Mapping the Complement Factor H-Related Protein 1 (CFHR1):C3b/C3d Interactions

Hannan, Jonathan P.; Laskowski, Jennifer; Thurman, Joshua M.; Hageman, Gregory S.; Holers, V. Michael

doi:10.1371/journal.pone.0166200

Cited by 25 publications

(20 citation statements)

References 49 publications

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“…6). Both FH and FHR-1 bind to C3b/C3d via their C termini, and a recent study confirmed that in FHR-1 the C-terminal C3b binding site of FH is essentially conserved (60). Previously, both weaker (a K D value of 6.4 mM for the interaction of CCPs 3-5 of FHR-1 with C3b versus 2.6 mM for CCPs 18-20 of FH with C3b) (12,61) and similarly strong (a K D value of ∼4 mM for the interaction of FHR-1-like mutant FH19-20 with C3b versus ∼6 mM for FH19-20) (19,62,63) binding of FHR-1 to C3b as compared with FH were described; in our convertase assay, no significant competition was observed.…”

Section: Discussionmentioning

confidence: 83%

FHR-1 Binds to C-Reactive Protein and Enhances Rather than Inhibits Complement Activation

Csincsi

Szabó

Bánlaki

et al. 2017

The Journal of Immunology

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Factor H-related protein (FHR) 1 is one of the five human FHRs that share sequence and structural homology with the alternative pathway complement inhibitor FH. Genetic studies on disease associations and functional analyses indicate that FHR-1 enhances complement activation by competitive inhibition of FH binding to some surfaces and immune proteins. We have recently shown that FHR-1 binds to pentraxin 3. In this study, our aim was to investigate whether FHR-1 binds to another pentraxin, C-reactive protein (CRP), analyze the functional relevance of this interaction, and study the role of FHR-1 in complement activation and regulation. FHR-1 did not bind to native, pentameric CRP, but it bound strongly to monomeric CRP via its C-terminal domains. FHR-1 at high concentration competed with FH for CRP binding, indicating possible complement deregulation also on this ligand. FHR-1 did not inhibit regulation of solid-phase C3 convertase by FH and did not inhibit terminal complement complex formation induced by zymosan. On the contrary, by binding C3b, FHR-1 allowed C3 convertase formation and thereby enhanced complement activation. FHR-1/CRP interactions increased complement activation via the classical and alternative pathways on surfaces such as the extracellular matrix and necrotic cells. Altogether, these results identify CRP as a ligand for FHR-1 and suggest that FHR-1 enhances, rather than inhibits, complement activation, which may explain the protective effect of FHR-1 deficiency in agerelated macular degeneration.

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Section: Discussionmentioning

confidence: 83%

FHR-1 Binds to C-Reactive Protein and Enhances Rather than Inhibits Complement Activation

Csincsi

Szabó

Bánlaki

et al. 2017

The Journal of Immunology

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“…This also revealed the presence of three critical residues that stabilize dimerization and are present in FHR-1, FHR-2, and FHR-5, suggesting that the three proteins would homo- and heterodimerize with each other. Dimerization was shown to increase the avidity of FHR-1 and FHR-5 for C3b and enhance complement activation, by enhancing their competition with FH activity in a guinea pig erythrocyte hemolysis assay ( 11 , 23 , 24 ). Although homodimerization has been confirmed for recombinant (r) FHR-1 and rFHR-2 ( 24 , 25 ), the presence of dimers in plasma has not yet been formally demonstrated.…”

Section: Introductionmentioning

confidence: 99%

Factor H-Related (FHR)-1 and FHR-2 Form Homo- and Heterodimers, while FHR-5 Circulates Only As Homodimer in Human Plasma

et al. 2017

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The complement factor H-related (FHR) proteins are hypothesized to fine-tune the regulatory role of complement factor H (FH) in the alternative pathway of the complement system. Moreover, FHR-1, FHR-2, and FHR-5 have been proposed to be dimers, which further complicates accurate analysis. As FHRs are highly similar among themselves and toward FH, obtaining specific reagents for quantification of serum levels and functional analysis is challenging. In this study, we generated antibodies and developed ELISAs to measure FHR-1, FHR-2, and FHR-5 in serum. We used both recombinant and serum-derived proteins to show that four dimers occur in human circulation: homodimers of FHR-1, FHR-2, and FHR-5, as well as FHR-1/FHR-2 heterodimers. Heterodimers containing FHR-5 were not found. In individuals with homozygous CFHR1 deletions or compound heterozygous CFHR2 missense/nonsense mutations identified in this study, the respective FHR-1 and FHR-2 homo- and heterodimers were absent. Using FRET, we found that recombinant FHR dimers exchange monomers rapidly. This was confirmed ex vivo, using FHR-1- and FHR-2-deficient sera. Of all FHR dimers, FHR-5/5 homodimers demonstrated strong binding affinity toward heparin. Specific ELISAs demonstrated that serum levels of FHR-1/1, FHR-1/2, FHR-2/2, and FHR-5/5 dimers were low compared to FH, which circulates at a 10- to 200-fold molar excess. In summary, FHR-1, FHR-2, and FHR-5 homodimerize, with FHR-1 and FHR-2 forming heterodimers as well, and equilibrate quickly in plasma.

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“…CFHR1 blocks C5 convertase activity and interferes with C5b surface association to regulate the complement system ( Hannan et al, 2016 ). It competes with complement factor H (CFH) to bind to C3b, thereby functioning as an antagonist of CFH-directed regulation at cell surfaces.…”

Section: Discussionmentioning

confidence: 99%

Novel circulating protein biomarkers for thyroid cancer determined through data-independent acquisition mass spectrometry

Liu

et al. 2020

PeerJ

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Background Distinguishing between different types of thyroid cancers (TC) remains challenging in clinical laboratories. As different tumor types require different clinical interventions, it is necessary to establish new methods for accurate diagnosis of TC. Methods Proteomic analysis of the human serum was performed through data-independent acquisition mass spectrometry for 29 patients with TC (stages I–IV): 13 cases of papillary TC (PTC), 10 cases of medullary TC (MTC), and six cases follicular TC (FTC). In addition, 15 patients with benign thyroid nodules (TNs) and 10 healthy controls (HCs) were included in this study. Subsequently, 17 differentially expressed proteins were identified in 291 patients with TC, including 247 with PTC, 38 with MTC, and six with FTC, and 69 patients with benign TNs and 176 with HC, using enzyme-linked immunosorbent assays. Results In total, 517 proteins were detected in the serum samples using an Orbitrap Q-Exactive-plus mass spectrometer. The amyloid beta A4 protein, apolipoprotein A-IV, gelsolin, contactin-1, gamma-glutamyl hydrolase, and complement factor H-related protein 1 (CFHR1) were selected for further analysis. The median serum CFHR1 levels were significantly higher in the MTC and FTC groups than in the PTC and control groups (P < 0.001). CFHR1 exhibited higher diagnostic performance in distinguishing patients with MTC from those with PTC (P < 0.001), with a sensitivity of 100.0%, specificity of 85.08%, area under the curve of 0.93, and detection cut-off of 0.92 ng/mL. Conclusion CFHR1 may serve as a novel biomarker to distinguish PTC from MTC with high sensitivity and specificity.

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Mapping the Complement Factor H-Related Protein 1 (CFHR1):C3b/C3d Interactions

Cited by 25 publications

References 49 publications

FHR-1 Binds to C-Reactive Protein and Enhances Rather than Inhibits Complement Activation

FHR-1 Binds to C-Reactive Protein and Enhances Rather than Inhibits Complement Activation

Factor H-Related (FHR)-1 and FHR-2 Form Homo- and Heterodimers, while FHR-5 Circulates Only As Homodimer in Human Plasma

Novel circulating protein biomarkers for thyroid cancer determined through data-independent acquisition mass spectrometry

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