SGK3 Triggered Ubiquitin-proteasome Degradation Of Nephrin Is Involved In Podocyte Injury

Purpose: Podocyte injury is closely related to the occurrence and progression of proteinuria.Serum-and glucocorticoid-inducible kinase 3(SGK3)is involved in podocyte damage via regulation podocyte cell viability,as well as the expression of Podocin,CD2 AP and Podocalyxin(PC),but whether SGK3 could participate in podocyte injury by regulating Nephrin is not clear.Here we focused on weather and how SGK3 affects Nephrin.Method: First the immortalized mouse podocytes cultured in vitro were treated with 0,25 and 50 ug/ml PAN respectively in order to establish a podocyte injury model in vitro.Then podocytes was transiently transfected with SGK3 sh RNA,SGK3-K191 M plasmid,or SGK3-S486 D plasmid and treated with PAN for 24 h additional.Next podocytes was transiently transfected with wild-type Nedd4-2 plasmid,Nedd4-2 sh RNA,wild-type GSK3β plasmid or Li Cl treatment.Immunoblotting was used to detect the protein expression of Nephrin and the ubiquitination of Nephrin was detected by ubiquitination assay.Results: The expression of Nephrin was down-regulated in PAN-induced podocyte injury,and PAN treatment increase Nephrin ubiquitination-proteasome degradation.Moreover,SGK3 sh RNA and SGK3-K191 M transfected decrease the protein expression of Nephrin.The ubiquitination level of Nephrin was increased after SGK3-K191 M transfection and induced Nephrin degraded by proteasome.Continuously activited SGK3 could partially preserved PAN-induced decreased protein expression of Nephrin.Overexpression of Nedd4-2 reduced protein expression of Nephrin in podocytes,while Nephrin protein expression was increased after transfection with Nedd4-2 sh RNA.Simultaneously overexpression of GSK3β resulted in decreased the protein expression of Nephrin in podocytes,while the protein expression of Nephrin was increased after GSK3β activity inhibition.Conclusion: SGK3 inactivation leads to Nephrin degradation by ubiquitin-proteasome,Continuous activation of SGK3 could partially preserved PAN-induced downregulation of Nephrin protein expression.SGK3 inactivation triggered down-regulation of Nephrin protein expression via increasing Nedd4-2 and GSK3β activity probably.