The C-type lectin-like receptor 2 (CLEC-2) is expressed on platelets and mediates binding to podoplanin (PDPN) on various cell types. The binding to circulating tumor cells (CTCs) leads to platelet activation and promotes metastatic spread. An increased level of soluble CLEC-2 (sCLEC-2), presumably released from activated platelets, was shown in patients with thromboinflammatory and malignant disease. However, the functional role of sCLEC-2 and the mechanism of sCLEC-2 release are not known. In this study, we focused on the effect of platelet activation on CLEC-2 expression and the sCLEC-2 plasma level in patients with cancer. First, citrated blood from healthy volunteer donors (n= 20) was used to measure the effect of platelet stimulation by classical agonists and PDPN on aggregation, CLEC-2 expression on platelets with flow cytometry, sCLEC-2 release to the plasma with ELISA and total CLEC-2 expression with Western blot analysis. Second, sCLEC-2 was determined in plasma samples from healthy donors (285) and patients with colorectal carcinoma (CRC; 194), melanoma (160), breast cancer (BC; 99) or glioblastoma (49). PDPN caused a significant increase in the aggregation response induced by classical agonists. ADP or PDPN stimulation of platelets caused a significant decrease in CLEC-2 on platelets and sCLEC-2 in the plasma, whereas total CLEC-2 in platelet lysates remained the same. Thus, the increased plasma level of sCLEC-2 is not a suitable biomarker of platelet activation. In patients with CRC (median 0.9 ng/mL), melanoma (0.9 ng/mL) or BC (0.7 ng/mL), we found significantly lower sCLEC-2 levels (p< 0.0001), whereas patients with glioblastoma displayed higher levels (2.6 ng/mL;p= 0.0233) compared to healthy controls (2.1 ng/mL). The low sCLEC-2 plasma level observed in most of the tumor entities of our study presumably results from the internalization of sCLEC-2 by activated platelets or binding of sCLEC-2 to CTCs.
C型凝集素样受体2（CLEC-2）表达于血小板表面，介导其与多种细胞类型上表达的血小板反应蛋白（PDPN）的结合。该受体与循环肿瘤细胞（CTCs）的结合可导致血小板活化并促进肿瘤转移扩散。在血栓炎症性疾病和恶性肿瘤患者中，观察到可能由活化血小板释放的可溶性CLEC-2（sCLEC-2）水平升高。然而，sCLEC-2的功能作用及其释放机制尚不明确。本研究聚焦于血小板活化对癌症患者CLEC-2表达及血浆sCLEC-2水平的影响。首先，采集健康志愿者（n=20）的枸橼酸化血液，通过经典激动剂和PDPN刺激血小板，采用流式细胞术检测血小板CLEC-2表达，ELISA法测定血浆sCLEC-2释放水平，Western blot分析总CLEC-2表达，并观察血小板聚集反应。其次，检测健康供体（285例）与结直肠癌（194例）、黑色素瘤（160例）、乳腺癌（99例）及胶质母细胞瘤（49例）患者的血浆sCLEC-2水平。结果显示，PDPN能显著增强经典激动剂诱导的血小板聚集反应。ADP或PDPN刺激导致血小板表面CLEC-2表达及血浆sCLEC-2水平显著降低，而血小板裂解液中的总CLEC-2含量保持不变。这表明血浆sCLEC-2升高并非血小板活化的合适生物标志物。与健康对照组（2.1 ng/mL）相比，结直肠癌（中位数0.9 ng/mL）、黑色素瘤（0.9 ng/mL）和乳腺癌（0.7 ng/mL）患者的sCLEC-2水平显著降低（p<0.0001），而胶质母细胞瘤患者水平较高（2.6 ng/mL；p=0.0233）。本研究中多数肿瘤类型观察到的低血浆sCLEC-2水平，可能源于活化血小板对sCLEC-2的内化作用或sCLEC-2与CTCs的结合。
肿瘤(癌症)患者之家