Abstract
Etanercept is a soluble form of the tumor necrosis factor receptor 2 (TNFR2) that inhibits pathological tumor necrosis factor (TNF) responses in rheumatoid arthritis and other inflammatory diseases. However, besides TNF, etanercept also blocks lymphotoxin-α (LTα), which has no clear therapeutic value and might aggravate some of the adverse effects associated with etanercept. Poxviruses encode soluble TNFR2 homologs, termed viral TNF decoy receptors (vTNFRs), that display unique specificity properties. For instance, cytokine response modifier D (CrmD) inhibits mouse and human TNF and mouse LTα, but it is inactive against human LTα. Here, we analyzed the molecular basis of these immunomodulatory activities in the ectromelia virus-encoded CrmD. We found that the overall molecular mechanism to bind TNF and LTα from mouse and human origin is fairly conserved in CrmD and dominated by a groove under its 50s loop. However, other ligand-specific binding determinants optimize CrmD for the inhibition of mouse ligands, especially mouse TNF. Moreover, we show that the inability of CrmD to inhibit human LTα is caused by a Glu-Phe-Glu motif in its 90s loop. Importantly, transfer of this motif to etanercept diminished its anti-LTα activity in >60-fold while weakening its TNF-inhibitory capacity in 3-fold. This new etanercept variant could potentially be used in the clinic as a safer alternative to conventional etanercept. This work is the most detailed study of the vTNFR-ligand interactions to date and illustrates that a better knowledge of vTNFRs can provide valuable information to improve current anti-TNF therapies.
Highlights
The tumor necrosis factor ␣ (TNF)-binding domain of cytokine response modifier D (CrmD) is proposed to be formed by four cysteine-rich domain (CRD) [10]; the amino acids that mark the end of the TNF-binding moiety and the beginning of the antichemokine smallpox-encoded chemokine receptor (SECRET) domain have never been experimentally identified
Multiple efforts have been made to characterize the immunomodulatory capacities of viral TNF decoy receptors (vTNFRs) in vivo and in vitro; the molecular mechanisms of vTNFR–ligand interactions remain poorly analyzed
Our work proves that structural analyses of vTNFRs can be of great value to improve anti-TNF therapies based on soluble decoy receptors
Summary
The TNF-binding domain of CrmD is proposed to be formed by four CRDs [10]; the amino acids that mark the end of the TNF-binding moiety and the beginning of the antichemokine SECRET domain have never been experimentally identified. We compared the chemokine-binding affinities of two CrmD truncated mutants for two different forms of the SECRET domain: SECRET163 (Phe163–Asp320), containing the Phe163 and Asn164 conserved in the SCPs, and SECRET181 (Ser181– Asp320), which includes the C-terminal sequence immediately after the putative CRD4 of CrmD (Fig. 1B). A 10 M excess of both CrmD and CRD-CrmD protected at least 50% of the cells against mTNF (Fig. 2D) These results confirmed our conclusions based on the binding assays and indicated that the second half of the putative CRD4 is not involved in TNF binding but it is most likely part of the SECRET domain
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
