The phenotype of a "Cdc2 kinase target site-deficient" mutant of oncoprotein 18 reveals a role of this protein in cell cycle control.
Oncoprotein 18 (Op18) is a cytosolic protein that is expressed in all proliferating cells. This phosphoprotein is up-regulated in a variety of human neoplasm, and phosphorylation of its two Cdc2 kinase target sites, Ser-25 and Ser-38, fluctuates dramatically during the cell cycle. We have investigated the potential role of the Cdc2 kinase-mediated phosphorylation of these two sites by expressing a "Cdc2 kinase target site-deficient" mutant of Op18 (Op18-S25,38A), and analyzed the phenotype on the level of cell cycle regulation. The result shows that induced expression of Op18-S25,38A results in rapid accumulation of cells in the G2 phase of the cell cycle. The block in G2 seems transient, since prolonged incubation was found to result in a large fraction of the transfected cells entering S phase in the absence of mitosis, i.e. endoreduplication. In addition, a fraction (30%) of the transfected cells was blocked in mitosis. Whereas the morphology of the G2 arrested cells appeared normal, expression of Op18-S25,38A caused a serious defect during mitotic chromosome segregation. Analyses of the mechanism behind the phenotype of Op18-S25,38A suggest an essential role for Op18 during cell division and that the mutant interferes with the function of the endogenous gene product.
Marklund
U
U
Department of Cell and Molecular Biology, University of Umeå, Sweden.
Osterman
O
O
Melander
H
H
Bergh
A
A
Gullberg
M
M
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002104:Cadmium / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D002455:Cell Division; D002460:Cell Line; D017931:DNA Primers; D004492:Edetic Acid / Q000494:pharmacology; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D008868:Microtubule Proteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D010641:Phenotype; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism*; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis; D012694:Serine; D050777:Stathmin; D014162:Transfection; D014407:Tumor Cells, Cultured
D017931:DNA Primers; D008868:Microtubule Proteins; D009838:Oligodeoxyribonucleotides; D010750:Phosphoproteins; D012333:RNA, Messenger; C493995:STMN1 protein, human; D050777:Stathmin; D002104:Cadmium; D012694:Serine; D004492:Edetic Acid; D016203:CDC2 Protein Kinase