Studies on the role of platelet eicosanoid metabolism and integrin α_IIbβ₃ in tumor‐cell‐induced platelet aggregation

Abstract

Platelet eicosanoid metabolism resulting from tumor-cell-induced platelet aggregation (TCIPA) was examined in a homologous in vitro system. Rat Walker 256 carcinosarcoma cells induced the aggregation of rat platelets via a thrombin-dependent mechanism with concomitant production of eicosanoid metabolites (e.g., 12-HETE, TXA2). TCIPA was dependent on the concentration of tumor cells inducing aggregation, as well as cyclooxygenase and lipoxygenase products. Cyclooxygenase inhibitors, but not lipoxygenase inhibitors, blocked platelet aggregation induced in vitro by a low concentration of agonist. At a high agonist concentration, neither cyclooxygenase nor lipoxygenase inhibitors alone affected platelet aggregation; however, the combined inhibition of both the cyclooxygenase and lipoxygenase pathways resulted in subsequent inhibition of platelet aggregation regardless of agonist concentration. The extent of platelet TXA2 and 12-HETE biosynthesis was likewise dependent on and correlated with agonist concentration. The inhibitors used in this study did not significantly inhibit protein kinase C activity at the doses tested. Platelet surface glycoprotein alpha IIb beta 3 play an important role in platelet aggregation. The effect of platelet cyclooxygenase and lipoxygenase inhibition in regulating alpha IIb beta 3 surface expression was examined by flow cytometric analysis. Thrombin stimulation of washed rat platelets resulted in significantly increased surface expression of platelet alpha IIb beta 3 integrin complex. The enhanced surface expression was not inhibited by a cyclooxygenase inhibitor (aspirin), a thromboxane synthase inhibitor (CGS-14854) or a thromboxane receptor antagonist (SQ 29,548), nor was it stimulated by a thromboxane A2 mimic (pinane-thromboxane A2). However, alpha IIb beta 3 expression was blocked by lipoxygenase inhibition and stereospecifically increased by the platelet lipoxygenase metabolite 12(S)-HETE. These results suggest that both the platelet lipoxygenase and cyclooxygenase pathways are important for TCIPA but that different mechanisms of action are involved.

12(S)-hydroxyeicosatetraenoic acid increases the actin microfilament content in B16a melanoma cells: A protein kinase-dependent process

“…We suspect that this is possible since the physiological levels of 12(S)-HETE (0.1-1.0 µM) have been shown to mimic the thrombin effect on platelet ␣IIb␤3 expression (Steinert et al, 1993) which has been correlated with tumor-cell adhesion to endothelial cells and cancer metastasis (Honn and Tang, 1992). Furthermore, our preliminary studies have shown that both nordihydroguaiaretic acid (a general LOX inhibitor) and N-benzyl-B-hydroxy-5-phenylpentanamide (12-LOX inhibitor) induce B16a cell death, which results in a subsequent appearance of non-specific cleavage of actin (data not shown).…”

Coagulation Facilitates Tumor Cell Spreading in the Pulmonary Vasculature during Early Metastatic Colony Formation

“…Morphologic observations show tumor cells closely associated with platelets after vascular arrest (10,11). A variety of platelet factors contribute to this binding including the glycoproteins, integrin ␣ IIb ␤ 3 (12)(13)(14). P-selectin has also been shown to facilitate metastasis of tumor cells bearing P-selectin ligand (15).…”

Platelet-Mimicry of Cancer Cells: Epiphenomenon with Clinical Significance

“…Systematic studies correlating the in vitro and in vivo interactions of cancer cells with platelets have provided the most comprehensive picture to date of this complex process [1, 7, 12, 13] (fig. 1; table 1).…”

“…Studies on the molecular mechanisms of the interaction of cancer cells with platelets revealed that the earliest player in this interaction is P-selectin in platelets and P-selectin glycoprotein ligand-1/CD162, heparan sulfate proteoglycan (HSPG) and sialyl-Lewis A/X in cancer cells, corresponding to the rolling/docking phases [20, 21] (table 1). The subsequent phase of the interaction of cancer cells with platelets involves β3 integrin-mediated processes (where thrombospondin and fibrinogen can serve as molecular bridges) [12, 13], while the later phase is characterized by activation of both partners involving the prothrombogenic proteins such as tissue factor (TF), cancer procoagulant [2, 5] or HLA-DR [22]. Revealing the molecular background of the activation phase of both tumor cells and platelets, the involvement of the lipid-signaling pathway was demonstrated [13].…”

“…The subsequent phase of the interaction of cancer cells with platelets involves β3 integrin-mediated processes (where thrombospondin and fibrinogen can serve as molecular bridges) [12, 13], while the later phase is characterized by activation of both partners involving the prothrombogenic proteins such as tissue factor (TF), cancer procoagulant [2, 5] or HLA-DR [22]. Revealing the molecular background of the activation phase of both tumor cells and platelets, the involvement of the lipid-signaling pathway was demonstrated [13]. Activation of platelets depended on the agonist strength (tumor cell number), since at a low concentration p12-LOX and at a high agonist concentration both LOX and COXs (COX-1 and thromboxane synthase, TXS) were found to be involved.…”