Effect of cycloheximide or puromycin on induction of thermotolerance by sodium arsenite in Chinese hamster ovary cells: Involvement of heat shock proteins

Abstract

After sodium arsenite (100 μM) treatment, the synthesis of three major heat shock protein families (HSPs; Mr = 110,000, 87,000, and 70,000), as studied with one-dimensional gels, was enhanced twofold relative to that of unheated cells. The increase of unique HSPs, if studied with two-dimensional gels, would probably be much greater. In parallel, thermotolerance was observed as a 100,000-fold increase in survival from 10⁻⁶ to 10⁻¹ after 4 hr at 43°C, and as a thermotolerance ratio (TTR) of 2–3 at 10⁻³ isosurvival for heating at 45.5°C. Cycloheximide (CHM: 10 μg/ml) or puromycin (PUR: 100 μg/ml), which inhibited total protein synthesis and HSP synthesis by 95%, completely suppressed the development of thermotolerance when either drug was added after sodium arsenite treatment and removed prior to the subsequent heat treatment. Therefore, thermotolerance induced by arsenite treatment correlated with an increase in newly synthesized HSPs. However, with or without arsenite treatment, CHM or PUR added 2–6 hr before heating and left on during heating caused a 10,000–100,000-fold enhancement of survival when cells were heated at 43°C for 4 hr, even though very little synthesis of heat shock proteins occurred. Moreover, these cells manifesting resistance to heating at 43°C after CHM treatment were much different than those manifesting resistance to 43°C after arsenite treatment. Arsenite-treated cells showed a great deal of thermotolerance (TTR of about 10) when they were heated at 45°C after 5 hr of heating at 43°C, compared with less thermotolerance (TTR of about 2) for the CHM-treated cells heated at 45°C after 5 hr of heating at 43°C. Therefore, there are two different phenomena. The first is thermotolerance after arsenite treatment (observed at 43°C or 45.5°C) that apparently requires synthesis of HSPs. The second is resistance to heat after CHM or PUR treatment before and during heating (observed at 43°C with little resistance at 45.5°C) that apparently does not require synthesis of HSPs. This phenomenon not requiring the synthesis of HSPs also was observed by the large increase in thermotolerance to 45°C caused by heating at 43°C, with or without CHM, after cells were incubated for 6 hr following arsenite pretreatment. For both phenomena, a model based on synthesis and redistribution of HSPs is presented.