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Journal of Hematology & Oncology Oct 2018The interaction of tumor cells with platelets is a prerequisite for successful hematogenous metastatic dissemination. Upon tumor cell arrival in the blood, tumor cells... (Review)
Review
The interaction of tumor cells with platelets is a prerequisite for successful hematogenous metastatic dissemination. Upon tumor cell arrival in the blood, tumor cells immediately activate platelets to form a permissive microenvironment. Platelets protect tumor cells from shear forces and assault of NK cells, recruit myeloid cells by secretion of chemokines, and mediate an arrest of the tumor cell platelet embolus at the vascular wall. Subsequently, platelet-derived growth factors confer a mesenchymal-like phenotype to tumor cells and open the capillary endothelium to expedite extravasation in distant organs. Finally, platelet-secreted growth factors stimulate tumor cell proliferation to micrometastatic foci. This review provides a synopsis on the current literature on platelet-mediated effects in cancer metastasis and particularly focuses on platelet adhesion receptors and their role in metastasis. Immunoreceptor tyrosine-based activation motif (ITAM) and hemi ITAM (hemITAM) comprising receptors, especially, glycoprotein VI (GPVI), FcγRIIa, and C-type lectin-like-2 receptor (CLEC-2) are turned in the spotlight since several new mechanisms and contributions to metastasis have been attributed to this family of platelet receptors in the last years.
Topics: Animals; Blood Platelets; Humans; Neoplasm Metastasis; Neoplasms
PubMed: 30305116
DOI: 10.1186/s13045-018-0669-2 -
Cancer Metastasis Reviews Jun 2017Platelets play an important role in the vessel. Following their formation from megakaryocytes, platelets exist in circulation for 5-7 days and primarily function as... (Review)
Review
Platelets play an important role in the vessel. Following their formation from megakaryocytes, platelets exist in circulation for 5-7 days and primarily function as regulators of hemostasis and thrombosis. Following vascular insult or injury, platelets become activated in the blood resulting in adhesion to the exposed extracellular matrix underlying the endothelium, formation of a platelet plug, and finally formation and consolidation of a thrombus consisting of both a core and shell. In pathological conditions, platelets are essential for formation of occlusive thrombus formation and as a result are the primary target for prevention of arterial thrombus formation. In addition to regulation of hemostasis in the vessel, platelets have also been shown to play an important role in innate immunity as well as regulation of tumor growth and extravasations in the vessel. These primary functions of the platelet represent its normal function and versatility in circulation.
Topics: Animals; Blood Platelets; Hemostasis; Humans; Thrombosis
PubMed: 28667366
DOI: 10.1007/s10555-017-9677-x -
Cytometry. Part B, Clinical Cytometry Jan 2020Platelet flow cytometry is widely used in cardiovascular medicine as the platelet surface is rich in clinical biomarkers. Surface profiling is critical in disease... (Review)
Review
Platelet flow cytometry is widely used in cardiovascular medicine as the platelet surface is rich in clinical biomarkers. Surface profiling is critical in disease management, but current assays can abet clinical errors as they are suboptimal and prone to bias. Accordingly, the technical and analytical advances that can be used to create high quality assays with minimal error and maximal sensitivity were reviewed. Specifically, the best practices for instrument setup, quality control, panel design, titration, gating, and compensation were described. Adherence to these practices will enhance the validity and reliability of platelet flow cytometry in clinical/research settings. © 2019 International Clinical Cytometry Society.
Topics: Animals; Biomarkers; Blood Platelets; Flow Cytometry; Humans; Quality Control; Reproducibility of Results
PubMed: 30779477
DOI: 10.1002/cyto.b.21774 -
Blood Jun 2021Platelets play significant and varied roles in cancer progression, as detailed throughout this review series, via direct interactions with cancer cells and by long-range... (Review)
Review
Platelets play significant and varied roles in cancer progression, as detailed throughout this review series, via direct interactions with cancer cells and by long-range indirect interactions mediated by platelet releasates. Microvesicles (MVs; also referred to as microparticles) released from activated platelets have emerged as major contributors to the platelet-cancer nexus. Interactions of platelet-derived MVs (PMVs) with cancer cells can promote disease progression through multiple mechanisms, but PMVs also harbor antitumor functions. This complex relationship derives from PMVs' binding to both cancer cells and nontransformed cells in the tumor microenvironment and transferring platelet-derived contents to the target cell, each of which can have stimulatory or modulatory effects. MVs are extracellular vesicles of heterogeneous size, ranging from 100 nm to 1 µm in diameter, shed by living cells during the outward budding of the plasma membrane, entrapping local cytosolic contents in an apparently stochastic manner. Hence, PMVs are encapsulated by a lipid bilayer harboring surface proteins and lipids mirroring the platelet exterior, with internal components including platelet-derived mature messenger RNAs, pre-mRNAs, microRNAs, and other noncoding RNAs, proteins, second messengers, and mitochondria. Each of these elements engages in established and putative PMV functions in cancer. In addition, PMVs contribute to cancer comorbidities because of their roles in coagulation and thrombosis and via interactions with inflammatory cells. However, separating the effects of PMVs from those of platelets in cancer contexts continues to be a major hurdle. This review summarizes our emerging understanding of the complex roles of PMVs in the development and progression of cancer and cancer comorbidities.
Topics: Animals; Blood Platelets; Cell Communication; Extracellular Vesicles; Humans; Neoplasms; RNA, Neoplasm; Tumor Microenvironment
PubMed: 33940593
DOI: 10.1182/blood.2019004119 -
Blood Reviews May 2015Upon activation, platelets secrete more than 300 active substances from their intracellular granules. Platelet dense granule components, such as ADP and polyphosphates,... (Review)
Review
Upon activation, platelets secrete more than 300 active substances from their intracellular granules. Platelet dense granule components, such as ADP and polyphosphates, contribute to haemostasis and coagulation, but also play a role in cancer metastasis. α-Granules contain multiple cytokines, mitogens, pro- and anti-inflammatory factors and other bioactive molecules that are essential regulators in the complex microenvironment of the growing thrombus but also contribute to a number of disease processes. Our understanding of the molecular mechanisms of secretion and the genetic regulation of granule biogenesis still remains incomplete. In this review we summarise our current understanding of the roles of platelet secretion in health and disease, and discuss some of the hypotheses that may explain how platelets may control the release of its many secreted components in a context-specific manner, to allow platelets to play multiple roles in health and disease.
Topics: Animals; Blood Platelets; Hemostasis; Humans; Inflammation; Neoplasms; Platelet Activation; Wound Healing
PubMed: 25468720
DOI: 10.1016/j.blre.2014.10.003 -
Transfusion Medicine Reviews Oct 2020Platelets are the primary cellular mediators of hemostasis and this function firmly acquaints them with a variety of inflammatory processes. For example, platelets can... (Review)
Review
Platelets are the primary cellular mediators of hemostasis and this function firmly acquaints them with a variety of inflammatory processes. For example, platelets can act as circulating sentinels by expressing Toll-like receptors (TLR) that bind pathogens and this allows platelets to effectively kill them or present them to cells of the immune system. Furthermore, activated platelets secrete and express many pro- and anti-inflammatory molecules that attract and capture circulating leukocytes and direct them to inflamed tissues. In addition, platelets can directly influence adaptive immune responses via secretion of, for example, CD40 and CD40L molecules. Platelets are also the source of most of the microvesicles in the circulation and these miniscule elements further enhance the platelet's ability to communicate with the immune system. More recently, it has been demonstrated that platelets and their parent cells, the megakaryocytes (MK), can also uptake, process and present both foreign and self-antigens to CD8+ T-cells conferring on them the ability to directly alter adaptive immune responses. This review will highlight several of the non-hemostatic attributes of platelets that clearly and rightfully place them as integral players in immune reactions.
Topics: Adaptive Immunity; Biomarkers; Blood Platelets; Humans; Immunity, Innate; Immunomodulation; Inflammation; Megakaryocytes; Platelet Transfusion
PubMed: 33051111
DOI: 10.1016/j.tmrv.2020.09.005 -
Blood Jul 2015Although once primarily recognized for its roles in hemostasis and thrombosis, the platelet has been increasingly recognized as a multipurpose cell. Indeed, circulating... (Review)
Review
Although once primarily recognized for its roles in hemostasis and thrombosis, the platelet has been increasingly recognized as a multipurpose cell. Indeed, circulating platelets have the ability to influence a wide range of seemingly unrelated pathophysiologic events. Here, we highlight some of the notable observations that link platelets to inflammation, reinforcing the platelet's origin from a lower vertebrate cell type with both hemostatic and immunologic roles. In addition, we consider the relevance of platelets in cancer biology by focusing on the hallmarks of cancer and the ways platelets can influence multistep development of tumors. Beyond its traditional role in hemostasis and thrombosis, the platelet's involvement in the interplay between hemostasis, thrombosis, inflammation, and cancer is likely complex, yet extremely important in each disease process. The existence of animal models of platelet dysfunction and currently used antiplatelet therapies provide a framework for understanding mechanistic insights into a wide range of pathophysiologic events. Thus, the basic scientist studying platelet function can think beyond the traditional hemostasis and thrombosis paradigms, while the practicing hematologist must appreciate platelet relevance in a wide range of disease processes.
Topics: Animals; Anticarcinogenic Agents; Aspirin; Blood Platelets; Cell Death; Cell Proliferation; Cell-Derived Microparticles; Humans; Inflammation; Models, Biological; Neoplasm Invasiveness; Neoplasm Metastasis; Neoplasms; Neoplastic Stem Cells; Neovascularization, Pathologic; Neutrophils; Signal Transduction; Thrombosis; Tumor Escape
PubMed: 26109205
DOI: 10.1182/blood-2014-08-531582 -
Blood Jun 2021Platelets have been hypothesized to promote certain neoplastic malignancies; however, antiplatelet drugs are still not part of routine pharmacological cancer prevention...
Platelets have been hypothesized to promote certain neoplastic malignancies; however, antiplatelet drugs are still not part of routine pharmacological cancer prevention and treatment protocols. Paracrine interactions between platelets and cancer cells have been implicated in potentiating the dissemination, survival within the circulation, and extravasation of cancer cells at distant sites of metastasis. Signals from platelets have also been suggested to confer epigenetic alterations, including upregulating oncoproteins in circulating tumor cells, and secretion of potent growth factors may play roles in promoting mitogenesis, angiogenesis, and metastatic outgrowth. Thrombocytosis remains a marker of poor prognosis in patients with solid tumors. Experimental data suggest that lowering of platelet count may reduce tumor growth and metastasis. On the basis of the mechanisms by which platelets could contribute to cancer growth and metastasis, it is conceivable that drugs reducing platelet count or platelet activation might attenuate cancer progression and improve outcomes. We will review select pharmacological approaches that inhibit platelets and may affect cancer development and propagation. We begin by presenting an overview of clinical cancer prevention and outcome studies with low-dose aspirin. We then review current nonclinical development of drugs targeted to platelet binding, activation, and count as potential mitigating agents in cancer.
Topics: Aspirin; Blood Platelets; Humans; Neoplasms; Platelet Activation; Platelet Aggregation Inhibitors
PubMed: 33940597
DOI: 10.1182/blood.2019003977 -
Clinical Chemistry and Laboratory... Nov 2019This review evaluates the role of platelets in bleeding risk among patients with hematological disease and thrombocytopenia. Platelets are pivotal in primary hemostasis,... (Review)
Review
This review evaluates the role of platelets in bleeding risk among patients with hematological disease and thrombocytopenia. Platelets are pivotal in primary hemostasis, and possess non-hemostatic properties involved in angiogenesis, tissue repair, inflammation and metastatis. Also, platelets safeguard vascular integrity in inflamed vessels. Overall, bleeding risk depends on the underlying disease, and patients with cancer and platelet count <6-10 × 109/L have a markedly increased bleeding risk, while the platelet count does not correlate with bleeding risk at higher platelet counts. Other factors might affect platelet properties and thus bleeding risk, for example, drugs, low hematocrit, coagulation system impairments or transfusion of dysfunctional donor platelets. For patients with leukemia and immune thrombocytopenia, reduced platelet activation, platelet aggregation, or thrombopoiesis, reflected by the reduced presence of reticulated platelets, are associated with bleeding phenotype. However, mechanistic insight into the cause of reduced platelet function in different thrombocytopenic conditions is sparse, except for some inherited platelet disorders. Promising tools for platelet function studies in thrombocytopenia are flow cytometry and biomarker studies on platelet constituents. An important message from this current paper is that bleeding risk assessment must be tailored to specific patient populations and cannot be applied broadly to all patients with thrombocytopenia.
Topics: Blood Coagulation; Blood Platelets; Blood Transfusion; Female; Hematologic Diseases; Hemorrhage; Hemostasis; Humans; Leukopenia; Male; Platelet Activation; Platelet Aggregation; Platelet Count; Platelet Function Tests; Risk Factors; Thrombocytopenia
PubMed: 31465290
DOI: 10.1515/cclm-2019-0380 -
The Journal of Cell Biology Jun 2013Circulating blood platelets are specialized cells that prevent bleeding and minimize blood vessel injury. Large progenitor cells in the bone marrow called megakaryocytes... (Review)
Review
Circulating blood platelets are specialized cells that prevent bleeding and minimize blood vessel injury. Large progenitor cells in the bone marrow called megakaryocytes (MKs) are the source of platelets. MKs release platelets through a series of fascinating cell biological events. During maturation, they become polyploid and accumulate massive amounts of protein and membrane. Then, in a cytoskeletal-driven process, they extend long branching processes, designated proplatelets, into sinusoidal blood vessels where they undergo fission to release platelets. Given the need for platelets in many pathological situations, understanding how this process occurs is an active area of research with important clinical applications.
Topics: Animals; Blood Platelets; Cell Differentiation; Cytoskeleton; Humans; Megakaryocytes
PubMed: 23751492
DOI: 10.1083/jcb.201304054