Antiphospholipid Abs (APLAs) are associated with thrombosis and recurrent fetal loss. These Abs are primarily directed against phospholipid-binding proteins, particularly ␤ 2 GPI, and activate endothelial cells (ECs) in a ␤ 2 GPI-dependent manner after binding of ␤ 2 GPI to EC annexin A2. Because annexin A2 is not a transmembrane protein, the mechanisms of APLA/anti-␤ 2 GPI Ab-mediated EC activation are uncertain, although a role for a TLR4/myeloid differentiation factor 88-dependent pathway leading to activation of NF-B has been proposed. In the present study, we confirm a critical role for TLR4 in anti-␤ 2 GPI Ab-mediated EC activation and demonstrate that signaling through TLR4 is mediated through the assembly of a multiprotein signaling complex on the EC surface that includes annexin A2, TLR4, calreticulin, and nucleolin. An essential role for each of these proteins in cell activation is suggested by the fact that inhibiting the expression of each using specific siRNAs blocked EC activation mediated by APLAs/anti-␤ 2 GPI Abs. These results provide new evidence for novel proteinprotein interactions on ECs that may contribute to EC activation and the pathogenesis of APLA/anti-␤ 2 GPI-associated thrombosis and suggest potential new targets for therapeutic intervention in antiphospholipid syndrome. (Blood. 2012; 119(3):884-893) IntroductionAntiphospholipid syndrome (APS) is characterized by thrombosis and recurrent fetal loss in patients with circulating antiphospholipid Abs (APLAs) and is the most important cause of acquired thrombophilia. [1][2][3] Prospective studies have demonstrated that patients with APS experience significant morbidity and mortality despite recommendations for indefinite anticoagulation. 4 The term "antiphospholipid" is actually a misnomer, because the majority of APLAs are directed against phospholipid-binding proteins, of which ␤ 2 -glycoprotein I (␤ 2 GPI) is the most common. 5,6 The clinical importance of anti-␤ 2 GPI Abs has been demonstrated in several previous reports, 7 and recent studies have shown that affinity-purified human anti-␤ 2 GPI Abs induce thrombosis in mice. 8 Despite the clinical importance of APS, however, its pathogenesis has not been well defined. 1,3,9 One mechanism by which APLAs/anti-␤ 2 GPI Abs may promote thrombosis is through ␤ 2 GPI-dependent activation of endothelial cells (ECs). [10][11][12] ECs play a critical role in the maintenance of blood fluidity through expression of anticoagulant proteins on their luminal surface and the elaboration of antithrombotic substances. 13 However, EC activation leads to loss of these anticoagulant properties and transformation to a pro-adhesive, procoagulant phenotype. 13 APLAs/anti-␤ 2 GPI Abs induce EC activation in vitro and in vivo, as determined by their ability to increase the expression of adhesion molecules (E-selectin, ICAM-1, VCAM-1), and tissue factor (TF) and to enhance the expression, synthesis, and/or secretion of pro-inflammatory cytokines and chemokines. 3,[10][11][12] These effects may account for the ab...

The antiphospholipid syndrome (APS) is characterized by venous and/or arterial thrombosis, or recurrent fetal loss, in the presence of antiphospholipid antibodies (APL). The pathogenesis of APS is multifaceted and involves numerous mechanisms including activation of endothelial cells, monocytes, and/or platelets; inhibition of natural anticoagulant pathways such as protein C, tissue factor inhibitor, and annexin A5; activation of the complement system; and impairment of the fibrinolytic system. Fibrinolysis-the process by which fibrin thrombi are remodeled and degraded -involves the conversion of plasminogen to plasmin by tissue plasminogen activator (tPA) or urokinase-type plasminogen activator, and is tightly regulated. Although the role of altered fibrinolysis in patients with APS is relatively understudied, several reports suggest that deficient fibrinolytic activity may contribute to the pathogenesis of disease in these patients. This article discusses the function of the fibrinolytic system and reviews studies that have reported alterations in fibrinolytic pathways that may contribute to thrombosis in patients with APL. Some of these mechanisms include elevations in plasminogen activator inhibitor-1 levels, inhibitory antibodies against tPA or other components of the fibrinolytic system, antibodies against annexin A2, and finally, antibodies to β 2 -glycoprotein-I (β 2 GPI) that block the ability of β 2 GPI to stimulate tPAmediated plasminogen activation.

IntroductionThe antiphospholipid syndrome (APS) is characterized by arterial or venous thrombosis and/or recurrent fetal loss in the presence of antiphospholipid antibodies (APLAs). [1][2][3] It is now widely accepted that the majority of pathologic antibodies in patients with this disorder are actually directed against phospholipid-binding proteins, the most common of which is ␤ 2 -glycoprotein I (␤ 2 GPI).The pathogenesis of APS-associated thrombosis is multifactorial, and a number of mechanisms have been proposed. 4 These include inhibition of protein C activation and activity, 5,6 inhibition of annexin V assembly on exposed phospholipid surfaces, 7 and prevention of appropriate interactions of antithrombin with glycosaminoglycans, 8 among others. 4,9 Studies from our laboratory and others suggest that ␤ 2 GPI-dependent activation of vascular cells by APLA/anti-␤ 2 GPI antibodies plays a central role in disease pathogenesis 10,11 and may initiate the cascade of events that leads to thrombus development. For example, ␤ 2 GPI binds to endothelial cell annexin A2, and subsequent cross-linking of annexin A2-bound ␤ 2 GPI initiates endothelial cell activation through a pathway that may involve Toll-like receptor 4 (TLR-4) [11][12][13] and leads to activation of NF-B. 14 A similar pathway may be functional in monocytes, activation of which also contributes to the development of thrombosis in patients with APLA. 15 In addition, APLA may promote platelet activation in the presence of subthreshold concentrations of agonists, 16 although whether this is a receptor-mediated process, and if so, its relationship to platelet ␤ 2 GPI binding sites, such as GP1b 17 and apoER2, 18 requires further study.In endothelial cells, activation of NF-B stimulates an inflammatory and procoagulant response 19 and plays a critical role in the ability of APLA to promote thrombosis. 20 Thus, modulation of NF-B activity may provide an opportunity to reverse the pathologic vascular response in APS. The Krüppel-like factors (KLFs), 21 particularly KLF2 and KLF4, inhibit inflammatory cytokinemediated responses in endothelial cells, 22,23 at least in part through inhibition of NF-B activity. 23 However, expression of KLF2 itself may be inhibited by inflammatory cytokines and/or vascular injury, [23][24][25] although the expression of KLF4 appears to be increased under these conditions. 26 In considering the importance of NF-B in endothelial cell activation mediated by APLA/anti-␤ 2 GPI antibodies 14 and the potentially opposing effects of KLF2 and KLF4, we hypothesized that changes in expression of these transcription factors might influence the endothelial cell response to APLA/anti-␤ 2 GPI antibodies. Here, we report that, unlike responses to inflammatory cytokines, the expression of both KLF2 and KLF4 is decreased in response to APLA/anti-␤ 2 GPI antibodies. Moreover, restoring the expression of these KLFs blocks endothelial cell activation in response to APLA/anti-␤ 2 GPI antibodies. These activities result from inhibition of NF-B transcrip...

Persistent infection with oncogenic human papillomaviruses (HPVs) is the most important factor in the induction of uterine cervical cancer, a leading cause of cancer mortality in women worldwide. Upon cell transformation, continual expression of the viral oncogenes is required to maintain the transformed phenotype. The viral E6 protein forms a ternary complex with the cellular E6-AP protein and p53 protein which promotes the rapid degradation of p53. Recent studies have revealed that lignans from the creosote bush (3'-O-methyl-nordihydroguaiaretic acid) can repress the viral promoter responsible for E6 gene expression. Work reported here shows that the lignan can subvert viral oncogene function resulting in stabilized p53 protein within treated HPV-containing tumor cells. The stabilized p53 is transcriptionally active as demonstrated by a luciferase reporter vector and induction of genes for Bax and PUMA proteins. Apoptosis is detected by annexin V binding to treated cells as analyzed by flow cytometry. Programmed cell death is confirmed by the induction of active caspases and TUNEL assay. Initiator caspase-9 is activated first, followed later by the effector caspase-3 enzyme. The stabilization and induced apoptosis are not observed within treated HPV-negative cervical tumor cells. Quantitative real time RT-PCR analysis of endogenous E6 gene transcription from the integrated HPV 16 promoter shows at least a fivefold repression of expression as compared to untreated cells. These results indicate that the loss of E6 protein in treated cells could be, in part, responsible for the stabilization of p53 within the lignan treated cells.