Identification of a novel cyclin-like protein in human tumor cells.
Cyclins are key regulatory proteins that, in concert with cyclin-dependent protein kinase subunits (cdks), function to govern critical transitions and/or restriction points during the course of cell cycle progression. Recently, a number of putative mammalian G1 cyclins have been characterized at the molecular level; however, the specific activities of the cyclin/cdk complexes and the precise biochemical pathways regulated by the G1 cyclins remain to be elucidated. In the present study we identify a novel cyclin-like protein in pediatric bone and extremity tumors that appears to be related to, but is clearly distinct from, previously identified members of the cyclin D family, as determined by its profile of antibody cross-reactivity, apparent molecular size, chromatographic behavior, physicochemical properties, and pattern of peptide mapping. This 46-kDa cyclin-like protein, tentatively designated p46cyclin X, is first expressed in synchronized MG-63 osteosarcoma cells in mid-G1, well after the induction of p36cyclin D1, yet prior to the induction of cyclins E and A. Northern analysis, utilizing an oligonucleotide probe complementary to an epitope shared by cyclins D1, D2, and X, detected a novel mRNA species, the appearance of which correlates with p46cyclin X expression. The p46cyclin X protein in Ewing's sarcomas and Wilms' tumors is electrophoretically and chromatographically distinct from both p36cyclin D1 and p34cyclin D2. Moreover, the p46cyclin X protein is 1) precipitated by p9Ckshs1-agarose beads, 2) physically associated with p33cdk2, and 3) autophosphorylated in in vitro kinase reactions. Taken together with the biochemical data, the temporal expression of the p46cyclin X/p33cdk2 kinase system is suggestive of a potential role in regulating latter G1 events (i.e. START) in the commitment to S phase.
Division of Orthopaedic Surgery, Childrens Hospital Los Angeles, University of Southern California School of Medicine.
R T
RT
Williams
L
L
Wu
D A
DA
Carbonaro-Hall
V T
VT
Tolo
F L
FL
Hall
D000595:Amino Acid Sequence; D002453:Cell Cycle; D002648:Child; D002846:Chromatography, Affinity; D016213:Cyclins / Q000032:analysis*; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000032:analysis*; D012516:Osteosarcoma / Q000737:chemistry; D011233:Precipitin Tests; D014407:Tumor Cells, Cultured; D009396:Wilms Tumor / Q000737:chemistry
D016213:Cyclins; D009363:Neoplasm Proteins