Copper inhibits the induction of stress protein synthesis by elevated temperatures in embryos of the sea urchin Strongylocentrus purpuratus

Abstract

A major component of the cellular stress response entails the induced synthesis of a suite of stress proteins under environmentally adverse conditions that functions to protect organisms from environmentally induced damage. Here, we examined induction of the stress response in the embryos of the sea urchin Strongylocentrus purpuratus under a combination of environmentally realistic conditions. First, we examined the response elicited over a range of free cupric ion activities, (Cu2+), using a metal buffer system to control trace metal speciation. We observed no pronounced differences in translational patterns in embryos exposed to free cupric ion activities, (Cu2+), of 10(-13)-10(-9) M by metabolic labeling, 1-dimensional electrophoresis and autoradiography. Further separation by 2-dimensional electrophoresis, however, revealed electrophoretically discernable variants of several groups of proteins at the higher Cu concentrations and the synthesis of a 60 kDa protein at (Cu2+) of 10(-9) M. In addition, there were differences in the stress response induced by heat-shock treatment in embryos cultured in seawater with different Cu concentrations; radiolabel was incorporated into a greater number of cellular proteins in embryos at lower (Cu2+) and the induced synthesis of stress proteins was greater. These data suggest that elevations in (Cu2+) impair the ability of the embryos to mount the stress response upon exposure to elevated temperatures and that Cu may alter critical developmental pathways by inhibiting the synthesis of regulatory proteins. Such effects on gene expression can result in manifestations that have been widely attributed to Cu toxicity, including developmental abnormalities and increased sensitivity to environmental extremes. We suggest that the particular sensitivity of embryonic systems upon exposure to multiple stressors may be a consequence of these mechanisms.