Inhibitory effects of polypeptides derived from a snake venom C-type lectin, aggretin, on tumor cell-induced platelet aggregation

J Thromb Haemost. 2014 Apr;12(4):540-9. doi: 10.1111/jth.12519.

Abstract

Background and objectives: 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.

Methods and 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.

Keywords: CLEC1B protein, human; PDPN protein, human; neoplasm metastasis; platelet aggregation; snake venoms.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents / chemistry
  • Binding Sites
  • Carcinoma, Hepatocellular / metabolism
  • Cell Line, Tumor
  • Chickens
  • Endothelial Cells / cytology
  • Hep G2 Cells
  • Humans
  • Lectins, C-Type / chemistry*
  • Lectins, C-Type / therapeutic use*
  • Liver Neoplasms / metabolism
  • Lung Neoplasms / drug therapy
  • MCF-7 Cells
  • Membrane Glycoproteins / metabolism
  • Mice
  • Neoplasm Metastasis
  • Neoplasm Transplantation
  • Peptides / chemistry*
  • Platelet Aggregation / drug effects*
  • Protein Structure, Tertiary
  • Viper Venoms / chemistry*
  • Viper Venoms / therapeutic use*

Substances

  • Antineoplastic Agents
  • Lectins, C-Type
  • Membrane Glycoproteins
  • PDPN protein, human
  • Peptides
  • Viper Venoms
  • rhodocytin protein, Calloselasma rhodostoma