Degradation of B-Myb by ubiquitin-mediated proteolysis: involvement of the Cdc34-SCF(p45Skp2) pathway.
B-Myb, a highly conserved member of the Myb oncoprotein family, is a 110 kDa sequence-specific DNA binding protein expressed in virtually all proliferating cells. B-myb expression reaches its maximum at the G1/S phase boundary and during the S phase of the cell cycle. We have previously shown that B-Myb activity is cell cycle regulated and it is controlled by the antagonistic effects of cyclin D1 and A. Here we show that ectopic expression of cyclin A causes a pronounced reduction of B-Myb protein level. We provide evidence that in addition to triggering B-Myb activity an important effect of cyclin A is to facilitate multiple ubiquitination of B-Myb. The C-terminal domain of B-Myb is of key importance in mediating this effect of cyclin A. Contrary to full-length B-Myb, a C-terminal deletion mutant displays activity irrespective of cyclin A expression, does not undergo ubiquitination, and its half-life is not affected by cyclin A. Ectopic expression of either Cdc34 or the F-box protein p45Skp2, respectively the E2 and E3 components of a ubiquitination pathway that regulates the G1/S transition, accelerates degradation of B-Myb. We show that B-Myb physically and functionally interacts with components of the Cdc34-SCFp45Skp2 ubiquitin pathway and propose that B-Myb degradation may be required for controlling the correct alternation of events during progression through the cell division cycle. Oncogene (2000).
Charrasse
S
S
Department of Oncology, Novartis Pharma AG, Klybeckstrasse 141, 4057 Basel, Switzerland.
Carena
I
I
Brondani
V
V
Klempnauer
K H
KH
Ferrari
S
S
D064173:Anaphase-Promoting Complex-Cyclosome; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D019925:Cyclin A / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D008025:Ligases / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D044786:S-Phase Kinase-Associated Proteins; D015534:Trans-Activators / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*
D018797:Cell Cycle Proteins; D019925:Cyclin A; D004268:DNA-Binding Proteins; C064352:MYBL2 protein, human; D009097:Multienzyme Complexes; D044786:S-Phase Kinase-Associated Proteins; D015534:Trans-Activators; D014452:Ubiquitins; C577447:CDC34 protein, human; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D044767:Ubiquitin-Protein Ligases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008025:Ligases