Recruitment of monocytes/macrophages by tissue factor-mediated coagulation is essential for metastatic cell survival and premetastatic niche establishment in mice

Abstract

Tissue factor (TF) expression by tumor cells correlates with metastasis clinically and supports metastasis in experimental settings. However, the precise pathways coupling TF to malignancy remain incompletely defined. Here, we show that clot formation by TF indirectly enhances tumor cell survival after arrest in the lung, during experimental lung metastasis, by recruiting macrophages characterized by CD11b, CD68, F4/80, and CX 3 CR1 (but not CD11c) expression. Genetic or pharmacologic inhibition of coagulation, by either induction of TF pathway inhibitor expression or by treatment with hirudin, respectively, abrogated macrophage recruitment and tumor cell survival. Furthermore, impairment of macrophage function, in either Mac1-deficient mice or in CD11b-diphtheria toxin receptor mice in which CD11b-positive cells were ablated, decreased tumor cell survival without altering clot formation, demonstrating that the recruitment of functional macrophages was essential for tumor cell survival. This effect was independent of NK cells. Moreover, a similar population of macrophages was also recruited to the lung during the formation of a premetastatic niche. Anticoagulation inhibited their accumulation and prevented the enhanced metastasis associated with the formation of the niche. Our study, for the first time, links TF induced coagulation to macrophage recruitment in the metastatic process. (Blood. 2012;119(13): 3164-3175) IntroductionClinical and experimental studies over the past 30 years have established that the coagulation system actively supports tumor progression and metastasis. Consistent with these observations, expression of procoagulants by tumor cells, among them tissue factor (TF), cancer procoagulant, 1 and selectin ligands, correlates with advanced disease and poor outcome for multiple cancer types. 2,3 TF (also known as coagulation factor III or CD142) is the protease receptor that initiates coagulation after injury through the extrinsic pathway. Under normal physiologic conditions, TF expression is limited to extravascular sites that only become exposed to blood after trauma. In this case, the exposed TF binds to and activates the blood-borne coagulation factor FVII, triggering clot formation through a cascade of proteolytic events that results in thrombin formation, activation of platelets, and fibrin deposition. 4 In addition to triggering coagulation, the binding of FVIIa to TF activates intracellular signaling pathways through the TF cytoplasmic domain, by activating G-protein-coupled protease activated receptors (PARs), especially PAR2. 4 These signaling pathways support tumor angiogenesis 5,6 and regulate tumor progression. 7 Intracellular signaling pathways can be distinguished experimentally from the extracellular coagulative roles of TF by specific antibodies 7 or deletion of the cytoplasmic domain that eliminates many forms of TF signaling but still triggers coagulation. 6,8,9 TF enhances tumor growth and angiogenesis, [4][5][6][7]10 and specifically plays an important role in some experiment...

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