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Cisplatin is widely used for cancer chemotherapy, but nephrotoxicity is a major dose-limiting side effect. Our recent studies in vitro have shown that pituitary adenylate cyclase-activating polypeptide (PACAP) ameliorated cisplatin nephrotoxicity and that the renoprotection with PACAP38 was mediated by the PAC(1) receptor and through the p53-dependent and -independent suppression of apoptosis of human renal proximal tubular epithelial cells. In the present studies, PACAP38 prevented the rise in blood urea nitrogen and serum creatinine in mice treated with cisplatin. Cisplatin-exposed mice treated with PACAP38 had relatively well-preserved tubular integrity, even when the treatment started 24 h after cisplatin exposure. PACAP38 also reduced plasma and kidney levels of tumor necrosis factor-α and restored collagen IV levels. The damage to mouse kidney tubules caused by cisplatin involved p53 accumulation and was partially reversed by treatment with PACAP38. PACAP38 ameliorates cisplatin-induced acute kidney injury even when treatment started 24 h after the onset of injury and increases tubular regeneration, which further facilitates restoration of kidney function in addition to its anti-apoptotic effects.

BackgroundFree light chains (LCs) are among the many ligands that bind to cubilin/megalin for endocytosis via the clathrin-dependent endosomal/lysosomal pathway. Receptor associated protein (RAP), is a 39 kDA high-affinity, chaperone-like ligand for megalin that assists in the proper folding and functioning of megalin/cubilin. Although RAP is known to inhibit ligand binding to megalin/cubilin, its effect on LC endocytosis has not been shown directly.Methods and Principal FindingsWe investigated whether RAP can block the endocytosis of LC in cultured human proximal tubule cells and whether this can prevent LC cytotoxicity. Immunofluorescence microscopy and flow cytometry showed that fluorescently labeled LC endocytosis was markedly inhibited in HK-2 cells pretreated with human RAP. The effect of RAP was dose-dependent, and was predominantly on endocytosis as it had no effect on the small acid-washable fraction of LC bound to cell membrane. RAP significantly inhibited LC induced cytokine production and phosphorylation of ERK1/2 and p38 MAPK. Prolonged exposure to LC for 48 h resulted in epithelial-to-mesenchymal transformation in HK-2 cells as evidenced by marked reduction in the expression of the epithelial cell marker E-cadherin, and increased the expression of the mesenchymal marker α-SMA, which was also prevented by RAP in the endocytosis medium.ConclusionsRAP inhibited LC endocytosis by ∼88% and ameliorated LC-induced cytokine responses and EMT in human PTCs. The results not only provide additional evidence that LCs endocytosis occurs via the megalin/cubilin endocytic receptor system, but also show that blocking LC endocytosis by RAP can protect proximal tubule cells from LC cytotoxicity.