Apoptosis induced by the histone deacetylase inhibitor sodium butyrate in human leukemic lymphoblasts

Abstract

The histone deacetylase inhibitor and potential anti-cancer drug sodium butyrate is a general inducer of growth arrest, differentiation, and in certain cell types, apoptosis. In human CCRF-CEM, acute T lymphoblastic leukemia cells, butyrate, and other histone deacetylase inhibitors caused G2/M cell cycle arrest as well as apoptotic cell death. Forced G0/G1 arrest by tetracycline-regulated expression of transgenic p16/INK4A protected the cells from butyrate-induced cell death without affecting the extent of histone hyperacetylation, suggesting that the latter may be necessary, but not sufficient, for cell death induction. Nuclear apoptosis, but not G2/M arrest, was delayed but not prevented by the tripeptide broad-range caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp.fluoromethylketone (zVAD) and, to a lesser extent, by the tetrapeptide 'effector caspase' inhibitors benzyloxycarbonyl-Asp-Glu-Val-Asp.fluoromethylketone (DEVD) and benzyloxycarbonyl-Val-Glu-Ile-Asp.fluoromethyl-ketone (VEID); however, the viral protein inhibitor of 'inducer caspases', crmA, had no effect. Bcl-2 overexpression partially protected stably transfected CCRF-CEM sublines from butyrate-induced apoptosis, but showed no effect on butyrate-induced growth inhibition, further distinguishing these two butyrate effects. c-myc, constitutively expressed in CCRF-CEM cells, was down-regulated by butyrate, but this was not causative for cell death. On the contrary, tetracycline-induced transgenic c-myc sensitized stably transfected CCRF-CEM derivatives to butyrate-induced cell death.