Ning Wei, Ph.D. Research Scientist Yale University, OML 127 PO Box 208103, 266 Whitney Ave New Haven, CT 06520 Email: ning.wei@yale.edu Phone: (203) 432-3897

We work on an evolutionarily conserved protein complex known as the COP9 signalosome (CSN) and its related molecules in mammalian cell culture as well as mouse and Arabidopsis genetic systems. CSN subunits have been identified as signaling regulators influencing a wide range of cellular processes including stress and mitogen-activated protein kinase pathways, cell-cycle progression, cancer, nuclear hormone receptor mediated gene expression, plant light responses and flower development. Structurally, CSN is composed of 8 subunits homologous to the lid subcomplex of the 26S proteasome. The CSN signature domains are also found in components of translation initiation factor 3 (eIF3) complex. The biochemical activities of CSN are directly related to the ubiquitin-proteasome pathway.

Ubiquitin (Ub) is a polypeptide that can be attached by an isopeptide bond to the lysine side chain of specific protein substrates through an enzymatic cascade involving Ub-activating enzymes (E1), Ub conjugating enzymes (E2) and Ub ligases (E3). The poly-ubiquitin “tagged” proteins are normally targeted for degradation by the 26S proteasome so that they can be rapidly removed from the cell. Covalent modifications by Ub or Ub-like polypeptides are also used in cells as signals regulating events such as transcription, nuclear translocation, and DNA repair. CSN is involved in the conjugation cycles of the Ub-like protein Nedd8/Rub1, whose modification on cullin family proteins modulates the activity and assembly of cullin-based Ub ligase complexes. CSN acts to remove Nedd8/Rub1 from cullins through a metalloprotease activity.

With the de-neddylation activity together with the associated de-ubiquitin activity, CSN regulates the efficiencies of multiple cullin-based ubiquitin ligases targeting numerous protein substrates, many of which cell cycle regulators. This has been demonstrated in our recent mouse Csn2 knock-out study, in which de-regulated accumulation of cyclin E and tumor suppressor p53 have been found in mutant embryos. Disruption of the CSN complex in mice leads to early embryonic lethality, which echoes the lethal phenotype of csn mutants in Arabidopsis and Drosophila and highlights the fundamental nature of CSN functions in metazoans. Conditional knock-out of CSN in mouse is underway in an effort to investigate the cellular and physiological function of CSN in vertebrate animal development.

Components of CSN (CSN2 and CSN5/Jab1) have also been found to bind transcription factors and nuclear hormone receptors and are believed to have a role in gene expression. In addition, we have shown that CSN1 inhibits stress-activated MAP kinase pathway, suppresses c-Jun phosphorylation, and it can repress activation of c-fos expression in response to serum and UV-irradiation. In parallel, our Arabidopsis genetic study showed that the N-terminal domain (NTD) of CSN1 carries an unidentified function essential for plant development and is distinct from the cullin de-neddylation activity of the CSN complex. We are actively pursuing this new aspect of CSN functions.

We are also interested in a group of functionally related and highly conserved molecules such as cullins (Ub E3 ligases), DDB1(damaged DNA binding protein 1), COP1, and DET1. Cullins and DDB1 interact with CSN biochemically and functionally. COP1 is a component of Ub E3 ligase containing a RING and WD domain, which ubiquitinates c-Jun and p53 in humans, and photomorphogenic-activating transcription factors in Arabidopsis. DET1 binds histones in an acetylation-dependent manner and it forms a stable complex with DDB1. It is tempting to hypothesis that DET1 and DDB1 may represent a link between chromatin activity and the Ub regulatory mechanism. This will be another focus of our research.

Selected Publications

Lykke-Andersen K, Schaefer L, Menon S, Deng XW, Miller JB, Wei N. (2003) Disruption of the COP9 Signalosome Csn2 Subunit in Mice Causes Deficient Cell Proliferation, Accumulation of p53 and Cyclin E, and Early Embryonic Death. Mol Cell Biol. 23(19):6790-7.

Yang, X, Menon, S, Lykke-Andersen, K. Tsuge, T., Xiao, D. Wang, X., Rodriguez-Suarez, R. J., Zhang,H., and Wei, N (2002) The COP9 signalosome inhibits p27kip1 degradation and impedes G1-S phase progression via de-neddylation of SCF Cul1. Curr. Biol. 12, 667-672.

Tsuge T., Matsui M., and Wei N. (2001) The subunit 1 of the COP9 signalosome suppresses gene expression through its N-terminal domain and incorporates into the complex through the PCI domain. J. Mol. Biol. 305, 1-9.

Wei N., and Deng X.W. (1999). Making sense of the COP9 signalosome, a regulatory protein complex conserved from Arabidopsis to human. Trends Genetics. 15, 98-103.

Wang, H. Kang, D., Deng, X.-W., and Wei, N. (1999) Evidence for functional conservation of a mammalian homologue of the light-responsive plant protein COP1. Curr. Biol. 9, 711-714.

Wei, N., Tsuge, T., Serino., G., Dohmae, N., Takio, K., Matsui., M., and Deng, X.-W. (1998). The COP9 complex is conserved between plants and mammals and is related to the 26S proteasome regulatory complex. Curr. Biol. 8, 919-922.

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