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 1 (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 endoplasmic reticulum (ER) proteotoxic stress. To reduce it by reprogramming translation, the protein kinase R-like ER kinase (PERK)-eukaryotic initiation factor 2α (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 novel potential therapeutic avenues for stemming the progression of renal cystogenesis.

Glomerular Elasticity and Gene Expression Patterns Define Two Phases of Alport Nephropathy

“…TUDCA appears to have effects beyond those of a chemical chaperone(26–28) Our differential expression data comparing the 4 month Col4α3 −/− and Col4α3 −/− -T transcriptomes suggest that TUDCA also increases expression of genes that suppress Ras-MAPK, tyrosine kinase, and FGF signaling as well as TGF-β-induced epithelial-mesenchymal transformation, and actin remodeling ( Figure 4 ). These effects of TUDCA may contribute to its improvement in podocyte viability and suppression of tubulo-interstitial injury in Alport nephropathy.…”

“…TUDCA suppresses the effects of UPR activation, and in these studies preserves glomerular biophysical properties, reduces podocyte loss, tubulo-interstitial fibrosis and inflammation, proteinuria, and loss of excretory function. All of these beneficial effects may derive from improved podocyte function, but TUDCA may also have additional effects including suppression of inflammation (28, 59, 60). We find that TUDCA increases the expression of mRNAs that could suppress fibrosis, cell migration or inflammation.…”

“…To distinguish among these injury mechanisms, we treated one group of Col4a3 -/mice with Tauroursodeoxycholic acid (TUDCA, Col4a3 -/--T), a compound that functions as a chemical chaperone and that protects cells from UPR-mediated injury or death (24)(25)(26). We analyzed renal function, glomerular capillary elasticity, structure, and bulk renal RNA expression over the course of disease.…”

Inhibition of Asparagine Synthetase Effectively Retards Polycystic Kidney Disease Progression

“…The role of ISR, mainly the UPR branch, in the context of cystic kidney disorders is still debated. Indeed, it has been described that activation of the PERK-dependent branch and activation of the downstream ATF4 transcriptional program contributes to establishment of juvenile cystic kidney ciliopathy (Panda et al , 2022). On the other hand, Fedeles et al demonstrated that activation of the UPR pathway plays a protective role against cyst formation, but that the pathway itself is not deregulated in those kidneys (Fedeles et al , 2015).…”

Cleavage of periostin by MMP9 protects mice from kidney cystic disease

“…Jck mouse model results from a double point mutation in the Nek8 gene [18]. While mutations in this gene are responsible for nephronophthisis in humans [40], mutant mice display features that recapitulate an ADPKD phenotype [41,42]. The disease progresses relatively rapidly to end stage renal disease at 4 months.…”