Coexpression of TLR9 and VEGF-C is associated with lymphatic metastasis in prostate cancer

Abstract

Prostate cancer (PCa) is one of the most frequent cancers in men, and its biomolecular targets have been extensively studied. This study aimed to analyze the expression of toll-like receptor 9 (TLR9) and vascular endothelial growth factor C (VEGF-C) and the clinical value of the coexpression of TLR9 and VEGF-C in PCa. We retrospectively evaluated 55 patients with clinically localized, intermediate-risk, or high-risk PCa who underwent laparoscopic radical prostatectomy (LRP) and extended pelvic lymph node dissection (ePLND) without neoadjuvant hormonal therapy at a single institution from June 2013 to December 2016. In all 55 patients, the median number of lymph nodes (LNs) resected was 23 (range: 18-31), and a total of 1269 LNs were removed, of which 78 LNs were positive. Seventeen patients had positive LNs, with a positive rate of 30.9%. In addition, the immunohistochemical results in the above patients revealed that high TLR9 expression was correlated with higher Gleason score (GS) (P = 0.049), increased LN metastasis (P = 0.004), and more perineural invasion (PNI) (P = 0.033). Moreover, VEGF-C expression was associated with GS (P = 0.040), pathological stage (pT stage) (P = 0.022), LN metastasis (P = 0.003), and PNI (P = 0.001). Furthermore, a significant positive correlation between TLR9 and VEGF-C was found (P < 0.001), and the TLR9/VEGF-C phenotype was associated with LN metastasis (P = 0.047). Collectively, we propose that TLR9 stimulation may promote LN metastasis in PCa cells through the upregulation of VEGF-C expression, thereby affecting the prognosis of PCa patients. Therefore, these markers may serve as valuable targets for the treatment of PCa.

Keywords: biochemical progression-free survival; coexpression; lymphatic metastasis; prostate cancer; toll-like receptor 9; vascular endothelial growth factor C.

Figure 1

Immunohistochemical staining for TLR9 and VEGF-C in human prostate cancer. (a) Low expression of TLR9 in PCa. (b) High expression of TLR9 was found in PCa tissues, while the scattered benign prostatic glands were only weakly positive at the edge of the glands (black arrow). (c) In addition to being expressed in PCa tissues, TLR9 was also found in lymphocytes (black arrow) and stromal cells (red arrow). (d) Low expression of VEGF-C in PCa. (e) High expression of VEGF-C was found in PCa tissues, by contrast, the benign prostatic glands have almost no positive staining (black arrow). (f) Not only cancer cells but also lymphatic endothelial cells (black arrow) and vascular endothelial cells (red arrow) expressed VEGF-C. (g) High expression of VEGF-C was also found in nervous tissues (black arrow). PCa: prostate cancer; TLR9: toll-like receptor 9; VEGF-C: vascular endothelial growth factor C.

Figure 2

Coexpression of TLR9 and VEGF-C. (a–f) Immunohistochemical staining of serial sections of PCa tissues: (a) HE staining of PCa tissues; low expression of (b) TLR9 and (c) VEGF-C; (d) HE staining of PCa tissues; high expression of (e) TLR9 and (f) VEGF-C. (g) Scatter plot indicating the correlation between TLR9 and VEGF-C expression in PCa patients. (h) Number of cases of various TLR9/VEGF-C phenotypes in PCa. T^h: TLR9 high expression; T^l: TLR9 low expression; V^h: VEGF-C high expression; V^l: VEGF-C low expression; PCa: prostate cancer; TLR9: toll-like receptor 9; VEGF-C: vascular endothelial growth factor C; HE: hematoxylin-eosin.

Figure 3

b-PFS curves according to (a) TLR9 and (b) VEGF-C expression levels. Patients with low expression of TLR9 (P = 0.021) or VEGF-C (P = 0.023) exhibited better prognosis than patients with high expression of these proteins. T^h: TLR9 high expression; T^l: TLR9 low expression; V^h: VEGF-C high expression; V^l: VEGF-C low expression; b-PFS: biochemical progression-free survival; TLR9: toll-like receptor 9; VEGF-C: vascular endothelial growth factor C.