Exp Mol Med.  2005 Jun;37(3):204-212.

Co-localization and interaction of organic anion transporter 1 with caveolin-2 in rat kidney

• Kwak JO
• Kim HW
• Oh KJ
• Kim DS
• Han KO
• Cha SH

Abstract

The organic anion transporters (OAT) have recently been identified. Although the some transport properties of OATs in the kidney have been verified, the regulatory mechanisms for OAT's functions are still not fully understood. The rat OAT1 (rOAT1) transports a number of negatively charged organic compounds between the cells and their extracellular milieu. Caveolin (Cav) also plays a role in membrane transport. Therefore, we investigated the protein-protein interactions between rOAT1 and caveolin-2. In the rat kidney, the expressions of rOAT1 mRNA and protein were observed in both the cortex and the outer medulla. With respect to Cav-2, the expressions of mRNA and protein were observed in all portions of the kidney (cortex < outer medulla = inner medulla). The results of Western blot analysis using the isolated caveolae-enriched membrane fractions or the immunoprecipitates by respective antibodies from the rat kidney showed that rOAT1 and Cav-2 co-localized in the same fractions and they formed complexes each other. These results were confirmed by performing confocal microscopy with immunocytochemistry using the primary cultured renal proximal tubular cells. When the synthesized cRNA of rOAT1 along with the antisense oligodeoxynucleotides of Xenopus Cav-2 were co-injected into Xenopus oocytes, the [14C]p-aminohippurate and [3H]methotrexate uptake was slightly, but significantly decreased. The similar results were also observed in rOAT1 over-expressed Chinese hamster ovary cells. These findings suggest that rOAT1 and caveolin-2 are co-expressed in the plasma membrane and rOAT1's function for organic compound transport is upregulated by Cav-2 in the normal physiological condition.

Keyword

antisense oligodeoxynucleotide (ODN); caveolin-2 (Cav-2); organic anion transporter 1 (OAT1); renal proximal tubule

MeSH Terms

Animals
Biological Transport, Active/*physiology
CHO Cells
Caveolins/*metabolism
Cell Membrane/*metabolism
Cells, Cultured
Hamsters
Immunoprecipitation
Kidney Tubules, Proximal/*metabolism
Methotrexate/metabolism
Microscopy, Confocal
Oligonucleotides, Antisense/pharmacology
Oocytes/metabolism
Organic Anion Transport Protein 1/antagonists & inhibitors/genetics/*metabolism
RNA, Complementary/metabolism
RNA, Messenger/genetics/metabolism
Rats
Research Support, Non-U.S. Gov't
Xenopus laevis/metabolism
p-Aminohippuric Acid/metabolism