NEURONAL DIFFERENTIATION IN PC12 CELLS IS ACCOMPANIED BY DIMINISHED INDUCIBILITY OF HSP70 AND HSP60 IN RESPONSE TO HEAT AND ETHANOL

The stress response of PC12 cells was characterized by evaluating the production of heat shock proteins of the 70 kDa (Hsp70), 60 kDa (Hsp60 ) and 90 kDa (Hsp90) families by western blot analysis. Induction of H sp synthesis was elicited by brief exposure to elevated temperatures o r by addition of ethanol to the cultures. Normal PC12 cells responded to stress with rapid up-regulation of Hsp70 and Hsp60 production. Howe ver, fully differentiated PC12 cells (induced by nerve growth factor, NGF) failed to produce Hsp70 or Hsp60 in response to heat or ethanol t reatment. The disappearance of the heat shock response of the cells wa s directly related to the extent of neuronal differentiation. The cell ular levels of the constitutive proteins, Hsc70 and Hsp90, were not al tered by differentiation of the cells. Production of Hsps was restored in the differentiated cells by removal of NGF which coincided with th e loss of neurite expression and retraction of processes.