Cyclin A/cdk2 has a role in progression through S phase, and a large pool is also activated in G 2 phase. Here we report that this G 2 phase pool regulates the timing of progression into mitosis. Knock down of cyclin A by siRNA or addition of a specific cdk2 small molecule inhibitor delayed entry into mitosis by delaying cells in G 2 phase. The G 2 phase-delayed cells contained elevated levels of inactive cyclin B/cdk1. However, increased microtubule nucleation at the centrosomes was observed, and the centrosomes stained for markers of cyclin B/cdk1 activity. Both microtubule nucleation at the centrosomes and the phosphoprotein markers were lost with short-term treatment of the cdk1/2 inhibitor roscovitine but not the Mek1/2 inhibitor U0126. Cyclin A/cdk2 localized at the centrosomes in late G 2 phase after separation of the centrosomes but before the start of prophase. Thus G 2 phase cyclin A/cdk2 controls the timing of entry into mitosis by controlling the subsequent activation of cyclin B/cdk1, but also has an unexpected role in coordinating the activation of cyclin B/cdk1 at the centrosome and in the nucleus.

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Earlier work demonstrated that an activated estrogen receptor (ER) is required for long-term self-renewal of c-ErbB-expressing avian erythroid progenitors. Here, we demonstrate that activation of the ER does not only arrest or retard differentiation of early progenitors but that it affects erythroid differentiation at all stages of erythroid maturation. A search for genes whose expression is affected by the ER showed that the 17beta-estradiol-activated receptor suppressed the differentiation-associated up-regulation of Gata-1, SCL-1, and globin genes in partially mature cells. In the same cells, the expression of carbonic anhydrase II (CAII) and histone H5 was enhanced. This led to premature expression of CAII, a possible explanation for the toxic effects of overexpressed ER. Repression specifically required the transactivation domain AF-2, but neither an intact DNA-binding domain (DBD) nor the AF-1 domain. The transcriptional activation of CAII, however, required both an intact AF-2 and a functional DBD. The requirement for the AF-2, but not the DBD, suggested that the ER may compete with other nuclear hormone receptors for transcriptional coactivators that bind AF-2, a domain well conserved within this family of transcription factors. We show, however, that this model does not apply for the most likely candidate, the avian thyroid hormone receptor.

This is the first time that induction of apoptosis has been reported in C. trachomatis-infected cells when treated with a combination of innate immune activators and wedelolactone.

Productivity of three different promoters at various cell cycle stages and under two distinct growth conditions was examined in Chinese hamster ovary cells. Under the Growth Arrest and DNA Damage inducible GADD153 promoter, productivity of the short half-live variant of the enhanced green fluorescent protein (d2EGFP) and the secreted alkaline phosphatase (SEAP) was highest at the G1 phase of the cell cycle and at serum starvation, while under the cytomegalovirus (CMV) or the simian virus SV40 promoter, productivity was highest at S-phase and in complete medium. These results indicate the utility of the GADD153 promoter for production purposes under protein-free conditions.