Decreased expression of PinX1 protein is correlated with tumor development and is a new independent poor prognostic factor in ovarian carcinoma

Abstract

Human interacting protein X1 (PinX1) has been identified as a critical telomerase inhibitor and proposed to be a putative tumor suppressor gene. Loss of PinX1 has been found in a large variety of malignancies, but the expression status in epithelial ovarian tumors has not been investigated. In this study, immunohistochemistry for PinX1 protein was performed on a tissue microarray (TMA) of epithelial ovarian tumors (informatively containing 25 cystadenomas, 29 borderline tumors, and 157 invasive carcinomas) and 12 normal ovaries. Receiver-operator curve (ROC) analysis was used to determine cut-off scores for tumor positivity and to evaluate patients' survival status. The threshold for PinX1 positivity was determined to be above 60% (area under the curve = 0.856, P < 0.001) based on the area under the ROC. Positive expression of PinX1 was observed in 100% of normal ovarian tissues, in 84% of cystadenomas, in 75.9% borderline tumors, and 66.2% of ovarian carcinomas. Decreased expression of PinX1 was strongly related to patients with poor prognostic factors regarding presence of lymph node metastasis (P = 0.024), distant metastasis (P < 0.001), and late International Federation of Gynecology and Obstetrics (FIGO) stage (P < 0.001). In univariate survival analysis, a highly significant correlation between loss of PinX1 and shortened patient survival (mean, 48.2 months vs 99.2 months, P < 0.001) was displayed. Multivariate analysis demonstrated PinX1 expression (P = 0.027) was evaluated as an independent parameter. Our findings suggest that loss of PinX1 is an adverse independent molecular marker for epithelial ovarian carcinoma patients. PinX1 may be a novel target for telomerase-based anticancer therapy due to inhibiting telomerase activity.

Figure 1

Immunohistochemistry of PinX1 (interacting protein X1) in epithelial ovarian tumor tissue microarray and normal ovary. Positive expression of PinX1 was observed in epithelia cells of normal ovary (a), cystoadenoma (c), borderline tumor (e), and invasive carcinoma ([g], ×100). (b), (d), (f) and (h) demonstrated the higher magnification (×400) from the area of the box in (a), (c), (e), and (g), respectively, where more than 60% ovarian surface epithelial or tumor cells demonstrated immunostaining of PinX1 mainly in nuclei. Negative expression of PinX1 was detected in ovarian carcinoma ([i], ×100), with less than 60% positive staining tumor cells, higher magnification ([j], ×400) from the area of the square in (i).

Figure 2

Receiver–operator curves (ROC) were used to determine the cut‐off score for positive expression of PinX1 (interacting protein X1) protein. The sensitivity and specificity for each outcome were plotted: survival status (a), pT stage (b), pN stage (c), pM stage (d), tumor grade (e), and histological type (f).

Figure 3

Receiver–operator curve (ROC) analysis for different clinicopathological parameters and PinX1 (interacting protein X1) expression was performed to evaluate the survival status. International Federation of Gynecology and Obstetrics (FIGO) stage (area under the curve [AUC] = 0.702, P < 0.001), PinX1 expression (AUC = 0.666, P < 0.001), T stage (AUC = 0.626, P = 0.008), N stage (AUC = 0.617, P < 0.001), and M stage (AUC = 0.610, P < 0.001) implied significant statistical associations with the survival.

Figure 4

Kaplan–Meier survival analysis of PinX1 (interacting protein X1) expression in total patients and in the subset of stage III patients with invasive ovarian carcinoma (log‐rank test). Total, probability of survival of all patients with ovarian carcinoma: positive expression, n = 104; negative expression, n = 53 ([a], P < 0.001). Stage III, probability of survival of stage III patients with ovarian carcinoma: positive expression, n = 56; negative expression, n = 32 ([b], P = 0.40).