title: Human Speedy: a novel cell cycle regulator that enhances proliferation through activation of Cdk2.
abstract: The decision for a cell to self-replicate requires passage from G1 to S phase of the cell cycle and initiation of another round of DNA replication. This commitment is a critical one that is tightly regulated by many parallel pathways. Significantly, these pathways converge to result in activation of the cyclin-dependent kinase, cdk2. It is, therefore, important to understand all the mechanisms regulating cdk2 to determine the molecular basis of cell progression. Here we report the identification and characterization of a novel cell cycle gene, designated Speedy (Spy1). Spy1 is 40% homologous to the Xenopus cell cycle gene, X-Spy1. Similar to its Xenopus counterpart, human Speedy is able to induce oocyte maturation, suggesting similar biological characteristics. Spy1 mRNA is expressed in several human tissues and immortalized cell lines and is only expressed during the G1/S phase of the cell cycle. Overexpression of Spy1 protein demonstrates that Spy1 is nuclear and results in enhanced cell proliferation. In addition, flow cytometry profiles of these cells demonstrate a reduction in G1 population. Changes in cell cycle regulation can be attributed to the ability of Spy1 to bind to and prematurely activate cdk2 independent of cyclin binding. We demonstrate that Spy1-enhanced cell proliferation is dependent on cdk2 activation. Furthermore, abrogation of Spy1 expression, through the use of siRNA, demonstrates that Spy1 is an essential component of cell proliferation pathways. Hence, human Speedy is a novel cell cycle protein capable of promoting cell proliferation through the premature activation of cdk2 at the G1/S phase transition.
authors: Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093-0367, USA.
authors: Lisa A
authors: LA
authors: Porter
authors: Ryan W
authors: RW
authors: Dellinger
authors: John A
authors: JA
authors: Tynan
authors: Elizabeth A
authors: EA
authors: Barnes
authors: Monica
authors: M
authors: Kong
authors: Jean-Luc
authors: JL
authors: Lenormand
authors: Daniel J
authors: DJ
authors: Donoghue
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000502:physiology*; D002455:Cell Division; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D004247:DNA; D004789:Enzyme Activation; D016193:G1 Phase; D006801:Humans; D008322:Mammals; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured; D014981:Xenopus; D029867:Xenopus Proteins
chemical_list: D018797:Cell Cycle Proteins; D012333:RNA, Messenger; C486530:SPDYA protein, human; D029867:Xenopus Proteins; C119055:ls27 protein, Xenopus; D004247:DNA; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495891:Cdk2 protein, Xenopus; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases