p19Skp1 and p45Skp2 are essential elements of the cyclin A-CDK2 S phase kinase.
In normal human fibroblasts, cyclin A-CDK2 exists in a quaternary complex that contains p21 and PCNA. In many transformed cells, p21 disappears, and a substantial fraction of cyclin A-CDK2 complexes with p9CKS1/CKS2, p19, and p45. To investigate the significance of these rearrangements, we have isolated cDNAs encoding p19 and p45. In vitro reconstitution demonstrated that binding of p19 to cyclin A-CDK2 requires p45. Addition of these proteins to the kinase had no substantial effect on the kinase activity in vitro. Interference with p45 function in vivo by microinjection of antibodies or antisense oligonucleotides prevented entry into S phase in both normal and transformed cells. Cyclin A-CDK2 has previously been identified as a kinase whose activity is essential for S phase. Our results identify p45 as an essential element of this activity. The abundance of p45 is greatly increased in many transformed cells. This could result in changes in cell cycle control that contribute to the process of cellular transformation.
Zhang
H
H
Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, New York 11724, USA.
Kobayashi
R
R
Galaktionov
K
K
Beach
D
D
D000595:Amino Acid Sequence; D001483:Base Sequence; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle / Q000502:physiology; D018797:Cell Cycle Proteins / Q000502:physiology*; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism / Q000648:ultrastructure*; D016213:Cyclins / Q000378:metabolism / Q000648:ultrastructure*; D018076:DNA, Complementary / Q000302:isolation & purification; D005347:Fibroblasts / Q000166:cytology; D006367:HeLa Cells; D006801:Humans; D007668:Kidney / Q000166:cytology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011485:Protein Binding / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000648:ultrastructure*; D016196:S Phase / Q000502:physiology*; D044786:S-Phase Kinase-Associated Proteins; D014170:Transformation, Genetic / Q000502:physiology
D018797:Cell Cycle Proteins; D016213:Cyclins; D018076:DNA, Complementary; D044786:S-Phase Kinase-Associated Proteins; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases