Genetic regulation during heat shock and function of heat-shock proteins: a review

The induction by thermal stress of certain specific genes (heat-shock genes) first described in Drosophila has recently been observed in a wide variety of unicellular and multicellular organisms, emphasizing the basic importance of this ubiquitous response. Recent data dealing with the molecular mechanisms involved in the intensive transcriptional and posttranscriptional regulation during heat shock is reviewed with emphasis on the induction of the response and the putative function of the heat-shock proteins. A model showing the various interactions of cellular regulatory mechanisms operating in the heat-shocked cell is presented. While the list of agents or treatments inducing heat-shock proteins (hsp's) in various organisms is increasing, the identification of a hypothetical common inducing factor is elusive. The recently described reorganization of some cytoskeletal elements upon heat shock is discussed both in terms of its potential involvement in transcriptional and (or) translational regulation and of its putative relation with the cellular localization of the hsp's. Studies on the cellular localization of hsp's in various organisms do not show a clear uniform pattern which could help in elucidating the function of hsp's. On the other hand, studies on the thermal resistance of various cells types show a strong correlation between the induction of hsp's and the development of transitory thermotolerance. Such a protective function for hsp's can probably be extended to other types of cellular aggression.