Nucleolin involved in myocardial ischaemic preconditioning via post-transcriptional control of HSPA1A expression

AIMS: Recent studies have identified the critical roles of nucleolin in a variety of cellular processes, including regulation of viral replication and tumour formation. However, the possible roles of nucleolin in myocardial preconditioning remain undefined. METHODS AND RESULTS: We used an in vivo rat myocardial ischaemic preconditioning (IP) model (four cycles of 5 min ischaemia and 10 min reperfusion) and cellular hydrogen peroxide preconditioning (H2O2-PC) models. We found that nucleolin mRNA and protein expression showed a time-dependent increase during the recovery of myocardial ischaemic preconditioning in rats and H2O2-PC in neonatal rat cardiomyocytes. Nucleolin overexpression enhanced the protective effects of H2O2-PC, whereas nucleolin ablation abrogated the H2O2-PC-mediated protection in cardiomyocytes. On the other hand, nucleolin overexpression increased the stabilization of the HSPA1A mRNA and the expression of HSPA1A protein in cardiomyocytes, whereas nucleolin ablation abrogated the up-regulation of HSPA1A induced by H2O2-PC in cardiomyocytes. An interaction between nucleolin and HSPA1A mRNA was further identified using the RNA-protein interaction studies. Reporter gene assays, which depended on the untranslated regions (UTR) of HSPA1A mRNA, revealed that the post-transcriptional regulation was mainly attributed to the 3' UTR. Finally, HSPA1A anti-sense oligonucleotides (asODNs) attenuated the protective effect of nucleolin in cardiomyocytes. CONCLUSION: These results indicate that nucleolin is up-regulated and involved in myocardial protection of ischaemic preconditioning via a post-transcriptional control of HSPA1A expression.