The amount of estrogen receptor α increases after heat shock in a cholinergic cell line from the basal forebrain

Abstract

Estrogen exerts a neuroprotective action in response to a variety of cell stresses. However, to what extent intracellular estrogen receptors are involved in these functions remains to be determined. We have found that SN56 cells, a neuronal-derived cholinergic cell line which produces luteinizing hormone-releasing hormone and contains the mRNAs encoding estrogen and progesterone receptors, also express estrogen receptor alpha, as well as the heat shock protein 90. Exposure of these cells to drastic temperature elevation for 1 h immediately increased the intracellular levels of these two proteins, whereas it rapidly reduced the content of estrogen receptor alpha mRNA. In addition, the amount of estrogen receptor alpha-heat shock protein 90 complexes was increased in response to thermal stress. Pre-treatment with geldanamycin, a potent inhibitor of heat shock protein 90, decreased the amount of estrogen receptor alpha, suggesting that its elevation after the heat insult may be related to its association with heat shock protein 90. In contrast, exposure of heat-shocked cells to 17beta-estradiol reduced the number of estrogen receptor alpha-heat shock protein 90 complexes, suggesting that the receptor conserves the affinity for its cognate ligand under these conditions. Therefore, the interaction of the estrogen receptor with heat shock protein 90 may serve to prevent its degradation during the thermal insult, as well as to maintain it in a high-affinity hormone-binding conformation. Since neuroprotective estrogen effects have been described in a variety of cytotoxic situations, these findings may be suggestive of an integrated neuronal response to injury, which includes the protection of available estrogen receptors through their association with heat shock protein 90.