The tumor- and apoptosis-associated annexin A2 is a new ligand for FHL-1 and Factor H-related proteins – annexin-bound FHR-5 enhances alternative pathway activation

Le résumé fourni par la source

Annexin A2 (ANXA2) is a membrane-binding protein with diverse intra- and extracellular roles and involvement in certain tumorous and immune processes. Elevated ANXA2 cell-surface levels are characteristic of apoptotic cells where it serves as a ligand for factor H (FH) 1 . In mice, ANXA2 enhanced complement activation both in vitro and in vivo by blocking complement regulatory functions of FH, suggesting a mechanism by which ANXA2 contributes to complement-mediated diseases 2 . However, interactions between ANXA2 and other FH family proteins have not yet been studied, and little is known about the implications of ANXA2 as a ligand for FH or the FH-related proteins (FHRs). We purified FH from normal human serum (NHS) and produced recombinant FH fragments, FH-like protein 1 (FHL-1), FHRs, full-length and N-terminally truncated ANXA2 to map the respective binding sites on FH and ANXA2, and to test whether the FHRs bind ANXA2 using ELISA. We studied the functional effects of these interactions using ANXA2 as a surface-bound ligand in cofactor activity and alternative pathway (AP) activation assays. Our results indicate that the N-terminal peptide of ANXA2 plays no significant role in binding to FH family proteins. Previously, the binding site for ANXA2 on FH was mapped to complement control protein domains (CCP) 6-8 1 . In our assays, all proteins containing FH CCP 19-20 or highly similar domains (FHR-1A, FHR-1B, FH fragments CCP 15-20 and 19-20) bound to ANXA2, suggesting the existence of a second binding site in the C-terminal region of FH. Additionally, FHL-1 and FHRs except FHR-2 bound ANXA2. We demonstrated that FH and FHL-1 retain their cofactor activity when bound to ANXA2. Accordingly, immobilized ANXA2 does not activate the AP in NHS. On the other hand, in NHS supplemented with FHR-5, we observed significant AP activation, detected as factor B, properdin and C5 deposition. In conclusion, ANXA2 is a common self-ligand for FH family proteins that does not inhibit cofactor activity of FH or FHL-1. Moreover, FHR-5 can enhance AP activity on ANXA2-covered surfaces. Taken together, our findings suggest that ANXA2 plays an important role in the balanced regulation of local complement activation on certain self-surfaces. 1. Leffler J. et al. J Biol Chem. (2010) 285:3766–3776. 2. Renner B et al. J Immunol. (2016) 196:1355–1365. Supported by grants from the National Research, Development and Innovation Office (PharmaLab National Laboratory, RRF-2.3.1-21-2022-00015, OTKA K146911), the Hungarian Research Network (0106307), the European Union (nr. 899163 SciFiMed project).

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.