Disruption of the COP9 Signalosome Csn2 Subunit in Mice Causes Deficient Cell Proliferation, Accumulation of p53 and Cyclin E, and Early Embryonic Death

Abstract

Csn2 (Trip15/Cops2/Alien) encodes the second subunit of the COP9 signalosome (CSN), an eight-subunit heteromeric complex homologous to the lid subcomplex of the 26S proteasome. CSN is a regulator of SCF (Skp1-cullin-F-box protein)ubiquitin ligases, mostly through the enzymatic activity that deconjugates the ubiquitin-like protein Nedd8 from the SCF Cul1 component. In addition, CSN associates with protein kinase activities targeting p53, c-Jun, and IκB for phosphorylation. Csn2 also interacts with and regulates a subset of nuclear hormone receptors and is considered a novel corepressor. We report that targeted disruption of Csn2 in mice caused arrest of embryo development at the peri-implantation stage. Csn2^−/− blastocysts failed to outgrow in culture and exhibited a cell proliferation defect in inner cell mass, accompanied by a slight decrease in Oct4. In addition, lack of Csn2 disrupted the CSN complex and resulted in a drastic increase in cyclin E, supporting a role for CSN in cooperating with the SCF-ubiquitin-proteasome system to regulate protein turnover. Furthermore, Csn2^−/− embryos contained elevated levels of p53 and p21, which may contribute to premature cell cycle arrest of the mutant.

ACKNOWLEDGMENTS

We thank Stephanie Donaldson for expert advice on blastocyst isolation and in vitro culture, Steven Bennett and Russell Mortimer of the research histology lab at the Yale School of Medicine for embryo sections, and Di Xiao for technical assistance. We thank Yossi Shiloh, Tomoki Chiba, Katherina Walz, and Jiong Yan for helpful discussions. L.S. and J.B.M. thank En Li (Massachusetts General Hospital) for help with gene targeting.

This work was supported in part by grants to N.W. from NIH (GM61812) and EntreMed, Inc., and by grants to J.B.M. from NIH (AR49496, ES11384, HL64641), USDA, and the Muscular Dystrophy Association L.S. was supported by a postdoctoral fellowship from NIAMS.