Roles of transporter adaptors as regulatory mechanism for drug absorption and disposition

许多类型的外源性转运体已经被确定。它们通常对各种类型的底物表现出多特异性识别，并介导治疗剂的膜渗透，从而在药物吸收和处置中发挥重要作用。我们最近根据体外实验数据提出，涉及外源转运体的蛋白-蛋白相互作用可能影响其在质膜上的功能、定位和表达。直接与转运蛋白相互作用的所谓接头蛋白包括PDZ （PSD95）、Dig和ZOO结构域蛋白。本项目的目的是阐明这些接头蛋白在体内的药代动力学作用。通过敲除pdzk1基因（pdzk1^+）小鼠，发现pdzk1与pdzk1接头的相互作用对于三种溶质载体Slc15a1（寡肽转运体PEPTD）、S1c22a5（肉碱/有机阳离子转运体OCTN2）和Slco 1a（有机阳离子转运体OATP1A）在小鼠小肠中的细胞表面定位至关重要。电镜显示PEPT1定位于pdzk1^+小鼠的细胞内囊泡结构。在pdzk1^+小鼠中，与野生小鼠相比，胃肠道对头孢氨苄（PEPT1和肉碱的底物，OCTN2的底物）的吸收延迟。此外，pdzk1^+小鼠小肠顶端膜对硫酸雌酮（OATP1A的底物）的摄取也减少。因此，PDZK1作为转运蛋白的调节因子起着关键作用，从而影响这些相互作用的转运蛋白对底物的吸收。由于PDZ适配器在其结构中具有多个PDZ结构域，并且每个PDZ结构域可以与转运蛋白的细胞质区域相互作用，因此可以推测转运蛋白定位于由多个转运蛋白和适配器组成的网络中。我们还发现，在小gtp结合蛋白rab8 （rab8^+）的基因敲除小鼠中，PEPT1和Slc5a1（钠/葡萄糖共转运蛋白，SGLT1）的顶端定位几乎完全减少。在rab8^+中，胃肠道对glycylsarcos （PEPT1的底物）和α-甲基葡萄糖（SGLT1的底物）的摄取同时减少。因此，我们的研究结果表明rab8对于两种转运体的适当定位和消化作为这些转运体底物的各种营养物质是必要的。少

Many types of xenobiotic transporters have been identified. They generally exhibit multispecific recognition of various types of substrates, and mediate membrane permeation of therapeutic agents, thereby playing important roles in drug absorption and disposition. We have recently proposed that protein-protein interactions involving the xenobiotic transporters may affect their function, localization and expression on plasma membranes based on in vitro experimental data. So-called adaptor proteins that directly interact with the transporters include PDZ (PSD95, Dig and ZOO domain-containing proteins. This project was performed with an aim to clarify pharmacokinetic roles of such adaptor proteins in vivo. Using pdzk1 gene knockout (pdzk1^+) mice, it was found that interaction with a PDZ adaptor PDZK1 is essential for the cell-surface localization of three solute carriers, Slc15a1 (oligopeptide transporter PEPTD, S1c22a5 (carnitine/organic cation transporter OCTN2) and Slco 1a (organic ani … More on transporting polypeptide, OATP1A) in mouse small intestine. Electron microscopy revealed localization of PEPT1 in intracellular vesicular structures in pdzk1^+ mice. In pdzk1^+ mice, gastrointestinal absorption of cephalexin, a substrate of PEPT1 and carnitine, a substrate of OCTN2 was delayed, compared with wild mice. In addition, uptake of estrone sulfate, a substrate of OATP1A from apical membrane of small intestine was also decreased in pdzk1^+ mice. Thus, PDZK1 plays pivotal roles as a regulator of transporters, thereby affecting the absorption of substrates of those interacting transporters. Since PDZ adaptors have multiple PDZ domains in their structure, and each PDZ domain can interact with the cytosolic region of the transporters, it can be speculated that transporters are localized within networks consisting of several transporters and adaptors. We have also found that apical localization of PEPT1 and Slc5a1 (sodium/glucose cotransporter, SGLT1) was almost completely reduced in gene knockout mice for small GTP-binding protein rab8 (rab8^+). Gastrointestinal uptake across the apical membranes of glycylsarcosine, a substrate of PEPT1 and α-methylglucose, a substrate of SGLT1 was concomitantly reduced in rab8^+. Thus, our results demonstrate that rab8 is necessary for the proper localization of the two transporters and digestion of various nutrients which are the substrate of those transporters. Less