The subcellular locations of p15(Ink4b) and p27(Kip1) coordinate their inhibitory interactions with cdk4 and cdk2.
In dividing cells, p27(Kip1) is predominantly bound to cyclin D-cdk4 without inhibiting this kinase. Upon being induced by TGF-beta or with a conditional expression system in lung epithelial cells, p15(Ink4b) binds to and inhibits the cyclin D-dependent kinases, prevents p27 binding to these cdk complexes, and promotes p27 binding and inhibition of cyclin-cdk2. In vitro, however, p15 prevents p27 binding only if it has access to cyclin D-cdk4 first. We present evidence that the different subcellular location of p15 and p27 ensures the prior access of p15 to cdk4. In the cell, p15 is localized mostly in the cytoplasm, whereas p27 is nuclear. p15 prevails over p27 or a p27 construct consisting of the cdk inhibitory domain tagged with a nuclear localization signal. However, when p15 and p27 are forced to reside in the same subcellular location, either the cytoplasm or the nucleus, p15 no longer prevents p27 from binding to cdk4. These properties allow p15 and p27 to coordinately inhibit cdk4 and cdk2.
Reynisdóttir
I
I
Cell Biology Program and Howard Hughes Medical Institute, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Massagué
J
J
D000818:Animals; D042846:CDC2-CDC28 Kinases; D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002455:Cell Division; D002460:Cell Line; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008907:Mink; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D011518:Proto-Oncogene Proteins; D013347:Subcellular Fractions / Q000378:metabolism*; D025521:Tumor Suppressor Proteins
C493966:CDKN2B protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D008869:Microtubule-Associated Proteins; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495900:CDK4 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases