Decreased heat shock response upon adipose differentiation of 3T3-L1 cells

In order to gain a better understanding of the regulation of heat shock gene (hsp) expression in terminal cell differentiation, we evaluated the effects of heat shock on the synthesis of HSPs, the abundance of mRNAhsp, and the heat shock transcription factor (HSTF) DNA-binding activity in the 3T3-L1 fibroblasts and adipocytes. We showed that the heat shock (42 degrees C) induction of synthesis of HSPs was significantly greater in the undifferentiated fibroblast than the differentiated adipocyte cultures. In particular, the heat shock induced synthesis of HSP 72 was at least 10 times greater in the fibroblasts than in the adipocytes. Analysis of mRNA of hsp 89 alpha, hsp 89 beta, hsp 70, and hsp 25 by Northern blot hybridization showed that the expression of these mRNAs was very, if not strictly, dependent on heat shock of the cells; the abundance of these heat inducible mRNAs was significantly higher in fibroblasts than in adipocytes. Quantitation of the HSTF DNA-binding activity by gel retardation assay demonstrated a specific decrease in this activity in the differentiated cells. These results provide evidence of a decreased transcriptional activation of heat shock genes upon adipose cell differentiation.