BRCA1 and GADD45 mediated G2/M cell cycle arrest in response to antimicrotubule agents

BRCA1 is a tumour suppressor gene implicated in the predisposition to early onset breast and ovarian cancer. We have generated cell lines with inducible expression of BRCA1 to evaluate its role in mediating the cellular response to various chemotherapeutic drugs commonly used in the treatment of breast and ovarian cancer. Induction of BRCA1 in the presence of Taxol and Vincristine resulted in a dramatic increase in cell death; an effect that was preceded by an acute arrest at the G2/M phase of the cell cycle and which correlated with BRCA1 mediated induction of GADD45. A proportion of the arrested cells were blocked in mitosis suggesting activation of both a G2 and a mitotic spindle checkpoint. In contrast, no specific interaction was observed between BRCA1 induction and treatment of cells with a range of DNA damaging agents including Cisplatin and Adriamycin. Inducible expression of GADD45 in the presence of Taxol induced both G2 and mitotic arrest in these cells consistent with a role for GADD45 in contributing to these effects. Our results support a role for both BRCA1 and GADD45 in selectively regulating a G2/M checkpoint in response to antimicrotubule agents and raise the possibility that their expression levels in cells may contribute to the toxicity observed with these compounds.

Effects of the aurora kinase inhibitors AZD1152-HQPA and ZM447439 on growth arrest and polyploidy in acute myeloid leukemia cell lines and primary blasts.

BACKGROUND:
Aurora kinases play an essential role in the orchestration of chromosome separation and cytokinesis during mitosis. Small-molecule inhibition of the aurora kinases has been shown to result in inhibition of cell division, phosphorylation of histone H3 and the induction of apoptosis in a number of cell systems. These characteristics have led aurora kinase inhibitors to be considered as potential therapeutic agents.
DESIGN AND METHODS:
Aurora kinase gene expression profiles were assessed in 101 samples from patients with acute myeloid leukemia. Subsequently, aurora kinase inhibitors were investigated for their in vitro effects on cell viability, histone H3 phosphorylation, cell cycle and morphology in acute myeloid leukemia cell lines and primary acute myeloid leukemia samples.
RESULTS:
The aurora kinase inhibitors AZD1152-HQPA and ZM447439 induced growth arrest and the accumulation of hyperploid cells in acute myeloid leukemia cell lines and primary acute myeloid leukemia cultures. Furthermore, both agents inhibited histone H3 phosphorylation and this preceded perturbations in cell cycle and the induction of apoptosis. Single cell cloning assays were performed on diploid and polyploid cells to investigate their colony-forming capacities. Although the polyploid cells showed a reduced capacity for colony formation when compared with their diploid counterparts, they were consistently able to form colonies.
CONCLUSIONS:
AZD1152-HQPA- and ZM447439 are effective apoptosis-inducing agents in acute myeloid leukemia cell lines and primary acute myeloid leukemia cultures. However, their propensity to induce polyploidy does not inevitably result in apoptosis.

The tumor suppressor gene DLEC1 is frequently silenced by DNA methylation in hepatocellular carcinoma and induces G1 arrest in cell cycle

Background/Aims: The chromosome locus 3p21.3 is a