Involvement of the Snake Toxin Receptor CLEC-2, in Podoplanin-mediated Platelet Activation, by Cancer Cells

Katsue Suzuki-Inoue,Yukinari Kato,Osamu Inoue,Mika Kato Kaneko,Kazuhiko Mishima,Yutaka Yatomi,Yasuo Yamazaki,Hisashi Narimatsu,Yukio Ozaki

doi:10.1074/jbc.m702327200

Abstract

Podoplanin (aggrus), a transmembrane sialoglycoprotein, is involved in tumor cell-induced platelet aggregation, tumor metastasis, and lymphatic vessel formation. However, the mechanism by which podoplanin induces these cellular processes including its receptor has not been elucidated to date. Podoplanin induced platelet aggregation with a long lag phase, which is dependent upon Src and phospholipase Cgamma2 activation. However, it does not bind to glycoprotein VI. This mode of platelet activation was reminiscent of the snake toxin rhodocytin, the receptor of which has been identified by us as a novel platelet activation receptor, C-type lectin-like receptor 2 (CLEC-2) (Suzuki-Inoue, K., Fuller, G. L., Garcia, A., Eble, J. A., Pohlmann, S., Inoue, O., Gartner, T. K., Hughan, S. C., Pearce, A. C., Laing, G. D., Theakston, R. D., Schweighoffer, E., Zitzmann, N., Morita, T., Tybulewicz, V. L., Ozaki, Y., and Watson, S. P. (2006) Blood 107, 542-549). Therefore, we sought to evaluate whether CLEC-2 serves as a physiological counterpart for podoplanin. Association between CLEC-2 and podoplanin was confirmed by flow cytometry. Furthermore, their association was dependent on sialic acid on O-glycans of podoplanin. Recombinant CLEC-2 inhibited platelet aggregation induced by podoplanin-expressing tumor cells or lymphatic endothelial cells, suggesting that CLEC-2 is responsible for platelet aggregation induced by endogenously expressed podoplanin on the cell surfaces. These findings suggest that CLEC-2 is a physiological target protein of podoplanin and imply that it is involved in podoplanin-induced platelet aggregation, tumor metastasis, and other cellular responses related to podoplanin.

Highlights

There has been an increasing body of evidence that platelets are involved in cancer metastasis and/or progression [1, 2]
These findings suggest that C-type lectin-like receptor 2 (CLEC-2) is a physiological target protein of podoplanin and imply that it is involved in podoplanin-induced platelet aggregation, tumor metastasis, and other cellular responses related to podoplanin
We have recently identified a novel class of platelet activation receptor, C-type lectin-like receptor 2 (CLEC-2), which belongs to a non-classical C-type lectin, as a receptor on the platelet membrane for a plateletaggregating snake venom, rhodocytin [17]

Summary

Introduction

There has been an increasing body of evidence that platelets are involved in cancer metastasis and/or progression [1, 2]. Recombinant CLEC-2 inhibited platelet aggregation induced by podoplanin-expressing tumor cells or lymphatic endothelial cells. 2.5 ϫ 107/ml podoplanin-expressed cell lines were incubated with 2.5 mg/ml of the indicated recombinant proteins for 10 min at room temperature before addition to washed platelets.

Results

Conclusion