TIP120A associates with cullins and modulates ubiquitin ligase activity.
The cullin-containing ubiquitin-protein isopeptide ligases (E3s) play an important role in regulating the abundance of key proteins involved in cellular processes such as cell cycle and cytokine signaling. They have multisubunit modular structures in which substrate recognition and the catalysis of ubiquitination are carried out by distinct polypeptides. In a search for proteins involved in regulation of cullin-containing E3 ubiquitin ligases we immunopurified CUL4B-containing complex from HeLa cells and identified TIP120A as an associated protein by mass spectrometry. Immunoprecipitation of cullins revealed that all cullins tested specifically interacted with TIP120A. Reciprocal immunoaffinity purification of TIP120A confirmed the stable interaction of TIP120A with cullin family proteins. TIP120A formed a complex with CUL1 and Rbx1, but interfered with the binding of Skp1 and F-box proteins to CUL1. TIP120A greatly reduced the ubiquitination of phosphorylated IkappaBalpha by SCF(beta-TrCP) ubiquitin ligase. These results suggest that TIP120A functions as a negative regulator of SCF E3 ubiquitin ligases and may modulate other cullin ligases in a similar fashion.
Min
Kyoeng-Woo
KW
Department of Biochemistry and Protein Network Research Center, Yonsei University, Seoul 120-749, Korea.
Hwang
Ji-Won
JW
Lee
Jong-Sik
JS
Park
Yoon
Y
Tamura
Taka-aki
TA
Yoon
Jong-Bok
JB
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D044842:Cullin Proteins; D004268:DNA-Binding Proteins; D044783:F-Box Proteins; D006367:HeLa Cells; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D008025:Ligases / Q000378:metabolism*; D008969:Molecular Sequence Data; D000072000:NF-KappaB Inhibitor alpha; D010453:Peptide Synthases / Q000502:physiology; D044843:SKP Cullin F-Box Protein Ligases; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
D001426:Bacterial Proteins; C486317:CAND1 protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C100318:Cullin 1; D044842:Cullin Proteins; D004268:DNA-Binding Proteins; D044783:F-Box Proteins; D020672:I-kappa B Proteins; C000606204:NFKBIA protein, human; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D025801:Ubiquitin; D000072000:NF-KappaB Inhibitor alpha; D044843:SKP Cullin F-Box Protein Ligases; C120507:SKP1 protein, S cerevisiae; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; D010453:Peptide Synthases