Adenosine Deaminase Acts as a Natural Antagonist for Dipeptidyl Peptidase 4-Mediated Entry of the Middle East Respiratory Syndrome Coronavirus

Abstract

In 2012, a previously unknown human coronavirus (CoV), now named Middle East respiratory syndrome CoV (MERS-CoV), was isolated from the sputum of a 60-year-old man in Saudi Arabia who presented with acute pneumonia with a fatal outcome (1, 2). To date, several infection clusters have been reported over a 1-year period, with around 50% of the reported human cases being fatal (3). MERS-CoV represents a novel betacoronavirus species, with the closest known relatives being clade 2c bat CoVs detected in bats (4, 5). Although MERS-CoV replicates in cells of bats, pigs, and (non-)human primates (6), its ability to infect some animal species may be restricted given the fact that hamsters were shown to resist MERS-CoV infection (7). However, these host factors have not been well characterized.We recently identified dipeptidyl peptidase 4 (DPP4) as a functional MERS-CoV receptor in human and bat cells (8). To further analyze DPP4 usage by MERS-CoV in vivo, ferrets (Mustela putorius furo; n ϭ 4), known to be susceptible to several respiratory viruses, including severe acute respiratory syndrome CoV (SARS- staining or S1-Fc binding on ferret kidney cells incubated with either goat anti-DPP4 polyclonal serum or S1-Fc (5 g/ml) followed by incubation with fluorescein isothiocyanate (FITC)-labeled rabbit anti-goat IgG antibody or FITC-labeled goat anti-human IgG, respectively (red lines). Normal goat serum, feline CoV S1-Fc protein (blue lines), and mock-incubated cells (gray shading) were used as controls. (E) MERS-CoV infection of primary ferret kidney cells transfected with a control plasmid or with a plasmid encoding hDPP4, stained for DPP4, S1 binding, and MERS-CoV as described previously (13).

Coronavirus Host Range Expansion and Middle East Respiratory Syndrome Coronavirus Emergence: Biochemical Mechanisms and Evolutionary Perspectives

“…Cockrell et al (61) found that introducing part of this region (residues 279 to 346) from hDPP4 into mouse DPP4 (mDPP4) resulted in successful infection in vitro. This result is supported by a similar experiment conducted using ferret DPP4 (fDPP4), in which swapping residues 247 to 504 of hDPP4 into the fDPP4 backbone supported MERSCoV infection (63). In addition, transfecting hDPP4 into mouse or hamster cell lines resulted in successful infection (61), suggesting that it is host cell receptor interactions that restrict MERSCoV host range, rather than the presence of other host-specific restriction factors.…”

“…It has been well studied due to the role it plays in glucose metabolism, immune responses, adhesion, and apoptosis (57). Whereas MERS-CoV can enter cells using DPP4 from humans, nonhuman primates, bats (58), camels, horses, and to a lesser extent goats (59,60), it is unable to enter cells using DPP4 from traditional small animal model species such as mice (61,62), ferrets (63), and hamsters (58,64). This species restriction prevents the adequate study of MERS-CoV pathogenesis and limits the development of vaccine strategies or alternate therapeutics.…”

A Comparative Review of Animal Models of Middle East Respiratory Syndrome Coronavirus Infection

“…70 MERS-CoV S cannot bind to DPP4 in species that have significant differences in these 14 amino acids as compared with human DPP4 (hDPP4), such as ferrets, hamsters, and mice; thus, these species are resistant to infection. 21,40,62,69 Species with few or no differences in the 14 amino acids seem to be susceptible to MERS-CoV, including rhesus macaques, common marmosets, and camels. 25,50,69 In addition to analyzing the DPP4 amino acid sequence, evaluating the binding energies between MERS-CoV and DPP4 has proven useful in assessing whether MERS-CoV S can bind to DPP4 from different species.…”

“…17,21,62 Despite a lack of conventional small animal models, researchers have identified several other species that are susceptible to MERS-CoV infection, including rabbits, hDPP4-transduced or hDPP4-transgenic mice, rhesus macaques, and common marmosets (summarized in Tables 1 and 2). Each animal model of MERS-CoV infection is discussed in detail.…”

What are our pharmacotherapeutic options for MERS-CoV?

“…The development of inhibitors that target the binding site and receptors (DPP4) may prove to be of benefit for the therapy of MERS-CoV infection [9]. An in vitro study of MERS-CoV infection in ferrets showed that adenosine deaminase, a DPP4 binding protein, competed for virus binding and exhibited a natural antagonist for MERS-CoV infection [9]. For the search of an effective therapy, the domains of DPP4 (CD26) were required for the binding of MERS-CoV [8,10].…”