Unspliced X-box-binding protein 1 (XBP1) protects endothelial cells from oxidative stress through interaction with histone deacetylase 3.
Bottom Line: In this study, we found that disturbed flow activated anti-oxidative reactions via up-regulating heme oxygenase 1 (HO-1) in an X-box-binding protein 1 (XBP1) and histone deacetylase 3 (HDAC3)-dependent manner.Knockdown of HDAC3 ablated XBP1u-mediated effects.Thus, we demonstrate that XBP1u and HDAC3 exert a protective effect on disturbed flow-induced oxidative stress via up-regulation of mTORC2-dependent Akt1 phosphorylation and Nrf2-mediated HO-1 expression.
Affiliation: From the Cardiovascular Division, King's College London, London SE5 9NU, United Kingdom.Show MeSH
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Mentions: Our previous studies have demonstrated that disturbed flow sustainably activates XBP1 expression and splicing (14) and that disturbed flow activates HDAC3 in a KDR/PI3K-Akt pathway-dependent manner (19). In this study, we found that disturbed flow-induced up-regulation of XBP1u was ablated by the presence of KDR inhibitor SU5416 and PI3K/Akt inhibitor LY294002, whereas XBP1 splicing was only ablated by SU5416 (Fig. 1A). This suggests that XBP1u was regulated by a similar mechanism to HDAC3 (19). As disturbed flow concomitantly up-regulated HDAC3, XBP1u, and XBP1s, we wondered whether there was cross-talk between HDAC3 and both XBP1 isoforms. XBP1s is produced by IRE1α activation (11) and down-regulation of XBP1s can be achieved by knockdown of IRE1α. Knockdown of XBP1 or IRE1α abolished disturbed flow-induced HDAC3 up-regulation (Fig. 1B), indicating that there is relationship between both XBP1 isoforms and HDAC3 under disturbed flow. To further examine the involvement of XBP1s in flow-induced HDAC3 up-regulation, exogenous overexpression of XBP1s was introduced into HUVECs via adenoviral gene transfer. As shown in Fig. 1C, overexpression of XBP1s actually decreased HDAC3 protein due to transcriptional repression as revealed by the HDAC3-Luc reporter analysis (Fig. 1D). Overexpression of XBP1u had no effect on HDAC3 transcription (Fig. 1D) but antagonized the effect of XBP1s and protected HDAC3 protein levels (Fig. 1E). A ChIP assay revealed that both XBP1u and XBP1s could bind to the −960 ∼ −1195 region of HDAC3 promoter (Fig. 1F). Under static condition, more XBP1u bound to this region, whereas during disturbed flow, more XBP1s bound to this region. These results suggest that there may be a cross-talk between HDAC3 and XBP1u.
Affiliation: From the Cardiovascular Division, King's College London, London SE5 9NU, United Kingdom.