Mechanisms governing maintenance of Cdk1/cyclin B1 kinase activity in cells infected with human cytomegalovirus.
Previous work has demonstrated dysregulation of key cell cycle components in human cytomegalovirus (HCMV)-infected human fibroblasts, resulting in cell cycle arrest (F. M. Jault, J.-M. Jault, F. Ruchti, E. A. Fortunato, C. L. Clark, J. Corbeil, D. D. Richman, and D. H. Spector, J. Virol. 69:6697-6704, 1995). The activation of the mitotic kinase Cdk1/cyclin B, which was detected as early as 8 h postinfection (p.i.) and maintained throughout the time course, was particularly interesting. To understand the mechanisms underlying the induction of this kinase activity, we have examined the pathways that regulate the activation of Cdk1/cyclin B1 complexes. The accumulation of the cyclin B1 subunit in HCMV-infected cells is the result of increased synthesis and reduced degradation of the protein. In addition, the catalytic subunit, Cdk1, accumulates in its active form in virus-infected cells. The decreased level of the Tyr15-phosphorylated form of Cdk1 in virus-infected fibroblasts is due in part to the down-regulation of the expression and activity of the Cdk1 inhibitory kinases Myt1 and Wee1. Increased degradation of Wee1 via the proteasome also accounts for its absence at 24 h p.i. At late times, we observed accumulation of the Cdc25 phosphatases that remove the inhibitory phosphates from Cdk1. Interestingly, biochemical fractionation studies revealed that the active form of Cdk1, a fraction of total cyclin B1, and the Cdc25 phosphatases reside predominantly in the cytoplasm of infected cells. Collectively, these data suggest that the maintenance of Cdk1/cyclin B1 activity observed in HCMV-infected cells can be explained by three mechanisms: the accumulation of cyclin B1, the inactivation of negative regulatory pathways for Cdk1, and the accumulation of positive factors that promote Cdk1 activity.
Sanchez
Veronica
V
Molecular Biology Section and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0366, USA.
McElroy
Anita K
AK
Spector
Deborah H
DH
D016203:CDC2 Protein Kinase / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D003587:Cytomegalovirus / Q000472:pathogenicity*; D003586:Cytomegalovirus Infections / Q000821:virology; D004789:Enzyme Activation; D005347:Fibroblasts / Q000821:virology; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D006801:Humans; D008565:Membrane Proteins; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism
C534699:CCNB1 protein, human; D018797:Cell Cycle Proteins; D019926:Cyclin B; D056744:Cyclin B1; D008565:Membrane Proteins; D009687:Nuclear Proteins; D011505:Protein-Tyrosine Kinases; C499349:WEE1 protein, human; C490679:PKMYT1 protein, human; D017346:Protein Serine-Threonine Kinases; D016203:CDC2 Protein Kinase