Feline Interleukin-31 Shares Overlapping Epitopes with the Oncostatin M Receptor and IL-31RA

Interleukin-31
(IL-31) is a major protein involved in severe inflammatory
skin disorders. Its signaling pathway is mediated through two type
I cytokine receptors, IL-31RA (also known as the gp130-like receptor)
and the oncostatin M receptor (OSMR). Understanding molecular details
in these interactions would be helpful for developing antagonist anti-IL-31
monoclonal antibodies (mAbs) as potential therapies. Previous studies
suggest that human IL-31 binds to IL-31RA and then recruits OSMR to
form a ternary complex. In this model, OSMR cannot interact with IL-31
in the absence of IL-31RA. In this work, we show that feline IL-31
(fIL-31) binds independently with feline OSMR using surface plasmon
resonance, an enzyme-linked immunosorbent assay, and yeast surface
display. Moreover, competition experiments suggest that OSMR shares
a partially overlapping epitope with IL-31RA. We then used deep mutational
scanning to map the binding sites of both receptors on fIL-31. In
agreement with previous studies of the human homologue, the binding
site for IL31-RA contains fIL-31 positions E20 and K82, while the
binding site for OSMR comprises the “PADNFERK” motif
(P103–K110) and position G38. However, our results also revealed
a new overlapping site, composed of positions R69, R72, P73, D76,
D81, and E97, between both receptors that we called the “shared
site”. The conformational epitope of an anti-feline IL-31 mAb
that inhibits both OSMR and IL-31RA also mapped to this shared site.
Combined, our results show that fIL-31 binds IL-31RA and OSMR independently
through a partially shared epitope. These results suggest reexamination
of the putative canonical mechanisms for IL-31 signaling in higher
animals.