The ubiquitin- and proteasome-dependent degradation of COX-2 is regulated by the COP9 signalosome and differentially influenced by coxibs.
The cyclooxygenase-2 (COX-2) enzyme is induced upon inflammation and in neoplastic tissues. It produces prostaglandins that stimulate tumor angiogenesis and tumor growth. Therefore, destruction and/or specific inhibition of COX-2 should be an important aspect of future tumor therapy. Recently, clinical application of specific COX-2 inhibitors called coxibs became doubtfully because they produce serious renal and cardiovascular complications under long term application. The exact underlying mechanisms are poorly understood and the different effects of diverse coxibs are not explained. It has been demonstrated before that COX-2 is degraded by the ubiquitin (Ub) proteasome system (UPS). However, how ubiquitination is accomplished and regulated was unclear. An important regulator of the UPS is the COP9 signalosome (CSN), which controls the stability of many proteins. Here we show that the proteasome-dependent degradation of COX-2 in HeLa cell lysate and in HeLa cells was stimulated by curcumin, an inhibitor of CSN-associated kinases. These data suggest a function of the CSN in the degradation of COX-2. In addition, proteolysis of COX-2 was significantly accelerated by parecoxib, but not by celecoxib or rofecoxib. By density gradient centrifugation and immunoprecipitation we demonstrate that COX-2 physically interacts with the CSN. Moreover, COX-2 is associated with large complexes consisting of the CSN, cullin-RING Ub ligases and the 26S proteasome. Pulldown experiments with Flag-COX-2 revealed cullin 1 and cullin 4 as components of the large super-complexes. Cullin 1 and 4 are scaffolding proteins of Ub ligases that presumably ubiquitinate COX-2. Treatment of HeLa cells with parecoxib results in an accelerated degradation of endogenous COX-2 accompanied by an increase of COX-2-Ub conjugates. In HeLa cells parecoxib is converted to the selective COX-2 inhibitor valdecoxib. Addition of valdecoxib also stimulates COX-2 degradation in HeLa cells. We therefore conclude that valdecoxib specifically interacts with COX-2 and induces a conformation accessible for ubiquitination and degradation.
Neuss
Heiko
H
Department of General, Visceral, Vascular and Thoracic Surgery, Charité-Universitätsmedizin Berlin, Monbijoustrasse 2, 10117, Berlin, Germany.
Huang
Xiaohua
X
Hetfeld
Bettina K J
BK
Deva
Rupal
R
Henklein
Petra
P
Nigam
Santosh
S
Mall
Julian W
JW
Schwenk
Wolfgang
W
Dubiel
Wolfgang
W
D015153:Blotting, Western; D000075686:COP9 Signalosome Complex; D018797:Cell Cycle Proteins / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D044842:Cullin Proteins / Q000378:metabolism; D003474:Curcumin / Q000494:pharmacology; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology*; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D007555:Isoxazoles / Q000494:pharmacology; D046912:Multiprotein Complexes / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects
D018797:Cell Cycle Proteins; C100318:Cullin 1; D044842:Cullin Proteins; D052246:Cyclooxygenase 2 Inhibitors; D007555:Isoxazoles; D046912:Multiprotein Complexes; D025801:Ubiquitin; C409945:parecoxib; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D044767:Ubiquitin-Protein Ligases; D010447:Peptide Hydrolases; D000075686:COP9 Signalosome Complex; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D003474:Curcumin