THE MITOCHONDRIA ARE RECOGNITION ORGANELLES OF CELL STRESS

The cellular response to stress includes synthesis of specific stress proteins in the presence of a generalized suppression of protein synth esis. The response occurs in intact animals, individually stressed org ans of intact animals, donor organs upon removal, regardless of preser vation methods, and cells in culture. The molecular biology of stress protein induction is not understood. While stress proteins are benefic ial, overall suppression of protein synthesis, if prolonged, is harmfu l. Since altered energy metabolism is integral to stress induction, we examined the mitochondria to determine if they could provide a possib le molecular mechanism for initiating the response. Rat myoblasts were incubated at varying temperatures for up to 120 min in [S-35]methioni ne. Proteins were separated electrophoretically and newly synthesized proteins visualized autoradiographically. Isolated mitochondria from r esting rat myoblasts were then stressed, label incorporation determine d, and newly synthesized protein was visualized. Stress sharply suppre ssed protein synthesis in mitochondria but autoradiograms of stressed mitochondria showed that a single stress protein of 18 kDa was synthes ized. Mitochondria independently respond to stress and synthesize a st ress protein from their own DNA. This protein may provide an intermedi ary pathway that links stressful conditions in the environment to the overall response observed in the cell. (C) 1996 Academic Press, Inc.