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 8

MAGI1 regulates d-flow–induced XBP-1 expression.

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MAGI1 regulates d-flow–induced XBP-1 expression. (A) Gene enrichment ana...
(A) Gene enrichment analyses (right-tailed Fisher’s exact test) were performed according to IPA downstream effect analysis, and we identified Cardiovascular Disease, Organism Injury and Abnormalities, and Reproductive System Disease as the highest scoring IPA interaction networks in our microarray data set. Green and red symbols denote genes with lower and higher expression, respectively, in MAGI1 siRNA-treated ECs compared with that in control siRNA-treated cells. The arrows with solid lines indicate direct (usually physical) interactions between two molecules in the direction of the arrows, whereas arrows with dashed lines denote indirect interactions (e.g., molecule/gene A affects molecule/gene B). The abbreviations are defined in Supplemental Table 3. (B and C) Levels of spliced and total Xbp1 (B) and Tnfsf15 (C) mRNA expression were reduced in MAGI1 siRNA–treated (siMAGI1-treated) ECs under d-flow stimulation. Data represent mean ± SEM (n = 3). *P < 0.05; **P < 0.01. siCont, control siRNA. (D) d-flow–mediated EC apoptosis was inhibited by treatment with MAGI1 siRNA. Data represent mean ± SEM (n = 3–4). *P < 0.05; **P < 0.01. (E) MAGI1-ATF6 binding was assessed using a CheckMate Mammalian Two-Hybrid Assay. Human aortic endothelial cells (HAECs) were transfected with human pACT-MAGI1, pBIND-ATF6, and a luciferase reporter vector (PG5-Luc), and their luciferase activity was measured. Relative MAGI1-ATF6 binding data are presented as firefly/Renilla luciferase activity ratios. Data represent mean ± SEM (n = 12). RLU, relative light units. **P < 0.01. (F and G) HAECs transduced with Ad-Flag-MAGI1-WT were treated with Thb (10 U/ml) for 16 hours. MAGI1-ATF6 binding was measured via co-IP with anti-Flag followed by IB with anti-ATF6 and then anti-Flag to confirm that equal amounts of protein were pulled down. The rows below the dotted line in F show Flag-MAGI1 and ATF6 levels in the total cell lysates. These are representative figures from 6 different experiments. Quantification data are shown in G. *P < 0.05 (G). Data represent mean ± SEM (n = 6). Statistical differences between 2 independent groups (E) 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, C, D, and G).