The NEDD8 system is essential for cell cycle progression and morphogeneticpathway in mice

NEDD8/Rub1 is a ubiquitin (Ub)-like molecule that covalently ligates to tar get proteins through an enzymatic cascade analogous to ubiquitylation. This modifier is known to target all cullin (Cul) family proteins. The latter a re essential components of Skp1/Cul-1/F-box protein (SCF)-like Ub ligase co mplexes, which play critical roles in Ub-mediated proteolysis. To determine the role of the NEDD8 system in mammals, we generated mice deficient in Ub a3 gene that encodes a catalytic subunit of NEDD8-activating enzyme. Uba3(- /-) mice died in utero at the periimplantation stage. Mutant embryos showed selective apoptosis of the inner cell mass but not of trophoblastic cells. However, the mutant trophoblastic cells could not enter the S phase of the endoreduplication cycle. This cell cycle arrest was accompanied with aberr ant expression of cyclin E and p57(Kip2). These results suggested that the NEDD8 system is essential for both mitotic and the endoreduplicative cell c ycle progression. beta -Catenin, a mediator of the Wnt/ wingless signaling pathway, which degrades continuously in the cytoplasm through SCF Ub ligase , was also accumulated in the Uba3(-/-) cytoplasm and nucleus. Thus, the NE DD8 system is essential for the regulation of protein degradation pathways involved in cell cycle progression and morphogenesis, possibly through the function of the Cul family proteins.