D. Russellharde et al., RECONSTITUTION OF A HIGH-AFFINITY BINDING-SITE FOR TYPE-I INTERFERONS, The Journal of biological chemistry, 270(44), 1995, pp. 26033-26036
The type I interferon (IFN) receptor complex is assumed to be composed
of multiple protein subunits, Recently, two proteins have been identi
fied as potential receptor components, both of which share a high degr
ee of structural homology with the immunoglobulin superfamily, One of
these proteins, referred to as the human interferon alpha receptor (IF
NAR), has been shown to be involved in interferon signal transduction,
but it does not bind IFN with high affinity, A second putative recept
or protein, named FLP40, has been cloned from human Daudi cells, Trans
fection of FLP40 into murine NIH 3T3 cells does not result in high aff
inity IFN binding, In this study, we demonstrate that when expressed i
n murine L929 cells neither IFNAR nor FLP40 by themselves are capable
of binding human IFN-alpha 8. Co-expression of IFNAR and FLP40 results
in cells capable of binding IFN-alpha 8 and IFN-alpha 2. Scatchard an
alysis of binding demonstrated the presence of high (K-D 350 pM) and l
ow (K-D 4.0 nM) affinity binding sites, Binding of radiolabeled IFN-al
pha 8 can be competed with either unlabeled IFN-alpha 8 or a recombina
nt form of human interferon beta, IFN-beta 1b, but not with IFN-gamma.
Ligand binding of LFN-alpha 8 can be inhibited by antibodies directed
against IFNAR providing further support for a role for this protein i
n the formation of a ligand binding site, This is the first demonstrat
ion indicating that two previously identified IFN receptor proteins, w
hich individually do not bind type I IFN with high affinity, cooperate
in the formation of a type I IFN receptor ligand binding complex.