Hsp27 binding to the 3'UTR of bim mRNA prevents neuronal death during oxidative stress-induced injury: a novel cytoprotective mechanism.
Bottom Line: This effect could not be explained by proteasomal degradation of Bim or bim promoter inhibition; however, it was associated with a specific increase in the levels of bim mRNA and with its binding to Hsp27.Finally, we determined that enhanced Hsp27 expression in neurons exposed to H2O2 or glutamate prevented the translation of a reporter plasmid where bim-3'UTR mRNA sequence was cloned downstream of a luciferase gene.These results suggest that repression of bim mRNA translation through binding to the 3'UTR constitutes a novel cytoprotective mechanism of Hsp27 during stress in neurons.
Affiliation: Department of Physiology and Medical Physics and RCSI Centre for the Study of Neurological Disorders, Royal College of Surgeons in Ireland, Dublin 2, Ireland Department of Biochemistry and Molecular Biology I, School of Biology, Complutense University, 28040 Madrid, Spain email@example.com firstname.lastname@example.org.Show MeSH
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Mentions: We next sought to determine the mechanism used by Hsp27 to prevent Bim induction during oxidative stress–induced cell death. First, we analyzed a possible effect of Hsp27 on bim promoter activation by the AKT/FOXO3 pathway. Overexpression of the pNEO-Hsp27 construct in CGNs did not prevent the down-regulation of pAKT (Ser-473) and pFOXO3 (Thr-32) levels induced by H2O2 (37.5 μM) treatment (Figure 3A). We also examined the JNK/AP1 signaling pathway, which is activated by oxidative stress and involved in bim promoter activation (Torres and Forman, 2003; Biswas et al., 2007). Treatment of CGNs with H2O2 (37.5 μM) increased JNK activation, as detected by the up-regulation of pJNK (Thr-183/Tyr-185) levels (Figure 3A). However, overexpression of the pNEO-Hsp27 did not prevent this effect. Finally, we cotransfected CGNs with the luciferase reporter plasmid bearing the bim promoter sequence and the pNEO-Hsp27 construct or alternatively its control vector. Hsp27 overexpression did not prevent the up-regulation of the bim promoter after H2O2 addition (Figure 3B). These results indicate that the effect of Hsp27 on Bim expression does not depend on the regulation of its promoter.
Affiliation: Department of Physiology and Medical Physics and RCSI Centre for the Study of Neurological Disorders, Royal College of Surgeons in Ireland, Dublin 2, Ireland Department of Biochemistry and Molecular Biology I, School of Biology, Complutense University, 28040 Madrid, Spain email@example.com firstname.lastname@example.org.