Bombesin receptor-activated protein exacerbates cisplatin-induced AKI by regulating the degradation of SIRT2

Acute kidney injury (AKI) is a public health problem with no specific therapies in the clinic, and the underlying pathogenesis of AKI remains obscure. Bombesin receptor-activated protein(BRAP, C6ORF89 protein) was initially discovered as a ligand for a previously orphan G protein-coupled receptor bombesin-like receptor-3. At present, accepted biological effects of BRAP include cell cycle progression, wound repair, and the activation of histone deacetylases. However, its role in kidney disease is unknown. In this study, we have investigated the role of BRAP and underlying mechanisms involved in cisplatin-induced AKI. BRAP was down-regulated in mice and human kidneys with AKI. Global Bc004004(homologous of C6ORF89 in mice) deletion alleviated tubular cell Apoptosis and Necroptosis in cisplatin-induced AKI mice, whereas local overexpression of BRAP in kidneys aggravated them. The pan-caspase inhibitor Z-VAD pretreatments attenuated cisplatin-induced blood creatinine increase and kidney injury in wild-type mice, but not in BRAP-/- mice. The activation of MLKL was magnified by Z-VAD in cisplatin-treated mice, especially in BRAP-/- mice. The cytoprotective effect of Z-VAD was more substantial than Necrostatin-1(Nec-1, an inhibitor of Necroptosis) in CP-treated human kidney proximal tubular epithelial (HK2) cells. Furthermore, Nec-1pretreatment reduced the CP-induced cell death in BRAP overexpression HK2 cells but did not work in cells with normal BRAP levels. We determined that cisplatin treatment activated NF-κB subunit P65, and inhibition of P65 increased the mRNA levels of BRAP in HK2cells. ChIP assay and Dual-luciferase reporter gene assay verified P65 binding to the C6ORF89 promoter and reduced its mRNA expression upon cisplatin treatment. Next, we found that SIRT2 was downregulated in cisplatin-induced AKI, and BRAP levels directly impacted the protein levels of SIRT2. Our findings further confirmed that BRAP regulates the SIRT2 protein levels by affecting SIRT2's interactions with E3 ubiquitin ligase HRD1 and subsequent proteasomal degradation. Collectively, our results demonstrated that BRAP played an important role in tubular cell Apoptosis and Necroptosis during cisplatin-induced AKI. Safe and efficient BRAP inhibitors might be effective therapeutic options for AKI.