Increasing evidence suggests that platelets play a predominant role in colon and
breast cancer metastasis, but the underlying molecular mechanisms remain elusive.
Glycoprotein VI (GPVI) is a platelet-specific receptor for
collagen and
fibrin that triggers platelet activation through immunoreceptor tyrosine-based activation motif (ITAM) signaling and thereby regulates diverse functions, including platelet adhesion, aggregation, and procoagulant activity. GPVI has been proposed as a safe antithrombotic target, because its inhibition is protective in models of arterial
thrombosis, with only minor effects on hemostasis. In this study, the genetic deficiency of platelet GPVI in mice decreased experimental and spontaneous
metastasis of colon and
breast cancer cells. Similar results were obtained with mice lacking the
spleen-tyrosine kinase Syk in platelets, an essential component of the ITAM-signaling cascade. In vitro and in vivo analyses supported that mouse, as well as human GPVI, had platelet adhesion to colon and
breast cancer cells. Using a CRISPR/Cas9-based gene knockout approach, we identified
galectin-3 as the major counterreceptor of GPVI on
tumor cells. In vivo studies demonstrated that the interplay between platelet GPVI and
tumor cell-expressed
galectin-3 uses ITAM-signaling components in platelets and favors the extravasation of
tumor cells. Finally, we showed that JAQ1 F(ab')2-mediated inhibition of GPVI efficiently impairs platelet-
tumor cell interaction and
tumor metastasis. Our study revealed a new mechanism by which platelets promote the
metastasis of colon and
breast cancer cells and suggests that GPVI represents a promising target for antimetastatic
therapies.