Targeting a novel domain in podoplanin for inhibiting platelet-mediated tumor metastasis

// Takaya Sekiguchi 1, 2 , Ai Takemoto 1 , Satoshi Takagi 1 , Kazuki Takatori 1, 2 , Shigeo Sato 1 , Miho Takami 1 , Naoya Fujita 1, 2 1 Division of Experimental Chemotherapy, Cancer Chemotherapy Center, Japanese Foundation for Cancer Research, Tokyo, Japan 2 Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Japan Correspondence to: Naoya Fujita, e-mail: naoya.fujita@jfcr.or.jp Keywords: podoplanin, platelets, platelet aggregation, neutralizing antibody, tumor metastasis Received: August 28, 2015      Accepted: November 22, 2015      Published: December 14, 2015 ABSTRACT Podoplanin/Aggrus is a sialoglycoprotein expressed in various cancers. We previously identified podoplanin as a key factor in tumor-induced platelet aggregation. Podoplanin-mediated platelet aggregation enhances tumor growth and metastasis by secreting growth factors and by forming tumor emboli in the microvasculature. Thus, precise analysis of the mechanisms of podoplanin-mediated platelet aggregation is critical for developing anti-tumor therapies. Here we report the discovery of a novel platelet aggregation-inducing domain, PLAG4 (81-EDLPT-85). PLAG4 has high homology to the previously reported PLAG3 and contributes to the binding of its platelet receptor CLEC-2. Mutant analyses indicated that PLAG4 exhibits a predominant platelet-aggregating function relative to PLAG3 and that conserved Glu 81 /Asp 82 /Thr 85 residues in PLAG4 are indispensable for CLEC-2 binding. By establishing anti-PLAG4-neutralizing monoclonal antibodies, we confirmed its role in CLEC-2 binding, platelet aggregation, and tumor emboli formation. Our results suggest the requirement of simultaneous inhibition of PLAG3/4 for complete suppression of podoplanin-mediated tumor growth and metastasis.