Ubiquitination, endocytosis, and lysosomal degradation of the IFNAR1 (interferon 
alpha receptor 1) subunit of the type I interferon (IFN) receptor is mediated by 
the SCFbeta-Trcp (Skp1-Cullin1-F-box protein beta transducin repeat-containing 
protein) E3 ubiquitin ligase in a phosphorylation-dependent manner. In addition, 
stability of IFNAR1 is regulated by its binding to Tyk2 kinase. Here we 
characterize the determinants of IFNAR1 ubiquitination and degradation. We found 
that the integrity of two Ser residues at positions 535 and 539 within the 
specific destruction motif present in the cytoplasmic tail of IFNAR1 is 
essential for the ability of IFNAR1 to recruit beta-Trcp as well as to undergo 
efficient ubiquitination and degradation. Using an antibody that specifically 
recognizes IFNAR1 phosphorylated on Ser535 we found that IFNAR1 is 
phosphorylated on this residue in cells. This phosphorylation is promoted by 
treatment of cells with IFNalpha. Although the cytoplasmic tail of IFNAR1 
contains seven Lys residues that could function as potential ubiquitin acceptor 
sites, we found that only three (Lys501, Lys525, and Lys526), all located 
proximal to the destruction motif, are essential for ubiquitination and 
degradation of IFNAR1. Expression of Tyk2 stabilized IFNAR1 in a manner that was 
dependent neither on its binding to beta-Trcp nor IFNAR1 ubiquitination. We 
discuss the complexities and specifics of the ubiquitination and degradation of 
IFNAR1, which is a beta-Trcp substrate that undergoes degradation via a 
lysosomal pathway.