Rescue of a human cell line from endogenous Cdk1 depletion by Cdk1 lacking inhibitory phosphorylation sites.
Cells that transiently overexpress cyclin-dependent kinase 1 lacking inhibitory phosphorylation sites (Cdk1-AF) undergo premature and catastrophic mitosis, reflecting the key role for Cdk1 in promoting a timely transit from G(2) into mitosis. Conversely, cells depleted of Cdk1 undergo repeated S phases without intervening mitoses (endoreduplication), reflecting a role for Cdk1 in preventing premature S phases. It is not known how Cdk1 prevents entry into S phase at times in G(2) when it does not promote mitosis. Also uncertain is the extent of redundancy between inhibitory phosphorylation and other mechanisms for controlling Cdk1 activity. We describe here human cells that not only tolerate stable Cdk1-AF expression but also rely on it for survival when endogenous Cdk1 is depleted. When residual endogenous Cdk1 expression is further depleted, however, proliferation of Cdk1-AF-rescued cells is inhibited. Interestingly, this inhibition is not accompanied by endoreduplication. These results are consistent with a two-threshold model for Cdk1 kinase activity, one for suppressing endoreduplication and one for promoting mitosis. They also indicate that inhibitory phosphorylation is indispensable for only a fraction of the total cellular complement of Cdk1.
Gupta
Mita
M
Department of Haematology and Medical Research Council Clinical Sciences Centre, Faculty of Medicine, Imperial College, London W12 0NN, United Kingdom.
Trott
Deborah
D
Department of Haematology and Medical Research Council Clinical Sciences Centre, Faculty of Medicine, Imperial College, London W12 0NN, United Kingdom.
Porter
Andrew C G
ACG
Department of Haematology and Medical Research Council Clinical Sciences Centre, Faculty of Medicine, Imperial College, London W12 0NN, United Kingdom. Electronic address: andy.porter@imperial.ac.uk.
D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D015870:Gene Expression; D018390:Gene Targeting; D006801:Humans; D008954:Models, Biological; D010766:Phosphorylation / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D014158:Transcription, Genetic
D034741:RNA, Small Interfering; D016203:CDC2 Protein Kinase