Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB111

Poster Communications

Platelets and von-Willebrand Factor - A two-component adhesive for hematogenous metastasis

J. Haller1, A. Spanhofer1, D. Berger1, H. Schillers1

1. Institute of Physiology II, University of Münster, Muenster, Germany.

Metastasis is still a huge problem in clinical treatment of several types of cancer. Platelets play a pivotal role during hematogenous metastasis by protecting cancer cells from immune surveillance by forming a protective coat. We discovered a different way how platelets are interacting with cancer cells. Own observations showed that A549 lung cancer cells phagocytize platelets and recycle platelet proteins to their plasma membrane, including GP IX (CD42a), a constituent of the von-Willebrand-Factor-receptor-complex. Platelets also contain von-Willebrand-Factor (vWF) and first data showed that vWF might be utilized as well by cancer cells. VWF is stored in platelet alpha granules and released upon platelet activation. It is a huge multimeric protein with several negative, positive, hydrophilic and lipophilic domains which can bind to many different targets. We assume that cancer cells use platelets` vWF as a glue to adhere to the vessel wall: VWF is released upon contact to cancer cells, binds to the cancer cell by phagocytic recycled von-Willebrand-Factor-receptor-complex and serves as bridging element to the vessel wall. Methods AFM-based single-cell force spectroscopy (SCFS) was used to quantify the adhesion between immobilized vWF and A549 lung cancer cells. A549 cells were incubated with PKH-stained platelets for 60 minutes. Platelet uptake was verified in situ by fluorescence microscopy. A549 cells without platelet contact served as control. Single A549 cells were glued to a tipless cantilever and force-distance cycles were performed on vWF-coated surface. Results The adhesion of A549 cells to vWF reaches a median of 416,89 pN (Q1: 357,53 pN; Q3: 515,11 pN) and a detachment work of 1,29 fJ (Q1: 1,19 fJ; Q3: 2,67 fJ) whereas A549 cells incubated with platelets prior to adhesion measurements show a much larger median adhesion 633,02 pN (Q1: 361,78 pN; Q3: 4131,75 pN) and a detachment work of 3,69 fJ (Q1: 0,9 fJ; Q3: 34,01 fJ). In some experiments including platelet incubation the adhesion was so strong that A549 cells were ripped of the cantilever. It also seems to be the case that A549 cells after platelet incubation immediately stick to the surface after adding them to the experimental dish. Conclusion Phagocytosis of platelets increases the adhesion of A549 lung cancer cells to vWF dramatically. We suppose that platelet uptake is accompanied with vWF release and followed by phagocytic recycling of GP IX which enables the cancer cell to adhere to vWF. It is conceivable that cancer cells use this strategy for sustained tethering to the vessel wall as the first step of metastasis. Adhesion might be reduced and therefore hematogenous metastasis impeded by interfering with phagocytosis of platelets, the phagocytic recycling pathways of cancer cells or the von-Willebrand-Factor-receptor-complex.

Where applicable, experiments conform with Society ethical requirements