| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1996: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1995: ¥1,100,000 (Direct Cost: ¥1,100,000)
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| Research Abstract |
The reults obtained so far all indicate a role for c-myb in maintaining the proliferative state of hematopoietic prgenitor cells. Disruption of this leucine zipper by site-directed mutagenesis markedly increases both trans-activating and transforming capacities. Since the leucine zipper motif was originallyn identified as mediating dimerization of several DNA-binding proteins, these results indicate that c-Myb activity is negatively regulated through the leucine zipper and imply the presence of an inhibitor (s) of c-Myb.
Homozygous c-myb mutant mice generated by homologous recombination in embryonic stem cells die at the embryonic stage due to a specific failure of fetal hepatic haematopoiesis. Therefore, this mutant cannot used for the analyzes of c-myb function in the adult tissues. We have tried to make the point mutant mice of c-myb by two step homologous recombination in ES cells. In these point mutants, the c-Myb activity is expected to be 1/10 or 10-fold compared with the wild type, and the mutant mice is not lethal at embryonic stage. We have made the heterozygous point mutants, so that the expected homozgous mutants will be very useful for the analyzes of myb function.
We have found that c-Myb binds to CBP in a phosphorylation-independent manner. Since CBP interacts with TFIIB,CBP mediates CREB-or c-Myb-dependent transcriptional activation as a bridge between phosphorylated CREB or c-Myb and the RNA polymerase II complex. Recently, CBP was demonstated to function as a transcriptional coactivator for many other transcriptional activators including c-Jun and c-Fos. Interestingly, mutations in the human CBP gene cause Rubinstein-Taybi syndrome through haploinsufficiency, suggesting that theamount of CBP in cells is not excessive and a 50% decrease in the amount affects normal development. Therefore, cross talk between the c-Myb, c-Myb, cAMP,and AP-1 pathways through competition for binding to CBP is possible.
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