Department of Pharmaceutics, Rutgers, the State University of New Jersey, Piscataway, New Jersey.
Department of Pharmaceutics, Rutgers, the State University of New Jersey, Piscataway, New Jersey
Mol Pharmacol. 2020 Jun;97(6):384-391. doi: 10.1124/mol.119.118653. Epub 2020 Mar 31.
Organic anion transporter 1 (OAT1), expressed at the basolateral membrane of renal proximal tubule epithelial cells, mediates the renal excretion of many clinically important drugs. Previous study in our laboratory demonstrated that ubiquitin conjugation to OAT1 leads to OAT1 internalization from the cell surface and subsequent degradation. The current study showed that the ubiquitinated OAT1 accumulated in the presence of the proteasomal inhibitors MG132 and ALLN rather than the lysosomal inhibitors leupeptin and pepstatin A, suggesting that ubiquitinated OAT1 degrades through proteasomes. Anticancer drugs bortezomib and carfilzomib target the ubiquitin-proteasome pathway. We therefore investigate the roles of bortezomib and carfilzomib in reversing the ubiquitination-induced downregulation of OAT1 expression and transport activity. We showed that bortezomib and carfilzomib extremely increased the ubiquitinated OAT1, which correlated well with an enhanced OAT1-mediated transport of p-aminohippuric acid and an enhanced OAT1 surface expression. The augmented OAT1 expression and transport activity after the treatment with bortezomib and carfilzomib resulted from a reduced rate of OAT1 degradation. Consistent with this, we found decreased 20S proteasomal activity in cells that were exposed to bortezomib and carfilzomib. In conclusion, this study identified the pathway in which ubiquitinated OAT1 degrades and unveiled a novel role of anticancer drugs bortezomib and carfilzomib in their regulation of OAT1 expression and transport activity. SIGNIFICANCE STATEMENT: Bortezomib and carfilzomib are two Food and Drug Administration-approved anticancer drugs, and proteasome is the drug target. In this study, we unveiled a new role of bortezomib and carfilzomib in enhancing OAT1 expression and transport activity by preventing the degradation of ubiquitinated OAT1 in proteasomes. This finding provides a new strategy in regulating OAT1 function that can be used to accelerate the clearance of drugs, metabolites, or toxins and reverse the decreased expression under disease conditions.
有机阴离子转运蛋白 1（OAT1）表达在肾近端小管上皮细胞的基底外侧膜上，介导许多临床重要药物的肾排泄。我们实验室的先前研究表明，泛素与 OAT1 缀合导致 OAT1 从细胞表面内化，随后降解。本研究表明，在蛋白酶体抑制剂 MG132 和 ALLN 的存在下，泛素化的 OAT1 积累而不是溶酶体抑制剂亮抑蛋白酶肽和抑肽酶 A，表明泛素化的 OAT1 通过蛋白酶体降解。抗癌药物硼替佐米和卡非佐米靶向泛素-蛋白酶体途径。因此，我们研究了硼替佐米和卡非佐米在逆转泛素诱导的 OAT1 表达和转运活性下调中的作用。我们表明，硼替佐米和卡非佐米极显著增加了泛素化的 OAT1，这与增强的对氨基马尿酸的 OAT1 介导转运和增强的 OAT1 表面表达密切相关。硼替佐米和卡非佐米处理后 OAT1 表达和转运活性的增加是由于 OAT1 降解率降低所致。与此一致，我们发现暴露于硼替佐米和卡非佐米的细胞中 20S 蛋白酶体活性降低。总之，本研究确定了泛素化的 OAT1 降解的途径，并揭示了抗癌药物硼替佐米和卡非佐米在调节 OAT1 表达和转运活性中的新作用。
硼替佐米和卡非佐米是两种获得美国食品和药物管理局批准的抗癌药物，蛋白酶体是药物靶点。在这项研究中，我们揭示了硼替佐米和卡非佐米通过防止泛素化的 OAT1 在蛋白酶体中的降解来增强 OAT1 表达和转运活性的新作用。这一发现为调节 OAT1 功能提供了一种新策略，可用于加速药物、代谢物或毒素的清除，并逆转疾病状态下表达的降低。
