Wednesday March 11 2009
CEA
COP9 signalosome- and 26S Proteasome-dependent regulation of SCFTIR1 accumulation in Arabidopsis.
J Biol Chem (2009) sous presse
CEA
Ubiquitination and proteasome-mediated degradation of proteins are crucial for eukaryotic physiology and development. The largest class of E3 ubiquitin ligases are the cullin-RING ligases (CRLs) which are themselves positively regulated through conjugation of the ubiquitin-like peptide RUB/NEDD8 to cullins. RUB modification is antagonized by the COP9 signalosome (CSN), an evolutionary conserved eight-subunit complex which is essential in most eukaryotes and cleaves RUB from cullins. The CSN behaves genetically as an activator of CRLs, although it abolishes CRL activity in vitro. This apparent paradox was recently reconciled in different organisms, as the CSN was shown to prevent autocatalytic degradation of several CRL substrate adaptors. We tested for such a mechanism in the model plant Arabidopsis by measuring the impact of a newly identified viable csn2 mutant on the activity and the stability of SCF(TIR1), a receptor to the phytohormone auxin and probably the best-characterized plant CRL. Our analysis reveals that not only the F-box protein TIR1 but also relevant cullins are destabilized in csn2 and other Arabidopsis csn mutants. These results provide an explanation for the auxin resistance of csn mutants. We further observe in vivo post-translational modification of TIR1 dependent on the proteasome inhibitor MG-132 and provide evidence for proteasome-mediated degradation of TIR1, CUL1 and ASK1 (Arabidopsis SKP1 homolog). These results are consistent with CSN-dependent protection of Arabidopsis CRLs from autocatalytic degradation, as observed in other eukaryotes, and provide evidence for antagonist roles of the CSN and 26S proteasome in modulating accumulation of the plant CRL SCF(TIR1).
Stuttmann J, Lechner E, Guérois R, Parker JE, Nussaume L, Genschik P, Noël LD. (2009). COP9 signalosome- and 26S Proteasome-dependent regulation of SCFTIR1 accumulation in Arabidopsis. J Biol Chem sous presse.