Yes-associated protein is an independent prognostic marker in hepatocellular carcinoma

Abstract

Background: Yes-associated protein (YAP), a downstream target of the Hippo signaling pathway, was recently linked to hepatocarcinogenesis in a mouse hepatocellular carcinoma (HCC) model. The objective of the current study was to investigate the clinical significance of YAP in HCC and its prognostic values in predicting survival and tumor recurrence.

Methods: The authors collected 177 pairs of tumor and adjacent nontumor tissue from HCC patients with definitive clinicopathologic and follow-up data. YAP expression was determined by immunohistochemistry, Western blot analysis, and quantitative polymerase chain reaction. Association of YAP with each clinicopathologic feature was analyzed by Pearson chi-square test, and HCC-specific disease-free survival and overall survival by Kaplan-Meier curves and log-rank test. Multivariate Cox regression analyses of YAP in HCC were also performed.

Results: YAP was expressed in the majority of HCC cases (approximately 62%) and mainly accumulated in the tumor nucleus. Overexpression of YAP in HCC was significantly associated with poorer tumor differentiation (Edmonson grade; P = .021) and high serum alpha-fetoprotein (AFP) level (P < .001). Kaplan-Meier and Cox regression data indicated that YAP was an independent predictor for HCC-specific disease-free survival (hazards ratio [HR], 1.653; 95% confidence interval [95% CI], 1.081-2.528 [P = .02]) and overall survival (HR, 2.148; 95% CI, 1.255-3.677 [P = .005]).

Conclusions: YAP is an independent prognostic marker for overall survival and disease-free survival times of HCC patients and clinicopathologically associated with tumor differentiation and serum AFP level. It is a potential therapeutic target for this aggressive malignancy.

FIGURE 1

Overexpression of Yes-associated protein (YAP) in clinical samples of hepatocellular carcinoma (HCC) is shown. (A) Immunohistochemical staining of anti-YAP antibody in paired tumor (T) and adjacent nontumor (NT) tissue is shown. A total of 177 tumor/nontumor tissue pairs were tested, and representative photomicrographs are shown. Strong YAP immunoreactivity was found in both the cytoplasm and nucleus in tumor tissue, but not in the corresponding nontumor tissue (upper panels: scale bar, 80 μm; lower panels: scale bar, 20 μm). (B) Representative Western blot analysis of YAP expression in tumors and self-paired adjacent nontumor tissue is shown. (C) Semiquantitative Western blot analysis of lysates of 44 paired tissue samples is shown. β-Actin was used as an internal control. The means (n = 44) ± the standard error of the mean mean (SEM) are shown, and P values are given. The protein expression level was significantly increased in tumors (0.26) compared with nontumor tissue (0.13; P < .001). (D) TaqMan real-time polymerase chain reaction assay of YAP in HCC is shown. 18S rRNA levels were used as internal controls. The transcriptional fold change was calculated using liver samples from 3 healthy donors as a reference. The means (n = 20) ± SEM are shown, and P values are given. The mean fold change was 18.89 in tumors and 4.25 in nontumor tissue (P = .005).

FIGURE 2

Yes-associated protein (YAP) expression in hepatocellular carcinoma was associated with poor overall survival in 176 patients based on YAP immunoreactivity by immunohistochemistry.

FIGURE 3

Kaplan-Meier disease-free survival analyses of hepatocellular carcinoma (HCC) patients based on Yes-associated protein (YAP) immunoreactivity by immunohistochemistry are shown. (A) YAP expression in tumors was found to be associated with poor disease-free survival (DFS) in 166 patients who underwent curative surgery. (B) YAP expression in tumors was found to be associated with poor DFS in the subgroup of HCC patients (n = 81) without histopathologic evidence of tumor venous infiltration.