Polyphosphate blocks tumour metastasis via anti-angiogenic activity

266

423

Polyphosphate, a linear polymer of inorganic phosphate, is secreted by activated platelets and accumulates in many infectious microorganisms. We recently showed that polyphosphate modulates the blood coagulation cascade at 3 steps: it triggers the contact pathway, it accelerates factor V activation, and it enhances fibrin polymerization. We now report that polyphosphate exerts differential effects on blood clotting, depending on polymer length. Very long polymers (> 500mers, such as those present in microorganisms) were required for optimal activation of the contact pathway, while shorter polymers (ϳ 100mers, similar to the polymer lengths released by platelets) were sufficient to accelerate factor V activation and abrogate the anticoagulant function of the tissue factor pathway inhibitor. Optimal enhancement of fibrin clot turbidity by polyphosphate required > 250mers. Pyrophosphate, which is also secreted by activated platelets, potently blocked polyphosphate-mediated enhancement of fibrin clot structure, suggesting that pyrophosphate is a novel regulator of fibrin function. In conclusion, polyphosphate of the size secreted by platelets is very efficient at accelerating blood clotting reactions but is less efficient at initiating them or at modulating clot structure. Microbial polyphosphate, which is highly procoagulant, may function in host responses to pathogens. IntroductionPolyphosphate (polyP)-a linear polymer of inorganic phosphateaccumulates in a variety of microorganisms 1 and is secreted by activated human platelets. 2,3 We recently showed that polyP is a potent modulator of the human blood-clotting system. [3][4][5][6] The polymer lengths of polyP are known to vary substantially among different organisms and cell types, with relatively short polymers being secreted by human platelets (ϳ 60-100 phosphate units long) 2,3 and very long polymers accumulating in microorganisms (many hundreds to more than 1000 phosphate units long). 1 In this study, we demonstrate that shorter versus longer polymers of polyP have differential effects on the blood clotting system, with important physiologic/pathophysiologic implications. PolyP has been widely described in unicellular organisms such as bacteria, fungi, algae, and protozoa, where it plays diverse physiologic roles, including regulating growth, stress responses, and virulence. 1,7 Comparatively less is known about the metabolism or physiologic roles of polyP in mammalian cells, 8 although polyP is reported to induce apoptosis in plasma cells, 9 promote calcification in osteoblasts, 10 block metastasis of melanoma cells in a mouse model, 11 and possibly serve as a regulatory factor in proliferative signaling pathways. 12 PolyP is present at high concentrations in dense granules of human platelets and is secreted upon platelet activation. 2,3 PolyP has a half-life in plasma of approximately 90 minutes, because of degradation by phosphatases. 4,13 We recently showed that polyP is a potent hemostatic regulator, acting at 3 points in the blood clotting cascade: it...

Section: Introductionmentioning

confidence: 99%

Polyphosphate exerts differential effects on blood clotting, depending on polymer size

Smith¹,

Choi²,

Davis-Harrison³

et al. 2010

266

423

“…Ip6k1 2/2 mice, which display altered hemostasis due to lowered platelet polyP levels, serve as a unique model to study the combined effects of polyP at multiple stages of the clotting cascade. Other functions in which polyP participates include cancer cell proliferation and metastasis, [44][45][46] bone mineralization, 47 and energy metabolism. 48 Ip6k1 2/2 mice could also serve as a model to shed light on the mechanism and physiological significance of these and other functions of polyP.…”

Section: Ip6k1 Participates In Hemostasis 1483mentioning

confidence: 99%

Inositol hexakisphosphate kinase 1 maintains hemostasis in mice by regulating platelet polyphosphate levels

Ghosh

Shukla

Suman

et al. 2013

107

Key Points• Inositol hexakisphosphate kinase 1 (IP6K1) knockout mice display lower inorganic polyphosphate levels in platelets.• Low platelet polyphosphate leads to lengthened clotting time, altered clot architecture, and protection against pulmonary thromboembolism.Polyphosphate (polyP), a polymer of orthophosphate moieties released from the dense granules of activated platelets, is a procoagulant agent. Inositol pyrophosphates, another group of phosphate-rich molecules, consist of mono-and diphosphates substituted on an inositol ring. Diphosphoinositol pentakisphosphate (IP 7 ), the most abundant inositol pyrophosphate, is synthesized on phosphorylation of inositol hexakisphosphate (IP 6 ) by IP 6 kinases, of which there are 3 mammalian isoforms (IP6K1/2/3) and a single yeast isoform. Yeast lacking IP 6 kinase are devoid of polyP, suggesting a role for IP 6 kinase in maintaining polyP levels. We theorized that the molecular link between IP 6 kinase and polyP is conserved in mammals and investigated whether polyP-dependent platelet function is altered in IP6K1 knockout (Ip6k1) mice. We observe a significant reduction in platelet polyP levels in Ip6k1 2/2 mice, along with slower platelet aggregation and lengthened plasma clotting time. Incorporation of polyP into fibrin clots was reduced in Ip6k1 2/2 mice, thereby altering clot ultrastructure, which was rescued on the addition of exogenous polyP. In vivo assays revealed longer tail bleeding time and resistance to thromboembolism in Ip6k1 2/2 mice. Taken together, our data suggest a novel role for IP6K1 in regulation of mammalian hemostasis via its control of platelet polyP levels.

“…12 Although polyP has been studied less extensively in mammalian cells, 13 it has been reported to induce apoptosis in plasma cells, 14 promote calcification in osteoblasts, 15 and block metastasis of melanoma cells in a mouse model. 16 It has also been proposed to serve as a regulatory factor in proliferative signaling pathways. 17 Dense granules of human platelets strongly resemble acidocalcisomes and contain high levels of polyP having chain lengths of approximately 75 phosphate units.…”

Section: Introductionmentioning

confidence: 99%

Polyphosphate enhances fibrin clot structure

Smith

Morrissey

2008

192

185

Polyphosphate, a linear polymer of inorganic phosphate, is present in platelet dense granules and is secreted on platelet activation. We recently reported that polyphosphate is a potent hemostatic regulator, serving to activate the contact pathway of blood clotting and accelerate factor V activation. Because polyphosphate did not alter thrombin clotting times, it appeared to exert all its procoagulant actions upstream of thrombin. We now report that polyphosphate enhances fibrin clot structure in a calciumdependent manner. Fibrin clots formed in the presence of polyphosphate had up to 3-fold higher turbidity, had higher masslength ratios, and exhibited thicker fibers in scanning electron micrographs. The ability of polyphosphate to enhance fibrin clot turbidity was independent of factor XIIIa activity. When plasmin or a combination of plasminogen and tissue plasminogen activators were included in clotting reactions, fibrin clots formed in the presence of polyphosphate exhibited prolonged clot lysis times. Release of polyphosphate from activated platelets or infectious microorganisms may play an important role in modulating fibrin clot structure and increasing its resistance to fibrinolysis. Polyphosphate may also be useful in enhancing the structure of surgical fibrin sealants. (Blood. 2008;112: 2810-2816) IntroductionA fibrin clot is the final product of the blood clotting cascade. Thrombin catalyzes release of fibrinopeptide A from fibrinogen to create fibrin monomers, which then aggregate to protofibrils. Proteolytic release of fibrinopeptide B by thrombin permits lateral protofibril aggregation, resulting in a three-dimensional fibrin gel. Factor XIIIa, a transglutaminase activated by thrombin, covalently crosslinks these fibers to increase the strength and elasticity of the resulting clot. 1 Variables known to influence fibrin clot structure include fibrinogen and thrombin concentrations, 1 pH, 2,3 ionic strength, 3 chloride ion concentration, 2 and presence of calcium ions. 4 A variety of molecules are reported to affect fibrin clot structure, including homocysteine, 5 decorin core protein, 6 heparins, 7,8 dextran, 9 and hydroxyethylstarch. 10 In this study, we demonstrate that inorganic polyphosphate (polyP) strongly modulates fibrin clot structure.polyP is a negatively charged, linear polymer of phosphate units linked by high-energy phosphoanhydride bonds. polyP has a wide biologic distribution, 11 but its functions have been studied most extensively in prokaryotes and unicellular eukaryotes, in which high levels of polyP accumulate in organelles known as acidocalcisomes. In such organisms, polyP plays essential roles in stress responses and virulence. 12 Although polyP has been studied less extensively in mammalian cells, 13 it has been reported to induce apoptosis in plasma cells, 14 promote calcification in osteoblasts, 15 and block metastasis of melanoma cells in a mouse model. 16 It has also been proposed to serve as a regulatory factor in proliferative signaling pathways. 17 Dense granules of human...