ENHANCEMENT OF THE STRESS-RESPONSE BY LOW CONCENTRATIONS OF ARSENITE IN ARSENITE-PRETREATED REUBER H35 HEPATOMA-CELLS

The present study is aimed at determining whether the induction of hea t-shock protein (hsp) synthesis, heat-shock mRNAs, and tolerance devel opment after arsenite application has been sensitized to low concentra tions of arsenite in Reuber H35 rat hepatoma cells. Using a step-down arsenite treatment, consisting of a 1-hr pretreatment with 100 or 300 mu M followed by an incubation with a lower concentration (1-10 mu M), H35 cells were shown to exhibit increased sensitivity to low concentr ations of sodium arsenite shortly after exposure to the high arsenite concentration, but not any longer when the low concentration was appli ed 4 hr after pretreatment. In this paper it is shown that exposure of H35 cells to sodium arsenite concentrations of 100 or 300 mu M for 1 hr rapidly changes the sensitivity toward a second arsenite treatment with respect to the induction of the heat-shock response. It was obser ved that under conditions of enhanced sensitivity, an additional incre ase occurred in hsp synthesis as well as in hsp mRNA (as exemplified b y hsp68 mRNA behavior) when low concentrations of arsenite were applie d to arsenite pretreated cells. Since no effect of these low concentra tions was observed in nonpretreated cells, the effect of step-down tre atment results in a higher effect than could be expected based on summ ation. Furthermore, in sensitized cultures, cells are able to develop a higher level of tolerance in the presence of low concentrations of a rsenite. It can be concluded that during a transient period of enhance d sensitivity, low concentrations of the original stressor are able to enhance hsp synthesis and to induce a higher level of tolerance in co mparison with control cultures that are sensitized but not incubated i n the presence of low concentrations of the original stressor. (C) 199 5 Academic Press, Inc.