An Essential NRP1-Mediated Role for Tagln2 in Gastric Cancer Angiogenesis

Knowledge about the precise biological role and underlying mechanism of Tagln2 in tumor progression is relatively limited, especially in angiogenesis focused on tumor derived endothelial cells (ECs) has rarely been reported. Here, the function, molecular mechanism and potential clinical value of Tagln2 in gastric cancer (GC) angiogenesis were investigated. GC tissue microarrays were used to assess the expression of Tagln2 in ECs. The relationships between expression and clinicopathological features were analyzed to evaluate the clinical value of Tagln2. Gain- and loss-of-function approaches were performed in ECs to investigate the functions of Tagln2 in angiogenesis. A combination of angiogenesis antibody array, RNA-Seq analyses and a series of in vitro experiments were performed to reveal the proangiogenic mechanism mediated by NRP1. Immunohistochemistry performed on an independent tissue chip (n=75) revealed significant upregulation of Tagln2 in tumor-derived ECs which were specifically immunolabeled with CD34. Additionally, high Tagln2 levels correlated significantly with the presence of lymph node as well as distant metastases. Gain- and loss-of-function approaches highlighted the function of Tagln2 in promoting EC proliferation, motility, and capillary-like tube formation and in reducing apoptosis. Tagln2 upregulation led to significantly increased mRNA and protein levels of NRP1 and subsequently activated the NRP1/VEGFR2 and downstream MAPK signaling pathways. These data indicate the importance of Tagln2 in angiogenesis, as a potential therapeutic target, and as a candidate prognostic marker in GC.

Identification and verification of transgelin-2 as a potential biomarker of tumor-derived lung-cancer endothelial cells by comparative proteomics

To investigate heterogeneity of endothelial cells (ECs) in the tumor microenvironment and biomarkers for antitumor angiogenesis therapy, high-purity (>98%) normal (NECs) and tumor-derived CD105(+) ECs (TECs) were purified from a mouse Lewis lung carcinoma model bearing 0.5 cm tumors by immunomagnetic separation. Proteomics analysis revealed that 48 proteins (28 upregulated and 20 downregulated) were differentially regulated by at least 1.5-fold in TECs, and that these proteins were involved in metabolism, energy pathways, protein folding, cell growth and/or functioned as structural constituents of the cytoskeleton. Upregulation of heat shock protein 60 (Hspd1) and transgelin-2 (Tagln2) was revealed in TECs, and by immunohistochemistry (IHC) in paired tissues from 30 consecutive lung cancer (LC) patients. Higher expression levels of Hspd1, Tagln2 were detected in microvascular ECs of paratumor and tumor tissues than in paired normal counterparts. Stronger Tagln2 staining was associated with clinical stage, tumor size, and histological neural invasion. Higher Hspd1 (area under the curve [AUC], 0.82) and lower Tagln2 (AUC, 0.90) levels were detected in LC patient sera. Pearson correlation analysis revealed a positive correlation between serum Hspd1 and Tagln2 levels. In conclusion, higher Tagln2 levels were associated with tumor development, lymph node metastasis, and neural invasion in LC and may thus serve as a potential biomarker of tumor angiogenesis.

SIGNIFICANCE

High-purity endothelial cells (normal and tumor derived) were prepared to characterize ECs heterogeneity in the tumor microenvironment and to explore biomarkers of early stages of tumor development by proteomics. Candidate proteins Hspd1 and Tagln2, were further verification in the sera and tumor tissues of lung cancer patients. Moreover, higher Tagln2 was significantly associated with clinical tumor development, metastasis, and neural invasion. All these results indicated a crucial role for Tagln2 in TECs for tumor development and metastasis.