HRD1 prevents apoptosis in renal tubular epithelial cells by mediating eIF2α ubiquitylation and degradation

Abstract

Apoptosis of renal tubular epithelial cells is a key feature of the pathogenicity associated with tubulointerstitial fibrosis and other kidney diseases. One factor that regulates important cellular processes like apoptosis and cell proliferation is HRD1, an E3 ubiquitin ligase that acts by promoting ubiquitylation and degradation of its target protein. However, the detailed mechanisms by which HRD1 acts as a regulator of apoptosis in renal tubular epithelial cells have not been established. In our previous liquid chromatography-tandem mass spectrometry (LC-MS/MS) study (Mol Endocrinol. 2016;30:600–613), we demonstrated that one substrate of HRD1 was eIF2α, a critical protein in the PERK-eIF2α-ATF4-CHOP signaling pathway of endoplasmic reticulum (ER) stress. Here, we show that eIF2α expression was increased and HRD1 expression decreased when apoptosis was induced in HKC-8 cells by palmitic acid (PA) or high glucose (HG). HRD1 expression was also lower in kidney tissues from mice with diabetic nephropathy (DN) than in control mice. Forced expression of HRD1 also inhibited apoptosis in HKC-8 cells, while HRD1 overexpression decreased the expression of phosphorylated eIF2α and eIF2α. Further analysis indicated that HRD1 interacted with eIF2α and promoted its ubiquitylation and degradation by the proteasome. Moreover, the HRD1 protection of PA-treated HKC-8 cells was blunted by transfection with Myc-eIF2α. Thus, eIF2α ubiquitylation by HRD1 protects tubular epithelial cells from apoptosis caused by HG and PA, indicating a novel upstream target for therapeutic prevention of renal tubulointerstitial injury.

HUWE1 promotes EGFR ubiquitination and degradation to protect against renal tubulointerstitial fibrosis

“…31 Ubiquitination and degradation of a third negative signaling protein, eIF2α, by HRD1 prevent apoptosis in renal tubular cells. 28 We previously demonstrated that derlin-1 promotes ubiquitination and degradation of the epithelial sodium channel (ENaC), and we suggested that HUWE1 might act as an E3 ligase of α-ENaC.…”

“…The degradation of the negative signaling protein Smad7 by ubiquitination leads to TGF‐β activation, while the ubiquitination and degradation of another negative signaling protein IκB, a protein that is suppressed by NFκB and that plays a critical role in renal disease, allows the nuclear translocation of NFκB for participation in gene transcription . Ubiquitination and degradation of a third negative signaling protein, eIF2α, by HRD1 prevent apoptosis in renal tubular cells . We previously demonstrated that derlin‐1 promotes ubiquitination and degradation of the epithelial sodium channel (ENaC), and we suggested that HUWE1 might act as an E3 ligase of α‐ENaC.…”

“…Growing evidence now supports the ubiquitination of target proteins in the pathogenesis of a variety of diseases, including kidney injury . The attachment of ubiquitin (8.5 kDa) to a substrate protein requires three distinct enzymes and steps.…”

“…Growing evidence now supports the ubiquitination of target proteins in the pathogenesis of a variety of diseases, including kidney injury. 25,27,28 The attachment of ubiquitin (8.5 kDa) to a substrate protein requires three distinct enzymes and steps. The first step activates ubiquitin by forming a thioester linkage between the E1 ubiquitin-activating enzyme and the autophagy-related phagophore-formation transporter (APT).…”

E3 Ubiquitin Ligase HRD1 Promotes Lung Tumorigenesis by Promoting Sirtuin 2 Ubiquitination and Degradation

“…The first identified substrate of HRD1 was 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMGCR), which is tightly regulated by metabolic feedback control (32). Later, it was reported that HRD1 also targets non-ERAD proteins to regulate various cellular processes (33)(34)(35)(36)(37)(38)(39) besides the ERAD component IRE1 (40). However, its involvement in lung tumorigenesis remains unknown.…”