Cyclins are regulatory subunits of cyclin-dependent kinases. Cyclin A, the first cyclin ever cloned, is thought to be an essential component of the cell-cycle engine. Mammalian cells encode two A-type cyclins, testis-specific cyclin A1 and ubiquitously expressed cyclin A2. Here, we tested the requirement for cyclin A function using conditional knockout mice lacking both A-type cyclins. We found...

BACKGROUND Cyclin E is the normal inducer of S phase in G1 cells of Drosophila embryos. Stable G1 quiescence requires the downregulation both of cyclin E and of other factors that can bypass the normal regulation of cell cycle progression. RESULTS High-level expression of cyclin A triggered the G1/S transition in wild-type embryos and in mutant embryos lacking cyclin E. Three types of control...

Cyclin E is a G1 cyclin that has been shown to be one of the key regulators of the G1-S transition and could consequently be a deregulated molecule in tumors. In the present study, we have characterized cyclin E expression by immunohistochemistry in 217 resected non-small cell lung cancers (NSCLCs) and found large variations in cyclin E expression among tumors. High-level cyclin E expression (a...

Cytostatic factor (CSF) arrests vertebrate eggs in metaphase of meiosis II through several pathways that inhibit activation of the anaphase-promoting complex/cyclosome (APC/C). In Xenopus, the Mos-MEK1-MAPK-p90(Rsk) cascade utilizes spindle-assembly-checkpoint components to effect metaphase arrest. Another pathway involves cyclin E-Cdk2, and sustained cyclin E-Cdk2 activity in egg extracts caus...

In animal cells, duplication of centrosomes and DNA is coordinated. Since CDK2/cyclin E triggers initiation of both events, activation of CDK2/cyclin E is thought to link these two events. We identified nucleophosmin (NPM/B23) as a substrate of CDK2/cyclin E in centrosome duplication. NPM/B23 associates specifically with unduplicated centrosomes, and NPM/B23 dissociates from centrosomes by CDK2...

Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a cyclin D homolog, K cyclin, that is thought to promote viral oncogenesis. However, expression of K cyclin in cultured cells not only triggers cell cycle progression but also engages the p53 tumor suppressor pathway, which probably restricts the oncogenic potential of K cyclin. Therefore, to assess the tumorigenic properties of K cyclin in...

Cell cycle deregulation and genomic instability play a major role in the aberrant cell proliferation that characterizes tumorigenesis. A novel role of the cyclin e isoform cyclin e2 in these processes is reported in the manuscript " Cyclin e2 induces genomic instability by mechanisms distinct from cyclin e1 " by Caldon et al. 1 in another issue of Cell Cycle, evidence that regulation of cyclin ...

Cell cycle deregulation and genomic instability play a major role in the aberrant cell proliferation that characterizes tumorigenesis. A novel role of the cyclin e isoform cyclin e2 in these processes is reported in the manuscript " Cyclin e2 induces genomic instability by mechanisms distinct from cyclin e1 " by Caldon et al. 1 in another issue of Cell Cycle, evidence that regulation of cyclin ...

Cell cycle deregulation and genomic instability play a major role in the aberrant cell proliferation that characterizes tumorigenesis. A novel role of the cyclin e isoform cyclin e2 in these processes is reported in the manuscript " Cyclin e2 induces genomic instability by mechanisms distinct from cyclin e1 " by Caldon et al. 1 in another issue of Cell Cycle, evidence that regulation of cyclin ...

In order to elucidate the mechanisms by which estrogens and antiestrogens modulate the growth of breast cancer cells, we have characterized the changes induced by estradiol that occur during the G1 phase of the cell cycle of MCF-7 human mammary carcinoma cells. Addition of estradiol relieves the cell cycle block created by tamoxifen treatment, leading to marked activation of cyclin E-cdk2 compl...