Cyclin G1 is the only cyclin that has either positive or negative effects on cell growth. Our previous study found decreased expression of cyclin G1 in human endometrial carcinoma tissues compared with normal endometrial tissues. The study aimed to evaluate cyclin G1 expression and its effect on proliferation of human endometrial carcinoma cells (ECCs). Cyclin G1-GFP (green fluorescence protein...

We have produced human cyclin A in Escherichia coli and investigated how it generates H1 kistone kinase activity when added to cyclin-free extracts prepared from parthenogenetically activated Xenopus eggs. Cyclin A was found to form a major complex with cdc2, and to bind cdk2/Eg1 only poorly. No lag phase was detected between the time when cyclin A was added and the time when H1 histone kinase ...

Cyclin E1 regulates the initiation of the S phase program in the mammalian cell division cycle. In normal cells, cyclin E1 protein expression is tightly controlled through a combination of transcriptional and proteolytic regulatory processes. However, in many types of human tumor, cyclin E1 expression is frequently dysregulated, including overexpression, nonperiodic expression relative to cell ...

We have previously shown that caspase-mediated cleavage of Cyclin E generates p18-Cyclin E in hematopoietic tumor cells. Its expression can induce apoptosis or sensitize to apoptotic stimuli in many cell types. However, p18-cyclin E has a much shorter half-life than Cyclin E, being more effectively ubiquitinated and degraded by the 26 S proteasome. A two-step process has emerged that regulates ...

Diabetes results from an inadequate mass of functional β cells, due to either β cell loss caused by autoimmune destruction (type I diabetes) or β cell failure in response to insulin resistance (type II diabetes). Elucidating the mechanisms that regulate β cell mass may be key to developing new techniques that foster β cell regeneration as a cellular therapy to treat diabetes. While previous stu...

Two B-type cyclins, B1 and B2, have been identified in mammals. Proliferating cells express both cyclins, which bind to and activate p34(cdc2). To test whether the two B-type cyclins have distinct roles, we generated lines of transgenic mice, one lacking cyclin B1 and the other lacking cyclin B2. Cyclin B1 proved to be an essential gene; no homozygous B1-null pups were born. In contrast, nulliz...

Mitosis is thought to be triggered by the activation of Cdk-cyclin complexes. Here we have used RNA interference (RNAi) to assess the roles of three mitotic cyclins, cyclins A2, B1, and B2, in the regulation of centrosome separation and nuclear-envelope breakdown (NEB) in HeLa cells. We found that the timing of NEB was affected very little by knocking down cyclins B1 and B2 alone or in combinat...

Ionizing radiation induces a G2 delay in eukaryotic cells. Since mitotic cyclins are required to trigger the transition from G2 into and through mitosis, we chose to investigate their expression after irradiation in HeLa cells. In normally cycling HeLa cells, both cyclin A and B mRNA and protein levels rise dramatically in G2/M and rapidly fall coincident with the completion of mitosis. The ris...