JP4223536B2 - Brain-type organic anion transporter and its gene - Google Patents

Description

  The present invention relates to a gene involved in organic anion (organic anion) transport and a polypeptide encoded by the gene.

The liver and kidney play an important role in the metabolism and extracorporeal elimination of xenobiotics and drugs. Tubular cells and hepatocytes are epithelial cells with polarity, and some anionic substances are taken into the kidney and liver via the basolateral membrane by transport carriers (transporters), and are also metabolized intracellularly. It is speculated that the produced organic anion is also discharged by the transporter.
Uptake of organic anions through the basolateral membrane of tubule cells and hepatocytes has been studied by an experimental system using an isolated organ perfusion method or an isolated cell membrane vesicle system.

However, it is difficult to analyze the organic anion transport through the basolateral membrane in detail by the conventional method, and it has been desired to analyze the transporter itself in detail.
On the other hand, it is speculated from a plurality of experimental results that organic anion transport is also performed in the brain. It is thought that organic anion transport in the brain is mainly responsible for excretion of endogenous and exogenous organic anions out of the brain.
Although organic anion transport in the brain is expected to play an important role in eliminating endogenous anions and foreign substances from the brain, it is difficult to perform physiological experiments. The details of its transportation are unknown.

Based on these backgrounds, the search for molecular entities of organic anion transporters was actively conducted in the 1990s. As a result, two organic anion transporters in the basolateral membrane of the liver were isolated by last year. (Hagenbuch, B. et al. Proc Natl Acad Sci USA 88, 10629-33, 1991, Jacquemin, E. et al., Proc Natl Acad Sci USA, 91, 133-7, 1994).
Last year, we succeeded in isolating the organic anion transporter OAT1, which plays the most important role in organic anion transport in the kidney (Sekine, T. et al., J Biol Chem 272, 18526- (9 pages, 1997), a patent application has already been filed. OAT1 is a transporter capable of transporting many organic anions having different chemical structures, and also transports various anionic drugs.

OAT1 expression is kidney-specific, and only very little expression is seen in the brain except for the kidney.
Recently, the present inventors further identified a liver-specific organic anion transporter (OAT2) having weak homology with OAT1 at the amino acid level of 40% (FEBS letter 429, 179-182, 1998) ( Japanese Patent Application No. 10-169174).
Isolation and identification of OAT1 and OAT2 indicate that organic anion transporters form a family. Furthermore, OAT2 is expressed specifically in the liver, suggesting that this family is not kidney specific but is expressed in various organs.

As described above, it is considered that an organic anion transport system is present in the brain, but the expression of OAT1 in the brain is very slight, and OAT2 does not exist. Based on these facts, the present inventors predicted the existence of an unknown transporter responsible for organic anion transport in the brain.
On the other hand, transport of organic anions in the basolateral membrane of the liver is complicated, and in particular, the outflow route into the blood of conjugates produced in large quantities in hepatocytes (most of which are organic anions) is still unclear. This organic anion transport in the liver cannot be explained only by the organic anion transporter including OAT2, and the presence of further unknown transporters is expected.

  An object of the present invention is to identify and provide a novel organic anion transporter gene involved in organic anion transport in the brain and liver and an organic anion transporter which is a polypeptide encoded by the gene. Other purposes will be clear from the following description.

  We have isolated the organic anion transporter OAT1, which plays the most important role in organic anion transport in the kidney (Sekine, T. et al., J Biol Chem 272, 18526-9, 1997). Furthermore, a liver-specific organic anion transporter (OAT2) was identified from structural similarity with OAT1 (Sekine, T. et al., FEBS letter 429, 179-182, 1998). Furthermore, OAT1 and OAT2 have already been reported to have weak homology with the organic cation transporter OCT1 (Grundemann, D. et al., Nature, 372, 549-52, 1994) (Sekine, T. et al., J Biol Chem 272, 18526-9, 1997).

  Based on these facts, a sequence common to OAT1, OAT2, and OCT1 was identified, and a degenerate primer was created from the sequence. Using this degenerate primer, a novel cDNA fragment having weak homology with OAT1, OAT2, and OCT1 was identified from rat brain mRNA by RT (reverse transcript) -PCR (polymerase chain reaction). Using this cDNA fragment, an unreported cDNA was identified from a rat cDNA library, and this protein was named as a brain-type organic anion transporter OAT3 (Organic Anion Transporter 3) as a third member of the OAT family. .

The present invention relates to an organic anion transporter OAT3, and the organic anion transporter OAT3 of the present invention transports (has the ability to incorporate) organic anions having different chemical structures and has a wide range of substrate selectivity. However, it did not transport TEA (tetraethylammonium), which is a typical organic cation. Therefore, the organic anion transporter OAT3 of the present invention has a wide range of substrate selectivity for the organic anion, but has substantially no substrate selectivity for TEA (tetraethylammonium), which is a typical organic cation. It is an organic anion transporter that is selectively distributed in organs such as the brain and liver.
The protein of the present invention has the amino acid sequence represented by SEQ ID NO: 2 (human) or 4 (rat), which is the organic anion transporter OAT3 described above, for example, the amino acid sequence represented by SEQ ID NO: 2 or 4 In which one or several amino acids are deleted, substituted or added.

The present invention also relates to a nucleic acid, preferably DNA or RNA, encoding the protein of the present invention containing the organic anion transporter OAT3. The nucleic acid of the present invention includes a nucleic acid capable of hybridizing to the nucleic acid under stringent conditions in addition to the one encoding the protein of the present invention.
In the present invention, hybridization under stringent conditions usually refers to hybridization in a hybridization solution having a salt concentration of 5 × SSC or equivalent at a temperature of 37 to 42 ° C. for about 12 hours. It can be carried out by performing pre-washing with 5 × SSC or a solution having a salt concentration equivalent thereto, and then washing with 1 × SSC or a salt concentration equivalent thereto. Further, in order to obtain higher stringency, the washing can be carried out by washing in a solution of 0.1 × SSC or a salt concentration equivalent thereto.
Furthermore, the present invention relates to a partial sequence of a nucleic acid encoding the protein of the present invention or a nucleotide that can hybridize to the sequence under stringent conditions.
The present invention also relates to an antibody against the protein of the present invention or a polypeptide immunologically equivalent thereto.

The organic anion transporter gene of the present invention can be isolated and obtained by screening using a tissue or cell of an organ such as a kidney or brain of a suitable mammal as a gene source. Mammals include non-human animals such as dogs, cows, horses, goats, sheep, monkeys, pigs, rabbits, rats, mice, and humans.
Screening and isolation of genes can be suitably performed by homology screening, PCR screening, and the like. The obtained cDNA can be sequenced by a conventional method, and the translation region can be analyzed to determine the amino acid sequence of the protein encoded thereby, that is, OAT3.
It can be verified, for example, as follows, that the obtained cDNA is a cDNA of an organic anion transporter gene, that is, the gene product encoded by the cDNA is an organic anion transporter. That is, the cRNA prepared from the obtained OAT3 gene is introduced into an oocyte for expression, and the ability to transport (incorporate) an organic anion into the cell is compared with a normal uptake experiment using an appropriate organic anion as a substrate (Sekine , T. et al., J Biol Chem 272, 18526-9, 1997), and can be confirmed by measuring the substrate uptake into cells.
In addition, the same uptake experiment can be applied to expressing cells to examine the transport characteristics and substrate specificity of OAT3.

  SEQ ID NO: 3 in the sequence listing shows the base sequence of rat organic anion transporter OAT3 cDNA obtained by such a method, and SEQ ID NO: 4 shows the amino acid sequence.

Isolation of homologous genes and chromosomal genes from different tissues and different organisms by screening appropriate cDNA libraries or genomic DNA libraries prepared with different gene sources using the cDNA of the obtained OAT3 gene can do.
SEQ ID NO: 1 of the sequence listing shows the base sequence of cDNA of human organic anion transporter OAT3 obtained by such a method, and SEQ ID NO: 2 shows its amino acid sequence.

In addition, using a synthetic primer designed based on the nucleotide sequence shown in the nucleotide sequence (SEQ ID NO: 1 or 3) of the disclosed gene of the present invention (SEQ ID NO: 1 or 3) or a part of the information, cDNA live is performed by a normal PCR method. A gene can be isolated from a rally.
DNA libraries such as cDNA libraries and genomic DNA libraries are described in, for example, “Molecular Cloning; Sambrook, J., Fritsh, EF and Maniatis, T., published by Cold Spring Harbor Laboratory Press in 1989”. Can be prepared. Alternatively, when there is a commercially available library, it may be used.

  The organic anion transporter (OAT3) of the present invention can be produced by a gene recombination technique using, for example, cDNA encoding the organic anion transporter. For example, DNA (such as cDNA) encoding an organic anion transporter can be incorporated into an appropriate expression vector, and the resulting recombinant DNA can be introduced into an appropriate host cell. Examples of the expression system (host vector system) for producing the polypeptide include bacterial, yeast, insect cell and mammalian cell expression systems. Of these, insect cells and mammalian cells are preferably used to obtain functional proteins.

  For example, when a polypeptide is expressed in a mammal, DNA encoding the organic anion transporter of the present invention is converted into an appropriate expression vector (for example, a retrovirus vector, papilloma virus vector, vaccinia virus vector, SV40 vector). Etc.) is inserted downstream of an appropriate promoter (for example, SV40 promoter, LTR promoter, elongation 1α promoter, etc.) to construct an expression vector. Next, an appropriate animal cell is transformed with the obtained expression vector, and the transformant is cultured in an appropriate medium to produce the desired polypeptide. Examples of mammalian cells used as a host include monkey COS-7 cells, Chinese hamster CHO cells, human Hela cells, or primary cultured cells derived from kidney tissue, puta kidney-derived LLC-PK1 cells, Fukuro rat kidney-derived OK cells, and the like. Is mentioned.

  As a cDNA encoding the organic anion transporter OAT3, for example, a cDNA having the base sequence shown in SEQ ID NO: 1 or 3 can be used, and the DNA corresponding to the amino acid sequence is not limited to the above cDNA. And DNA encoding the polypeptide can be used. In this case, 1 to 6 types of codons encoding one amino acid are known, and the selection of codons to be used may be arbitrary. For example, in consideration of the codon usage of the host used for expression, higher expression is achieved. An array can be designed. DNA having the designed base sequence can be obtained by chemical synthesis of DNA, fragmentation and binding of the cDNA, partial modification of the base sequence, and the like. Artificial modification of the base sequence and mutagenesis can be achieved by using site-specific mutagenesis “Mark, DF et al., Proc Natl Acad Sci USA, using primers made of synthetic oligonucleotides that encode the desired alterations. Vol. 18, pp. 5662-5666, 1984 ”.

The nucleotide (oligonucleotide or polynucleotide) that hybridizes under stringent conditions to the organic anion transporter gene of the present invention can be used as a probe for detecting the organic anion transporter gene, and the expression of the organic anion transporter. Can be used, for example, as antisense oligonucleotides, ribozymes, decoys.
The present invention also relates to a partial sequence of a nucleic acid encoding the protein of the present invention or a nucleotide that can hybridize to the sequence under stringent conditions. As such a nucleotide, for example, a nucleotide containing a partial sequence of 14 bases or more in succession in the base sequence represented by SEQ ID NO: 1 or 3 or a complementary sequence thereof can be used. In order to make it more specific, a longer sequence such as a sequence of 20 bases or more or 30 bases or more may be used as the partial sequence. These nucleotides can be labeled with a radioactive element, a fluorescent substance, a chemiluminescent substance, or the like, if necessary.
A nucleotide containing a partial sequence of 14 or more consecutive bases in the base sequence represented by SEQ ID NO: 1 or 3 of the present invention or a complementary sequence thereof is included in the base sequence encoding the organic anion transporter OAT3 of the present invention. Those having a specific base sequence are preferred, and may be labeled if necessary.

  In addition, the antibody can be obtained using the organic anion transporter of the present invention or a polypeptide having immunological equivalence to the same, and the antibody can be used for organic anion transporter detection or purification. The antibody can be produced using the organic anion transporter of the present invention, a fragment thereof, or a synthetic peptide having a partial sequence thereof as an antigen. A polyclonal antibody can be produced by an ordinary method of inoculating a host animal (eg, rat or rabbit) with an antigen and recovering immune serum, and a monoclonal antibody can be produced by a technique such as an ordinary hybridoma method. The antibody of the present invention may be a chimeric or human antibody by a conventional method.

  Hereinafter, the present invention will be described in more detail with reference to examples, but these examples do not limit the present invention.

  In the following examples, unless otherwise specified, each operation is performed according to the method described in “Molecular Cloning: Sambrook, J., Fritsh, EF and Maniatis, T. Published by Cold Spring Harbor Laboratory Press in 1989”. When a commercially available kit was used, it was used according to the instructions for the commercially available product.

Example 1
Isolation and analysis of multi-selective organic anion transporter 3 (OAT3) cDNA (1) Creation of degenerate primer based on nucleotide sequence information of OAT1, OAT2, and OCT1 From the isolated nucleotide sequence information of OAT1, OAT2 and the reported OCT1, degenerate from the amino acid sequence common to these three transporters (corresponding to 267-275 and 447-452 of the amino acid sequence of OAT1) A degenerate primer was created.

Total RNA was extracted from rat brain by the GITC method, and poly (A) + RNA was purified using an oligo dT column. From this rat brain poly (A) + RNA, cDNA was prepared using reverse transcriptase, and PCR was carried out using this as a template with the above degenerate primer. As a result, a PCR product of about 550 bp was obtained.
When this PCR product was cloned using a TA cloning kit (manufactured by Invitrogen) and several nucleotide sequences were determined, a new cDNA (B10) having 50% homology with OAT1 at the amino acid level was obtained. Obtained.

Northern hybridization with poly (A) + RNA extracted from various organs of rats using a probe labeled with B10 cDNA with ³² P, showed positive bands in the liver, kidney, brain and eyes. Was detected.

  Since the present inventors already had a good cDNA library of rat kidney, this rat kidney cDNA library was screened using the B10 probe. Hybridization was performed overnight in a hybridization solution at 37 ° C., and then the filter membrane was washed with 0.1 × SSC / 0.1% SDS at 37 ° C. As hybridization solutions, 50% formamide, 5 × standard NaCl citrate solution (standard saline citrate (SSC)), 3 × Denhardt's solution, 0.2% SDS, 10% dextran sulfate, 0.2 mg / ml denatured salmon sperm A pH 6.5 buffer solution containing DNA, 2.5 mM sodium pyrophosphate, 25 mM MES, 0.01% Antifoam B (manufactured by Sigma) was used. Clones isolated in λZipLox were further subcloned into plasmid vector-pZL by the in vivo excision method. As a result, a novel clone (rkl411) having organic anion transport activity was obtained (refer to Example 2 below for transport function analysis).

  The base sequence of the clone (rkl411) obtained as described above was determined as follows. First, a plurality of plasmid DNAs in which rkl411 was deleted from each side by about 300 bp were obtained using a kilosequence deletion kit (manufactured by Takara). The base sequences of these were analyzed using an automatic sequencer (Applied Biosystems). Furthermore, a specific oligonucleotide primer for rkl411 was synthesized, the base sequence was analyzed from the reverse direction using an automatic sequencer, and finally the entire base sequence of rkl411 was determined. This base sequence is described in SEQ ID NO: 3 in the sequence listing. The amino acid sequence of this protein is shown in SEQ ID NO: 4 in the sequence listing.

Example 2 (specification of the function of rkl411)
(1) cRNA (RNA complementary to cDNA) was prepared in vitro from the plasmid containing the clone (rkl411) obtained above using T7 RNA polymerase (Sekine, T., et al. J Biol Chem 272). Volume, 18526-9, 1997).
The obtained cRNA was injected into Xenopus oocytes according to a method already reported (Sekine, T., et al. J Biol Chem 272, 18526-9, 1997). Cell uptake experiments with various organic anions and organic cations labeled with radioactivity were performed. As a result, as shown in FIG. 1, it was found that the oocyte in which rkl411 was expressed showed uptake of ¹⁴ C-PAH (paraaminohippuric acid), ³ H-ochratoxin A, and ³ H-estrone sulfate. In contrast, ¹⁴ C-TEA (tetraethylammonium), which is a typical organic cation, was not transported.

  A Michaelis-Menten kinetic study of the organic anion transport of rkl411 was performed. By examining changes in the amount of PAH, estrone sulfate, and ochratoxin A taken up by rkl411 at various concentrations, the concentration dependence of transport of these substrates by rkl411 was examined. Radiolabeled PAH, estrone sulfate, and ochratoxin A uptake experiments were performed according to the method described above using oocytes injected with rkl411 cRNA. As a result (see FIG. 2), the Km values of PAH, estrone sulfate, and ochratoxin A were 4.7 μM, 2.3 μM, and 0.74 μM, respectively. The results are shown in Table 1 below.

(2) rkl411 substrate selectivity In order to further study of the uptake experiment system of ³ H- estrone sulfate by the oocytes injected with Rkl411 cRNA, by adding various anionic substances to the system, were examined their effects (Inhibition experiment). ^{The 3} H-estrone sulfate uptake experiment was performed using oocytes injected with rkl411 cRNA according to the method described above. Incorporation of ³ H-estrone sulfate was measured in the presence and absence of 1 mM of various compounds (unlabeled). As a result, various anionic substances (taurocholic acid, cholic acid, bromo monkey follower phthalein, probenecid, indocyanine green, bumetanide, cefoperazone, piroxicam, furosemide, azidothymidine, etc. benzylpenicillin) is of ³ H- estrone sulfate by rkl411 Transport was significantly inhibited (see Figure 3). On the other hand, cationic substances such as tetraethylammonium, guanidine, quinidine, and verapamil did not show an inhibitory action (see FIG. 3). From the above results, rkl411 is a multi-selective transporter, and mainly recognizes organic anions. Therefore, rkl411 was named OAT3 (organic anion transporter 3) with the third member of the OAT family.

Example 3
The expression (Northern blotting) of the OAT3 gene in each rat tissue was analyzed. The entire length of OAT3 cDNA was labeled with ³² P-dCTP, and using this as a probe, Northern blotting was performed on RNA extracted from various rat tissues as follows. 3 μg of poly (A) + RNA was electrophoresed on a 1% agarose / formaldehyde gel and then transferred to a nitrocellulose filter. This filter was hybridized overnight at 42 ° C. with a hybridization solution containing the full length of OAT3 cDNA labeled with ³² P-dCTP. The filter was washed at 65 ° C. with 0.1 × SSC containing 0.1% SDS.
As a result of the Northern blot (see FIG. 4), a strong band was detected in the vicinity of 2.4 Kb in the kidney, liver, and brain. Weaker expression was observed in the eyes.

Example 4
Since OAT3 was the strongest expressed in the brain among the members of the OAT family, as an attempt to guess its role in the brain, experiments on the inhibition of OAT3 transport by various metabolites (mainly organic anions) of neurotransmitters were conducted. went. As shown in FIG. 5, noradrenaline and serotonin metabolites inhibited the transport of estrone sulfate by OAT3, indicating that they themselves could be substrates for OAT3. This fact suggests that the neurotransmitter metabolites are excreted from the brain as one of the roles of OAT3 in the brain type.

Example 5
Isolation and analysis of human-type multi-selective organic anion transporter 3 (OAT3) cDNA When the EST (expressed sequence tag) database was searched using rat OAT3 cDNA already isolated by the present inventors, rat OAT3 And a human EST clone (H20345) with high homology. A part (333 bp) of the base sequence of this clone was synthesized using the PCR method. Using this cDNA fragment labeled with ³² P as a probe, screening was performed as follows.

  A human kidney cDNA library already held by the present inventors was screened using the probe. Hybridization was performed overnight in a hybridization solution at 37 ° C., and then the filter membrane was washed with 0.1 × SSC / 0.1% SDS at 37 ° C. As a hybridization solution, 50% formamide, 5 × SSC (standard saline citrate), 3 × denhard solution, 0.2% SDS, 10% dextran sulfate, 0.2 mg / ml denatured salmon sperm DNA, 2.5 mM pyrophosphate A pH 6.5 buffer solution containing sodium, 25 mM MES, 0.01% Antifoam (manufactured by Sigma) was used. Clones that had been confused in λZipLox were further subcloned into plasmid vector-pZL by the in vitro excision method. As a result, hOAT3 (human organic anion transporter 3) having organic anion transport activity was obtained. The analysis of the transport function of this will be described in Example 6 below.

The base sequence of hOAT3 was determined by the following method. Sequentially synthesize oligonucleotide primers specific to hOAT3, analyze the nucleotide sequence from both 5 'and 3' sides using an automatic sequencer (Applied Biosystems), and finally determine the entire nucleotide sequence of hOAT3. Were determined. The determined base sequence is shown in SEQ ID NO: 1 in the sequence listing. The amino acid sequence encoding hOAT3 from this cDNA sequence is shown in SEQ ID NO: 2 in the sequence listing.
The base sequences of cDNA are shown in Tables 2 to 6, and the amino acid sequences are shown in Table 3 in correspondence with the base sequences.

Example 6
Identification of the function of hOAT3 From the plasmid containing hOAT3 obtained above, cRNA (RNA complementary to cDNA) was obtained in vitro using the T7 RNA polymerase (Sekine, T., et al., J. Biol. Chem., 272, 18526-9 (1997)).
The obtained hOAT3 cRNA was used in accordance with the method of Sekine et al. (Sekine, T., et al., J. Biol. Chem., 272, 18526-9 (1997)). The oocytes were subjected to uptake experiments for various organic anions and organic cations labeled with radioactivity. Control oocytes (oocytes not injected with hOAT3 cRNA) and oocytes injected with hOAT3 cRNA were cultured in a buffer containing the following radioactive label for 1 hour, and then into the oocytes. The uptake of radiolabeled product was measured.
The results are shown in FIGS. In each figure, the white (open column) indicates the case where the control oocyte is used, and the black (closed column) indicates the case where the oocyte injected with hOAT3 cRNA is used. 6 ¹⁴ C-PAH (para-amino hippuric acid) (10 [mu] M), 7 ³ H- estrone sulfate (50 nM), 8 ³ H- dehydroepiandrosterone sulfate (50 nM), FIG. 9 is ³ H- okra Toxin A (100 nM), FIG. 10 shows ³ H-cimetidine (150 nM), FIG. 11 shows ³ H-estradiol glucuronide (50 nM), FIG. 12 shows ³ H-prostaglandin E2 (1 nM), and FIG. 13 shows ¹⁴ C-taurochol. Acid (1 μM), FIG. 14 is ¹⁴ C-glutaric acid (10 μM), FIG. 15 is ³ H-methotrexate (100 nM), FIG. 16 is ¹⁴ C-salicylic acid (1 μM), FIG. 17 is ¹⁴ C-indomethacin (10 μM), FIG. 18 shows the case of ¹⁴ C-cholic acid (10 μM).

As shown in these figures, these radiolabels showed higher values in oocytes expressing hOAT3 than in control oocytes, indicating that hOAT3 transported these compounds.
As a result, the oocytes expressing hOAT3 were ¹⁴ C-PAH (paraaminohippuric acid), ³ H-estrone sulfate, ³ H-dehydroepiandrosterone sulfate, ³ H-ochratoxin A, ³ H-cimetidine, ³ H-estradiol glucuronide, ³ H-prostaglandin E2, ¹⁴ C-taurocholic acid, ¹⁴ C-glutaric acid, ³ H-methotrexate, ¹⁴ C-salicylic acid, ¹⁴ C-indomethacin, ¹⁴ C-cholate It has been found. In contrast, hOAT3 did not transport a typical organic cation, ¹⁴ C-TEA (tetraethylammonium) (not shown in the figure).

  The Michaelis-Menten kinetics test for organic anion transport of hOAT3 was then performed. By examining changes in the amount of estrone sulfate and methotrexate taken up by hOAT3 at various concentrations, the concentration dependency of the transport of these substrates by hOAT3 was examined. Radiolabeled estrone sulfate and methotrexate uptake experiments were performed according to the method described above using oocytes injected with hOAT3 cRNA and control oocytes (not injected with cRNA). As a result, the Km values of estrone sulfate and methotrexate were 3.08 μM and 2.22 μM, respectively.

To further investigate the substrate selectivity of hOAT3, in the uptake experiment system of ³ H- estrone sulfate by the oocytes injected with hOAT3 cRNA, by adding various anionic substances to the system, it was examined their effects (inhibition experiment ).
^{The 3} H-estrone sulfate uptake experiment was performed using oocytes injected with hOAT3 cRNA according to the method described above.
That is, control oocytes (oocytes not injected with hOAT3 cRNA) and oocytes injected with hOAT3 cRNA were irradiated with 50 nM ³ H-estrone sulfate alone, or 500 μM or the concentration indicated in the figure. The cells were cultured for 1 hour in a buffer containing an unlabeled compound, and the uptake of ³ H-engineered sulfate was measured. The results show that the uptake of oocytes injected with hOAT3 cRNA in a buffer containing 50 nM ³ H-estostane sulfate alone is 100%, and each value in the buffer containing the inhibitor is expressed in%. displayed.

The result is shown in FIG. As shown in FIG. 19, all of these compounds inhibited ³ H-estrone sulfate uptake by oocytes injected with hOAT3 cRNA, indicating that these compounds interact with hOAT3. As a result, various anionic substances (estrone sulfate, PAH, taurocholic acid, probenecid, furosemide zidovudine, penicillin G, BSP, glutaric acid, indomethacin, methotrexate) significantly inhibited the transport of ³ H-estrone sulfate by hOAT3. (See FIG. 19). On the other hand, tetraethylammonium, which is a typical organic cation, showed no inhibitory action. From the above results, it was revealed that hOAT3 of the present invention is a multiselective organic anion transboter.

The present invention provides a novel organic anion transporter that has a wide substrate selectivity for organic anions and is selectively distributed in the brain, liver, and the like.
The organic anion transporter of the present invention is involved in the uptake of various drugs into cells, and is also involved in the dynamics of drugs in vivo. Therefore, the organic anion transporter of the present invention is useful not only for cell maintenance and activation but also for screening drug kinetics.

FIG. 1 shows organic anion uptake activity when the rat OAT3 of the present invention is expressed in Xenopus oocytes. FIG. 2 shows the results of a kinetic study of the transport of PAH, estrone sulfate and ochratoxin A using rat OAT3 oocytes of the present invention. FIG. 3 shows the test results of the inhibitory action of various organic substances in the organic anion transport of rat OAT3 of the present invention. FIG. 4 is a photograph replacing a drawing, showing the results of Northern blotting analysis of the rat OAT3 gene of the present invention. FIG. 5 shows the results of a transport inhibition test of rat OAT3 with various metabolites of brain-type neurotransmitters. FIG. 6 shows the uptake activity of ¹⁴ C-PAH (paraaminohippuric acid) when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 7 shows ³ H-estrone sulfate uptake activity when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 8 shows the uptake activity of ³ H-dehydroepiandrosterone sulfate when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 9 shows the uptake activity of ³ H-ochratoxin A when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 10 shows ³ H-cimetidine uptake activity when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 11 shows the uptake activity of ³ H-estradiol glucuronide when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 12 shows the uptake activity of ³ H-prostaglandin E2 when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 13 shows ¹⁴ C-taurocholic acid uptake activity when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 14 shows ¹⁴ C-glutaric acid uptake activity when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 15 shows the uptake activity of ³ H-methotrexate when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 16 shows the ¹⁴ C-salicylic acid uptake activity when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 17 shows the uptake activity of ¹⁴ C-indomethacin when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 18 shows ¹⁴ C-cholate uptake activity when hOAT3 of the present invention is expressed in Xenopus oocytes. FIG. 19 shows the test results of the inhibitory action of various organic substances in the transport of ³ H-estrone sulfate by hOAT3 of the present invention.

Claims (8)

A recombinant cell expressing an organic anion transporter OAT3 consisting of the amino acid sequence shown in SEQ ID NO: 4 in the sequence listing and the compound are cultured in a solution, and the ability of the compound to be incorporated into the recombinant cell is measured. Method. At least the following steps (1) to (3);
(1) A step of obtaining a recombinant cell that expresses the organic anion transporter OAT3 consisting of the amino acid sequence represented by SEQ ID NO: 4 in the sequence listing;
(2) adding the compound to the solution containing the recombinant cells obtained in step (1), measuring the amount of the compound taken up into the cells after culturing for a certain period of time, and (3) in step (2) 2. The method according to claim 1, further comprising a step of selecting a compound in which the obtained measured value shows a significant difference compared to the measured value when the same operation is performed using control cells. Method. At least the following steps (1) to (4);
(1) A step of obtaining a recombinant cell that expresses the organic anion transporter OAT3 consisting of the amino acid sequence represented by SEQ ID NO: 4 in the sequence listing;
(2) Select at least two compounds that have been confirmed to be incorporated into the recombinant cells by the organic anion transporter OAT3 and add them individually to the solution containing the recombinant cells obtained in step (1). And measuring the amount of each compound taken up into the recombinant cells after culturing for a certain period of time,
(3) Two or more compounds selected in step (2) are combined and added to the solution containing the recombinant cells obtained in step (1). After culturing for the same time under the same conditions as in step (2), A step of measuring the amount of each compound taken up into the recombinant cell, and (4) comparing the measurement value obtained in step (3) with the measurement value obtained in step (2). Observing the interaction between two or more compounds,
The measurement method according to claim 1, comprising: A method for measuring the ability of a compound to take up in brain cells, comprising culturing a compound and a recombinant cell that expresses the organic anion transporter OAT3 comprising the amino acid sequence shown in SEQ ID NO: 4 in the sequence listing in a solution . At least the following steps (1) to (3);
(1) A step of obtaining a recombinant cell that expresses the organic anion transporter OAT3 consisting of the amino acid sequence represented by SEQ ID NO: 4 in the sequence listing;
(2) adding the compound to the solution containing the recombinant cells obtained in step (1), measuring the amount of the compound taken up into the cells after culturing for a certain period of time, and (3) in step (2) A step of selecting a compound in which the obtained measurement value showed a significant difference compared to the measurement value when the same operation was performed using control cells,
The method of claim 4, comprising: The ability of the compound to be taken into the brain cell is an ability to take in based on the interaction between two or more compounds known to be taken into the brain cell, and at least the following steps (1) to (4) The measurement method according to claim 4, comprising:
(1) A step of obtaining a recombinant cell that expresses the organic anion transporter OAT3 consisting of the amino acid sequence represented by SEQ ID NO: 4 in the sequence listing;
(2) Select at least two compounds known to be taken up into brain cells, add each of them alone to the solution containing the recombinant cells obtained in step (1), and after culturing for a certain period of time, Measuring the amount of each compound taken up into the recombinant cell,
(3) Two or more compounds selected in step (2) are combined and added to the solution containing the recombinant cells obtained in step (1). After culturing for the same time under the same conditions as in step (2), A step of measuring the amount of each compound taken up into the recombinant cell, and (4) comparing the measurement value obtained in step (3) with the measurement value obtained in step (2). A step of observing the interaction between compounds known to be taken into two or more brain cells. At least the following steps (1) to (4);
(1) A step of obtaining a recombinant cell that expresses the organic anion transporter OAT3 consisting of the amino acid sequence shown in SEQ ID NO: 4 in the sequence listing;
(2) A compound that has been confirmed to be incorporated into the recombinant cells by the organic anion transporter OAT3 is added to the solution containing the recombinant cells obtained in step (1), and after culturing for a certain period of time, Measuring the uptake of the identified compound into
(3) The test compound is added to the solution containing the recombinant cells obtained in step (1) together with the same confirmed compound used in step (2), and cultured for the same time under the same conditions as in step (2). Measuring the amount of the confirmed compound incorporated into the recombinant cell; and (4) the measured value obtained in step (3) is significant compared to the measured value obtained in step (2). Selecting a test compound when showing a significant difference,
A method for screening a compound that promotes or inhibits the organic anion uptake ability of the organic anion transporter OAT3. At least the following steps (1) to (4);
(1) A step of obtaining a recombinant cell that expresses the organic anion transporter OAT3 consisting of the amino acid sequence shown in SEQ ID NO: 4 in the sequence listing;
(2) A compound known to be taken up into brain cells is added to the solution containing the recombinant cells obtained in step (1), and after culturing for a certain period of time, the amount of the known compounds taken up into the recombinant cells Measuring process,
(3) A test compound is added to the solution containing the recombinant cells obtained in step (1) together with the same compound used in step (2), and cultured for the same time under the same conditions as in step (2). A step of measuring the uptake amount of the confirmed compound into the recombinant cell, and (4) the measured value obtained in step (3) is significant compared with the measured value obtained in step (2). A step of selecting a test compound when showing a difference.
A method for screening for a substance that promotes or inhibits the ability of a compound known to be taken up into brain cells to be taken up into brain cells.