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The E3 ubiquitin ligase SCF(Fbxo7) mediates proteasomal degradation of UXT isoform 2 (UXT-V2) to inhibit the NF-κB signaling pathway.

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Spagnol, Valentine 
Oliveira, Caio AB 
Randle, Suzanne J 
Passos, Patrícia MS 
Correia, Camila RSTB 


BACKGROUND: Ubiquitously eXpressed Transcript isoform 2 (UXTV2) is a prefoldin-like protein involved in NF-κB signaling, apoptosis, and the androgen and estrogen response. UXT-V2 is a cofactor in the NF-κB transcriptional enhanceosome, and its knockdown inhibits TNF-α -induced NF-κB activation. Fbxo7 is an F-box protein that interacts with SKP1, Cullin1 and RBX1 proteins to form an SCF(Fbxo7) E3 ubiquitin ligase complex. Fbxo7 negatively regulates NF-κB signaling through TRAF2 and cIAP1 ubiquitination. METHODS: We combine co-immunoprecipitation, ubiquitination in vitro and in vivo, cycloheximide chase assay, ubiquitin chain restriction analysis and microscopy to investigate interaction between Fbxo7 and overexpressed UXT-V2-HA. RESULTS: The Ubl domain of Fbxo7 contributes to interaction with UXTV2. This substrate is polyubiquitinated by SCF(Fbxo7) with K48 and K63 ubiquitin chain linkages in vitro and in vivo. This post-translational modification decreases UXT-V2 stability and promotes its proteasomal degradation. We further show that UXTV1, an alternatively spliced isoform of UXT, containing 12 additional amino acids at the N-terminus as compared to UXTV2, also interacts with and is ubiquitinated by Fbxo7. Moreover, FBXO7 knockdown promotes UXT-V2 accumulation, and the overexpression of Fbxo7-ΔF-box protects UXT-V2 from proteasomal degradation and enhances the responsiveness of NF-κB reporter. We find that UXT-V2 colocalizes with Fbxo7 in the cell nucleus. CONCLUSIONS: Together, our study reveals that SCF(Fbxo7) mediates the proteasomal degradation of UXT-V2 causing the inhibition of the NF-κB signaling pathway. GENERAL SIGNIFICANCE: Discovering new substrates of E3 ubiquitin-ligase SCF(Fbxo7) contributes to understand its function in different diseases such as cancer and Parkinson.



E3 ubiquitin ligase, NF-kappa B (NF-κB), SCF(Fbxo7), UXT-V1, UXT-V2, Ubiquitylation (ubiquitination), Cell Cycle Proteins, Cell Line, Tumor, F-Box Proteins, HEK293 Cells, Humans, Molecular Chaperones, NF-kappa B, Proteasome Endopeptidase Complex, Protein Isoforms, Proteolysis, SKP Cullin F-Box Protein Ligases, Signal Transduction, Ubiquitination

Journal Title

Biochim Biophys Acta Gen Subj

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Elsevier BV
Biotechnology and Biological Sciences Research Council (BB/J007846/1)
Biotechnology and Biological Science Research Council [BB/J007846/1];