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

点击翻译按钮获取中文摘要

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