Inhibitory effects of polypeptides derived from a snake venom C-type lectin, aggretin, on tumor cell-induced platelet aggregation.
OBJECTIVE
Podoplanin, a transmembrane sialoglycoprotein, is expressed by lymphatic endothelial cells and many tumor cells, and is involved in tumor cell-induced platelet aggregation and tumor metastasis. A recent study found that C-type lectin-like receptor 2 (CLEC-2) is a physiologic receptor for podoplanin. Previous studies showed that aggretin, a snake venom-derived protein, activates platelets by targeting platelet CLEC-2. We hypothesized that the C-terminal fragment of aggretin may bind to platelet CLEC-2 and displace podoplanin, in turn exerting antitumor metastatic effects.


RESULTS
Aggretin α-chain C-terminus (residues 106-136; AACT) prolonged the lag phase of platelet aggregation induced by aggretin in human washed platelets, indicating that AACT may target the binding site of CLEC-2. HepG2 cells, which are podoplanin-expressing hepatoma cells, induced platelet aggregation with a lag phase. Pretreatment with AACT inhibited platelet aggregation and prolonged the lag phase induced by HepG2 cells. This inhibitory effect was also found with another hepatocarcinoma cell line, HuH-7. AACT inhibited the interaction between HuH-7 cells and platelets, and a specific binding assay demonstrated that CLEC-2 was the binding site for AACT on platelets. In addition, the invasive ability of HepG2 cells was abolished by AACT in a chick embryo chorioallantoic membrane model. Furthermore, formation of lung metastases after intravenous administration of HuH-7 cells was significantly reduced when mice were treated with AACT.


CONCLUSIONS
AACT interacts with CLEC-2 of platelets, leading to interference with platelet aggregation and the subsequent metastatic potential of tumor cells. These results suggest that aggretin AACT is a potential candidate for the treatment of tumor metastasis through CLEC-2 blockade.
Graduate Institute of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan.
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CH
Chang
C-H
CH
Chung
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CC
Hsu
H-C
HC
Peng
T-F
TF
Huang
D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D045744:Cell Line, Tumor; D002645:Chickens; D042783:Endothelial Cells / Q000166:cytology; D056945:Hep G2 Cells; D006801:Humans; D037181:Lectins, C-Type / Q000737:chemistry* / Q000627:therapeutic use*; D008113:Liver Neoplasms / Q000378:metabolism; D008175:Lung Neoplasms / Q000188:drug therapy; D061986:MCF-7 Cells; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D009362:Neoplasm Metastasis; D009368:Neoplasm Transplantation; D010455:Peptides / Q000737:chemistry*; D010974:Platelet Aggregation / Q000187:drug effects*; D017434:Protein Structure, Tertiary; D014757:Viper Venoms / Q000737:chemistry* / Q000627:therapeutic use*; D000098853:Podoplanin
D000970:Antineoplastic Agents; D037181:Lectins, C-Type; D008562:Membrane Glycoproteins; D010455:Peptides; D014757:Viper Venoms; C117468:PDPN protein, human; D000098853:Podoplanin; C112292:rhodocytin protein, Calloselasma rhodostoma
CLEC1B protein, human; PDPN protein, human; neoplasm metastasis; platelet aggregation; snake venoms