Increased expression of YAP1 in prostate cancer correlates with extraprostatic extension

Abstract

Objective: Yes associated protein 1 (YAP1) is a member of the Hippo pathway, acting as a transcriptional coactivator. To elucidate the role of YAP1 and phosphorylated (p)YAP1 in prostate cancer (PCa) tumorigenesis, we investigated their expression in clinical samples of PCa and cell lines.

Methods: Fifty-four tumor, adjacent nontumor, and prostate intraepithelial neoplasia (PIN) tissues from patients with PCa after radical prostatectomy were selected from a retrospective cohort and studied using immunohistochemistry (IHC). Protein and mRNA expression levels of YAP1 were evaluated by Western blot analysis and quantitative real-time reverse transcription PCR, respectively, in cancer cell lines. Publicly available gene expression datasets were downloaded to analyze YAP1 mRNA and protein levels in PCa tissue samples.

Results: IHC analysis of PCa tissues revealed that YAP1 staining intensities were moderate to weak in the nucleus and cytoplasm of tumor cells, whereas adjacent normal epithelia showed strong staining. We observed that benign prostates were characterized by higher expression levels of both nuclear (P=0.004) and cytosolic (P=0.005) YAP1. pYAP1 staining was weak in the cytoplasm and absent in the nucleus of all the tissues investigated. YAP1 expression was an indicator of extraprostatic extension (EPE). The level of YAP1 was negatively correlated with the level of the androgen receptor (AR) in The Cancer Genome Atlas dataset and Western blot analysis of cell lines.

Conclusions: Our study suggested that YAP1 expression is heterogeneous in PCa tissue samples; therefore, YAP1 might play different roles in different aspects of PCa progression. This might involve AR-YAP1 interplay in PCa.

Keywords: PCa; YAP1; pYAP1.

1

Representative photographs of cytoplasmic and nuclear YAP1 immunostaining. (IHC staining, 20×). (A) Benign. (B) PIN. (C) Cancer tissue areas of PCa patient. (D) pYAP1 immunostaining of the same patient’s PIN. (E) pYAP1 immunostaining of the same patient’s cancer tissue area. The areas are indicated with arrows.

2

CNA and mRNA expression of YAP1 in primary and metastatic PCa samples. (A) There is no statistically significant difference between mRNA values of YAP1 in 13 primary PCa sample and their matched metastatic lesions. (B) Metastatic PCa samples show high CNA of YAP1 compared to primary PCa samples. (C) Absolute numbers of cases from B.

3

Correlation of YAP1 and AR. (A) Correlation of YAP1 and AR in mRNA level is positive. The correlation coefficients are R=0.437 and R=0.326 according to Spearman rho and Pearson correlation, respectively (P < 0.0001). (B) Correlation of YAP1 and AR in protein level is negative. The correlation coefficients are R=–0.236 and R=–0.310 according to Spearman rho and Pearson correlation, respectively ( P < 0.0001).

4

Expression of YAP1 and AR in protein and mRNA level and their correlation in PCa cell lines. (A) Western blot analysis of YAP1 and AR revealed that the YAP1 protein was high in AR negative (DU145, PC3 and RWPE1) prostate cell lines. (B) Real time PCR analysis of AR mRNA level in prostate cell lines (The order of cell lines represented in the graph is the same as in figure C). (C) Real time PCR analysis of YAP1 mRNA level in prostate cell lines.