Receptor for activated C-kinase (RACK-1), a WD motif-containing protein, specifically associates with the human type IIFN receptor

The cytoplasmic domain of the human type I IFN receptor chain 2 (IFNAR2c or IFN-alphaR betaL) was used as bait in a yeast two-hybrid system to identif y novel proteins interacting with this region of the receptor. We report he re a specific interaction between the cytoplasmic domain of IFN-alphaR beta L and a previously identified protein, RACK-1 (receptor for activated C kin ase), Using GST fusion proteins encoding different regions of the cytoplasm ic domain of IFN-alphaR betaL, the minimum site for RACK-1 binding was mapp ed to aa 300-346, RACK-1 binding to IFN-alphaR betaL did not require the fi rst 91 aa of RACK-1, which includes two WD domains, WD1 and WD2. The intera ction between RACK-1 and IFN-alphaR beta, but not the human IFN receptor ch ain 1 (IFNAR1 or IFN-alphaR alpha), was also detected in human Daudi cells by coimmunoprecipitation. RACK-1 was shown to be constitutively associated with IFN-alphaR betaL, and this association was not effected by stimulation of Daudi cells with type I IFNs (IFN-beta 1b). RACK-1 itself did not becom e tyrosine phosphorylated upon stimulation of Daudi cells with IFN-beta 1b, However, stimulation of cells with either IFN-beta 1b or PMA did result in an increase in detectable immunofluorescence and intracellular redistribut ion of RACK-1.