Overexpression of Pleomorphic Adenoma Gene-Like 2 Is a Novel Poor Prognostic Marker of Prostate Cancer

Abstract

Pleomorphic adenoma gene like-2 (PLAGL2) is a member of the PLAG gene family. Previous studies have revealed that overexpression of PLAGL2 is associated with many human cancers. However, it has been reported that PLAGL2 also plays as a tumor suppressor. The precise role of PLAGL2 in prostate cancer (PCa) is still unknown. The aim of this study was to investigate the expression and prognostic value of PLAGL2 in PCa. Data from microarray datasets demonstrated that the DNA copy number and mRNA level of PLAGL2 were significantly increased in PCa compared with normal prostate. qRT-PCR and western blot analysis from paired PCa samples and prostate cell lines confirmed upregulated mRNA and protein expression levels in PCa. Immunohistochemistry analysis showed that staining of PLAGL2 in PCa tissues was significantly higher than that in benign prostatic hyperplasia (BPH) tissues. In addition, the high expression of PLAGL2 was only involved in preoperative PSA, but was not related to age, Gleason score, seminal vesicle invasion, surgical margin status, clinical stage and positive lymph node metastasis. Moreover, our results showed that PLAGL2 was an independent prognostic factor for biochemical recurrence (BCR)-free survival and overall survival (OS) of PCa patients, and overexpressed PLAGL2 was related to early development of BCR and poor OS. In conclusion, our findings suggest that PLAGL2 is overexpressed in PCa. The increased expression of PLAGL2 correlates to PCa progression following radical prostatectomy and may serve as a novel poor prognostic marker for PCa.

Fig 1. Analysis on PLAGL2 expression in PCa and normal prostate tissues with microarray datasets of PCa and log2 copy number unites of DNA or log2 median intensity mRNA.

(A, B) The PLAGL2 DNA copy number and mRNA level was significantly higher in PCa tissues than non-tumor prostate tissues. (C) The PLAGL2 mRNA level was significantly higher in metastatic PCa compared to primary PCa patients. (D) The PLAGL2 mRNA level was significantly increased in higher Gleason score compared with lower Gleason score. (E) The PLAGL2 DNA copy number was significantly higher in earlier recurrence of PCa patients.

Fig 2. Expression of PLAGL2 in paired PCa with adjacent normal prostate tissues and cell lines revealed by qRT-PCR and western blot.

(A) Levels of PLAGL2 mRNA in 25 PCa tissues were significantly higher than those in adjacent noncancerous tissues measured by qRT-PCR (P<0.0001). (B) The PLAGL2 protein level in PCa tissues was upregulated in comparison with adjacent noncancerous tissues measured by Western blot. (C) Western blot indicated the PLAGL2 protein showed higher expression in PCa tissues than in their adjacent normal counterparts. (D) The expression of PLAGL2 mRNA was higher in PCa cell lines (LNCaP, DU145 and PC3) than in RWPE-1 (P<0.0001). (E) Western blot indicated up-regulation of PLAGL2 protein in PCa cell lines (LNCaP, DU145 and PC3) in comparison with RWPE-1.

Fig 3. Immunohistochemical staining for PLAGL2 in PCa tissue and BPH tissue.

The PLAGL2 expression was predominantly localized in nuclei (positive staining indicated by arrows). (A) BPH tissue (low staining). (B) PCa tissue (low Gleason Score). (C) PCa tissue (high Gleason Score). ×400 magnification.

Fig 4. Association between PLAGL2 expression and BCR-free survival and OS of PCa patients assessed by Kaplan–Meier survival curves.

(A) The patients with high expression had significantly shorter median 5-year BCR-free survival than those with low PLAGL2 expression. (B) The patients with high expression had significantly shorter median 5-year OS than those with low PLAGL2 expression.