Chromosome condensation caused by loss of RCC1 function requires the cdc25C protein that is located in the cytoplasm.

Abstract

We cloned the hamster cdc25C cDNA by using the human cdc25C cDNA as a probe and prepared an antibody to Escherichia coli-produced hamster cdc25C protein that is specific to the human cdc25C protein. The microinjected antibody inhibited a chromosome condensation induced by tsBN2 mutation, indicating that the cdc25C protein is required for an activation of p34cdc2 kinase caused by loss of RCC1 function. The hamster cdc25C protein located in the cytoplasm, prominently in a periphery of the nuclei of cells arrested with hydroxyurea, and seemed to move into the nuclei by loss of RCC1 function. Also, we found a molecular shift of the cdc25C protein in cells showing premature chromosome condensation (PCC), in addition to normal mitotic cells. This molecular-shift appeared depending on an activation of p34Cdc2 kinase.

Hyperphosphorylation of the N-terminal Domain of Cdc25 Regulates Activity toward Cyclin B1/Cdc2 But Not Cyclin A/Cdk2

“…The low proportion of cdc25C in the hyperphosphorylated form in cells transiting mitosis suggests that either the hyperphosphorylated form is a very transient species, or that only a small proportion of cdc25C is required in its activated form in mitosis. It is at present unclear as to which of these possibilities represents the true physiological situation, although the hyperphosphorylation of the total pool of cdc25C has only been found in cells blocked in mitosis with nocodazole (8).…”

“…Xenopus cdc25 levels do not change, but its activity is also controlled by phosphorylation and dephosphorylation (3,4). In humans, three isoforms of cdc25 exist, cdc25A, -B, and -C. Cdc25A has a role in regulating the G 1 /S cell cycle phase transition whereas cdc25B and cdc25C regulated the G 2 /M transition (5)(6)(7)(8)(9). The level of mRNA for each isoform changes through the cell cycle, but the protein levels of only cdc25A and cdc25B have been reported to change in a cell cycle-dependent manner (5,7,9).…”

D‐type cyclin expression is decreased and p21 and p27 CDK inhibitor expression is increased when tsBN462 CCG1/TAFII250 mutant cells arrest in G1 at the restrictive temperature

“…The anti-mouse TBP antiserum was raised against mouse TBP protein produced in E. coli and kindly provided by Dr T. Tamura (Chiba University, Japan). The anti-Cdc25C, anti-cyclin A, anti-PSTAIR and anti-Cdk2 antibodies were kindly provided by Dr K. Yamashita (Seki et al 1992). The anti-Cdc2 antiserum was provided by Dr N. Watanabe (The Salk Institute, La Jolla, CA).…”

The Dual Specificity Phosphatase Cdc25B, but Not the Closely Related Cdc25C, Is Capable of Inhibiting Cellular Proliferation in a Manner Dependent upon Its Catalytic Activity

“…and Cdc25C are known to trigger mitosis by dephosphorylating Cdk1 on threonine 14 and tyrosine 15 (2)(3)(4)(5)(6). To more directly demonstrate that the antiproliferative ability of Cdc25B involves activation of the CDKs, recombinant adenoviruses expressing Cdc25B (Ad-25B), its catalytic inactive mutant (Admt25B) and Cdc25C (Ad-25C) were constructed.…”

“…The last step in activation of Cdk1 and Cdk2 is removal of the inhibitory phosphates from threonine 14 and tyrosine 15. In mammalian cells, this dephosphorylation event is accomplished by three related dual specificity phosphatases: Cdc25A, Cdc25B, and Cdc25C (2)(3)(4)(5)(6). Cdc25A is involved in the initiation of DNA replication as well as mitosis by targeting Cdk2 and Cdk1, respectively (7).…”