HOS, a human homolog of Slimb, forms an SCF complex with Skp1 and Cullin1 and targets the phosphorylation-dependent degradation of IκB and β-catenin

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Abstract
SCF E3 ubiquitin ligases mediate ubiquitination and proteasome-dependent degradation of phosphorylated substrates. We identified a human F-box/WD40 repeats protein (HOS), which is homologous to Slimb/hβTrCP. Being a part of SCF complex with Skp1 and Cullin1, HOS specifically interacted with the phosphorylated IκB and β-catenin, targeting these proteins for proteasome-dependent degradation in vivo. This targeting required Cullin1 as expression of a mutant Cullin1 abrogated the degradation of IκB and of β-catenin. Mutant HOS which lacks the F-box blocked TNFα-induced degradation of IκB as well as GSK3β-mediated degradation of β-catenin. This mutant also inhibited NF-κB transactivation and increased the β-catenin-dependent transcription activity of Tcf. These results demonstrate that SCFHOS E3 ubiquitin ligase regulate both NF-κB and β-catenin signaling pathways.