CYCLOHEXIMIDE DECREASES NASCENT POLYPEPTIDES LEVEL AND AFFECTS UP-REGULATION OF HSP70 GENE-EXPRESSION

1. Treatment with cycloheximide (CHM; 10 mu g/ml) 2 h before and durin g heating produced a 13-fold increase in survival from 1 x 10(-2) to 1 .3 x 10(-1) after 10 h at 43 degrees C in human colon carcinoma HT-29 cells. Little protection was observed if the drug was added only durin g heating. 2. Pretreatment with 10 mu g/ml CHM which inhibited protein synthesis by 95%, decreased the level of nascent polypeptides and sub sequently reduced the accumulation of polypeptides in the nucleus duri ng heat shock. 3. Adding CHM (10 mu g/ml) 2 h before and during heat f acilitated the dissociation of heat shock transcription factor-heat sh ock element (HSF-HSE) complex and consequently terminated transcriptio n activity earlier. 4. These findings related to the literature sugges t that the free pool of HSP70 is increased by inhibiting protein synth esis. An increase in the level of free HSP70 may more effectively prot ect or repair thermolabile targets and consequently affect the regulat ion of heat shock response.