The heat-shock phenomenon in cultured cells of rainbow trout hsp70 mRNA synthesis and turnover

Abstract

A distinct set of heat-shock polypeptides are induced in a cultured trout cell line (RTG-2) upon exposure to elevated temperature or to micromolar concentrations of sodium arsenite. We have examined the kinetics of hsp70 mRNA synthesis in trout cells induced by these stress conditions. Both heat shock and sodium arsenite result in rapid synthesis of trout hsp70 mRNA. Prolonged exposure (up to 24 h) to arsenite, however, causes continued synthesis and/or maintenance of hsp70 message, whereas a continuous heat shock beyond 2 h causes a decrease in hsp70 mRNA levels. This could be due to a difference in either the regulation of transcription by these two inducers or in their induction mechanism. The latter seems more likely, since arsenite exposure results in more effective induction of hsp70 synthesis and in better translational control of normal cellular mRNAs. Immunological detection of trout hsp70 with antibody to chicken hsp70 shows an increase in the polypeptide as early as 5 min after the start of arsenite induction, indicating a rapid and preferential expression of hsp70. Recovery of trout cells from stress was also monitored. Repression of hsp70 mRNA is very rapid, especially during recovery from a temperature stress. If cells are rescued from arsenite, they continue to synthesize hsp70 mRNA for approximately an additional 30 min, after which hsp70 mRNA levels decline.