Post-transcriptional regulation of HSP70 expression following oxidative stress in SH-SY5Y cells: the potential involvement of the RNA-binding protein HuR

Brain aging is associated with a progressive imbalance between intracellular concentration of Reactive Oxygen Species (ROS) and cells ability to activate defensive genes. Heat Shock Protein 70 (HSP70) has been shown to act as a fundamental defensive mechanism for neurons exposed to an oxidant challenge, and its expression decreases during senescence. In the present report we show that the RNA-binding protein ELAV/HuR can affect, post-transcriptionally, the fate of HSP70 mRNA following H2O2-mediated oxidative stress in SH-SY5Y human neuroblastoma cells. As a consequence of H2O2 treatment (1mM for 30 minutes), HSP70 mRNA accumulates in the ribosomes associated to the cytoskeleton, where parallel Western blotting experiments reveal statistically significant increase for both HuR and HSP70 protein levels. We also confirm the capability of HuR to bind to HSP70 mRNA, and describe how the biological effect of this ELAV protein on the HSP70 mRNA could be due to a direct phosphorylation in serine/threonine residues of HuR itself by the early (10 minutes) H2O2-mediated activation of PKCa. Our findings shed light on the post-transcriptional regulation of HSP70 expression, suggesting the existence of a new molecular cascade –involving PKC/HuR/HSP70- that possibly represents an early event in the cellular response to H2O2-mediated oxidative stress in SH-SY5Y human neuroblastoma cells. The present results lead us to speculate that an impairment in this regulatory mechanism might directly contribute to the defective cellular response to oxidative stress, thus helping to dissect a potential tool useful to counteract some aspects associated to cerebral senescence.