Increased serum CA125 levels are an important indicator for ovarian cancer. However, CA125 levels are not cancer-specific. Ovarian cancer, benign gynecological tumors and other cancers can cause elevation of serum CA125 levels. It is well known that proteins reflect the abnormal phenotype of pathological state and proteomics is one of the power tool to monitor and detect the changes in protein expression. In current study, iTRAQ technology was utilized to perform ovarian cancer plasma proteomics analysis, four proteins were identified as differential expressed proteins for the progression of ovarian cancer after controlling clinical confounding factors (age, menopausal state and admission date). In addition, an independent cohort analysis validated that CRP and ARHGEF 11 were proteins related to ovarian cancer disease progression. Combination of CRP, ARHGEF 11 and CA125 improved the predictability of CA125 alone in the distinguishment of cancer from non-cancer patients significantly, especially improved the specificity, which improved the deficiency of CA125 in the disease diagnosis.
Pathological damage of human organs could lead to the changes of the quality and quantity of plasma proteins, the analysis of plasma proteins is of great significance to the diagnosis of disease and the monitoring of the progression of cancers. Secretory protein is secreted by histiocytic cells exocytosis into the blood vessels and circulate. Current evidence presents different concentration tendency between the tissue and blood. Simon et al. Shows high levels of B7-H4 protein were detected in ovarian cancer tissue, while low level in all serum samples [22]. Welsh et al. reveals significant elevated levels of secretory protein MIC-1 in cancer tissues, as well as highly elevated levels in serum of patients with metastatic prostate, breast, and colorectal carcinomas [23, 24]. Our data suggest that up-regulation of secreted protein CRP in ovarian cancer tissues and plasma with the progression of cancers. A comprehensive and systematic analysis the level of CRP would provide a platform in monitoring of the progression of ovarian cancer.
CRP is a plasma protein of hepatic origin, which is a fairly sensitive marker of acute-phase inflammation [25]. The common conditions associated with elevations of CRP levels are bacterial infection, inflammatory diseases, cancer, tissue necrosis and trauma [26–28]. Previous studies revealed that elevated plasma CRP levels was associated with increased risk of breast cancer, lung cancer, prostate cancer and colorectal cancer [29–31]. Trautner et al. also found that elevated CRP levels are indicators of tumor recurrence and poor prognosis [32]. Agnoli et al. showed that high CRP was significantly associated with increased breast cancer risk among postmenopausal women [33] and Petekkaya et al. showed that breast cancer patients with a higher serum CRP had shorter survival time compared with normal patients [34]. In current study, we observed a significant positive correlation between plasma CRP levels and the occurrence of tumor, but we failed to demonstrate a statistically significant difference in CRP levels between ovarian cancer patients with early stage and late stage, while CRP levels tended to be higher in patients with advanced cancer patients. The same change tendency was observed in ovarian cancer tissue proteomics analysis. The underlying mechanism of the relationship between CRP and cancers are that tumor growth can cause tissue inflammation, which make cancerous cells secrete interleukin 6 (IL-6) and stimulate CRP production in liver [35–37]. The results indicated that CRP was an indicator for monitoring the progression of ovarian cancer.
Rho guanine nucleotide exchange factor 11 (ARHGEF 11) is also called PDZ-RhoGEF [38], which is highly expressed in the brain [39, 40]. Mizuki et al. found that ARHGEF 11 variants are associated with a higher risk for the onset of schizophrenia in Japanese and further explored the distribution, binding, and functions of ARHGEF 11 in the dendritic spine of the rat cerebral cortex [41]. It is also discovered that ARHGEF 11 associated with the risk for type 2 diabetes mellitu [42, 43]. There were no studies have revealed the relationship between ARHGEF 11 and cancer directly by far, it might be caused by the dysregulated in RhoGTPase signaling at epithelial tight junctions [44].
In summary, we performed a plasma proteomics study for ovarian cancer patients and controls. Our results indicate that plasma CRP levels help monitor the progression of ovarian tumor and combination of novel protein biomarkers have a good distinguishment between cancer and non-cancer patients. This study has some limitations. Due to the small sample size of validation set, we failed to validate a statistically significant difference in CRP levels between ovarian cancer patients with early stage and late stage. CRP is also a clinical indicator of inflammation, but our samples did not detect the CRP index in clinical practice, so we could not validate our results from the point of clinic. In future study, additional studies are required to further validate their performance as biomarkers.