Significance of circadian gene Period2 expression in epithelial ovarian cancer and the effect of gene overexpression on growth of ovarian cancer xenografts in nude mice

Abstract

To study the significance of circadian gene Period2 expression in epithelial ovarian cancer tissues and the effect of gene overexpression on the growth of ovarian cancer xenografts in nude mice. Twenty-two cases of ovarian cancer paraffin specimens in the First Hospital of Shanxi Medical University (ovarian cancer group) were chosed during Jau. 2010 to Dec. 2013, including 8 cases of stage I, 8 cases of stage II, and 6 cases of stage III, while 6 cases of benign ovarian epithelial tumor paraffin specimens were selected as control (benign tumor group). Period2 gene were detected by real-time quantitative PCR and western blot methods in different stages of ovarian cancer tumor tissues. Established the ovarian cancer xenografts in nude mice with ovarian cancer cell line SKOV3, and they were divided into 3 groups (n = 8), including the recombinant plasmid group, empty plasmid group and control group. Using gene transfection technique to transfer Period2 gene into tumor tissues, tested the expression of Period2 mRNA in tumor tissues by real-time quantitative PCR after transfection into all nude mice, monitored the transplant tumor growth and calculating the tumor inhibition rate, detected the antiapoptotic gene BRE, apoptosis related tumor necrosis factor receptor (TNFR1) and tumor suppressor gene NIX in tumor tissues by real-time PCR and western blot in different groups. (1) The expression level of Period2 mRNA in tumor tissues among ovarian cancer group stage I, II and III were respectively 2.59 ± 0.50, 0.47 ± 0.08 and 0.42 ± 0.08, but benign tumor group was 6.59 ± 1.05. The expression level of Period2 protein in ovarian cancer group stage I, II and III were respectively 0.835 ± 0.087, 0.412 ± 0.035 and 0.199 ± 0.031, while benign tumor group was 0.874 ± 0.094. The expression level of Period2 mRNA and protein in benign tumor group was higher than those in ovarian cancer group stage I, II or III (P < 0.01). With ovarian cancer stage increased, the expression of Period2 mRNA and protein were decreased or absent (P < 0.05). (2) Two weeks after transfection, the expression level of Period2 mRNA in recombinant plasmid group tumor tissue was significantly higher than those in the empty plasmid group or the control group (6.11 ± 0.56 vs 0.50 ± 0.09 vs 0.44 ± 0.08, respectively; P < 0.01), the transplanted tumor volume of recombinant plasmid group was significantly less than those in empty plasmid group or the control group [(486 ± 70) mm(3) vs (835 ± 106) mm(3) vs (846 ± 110) mm(3), respectively; P < 0.01], the tumor inhibition rate of the recombination plasmid group was as high as 42.9%, that was significantly higher than those in the empty plasmid group and the control group (3.8% and 0, respectively; P < 0.05). (3) The expression level of BRE mRNA and protein in transplanted tumor tissues in the recombinant plasmid group were significantly lower than those in empty plasmid group and the control group; the expression level of TNFR1 and NIX were significantly higher than those in the empty plasmid group and the control group (all P < 0.05). Period2 mRNA and protein expression are absent in ovarian cancer of advanced stage. Transfection and stable expression of Period2 gene could slow down the growth of ovarian cancer, and the tumor inhibition rate could be significantly increased. Period2 gene may promote ovarian cancer cells apoptosis through inhibition of BRE gene expression and promoting TNFR1, NIX gene expression to exert anti-tumor effect.