Involvement of annexin A2 in anti-β2GPI/β2GPI-induced tissue factor expression on monocytes

Abstract

Dear Editor:Growing evidence demonstrates that β 2 -glycoprotein I (β 2 GPI) is the key target for antiphospholipid antibodies which are closely associated with thrombotic events in antiphospholipid syndrome (APS) [1]. Anti-β 2 GPI/β 2 GPI complex can bind to the surface membrane of monocytes and endothelial cells, promoting tissue factor (TF) activity on these cells, and thus increasing the risk of thrombosis. However, the mechanisms underlying the actions of anti-β 2 GPI/β 2 GPI are not well understood. It was proposed that the effects of anti-β 2 GPI/β 2 GPI require the transduction of a signal into the cell and, therefore, involve a cell surface receptor. Since the effects of anti-β 2 GPI/β 2 GPI do not appear to be mediated by Fc receptors, nor by negatively-charged phospholipids of the cell membrane, investigators posit the existence of a distinct cell surface receptor for β 2 GPI.In previous work, McCrae and colleagues demonstrated annexin A2 (ANX2, formerly called annexin II) as a highaffinity receptor for β 2 GPI on endothelial cells (Ma et al) [2]. Furthermore, they showed that ANX2 mediates anti-β 2 GPI/β 2 GPI complex binding to endothelial cell surface, stimulating the activation of endothelium and increasing the levels of TF, VCAM-1 (vascular cell adhesion molecule 1) and other inflammatory molecules in circulation [3]. Their findings establish an important point that a cell surface receptor is critical in mediating the effects of autoantiphospholipid antibodies (APL) on endothelial cells. Our previous study showed that anti-β 2 GPI could induce monocyte TF activity in APS [4]. Finding the mediator for anti-β 2 GPI/β 2 GPI in monocytes would be a key step in further understanding APL associated pathology in APS.McCrae's observation on endothelial cells led us to ask similar questions for monocytes. Is ANX2 expressed on monocytes? Does ANX2 mediate anti-β 2 GPI/β 2 GPI binding to monocytes, leading to stimulation of TF expression?Using the specific anti-ANX2 antibody, we have demonstrated by western blotting that both peripheral blood monocytes and the monocytic cell line, MM6 cells, contained ANX2 protein (36 kDa) in their membrane lysates ( Figure 1A). The surface ANX2 expression on blood monocytes ( Figure 1B a-c) and MM6 cells ( Figure 1B d-f) was also detected by flow cytometry analysis. The mean fluorescence intensity of cells treated with the calcium chelator EGTA was obviously weaker than that of cells without the EGTA treatment, suggesting that ANX2 is a calcium-dependent protein, which is consistent with previously published results [5].We next investigated whether ANX2 can mediate anti-β 2 GPI/β 2 GPI binding to monocytes, and thus stimulating TF expression on these cells. The results showed that TF activity on monocytes induced by anti-β 2 GPI/β 2 GPI was decreased when cells were pre-incubated with the monoclonal anti-ANX2 antibody, while the control antibody had no such inhibitory effects. Importantly, anti-ANX2 antibody did not affect the effect of LPS on TF expression ( Figure 1C)....

Annexin A2 is involved in antiphospholipid antibody-mediated pathogenic effects in vitro and in vivo

“…Further evidence for the in vitro interaction of ␤ 2 GPI with anti-A2 Abs and anti-␤ 2 GPI was recently provided by Zhou et al, who showed that exogenous ␤ 2 GPI enhanced the effect of anti-A2 Abs and anti-␤ 2 GPI Abs on monocytes and stabilized the formation of a ternary complex, consisting of A2, ␤ 2 GPI, and the corresponding Ab (anti-A2 or anti-␤ 2 GPI). 51 In addition, Sorice et al recently showed evidence of anti-␤ 2 GPI and A2 interactions in lipid raft fractions of human monocyte plasma membranes. 52 In our study, it is noteworthy that the lack of A2 or the addition of an anti-A2 Ab seemed to produce a significant but incomplete inhibition of some of the pathogenic effects induced by aPL Abs both in vitro and in vivo, indicating that when A2 was present, a supplementation effect is observed.…”

“…These investigators showed further that A2 mediated binding of ␤ 2 GPI/anti-␤ 2 GPI complexes to monocytes and stimulated their expression of TF. 51 Cesarman et al reported that Abs directed to A2 are highly prevalent in thrombosis in the setting of APS. They also found that anti-A2 IgG from patients with APS induced TF expression on ECs as effectively as that observed by patient anti-␤ 2 GPI Abs.…”

Gemcitabine Resistance Induced by Interaction between Alternatively Spliced Segment of Tenascin-C and Annexin A2 in Pancreatic Cancer Cells

“…4) ANXA2 had been proposed to function inside the cell in sorting of endosomes and outside the cell in anticoagulant reactions. 5,6) Additionally, enhanced expression of ANXA2 in human pancreatic carcinoma cells and primary pancreatic cancers was observed. 7) ANXA2 overexpression predicted an rapid recurrence after surgery in pancreatic cancer patients undergoing gemcitabine-adjuvant chemotherapy.…”

“…10) Each subunit of TN-C contained a TA domain that formed a coiled-coil at the N-terminus, 14ϩ1/2 epidermal growth factor (EGF)-like domains, 8-15 fibronectin type III-like (FNIII) repeats (depending on alternative RNA splicing) and a fibrinogen-like domain (FBG). The universal FNIII domains (FNIII repeats 1-5 and FNIII repeats [6][7][8] were present in all TN-C variants. The largest TN-C variant also contains nine alternatively spliced domains (FNIII repeats A1-D, TNfnA-D, Fig.…”

The dual role of innate immunity in the antiphospholipid syndrome

“…8 β 2 GPI has been shown to interact with annexin A2 on both endothelial cells 7,9 and monocytes. 8,10 In the case of monocytes, at least, membrane association of β 2 GPI is with both annexin A2 and toll-like receptor 4 (TLR4), and it appears to occur within lipid rafts. 8 In vivo, in a rat model of mesenteric arterial thrombosis, human polyclonal anti-β 2 GPI antibodies lacked a procoagulant effect, while anti-β 2 GPI antibodies combined with LPS resulted in thrombotic occlusion.…”