SCF-SKP2 E3 ubiquitin ligase links mTORC1/ER stress/ISR with YAP activation in murine renal cystogenesis
Dibyendu K. Panda, … , Mark L. Lipman, Andrew C. Karaplis
Dibyendu K. Panda, … , Mark L. Lipman, Andrew C. Karaplis
Published November 3, 2022
Citation Information: J Clin Invest. 2022;132(24):e153943. https://doi.org/10.1172/JCI153943.
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Research Article Nephrology

SCF-SKP2 E3 ubiquitin ligase links mTORC1/ER stress/ISR with YAP activation in murine renal cystogenesis

Abstract

The Hippo pathway nuclear effector Yes-associated protein (YAP) potentiates the progression of polycystic kidney disease (PKD) arising from ciliopathies. The mechanisms underlying the increase in YAP expression and transcriptional activity in PKD remain obscure. We observed that in kidneys from mice with juvenile cystic kidney (jck) ciliopathy, the aberrant hyperactivity of mechanistic target of rapamycin complex 1 (mTORC1), driven by ERK1/2 and PI3K/AKT cascades, induced ER proteotoxic stress. To reduce this stress by reprogramming translation, the protein kinase R–like ER kinase–eukaryotic initiation factor 2α (PERK/eIF2α) arm of the integrated stress response (ISR) was activated. PERK-mediated phosphorylation of eIF2α drove the selective translation of activating transcription factor 4 (ATF4), potentiating YAP expression. In parallel, YAP underwent K63-linked polyubiquitination by SCF S-phase kinase-associated protein 2 (SKP2) E3 ubiquitin ligase, a Hippo-independent, nonproteolytic ubiquitination that enhances YAP nuclear trafficking and transcriptional activity in cancer cells. Defective ISR cellular adaptation to ER stress in eIF2α phosphorylation–deficient jck mice further augmented YAP-mediated transcriptional activity and renal cyst growth. Conversely, pharmacological tuning down of ER stress/ISR activity and SKP2 expression in jck mice by administration of tauroursodeoxycholic acid (TUDCA) or tolvaptan impeded these processes. Restoring ER homeostasis and/or interfering with the SKP2-YAP interaction represent potential therapeutic avenues for stemming the progression of renal cystogenesis.

Authors

Dibyendu K. Panda, Xiuying Bai, Yan Zhang, Nicholas A. Stylianesis, Antonis E. Koromilas, Mark L. Lipman, Andrew C. Karaplis

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Figure 8

SKP2 plays a central role in renal cystogenesis.

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SKP2 plays a central role in renal cystogenesis. (A) Representative H&am...
(A) Representative H&E, Picrosirius red (dark red indicating collagen), and trichrome (blue indicates fibrosis) staining and YAP and SKP2 immunostaining in kidney sections from mice in the control and treatment groups. (B) Higher magnification of SKP2 immunostaining in WT and jck kidneys demonstrating its differential subcellular distribution. Scale bars: 50 μm (A) and 100 μm (B). (C) Representative Western immunoblots for p-eIF2α/t-eIF2α. (D) Graphic representation of the quantified p-eIF2α/t-eIF2α ratio derived from Western blots using 4 kidney samples from mice in each of the groups. (E) Representative Western blot for p-YAP/t-YAP expression in kidneys from mice in the control and treatment groups. (F) Graphic representation of Ctgf expression using quantitative real-time PCR in the 4 kidney samples examined for each group using Actb as an internal control. (G) Representative Western blot analysis for SKP2, p27, PCNA, and MYC in kidneys from mice in each of the groups. (H) p27 and (I) p-YAP/t-YAP levels as determined by Western blotting in 2 representative kidneys from jck mice treated with vehicle or the SKP2 inhibitor SKPin C1. Each symbol in the graphs represents an individual animal. Data represent the mean ± SEM. *P < 0.05, **P < 0.01, and ***P < 0.001, by 1-way ANOVA followed by a Tukey-Kramer multiple-comparison test.