Abstract
Heat shock factor 1 (HSF1) mediates the cellular response to stress to increase the production of heat shock protein (HSP) chaperones for proper protein folding, trafficking, and degradation; failure of this homeostatic mechanism likely contributes to neurodegeneration. We show that the neuroprotective drug riluzole increased the amount of HSF1 in NG108-15 neuroprogenitor cells by slowing the specific turnover of HSF1 and supporting a more robust and sustained activation of HSF1. Using Hsp70-luciferase as a functional readout of the activity of HSF1, we show that riluzole amplified the heat shock induction of the reporter gene with an optimal increase at 1 μM. Immunocytochemical staining and Western blot quantitation of HSP70 in NG108-15 neuroprogenitor cells and embryonic spinal cord neurons provided corroborative evidence that riluzole amplified the HSF1-dependent regulation of HSP70 expression. Parallel studies on the GLT1 glutamate transporter showed that riluzole increased GLT1-reporter and GLT1 protein expression and that the increase was enhanced by heat shock and coincident with the increased expression of HSP70 and HSP90. This result is consistent with the anti-glutamatergic profile of riluzole and the presence of multiple heat shock elements on the GLT1 gene promoter, suggesting that riluzole may modulate GLT1 expression through HSF1. The increased HSP chaperones and GLT1 transporter blunted glutamate-induced and N-methyl D-aspartate receptor-mediated excitotoxic death. In summary, we show that riluzole increased the amount and activity of HSF1 to boost the expression of HSPs and GLT1 for neuroprotection under stress.
Highlights
Tionarily conserved response to diverse stressors, mediated by activation of the Heat shock factor 1 (HSF1) transcription factor, culminating in the induction of a family of heat shock proteins (HSPs) that function as chaperones to assist in the proper folding of non-native proteins and proteases to help in the degradation of damaged proteins for the protection and recovery from cellular damages [1,2,3]
There is a range in the magnitude of heat shock induction of reporter gene activity as we have previously reported for the hsp70-reporter [12, 15, 16]
Riluzole Enhances Basal and Heat-induced hsp70-luciferase Reporter Gene in NG108-15 Cells—To assess the functionality of the increased HSF1, we determined the effects of riluzole on Hsp70 promoter-driven luciferase reporter gene expression in undifferentiated and differentiated NG108-15 cells incubated under basal (37 °C) and heat shock (42 °C) conditions
Summary
Tionarily conserved response to diverse stressors, mediated by activation of the HSF1 transcription factor, culminating in the induction of a family of heat shock proteins (HSPs) that function as chaperones to assist in the proper folding of non-native proteins and proteases to help in the degradation of damaged proteins for the protection and recovery from cellular damages [1,2,3]. Cells were either harvested immediately after heat shock for Western blot detection of HSF1 or allowed to recover at 37 °C for time periods indicated for analysis of the induction of Hsp70-firefly luciferase reporter gene and HSP70/HSP90/GLT1 protein expression.
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