Objective T-LAK-cell-originated protein kinase (TOPK), a PSD95-Disc large-ZO1 (PDZ) binding kinase (PBK), is a novel member of the mitogen-activated protein kinase (MAPK) family. Studies have shown that TOPK plays a critical role in the function of tumor cells, including apoptosis and mitosis. However, little is known on the effect of TOPK in cisplatin-induced acute kidney injury (CP-AKI). This study aimed to investigate the role and mechanism of TOPK in CP-AKI. Methods Cisplatin was administered to C57BL/6 mice and cultured kidney tubular epithelial cells (TECs) to establish the CP-AKI murine or cellular models. TECs were then stimulated with the specific inhibitor of TOPK OTS514 or transfected with the recombinant-activated plasmid TOPK-T9E to inhibit or activate TOPK. The TECs were treated with AKT inhibitor VIII following stimulation with OTS514 or cisplatin. Western blotting and flow cytometry were used to evaluate the cell cycle and apoptosis of TECs. Results The analysis revealed that the TOPK activity was significantly suppressed by cisplatin, both in vivo and in vitro. Furthermore, the pharmacological inhibition of TOPK by OTS514, a specific inhibitor of TOPK, exacerbated the cisplatin-induced cell cycle arrest in the G2/M phase and apoptosis of cultured TECs. Moreover, the TOPK activation via the TOPK-T9E plasmid transfection could partially reverse the cell cycle arrest at the G2/M phase and apoptosis of cisplatin-treated TECs. In addition, AKT/protein kinase B (PKB), as a TOPK target protein, was inhibited by cisplatin in cultured TECs. The pharmaceutical inhibition of AKT further aggravated the apoptosis of TECs induced by cisplatin or TOPK inhibition. TOPK systematically mediated the apoptosis via the AKT pathway in the CP-AKI cell model. Conclusion These results indicate that TOPK activation protects against CP-AKI by ameliorating the G2/M cell cycle arrest and cell apoptosis.

Serum and glucocorticoid-inducible kinase 3 (SGK3) is involved in maintaining podocyte function by regulating the protein levels of podocin and CD2-associated protein. Nephrin is also one of the slit diaphragm proteins of podocytes, but whether SGK3 participates in podocyte injury by regulating the levels of nephrin remains unclear. In this study, we focused on whether SGK3 affects nephrin levels and the mechanisms involved in the same. In the kidneys of adriamycin (ADR)-induced podocyte injury mouse model, the protein levels of SGK3 and nephrin were significantly decreased. Furthermore, the expression of SGK3 was negatively correlated with the output of proteinuria, and positively correlated with the levels of nephrin. In ADR-treated conditionally immortalized mouse podocyte cells (MPCs), the protein levels of nephrin and SGK3 were inhibited, while the constitutive expression of SGK3 reversed the ADR-induced decline in nephrin protein levels. Furthermore, ADR treatment or SGK3 inactivation enhanced the ubiquitin-proteasome degradation of nephrin in MPCs, and dramatically activated downstream effector proteins of SGK3, neural precursor cells expressing developmentally downregulated protein 4 subtype 2 (Nedd4-2) and glycogen synthase kinase-3 β (GSK3β). Similarly, Nedd4-2 or GSK3β overexpression resulted in increased activity of Nedd4-2 or GSK3β, and significantly downregulated nephrin levels. Interestingly, ubiquitin-mediated protein degradation of nephrin was regulated by Nedd4-2, rather than by GSK3β. In summary, SGK3 inactivation downregulated the levels of nephrin by increasing Nedd4-2 and GSK3β activity in ADR-induced podocyte injury model; in particular, the SGK3/Nedd4-2 signaling pathway was found to be involved in ubiquitin-mediated proteasome degradation of nephrin.

Cisplatin-induced acute kidney injury (CP-AKI) is a severe complication in patients receiving CP chemotherapy. However, effective therapies for CP-AKI are currently lacking. Curcumin (CUR), a natural polyphenol, is extracted from the rhizome of turmeric and has been reported to have nephroprotective activity. However, the role of CUR in CP-AKI remains unclear. This study aimed to explore the mechanism of CUR in CP-AKI by combining a network pharmacology approach with experimental validations. The analysis revealed 176 potential targets of CUR based on the HERB database and 1,286 related targets of CP-AKI from the GeneCards, DrugBank, and OMIM databases. Further, 106 common targets of CUR against CP-AKI were obtained, and these common targets constructed a protein-protein interaction (PPI) network. In addition, the core targets were screened from the PPI network using Cytoscape. Molecular docking revealed that CUR displayed the best binding to AKT1. Gene Ontology (GO) analysis indicated that the primary biological processes of CUR against CP-AKI included cellular response to chemical stress and apoptotic regulation. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis suggested that the PI3K-Akt signaling pathway was most significantly enriched in CUR against CP-AKI. Western blotting and flow cytometry showed that CUR inhibited apoptosis induced by CP by activating the Akt signaling pathway in human kidney tubular epithelial cells (HK-2). Altogether, our findings demonstrated that CUR alleviated apoptosis by activating the Akt signaling pathway in CP-AKI in vitro . These data provide a scientific basis for future investigations into the clinical application of CUR against CP-AKI.