The SGK3-triggered ubiquitin–proteasome degradation of podocalyxin (PC) and ezrin in podocytes was associated with the stability of the PC/ezrin complex

Abstract

Podocyte damage is commonly accompanied by destabilization of the podocalyxin (PC)/ezrin complex. Serum- and glucocorticoid-inducible kinase 3 (SGK3) plays a role in the maintenance of podocyte function, but the details of this role are poorly understood. Herein we demonstrated that SGK3 and its downstream target protein neural precursor cell expressed developmentally downregulated protein 4 subtype 2 (Nedd4-2) triggered PC and ezrin interaction. In adriamycin (ADR)-induced nephritic mice, and after puromycin aminonucleoside (PAN)-induced podocyte damage in vitro, PC and ezrin protein expression levels decreased significantly, while Nedd4-2 activity increased. Moreover, PAN treatment increased PC and ezrin ubiquitination and decreased PC/ezrin interaction in cultured mouse podocytes. The downregulation of SGK3 activity in mouse podocytes resulted in decreased PC and ezrin protein expression and increased the ubiquitin–proteasome degradation of PC and ezrin. Furthermore, upregulation of SGK3 activity mostly reversed the PAN-induced decrease in PC and ezrin protein expression. Overexpression of Nedd4-2 led to decreased ezrin protein expression via the upregulation of ezrin ubiquitination. In contrast, Nedd4-2 knockdown resulted in increased ezrin protein expression but decreased ezrin ubiquitination. In PC-transfected human embryonic kidney (HEK293T) cells, SGK3 activity downregulation and Nedd4-2 overexpression resulted in decreased PC/ezrin interaction. These results suggested that SGK3 triggers the ubiquitin–proteasome degradation of PC and ezrin, while the SGK3/Nedd4-2 signaling pathway regulates ezrin, but not PC, ubiquitination. Thus SGK3 helps to regulate podocyte function by maintaining the stability of the PC/ezrin complex.

Serum and Glucocorticoid-Inducible Kinase 3/Nedd4-2 Signaling Pathway Participates in Podocyte Injury by Regulating the Stability of Nephrin

“…SGK3 is a serine/threonine protein kinase that is involved in regulating cell proliferation and ion transport ( Lang et al, 2006 ; He et al, 2011 ). Our previous studies have shown that SGK3 inactivation inhibited podocyte cell viability, downregulated the expression of podocin and CD2AP proteins, and increased ubiquitination-mediated degradation of podocalyxin and ezrin ( Peng et al, 2018 ; Yuan et al, 2018 ). The present study demonstrated that the decreased levels of SGK3 were positively correlated with the levels of nephrin in the kidneys of an ADR-nephritis mouse model.…”

“…Ubiquitination assays were performed as described ( Yuan et al, 2018 ). Mouse podocytes were treated with ADR (0.2 μg/ml) or transfected with plasmids and MG132 (10 μM) was added for 8 h before collected to prevent proteasomal degradation.…”

“…SGK3 can inactivate neural precursor cells expressing developmentally downregulated protein 4 subtype 2 (Nedd4-2) and glycogen synthase kinase-3β (GSK3β) via phosphorylation ( Dai et al, 2002 ; Yuan et al, 2018 ). Nedd4-2 is a member of the E3 ubiquitin ligase that mediates substrate protein ubiquitination mediated degradation by transferring ubiquitin from its homologous to the E6-AP carboxyl terminus (HECT) domain to substrate proteins ( Abriel and Staub, 2005 ; Rotin and Kumar, 2009 ).…”

“…Previous reports have demonstrated that GSK3β regulates the nuclear transcription of nephrin through the transcriptional repressor Snail ( Matsui et al, 2007 ; Wan et al, 2016 ; Wang et al, 2017 ). Our previous study showed that the SGK3/Nedd4-2 signaling pathway was involved in maintaining the stability of the podocalyxin/ezrin complex by affecting ezrin ubiquitination in podocytes ( Yuan et al, 2018 ). However, it remains to be determined whether SGK3/GSK3β or SGK3/Nedd4-2 signaling pathway regulates nephrin protein levels.…”

circCDYL2, Overexpressed in Highly Migratory Colorectal Cancer Cells, Promotes Migration by Binding to Ezrin

“…Ezrin expression can be regulated by miRNAs (34). Moreover, Ezrin can be degraded by the ubiquitination proteasome (35). Here, we found that circCDYL2 bound to Ezrin and upregulated its protein levels, indicating that circCDYL2 might stabilize Ezrin and protect it from degradation.…”