cancer

[Background]Ovarian cancer is a common malignant tumor of female reproductive organs. Its mortality rate is higher than other gynecological cancers. Due to absence of symptoms at early stage of ovarian cancer,70% of patients are diagnosed at late stage. So far there are no effective treatments. Debulking surgery followed by platinum-taxane based chemotherapy is the standard of care for patients with advanced stage ovarian cancer and overall 5-year survival is about 30%. Therefore, the study of malignant behavior of ovarian cancer becomes extremely important.PARP is a multifunctional posttranslational modification protein enzyme present in most eukaryotic cells. It is activated by DNA breaks and is considered to be a sensor of DNA damage. It catalyzes the poly ADP-ribosylation of various nucleoproteins, such as histones, RNA polymerase, DNA polymerase and DNA ligase. In recent years, several studies have found that PARP1 is overexpressed in many tumors, such as breast cancer, nasopharyngeal cancer, endometrial cancer and lung cancer, suggesting that PARP1 may be required for the survival of tumor cells. Several studies also have shown that PARP inhibitors can inhibit tumor growth and enhance the radiosensitivity of cancer cells. However, their mechanisms are not completely clear. In this study, we determined the PARP1 expression levels in ovarian cancer and studied its function. Results showed that PARP1 is overexpressed and PARP inhibitor PJ-34 can inhibit the growth of ovarian cancer cells through increasing ROS levels.[Methods]1、Western blotting and real-time PCR were used to determine PARP1 expression in ovarian cancer.2、Clonogenic assay was employed to assess proliferation of ovarican cancer cells treated by PJ-34.3、Flow cytometry method was used to determine the level of ROS in ovarian cancer cells treated with PJ-34.4、Clonogenic assay was employed to assess proliferation of ovarican cancer cells treated by PJ-34 and NAC.5、The levels of DNA double-strand breaks (DSBs) were determined by scoring y-H2AX foci and determing the total amount of y-H2AX,using immunofluorescence and Western blot, respectively6、Real-time PCR and Western blot were used to determine the expression levels of redox genes GPX1, GPX3, PRDX1, NOX4, NQO1 and HO-1 in ovarian cancer cells treated with PJ-34.[Results]1、PARP1 is highly expressed in ovarian cancer cells A2780, HEY, SKOV3, HO8910, HO8910PM and OVCAR3, and is expressed at a low level in the normal fallopian tube epithelial cells FTE-187.2、PJ-34 significantly inhibits the clonogenic ability of ovarian cancer cells A2780, HEY and HO8910, while having no effect on the normal fallopian tube epithelial cells FTE-187.3、ROS levels were increased in ovarian cancer cells A2780, HEY, SKOV3 and HO8910 when treated with PJ-34. ROS level was similarly elevated in A2780 cells when PARP1 was depleted by RNA interference.4、PARP1 inhibited cancer cells are more sensitive to hydrogen peroxide or MTH1 inhibitor TH287. The reduction in clonogenic ability caused by PARP1 inhibition could be partially rescued by antioxidant NAC.5、DNA double-strand breaks were induced by PARP1 inhibition in A2780 cells, but could be significantly attenuated by NAC.6、PARP1 function is required for the expression of GPX1 in A2780 ovarian cancer cells.[Conclusions]PARP1 is overexpressed in ovarian cancer. It promotes ovarian cancer cells survival by reducing oxidative stress and DNA damage.