| Abstrakt: |
Trichostatin A (TSA), a global repressor of histone deacetylase activity, inhibits the proliferation of a number of cell types. However, the identification of the mechanisms underlying TSA-mediated growth arrests has remained elusive. In order to resolve in more detail the cellular process modulated during the growth inhibition induced by TSA, we studied the effect of the drug on G0/G1traverse in mitogen-stimulated quiescent Balb/c-3T3 cells. Cyclin D1 and retinoblastoma proteins were induced following the mitogenic stimulation of both control and TSA-treated cells, and cyclin D1 formed complexes with CDK4 under both conditions. However, cyclin D1-associated kinase was not increased in growth-arrested cells. The lack of cyclin D-associated kinase was paralleled by an accumulation of RB in a hypophosphorylated form, as would be expected. In contrast, p130 became partially phosphorylated, accompanied by a marked increase in p130-dependent E2F DNA binding activity and a partial release of free E2F-4. Despite the presence of E2F complexes not bound to pocket proteins, late G1E2F-dependent gene expression was not observed. The lack of cyclin D1-associated kinase in TSA-treated cultures was potentially due to high levels of the cyclin-dependent inhibitor p27 kip1. However, the modulation of p27 kip1levels by the deacetylase inhibitor cannot be responsible for the induction of the cell cycle arrest, since the growth of murine embryo fibroblasts deficient in both p27 kip1and p21 cip1was also inhibited by TSA. These data support a model in which TSA inhibits very early cell cycle traverse, which, in turn, leads to a decrease in cyclin D1-associated kinase activation and a repression of late cell cycle-dependent events. Alterations in early G0/G1gene expression accompany the TSA-mediated growth arrest. |
