MAGI1 as a link between endothelial activation and ER stress drives atherosclerosis
Jun-ichi Abe, … , Scott E. Evans, Nhat-Tu Le
Jun-ichi Abe, … , Scott E. Evans, Nhat-Tu Le
Published April 4, 2019
Citation Information: JCI Insight. 2019;4(7):e125570. https://doi.org/10.1172/jci.insight.125570.
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Research Article Cardiology Cell biology

MAGI1 as a link between endothelial activation and ER stress drives atherosclerosis

Abstract

The possible association between the membrane-associated guanylate kinase with inverted domain structure-1 (MAGI1) and inflammation has been suggested, but the molecular mechanisms underlying this link, especially during atherogenesis, remain unclear. In endothelial cells (ECs) exposed to disturbed flow (d-flow), p90 ribosomal S6 kinase (p90RSK) bound to MAGI1, causing MAGI1-S741 phosphorylation and sentrin/SUMO-specific protease 2 T368 phosphorylation-mediated MAGI1-K931 deSUMOylation. MAGI1-S741 phosphorylation upregulated EC activation via activating Rap1. MAGI1-K931 deSUMOylation induced both nuclear translocation of p90RSK-MAGI1 and ATF-6-MAGI1 complexes, which accelerated EC activation and apoptosis, respectively. Microarray screening revealed key roles for MAGI1 in the endoplasmic reticulum (ER) stress response. In this context, MAGI1 associated with activating transcription factor 6 (ATF-6). MAGI1 expression was upregulated in ECs and macrophages found in atherosclerotic-prone regions of mouse aortas as well as in the colonic epithelia and ECs of patients with inflammatory bowel disease. Further, reduced MAGI1 expression in Magi1–/+ mice inhibited d-flow–induced atherogenesis. In sum, EC activation and ER stress–mediated apoptosis are regulated in concert by two different types of MAGI1 posttranslational modifications, elucidating attractive drug targets for chronic inflammatory disease, particularly atherosclerosis.

Authors

Jun-ichi Abe, Kyung Ae Ko, Sivareddy Kotla, Yin Wang, Jesus Paez-Mayorga, Ik Jae Shin, Masaki Imanishi, Hang Thi Vu, Yunting Tao, Miguel M. Leiva-Juarez, Tamlyn N. Thomas, Jan L. Medina, Jong Hak Won, Yuka Fujii, Carolyn J. Giancursio, Elena McBeath, Ji-Hyun Shin, Liliana Guzman, Rei J. Abe, Jack Taunton, Naoki Mochizuki, William Faubion, John P. Cooke, Keigi Fujiwara, Scott E. Evans, Nhat-Tu Le

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Figure 6

MAGI1-K931 deSUMOylation induces nuclear translocation of MAGI1 and p90RSK.

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MAGI1-K931 deSUMOylation induces nuclear translocation of MAGI1 and p90R...
(A) HUVECs transduced with Ad-Flag-MAGI1-WT or -K931R were treated with Thb (1 h) and then immunostained with an anti-Flag antibody (red). The cells were counterstained with DAPI to identify nuclei. Treatment with 10 U/ml Thb caused nuclear MAGI1 translocation (Ad-Flag-MAGI1-WT images). MAGI1-K931R was localized exclusively in the nucleus even in the absence of inflammatory stimulation (Ad-Flag-MAGI1-K931R images). MAGI1 was localized at the cell membrane (white arrows) under unstimulated conditions and in the nucleus (yellow arrows) after Thb treatment. (B) Quantification of the percentage of nuclear MAGI1 localization, as described in Methods. Data represent mean ± SEM (n = 5–9). **P < 0.01. (C) HUVECs transduced with Ad-Flag– MAGI1-K931R or Ad-LacZ were coimmunostained with an anti-Flag antibody (red) and anti-p90RSK antibody (green). p90RSK staining was cytoplasmic in cells transduced with Ad-LacZ but nuclear in cells transduced with Ad-FlagMAGI1-K931R. (D) Quantification of the percentage of cellular p90RSK localization, as described in Methods. Data represent mean ± SEM (n = 3). **P < 0.01. Scale bars: 20 μm. (E and F) HUVECs treated with MAGI1 or control siRNA were transduced with Ad-Flag p90RSK and stimulated with Thb (1 h). Thb induced nuclear p90RSK localization, as indicated by immunostaining of cells with an anti-Flag antibody; p90RSK nuclear translocation was inhibited by MAGI1 siRNA (siMAGI1). (F) Quantification of the percentage of nuclear p90RSK localization, as described in Methods. Data represent mean ± SEM (n = 3). **P < 0.01. Adenoviral transduction: MOI, 20. siCont, control siRNA. (G) Results of a CheckMate Mammalian Two-Hybrid assay showing increased p90RSK-ERK5 binding in HUVECs expressing the MAGI1-K931R mutant. p90RSK-ERK5 binding was detected when p90RSK and the ERK5 fragment (amino acid 571–807 fragment) (17) were coexpressed (lanes 4 and 5), and the binding was enhanced by MAGI1-K931R overexpression (lane 6). Data represent mean ± SEM (n = 5–6). RLU, relative light units. **P < 0.01. Statistical differences between 2 independent groups (D) were assessed using the Student’s t test (2-tailed) and 1-way ANOVA followed by Bonferroni’s post hoc testing for multiple groups (B, F, and G).