| Budget Amount *help |
¥14,400,000 (Direct Cost: ¥14,400,000)
Fiscal Year 2003: ¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 2002: ¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 2001: ¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 2000: ¥7,500,000 (Direct Cost: ¥7,500,000)
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| Research Abstract |
Jab1, also known as the fifth component of the COP9 signalosome(CSN), plays an important role in a number of biological processes including cell cycle control. The core of the CSN complex is composed of eight subunits (CSN1-8), and disruption of one component results in loss of the whole complex. So far, two enzymatic activities are known to be associated with CSN. One is protein kinases (casein kinase II, protein kinase D, and 5/6 kinase), which regulate the stability of proteins such as c-Jun and p53 by direct phosphorylation. The others is a metalloprotease activity, which regulates the SCF ubiquitin ligase by removing the covalently-coupled, ubiquitin-like peptide, Nedd8, from the cullin subunit. Besides the 450-550-kDa CSN complex, Jab1 is also found as a smaller (ca 10 0 kDa)cytoplasmic complex. It remains to be determined which enzymatic activity and which form of the complex is responsible for a variety of biological responses connected to Jab1.
To investigate the function of Ja
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b1 in vivo, we targeted the Jab1 locus by homologous recombination in mouse ES cells. No nullizygous mice were born live among 186 offspring of different Job1 heterozygous intercrosses, and the ratio of heterozygous mice to wild-type mice was 2.0 to 1, indicating that loss of Jab1 was embryonic lethal. Analysis of the embryos isolated from timed heterozygous intercrosses from embryonic day 8.5 to as early as E3.5 indicated that Jab1-/-embryos survived to the blastocyst Jab1-null embryonic cells, which also lacked other CSN components, expressed higher levels of p27, p53, and cyclin E, were positive for TUNEL assay and poorly incorporated BrdU, indicating that loss of Jab1 and the CSN complex results in impaired proliferation and accelerated apoptosis due to dysregulation of multiple cell cycle regulators. Interestingly, Jab1 heterozygous mice, although they were healthy and fertile, were smaller than the wild-type littermates. This was party due to less number of levels of p53, cyclin E and neddylated Cull were not changed. In these cells, the amount of Jab1-containing small complex but not that of CSN was selectively reduced. Cell cycle analysis of the synchronized MEFs showed that Jab1+/-MEFs failed to efficiently downregulate p27 during G1 and delayed the entry into S phase by 3 hours. Thus, these results suggest that Jab1 controls cell cycle progression in CSN-dependent and-independent ways. Less
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