Comparison of labeled heat shock proteins in neuronal and non-neuronal cells of Aplysia californica

Abstract

Aplysia californica has been used to study the protein synthetic response of nervous tissue to stress induced by elevated temperatures. The abdominal and pleural ganglia as well as associated connectives were exposed to various temperatures for 30 min, labeled with [33S]methionine at room temperature, and then analyzed by sodium dodecyl sulfate gel electrophoresis. All cells examined responded to temperatures of greater than 31°C by a reduction in levels of labeled actin, as well as by the enhanced labeling of proteins with apparent M(r) of 70,000 and 110,000. Two-dimensional electrophoresis indicated that the molecular weight and isoelectric focusing properties are similar to the heat shock proteins (HSPs) observed in other systems. In addition to these major HSPs, heat-induced proteins with molecular weights ranging from 70,000 to 90,000 were highly labeled in the neurosecretory bag cells. Further cell type-specific differences in the protein synthetic response to elevated temperatures were revealed by quantitation of the major HSPs. Levels of labeled HSPs were significantly lower in ganglion cells as compared to the non-neuronal connective cells. In addition, the decrease in actin levels appeared to be less dramatic in the ganglion cells. Analysis of the cellular compartmentalization of HSPs suggests that both neurons and glia are capable of HSP synthesis. Studies in the squid have demonstrated that HSPs are transferred from adaxonal glia into the axoplasm (Tytell, M., S.G. Greenberg, and R.J. Lasek, unpublished observation). This finding, coupled with the low levels of labeled HSPs in ganglion cells, supports the possibility that glia-axon protein transfer may play an important role in nerve cell survival during periods of stress. Preliminary findings of this study have been reported previously (Greenberg, S.G., P.F. Drake, and R.J. Lasek (1983) J. Cell Biol. 97: 152).