Ligand-independent interaction of the type I interferon receptor complex is necessary to observe its biological activity

Abstract

Ectopic coexpression of the two chains of the Type I and Type III interferon (IFN) receptor complexes (IFN-αR1 and IFN-αR2c, or IFN-λR1 and IL-10R2) yielded sensitivity to IFN-alpha or IFN-lambda in only some cells. We found that IFN-αR1 and IFN-αR2c exhibit FRET only when expressed at equivalent and low levels. Expanded clonal cell lines expressing both IFN-αR1 and IFN-αR2c were sensitive to IFN-alpha only when IFN-αR1 and IFN-αR2c exhibited FRET in the absence of human IFN-alpha. Coexpression of RACK-1 or Jak1 enhanced the affinity of the interaction between IFN-αR1 and IFN-αR2c. Both IFN-αR1 and IFN-αR2c exhibited FRET with Jak1 and Tyk2. Together with data showing that disruption of the preassociation between the IFN-gamma receptor chains inhibited its biological activity, we propose that biologically active IFN receptors require ligand-independent juxtaposition of IFN receptor chains assisted by their associated cytosolic proteins.

Keywords: CiFP; Confocal fluorescence spectroscopy; ECFP; EGFP; EYFP; FRET; IFN; IFN-α; IFN-γ; IFN-λ; Interferon receptor; OFP; RACK-1; Receptor reconstitution; StFP; enhanced citrine fluorescent protein; enhanced cyan fluorescent protein; enhanced green fluorescent protein; enhanced yellow fluorescent protein; fluorescence resonance energy transfer; interferon; interferon-alpha; interferon-gamma; interferon-lambda; orange fluorescent protein; receptor for activated protein kinase-1; strawberry fluorescent protein.