Tatsuhiko Adachi

Bio: Tatsuhiko Adachi is an academic researcher from Tokyo Institute of Technology. The author has contributed to research in topics: ATP-binding cassette transporter & Multidrug resistance-associated protein 2. The author has an hindex of 5, co-authored 7 publications receiving 529 citations.

MRP class of human ATP binding cassette (ABC) transporters: historical background and new research directions

Abstract: 1. The adenosine triphosphate (ATP) binding cassette (ABC) transporters form one of the largest protein families encoded in the human genome, and more than 48 genes encoding human ABC transporters have been identified and sequenced. It has been reported that mutations of ABC protein genes are causative in several genetic disorders in humans. 2. Many human ABC transporters are involved in membrane transport of drugs, xenobiotics, endogenous substances or ions, thereby exhibiting a wide spectrum of biological functions. According to the new nomenclature of human ABC transporter genes, the 'ABCC' gene sub-family comprises three classes involving multidrug resistance-associated proteins (MRPs), sulfonylurea receptors (SURs), and a cystic fibrosis transmembrane conductance regulator (CFTR). 3. Molecular cloning studies have identified a total of ten members of the human MRP class including ABCC11, ABCC12, and ABCC13 (pseudo-gene) that have recently been characterized. 4. This review addresses the historical background and discovery of the ATP-driven xenobiotic export pumps (GS-X pumps) encoded by MRP genes, biological functions of ABC transporters belonging to the MRP class, and regulation of gene expression of MRPs by oxidative stress.

Nrf2-dependent and -independent induction of ABC transporters ABCC1, ABCC2, and ABCG2 in HepG2 cells under oxidative stress.

Abstract: Nrf2, an NF-E2-related transcription factor, plays a critical role in transcriptional upregulation of many target genes, including those for metabolizing enzymes and transporters essential for cellular defense in response to oxidative and/or electrophilic stress. In the present study, we have studied the potential involvement of Nrf2 in induction of human ABC transporter genes under oxidative stress. We created a real-time PCR primer set to quantitatively investigate the induction of human ABC transporters by a redox-active compound tert-butylhydroquinone (tBHQ) in HepG2 cells. We found that mRNA levels of ABCC1, ABCC2, ABCC3, and ABCG2 were significantly elevated in dose- and time-dependent manners. Translocation of Nrf2 into the nuclei occurred concomitantly with the induction of ABCC1 and ABCC2 as well as both heavy and light chains of gamma-glutamylcysteine synthetase (gamma-GCSh and gamma-GCSI) during tBHQ treatments. To examine the potential involvement of Nrf2 in upregulation of the ABC transporters, we treated cells with siRNA to knockdown the expression of Nrf2. Under such Nrf2-knockdown conditions, tBHQ-induced mRNA levels of ABCC2 and ABCG2 were significantly suppressed as were mRNA levels of gamma-GCSh and gamma-GCSI. Interestingly, however, the elevated mRNA level of ABCC1 was little affected by Nrf2 siRNA treatment. We also addressed the involvement of Keap1, which is a negative regulator of Nrf2 by retrieving it in the cytoplasm. When HepG2 cells were treated with Keap1-specifc siRNA, a significant increase was observed in mRNA levels of ABCC1, ABCC2, and ABCG2 as well as gamma-GCSI, suggesting that induction of ABCC2 and ABCG2 by tBHQ is mediated by the Nrf2/Keap1 system, whereas the induction of ABCC1 may involve a Keap1-dependent but Nrf2-independent mechanism.

Nrf2-dependent induction of human ABC transporter ABCG2 and heme oxygenase-1 in HepG2 cells by photoactivation of porphyrins: biochemical implications for cancer cell response to photodynamic therapy.

Abstract: Photodynamic therapy is a recently developed anticancer treatment that utilizes the generation of singlet oxygen and other reactive oxygen species in cancer tissue. Nrf2, an NF-E2-related transcription factor, plays a pivotal role in transcriptional upregulation of many target genes, including those for metabolizing enzymes and transporters essential for cellular defense in response to oxidative stress. In the present study, we examined the potential involvement of Nrf2 in the induction of human ABC transporter ABCG2 and heme oxygenase-1 (HO-1). When HepG2 cells were incubated with non-toxic concentrations of delta-aminolevulinic acid, protoporphyrin IX, or pheophorbide a and then exposed to visible light for 90 min, the mRNA level of HO-1 began increasing markedly, reaching the maximal level in 4 h. Following the transient induction of HO-1, the mRNA level of ABCG2 gradually increased in a time-dependent manner, whereas the ABCB6 mRNA level was little affected. Nrf2-specific siRNA treatments suppressed the induction of both ABCG2 and HO-1 after the photoactivation of porphyrins, suggesting that Nrf2 is a common regulator for transcriptional activation of the ABCG2 and HO-1 genes. On the other hand, the mRNA level of HO-1 was remarkably enhanced by Zn(2+)-protoporphyrin IX or hemin even in the absence of light. This induction may be attributed to inactivation of Bach1, a repressor for the HO-1 gene, by those compounds. Since patients have demonstrated individual defferences in their response to photodynamic therapy, transcriptional activation of the ABCG2 and HO-1 genes in cancer cells may affect patients' responses to photodynamic therapy.

Identification of cysteine residues critically involved in homodimer formation and protein expression of human ATP-binding cassette transporter ABCG2: A new approach using the Flp recombinase system

Abstract: Since ABCG2 is a half-transporter in the ATP-binding cassette (ABC) transporter family, it has been suspected that ABCG2 functions as a homodimer In the present study, we have investigated the molecular mechanism underlying homodimer formation of ABCG2 Based on the amino acid sequence of ABCG2, three cysteine residues (Cys592, Cys603, and Cys608) are expected to exist in the extracellular loop To identify a cysteine residue(s) required for homodimer formation, we have substituted those cysteine residues to glycine by site-directed mutagenesis and stably expressed the resulting variants in Flp-In-293 cells Substitution of the amino acid at position 603 from cysteine to glycine (C603G) completely diminished homodimer formation, whereas substitution of both Cys592 and Cys608 to glycine residues (C592G/C608G) had no effect on homodimer formation These results strongly suggest that Cys603 is prerequisite for homodimer formation of ABCG2 via a disulfide bond On the other hand, immunohistochemistry experiments revealed that the C592G/C608G variant is mainly located in intracellular compartments The C592G/C608G variant exhibited lower activity of ATP-dependent methotrexate (MTX) transport, and its expression did not confer Flp-In-293 cells resistance to SN-38 or mitoxantrone Cys592 and Cys608 appear to be important for intracellular sorting of the de novo synthesized ABCG2 protein to the plasma membrane Taken together, cysteine residues in the extra-cellular loop are considered to play pivotal roles in homodimer formation and plasma membrane localization of ABCG2

Xenobiotic, Bile Acid, and Cholesterol Transporters: Function and Regulation

Abstract: Transporters influence the disposition of chemicals within the body by participating in absorption, distribution, and elimination. Transporters of the solute carrier family (SLC) comprise a variety of proteins, including organic cation transporters (OCT) 1 to 3, organic cation/carnitine transporters (OCTN) 1 to 3, organic anion transporters (OAT) 1 to 7, various organic anion transporting polypeptide isoforms, sodium taurocholate cotransporting polypeptide, apical sodium-dependent bile acid transporter, peptide transporters (PEPT) 1 and 2, concentrative nucleoside transporters (CNT) 1 to 3, equilibrative nucleoside transporter (ENT) 1 to 3, and multidrug and toxin extrusion transporters (MATE) 1 and 2, which mediate the uptake (except MATEs) of organic anions and cations as well as peptides and nucleosides. Efflux transporters of the ATP-binding cassette superfamily, such as ATP-binding cassette transporter A1 (ABCA1), multidrug resistance proteins (MDR) 1 and 2, bile salt export pump, multidrug resistance-associated proteins (MRP) 1 to 9, breast cancer resistance protein, and ATP-binding cassette subfamily G members 5 and 8, are responsible for the unidirectional export of endogenous and exogenous substances. Other efflux transporters [ATPase copper-transporting β polypeptide (ATP7B) and ATPase class I type 8B member 1 (ATP8B1) as well as organic solute transporters (OST) α and β] also play major roles in the transport of some endogenous chemicals across biological membranes. This review article provides a comprehensive overview of these transporters (both rodent and human) with regard to tissue distribution, subcellular localization, and substrate preferences. Because uptake and efflux transporters are expressed in multiple cell types, the roles of transporters in a variety of tissues, including the liver, kidneys, intestine, brain, heart, placenta, mammary glands, immune cells, and testes are discussed. Attention is also placed upon a variety of regulatory factors that influence transporter expression and function, including transcriptional activation and post-translational modifications as well as subcellular trafficking. Sex differences, ontogeny, and pharmacological and toxicological regulation of transporters are also addressed. Transporters are important transmembrane proteins that mediate the cellular entry and exit of a wide range of substrates throughout the body and thereby play important roles in human physiology, pharmacology, pathology, and toxicology.

Current states and future views in photodynamic therapy

Abstract: One of the long-standing goals of both researchers and oncologists is to establish a framework for the complete cure of cancer with less toxic adverse effect and improved quality of life (QOL) for patients. PDT (photodynamic therapy) has much attracted as less invasive method for treating cancer. The therapeutic properties of light have been known for thousands of years, but it was only in the last century that PDT was developed. The field on PDT is now so large. Here, we will focus on a few basic aspects such as porphyrinoid photosensitizers, non-porphyrinoid photosensitizers, 5-aminolevulinic acid and its derivatives, fullerenes as efficient photosensitizers, and, PDT and photodynamic diagnosis (PDD) for digestive cancer from the point of view of a clinical doctor, and, finally, future trends.

The Role of Transporters in the Pharmacokinetics of Orally Administered Drugs

Abstract: Drug transporters are recognized as key players in the processes of drug absorption, distribution, metabolism, and elimination. The localization of uptake and efflux transporters in organs responsible for drug biotransformation and excretion gives transporter proteins a unique gatekeeper function in controlling drug access to metabolizing enzymes and excretory pathways. This review seeks to discuss the influence intestinal and hepatic drug transporters have on pharmacokinetic parameters, including bioavailability, exposure, clearance, volume of distribution, and half-life, for orally dosed drugs. This review also describes in detail the Biopharmaceutics Drug Disposition Classification System (BDDCS) and explains how many of the effects drug transporters exert on oral drug pharmacokinetic parameters can be predicted by this classification scheme.

Non-alcoholic fatty liver disease (NAFLD) - pathogenesis, classification, and effect on drug metabolizing enzymes and transporters.

Abstract: Non-alcoholic fatty liver disease (NAFLD) is a spectrum of liver disorders. It is defined by the presence of steatosis in more than 5% of hepatocytes with little or no alcohol consumption. Insulin ...