Reiko Onuki

An RNA-dependent protein kinase is involved in tunicamycin-induced apoptosis and Alzheimer's disease

Various types of stress, such as disruption of calcium homeostasis, inhibition of protein glycosylation and reduction of disulfide bonds, result in accumulation of misfolded proteins in the endoplasmic reticulum (ER). The initial cellular response involves removal of such proteins by the ER, but excessive and/or long‐term stress results in apoptosis. In this study, we used a randomized ribozyme library and ER stress‐mediated apoptosis (tunicamycin‐induced apoptosis) in SK‐N‐SH human neuroblastoma cells as a selective phenotype to identify factors involved in this process. We identified a double‐stranded RNA‐dependent protein kinase (PKR) as one of the participants in this process. The level of nuclear PKR was elevated, but the level of cytoplasmic PKR barely changed in tunicamycin‐treated SK‐N‐SH cells. Furthermore, tunicamycin also raised levels of phosphorylated PKR in the nucleus. We also detected the accumulation of phosphorylated PKR in the nuclei of autopsied brain tissues in Alzheimers disease. Thus, PKR might play a role in ER stress‐induced apoptosis and in Alzheimers disease.

Inhibition of Bile Acid Transport across Na/Taurocholate Cotransporting Polypeptide (SLC10A1) and Bile Salt Export Pump (ABCB 11)-Coexpressing LLC-PK1 Cells by Cholestasis-Inducing Drugs

Vectorial transport of bile acids across hepatocytes is a major driving force for bile flow, and bile acid retention in the liver causes hepatotoxicity. The basolateral and apical transporters for bile acids are thought to be targets of drugs that induce cholestasis. Previously, we constructed polarized LLC-PK1 cells that express both a major bile acid uptake transporter human Na+/taurocholate cotransporting polypeptide (SLC10A1) (NTCP) and the bile acid efflux transporter human bile salt export pump (ABCB 11) (BSEP) and showed that monolayers of such cells can be used to characterize vectorial transcellular transport of bile acids. In the present study, we investigated whether cholestasis-inducing drugs could inhibit bile acid transport in such cells. Because fluorescent substrates allow the development of a high-throughput screening method, we examined the transport by NTCP and BSEP of fluorescent bile acids as well as taurocholate. The aminofluorescein-tagged bile acids, chenodeoxycholylglycylamidofluorescein and cholylglycylamidofluorescein, were substrates of both NTCP and BSEP, and their basal-to-apical transport rates across coexpressing cell monolayers were 4.3 to 4.5 times those of the vector control, although smaller than for taurocholate. The well known cholestatic drugs, rifampicin, rifamycin SV, glibenclamide, and cyclosporin A, reduced the basal-to-apical transport and the apical efflux clearance of taurocholate across NTCP- and BSEP-coexpressing cell monolayers. Further analysis indicated that the drugs inhibited both NTCP and BSEP. Our study suggests that such coexpressing cells can provide a useful system for the identification of inhibitors of these two transport systems, including potential drug candidates.

Double-strand RNA dependent protein kinase (PKR) is involved in the extrastriatal degeneration in Parkinson's disease and Huntington's disease.

Double-strand RNA dependent protein kinase (PKR) plays an important role in control of cell death. We previously reported that activation of PKR is associated with hippocampal neuronal loss in Alzheimers disease (AD). Recent studies have reported that Parkinsons (PD) and Huntingtons (HD) disease brains displayed progressive hippocampal neuronal loss in extrastriatal degeneration. However, association between PKR and hippocampal neuronal loss in PD and HD brains is not known. In this report, brain tissues from patients with PD and HD displayed strong induction of phosphorylated-PKR (p-PKR) in hippocampal neurons. Immunoblotting analysis also demonstrated that levels of nuclear p-PKR in the hippocampus affected by these diseases were increased compared with age-matched disease controls. These results suggest that a close association exists between PKR and extrastriatal degeneration in PD and HD pathology.

Confirmation by FRET in individual living cells of the absence of significant amyloid β-mediated caspase 8 activation

When cells are exposed to death-inducing molecules such as tumor necrosis factor-α or Fas, caspase 8 is activated and cleaves an apoptotic facilitator, Bid, that is a member of the Bcl-2 family. After additional modification, the C-terminal moiety of Bid is translocated to the mitochondria and induces the release of cytochrome c into the cytoplasm. In an attempt to directly observe the cleavage of Bid and the following events in living cells, we constructed a vector that encoded Bid fused with yellow fluorescent protein (YFP) and cyan fluorescent protein (CFP) (YFP-Bid-CFP). On expression of YFP-Bid-CFP in mammalian cells, we were able to observe the efficient transfer of energy from excited CFP to YFP within the YFP-Bid-CFP molecule and, importantly, the fusion protein YFP-Bid-CFP was fully functional in cells. When YFP-Bid-CFP was cleaved by caspase 8, on activation by anti-Fas Abs but not by Aβ or tunicamycin, no such transfer of energy was detected. To our knowledge, this is the first report of (i) visualization of the activation of Bid by proteolytic cleavage, with direct observation of the cleavage of YFP-Bid-CFP in the cytoplasm and subsequent translocation of the cleaved Bid to mitochondria and (ii) the absence of Aβ- or tunicamycin-mediated significant activation of caspase 8 in individual living cells.

Construction of a Functional Transporter Analysis System Using MDR1 Knockdown Caco-2 Cells

PurposeThe efflux transporter, P-glycoprotein (P-gp), located in the brush-border membrane of intestinal absorptive cells, reduces the bioavailability of a wide range of orally administered drugs. Using P-gp inhibitors in transport experiments in Caco-2 cell monolayers is widely accepted as an efficient way to estimate the contribution of P-gp to the intestinal absorption of drugs. However, there still remain some arguments that the inhibitors might affect the function of other proteins. Multidrug resistance 1 gene (MDR1) specifically inhibited Caco-2 cells were constructed, therefore, as a better in vitro evaluation system of intestinal drug absorption.MethodsThe effective sites of RNAi were selected using siRNA libraries and single siRNAs and MDR1 stable knockdown Caco-2 cells were constructed using a tRNAval-shRNA expression vector.ResultsIn siRNA stably expressed Caco-2 cells, the expression level of MDR1 was reduced at mRNA and protein levels. Transcellular transport studies using digoxin revealed that the P-gp function was suppressed completely, similar to that in verapamil-treated cells.ConclusionsMDR1 stable knockdown Caco-2 cells were successfully constructed by RNAi technology. This will consequently allow the development of a selection system for candidate drugs with improved absorption properties.

Construction of triple-transfected cells [organic anion-transporting polypeptide (OATP) 1B1/multidrug resistance-associated protein (MRP) 2/MRP3 and OATP1B1/MRP2/MRP4] for analysis of the sinusoidal function of MRP3 and MRP4.

Multidrug resistance-associated protein (MRP) 3/ABCC3 and MRP4/ABCC4 are ATP-binding cassette (ABC) transporters expressed in the sinusoidal membrane of hepatocytes. The purpose of the present study was to establish organic anion-transporting polypeptide (OATP) 1B1/MRP2/MRP3 and OATP1B1/MRP2/MRP4 triple transfectants as in vitro model of the hepatobiliary transport of anionic drugs. To find in vivo relevant Mrp3 probes, wild-type and Mrp3(−/−) mice were given gemfibrozil, 6-hydroxy-5,7-dimethyl-2-methylamino-4-(3-pyridymethyl)benzothiazole (E3040), troglitazone, bisphenol A, and 4-methylumbelliferone orally. Plasma concentrations of the glucuronide conjugates were significantly lower in Mrp3(−/−) mice than in wild-type mice. The systemic exposure of gemfibrozil, E3040, and troglitazone were similar in wild-type and Mrp3(−/−) mice. 4-Methylumbelliferone and bisphenol A were undetectable in the plasma. In MRP3-expressing membrane vesicles, ATP-dependent uptakes of the glucuronide conjugates of estradiol, gemfibrozil, E3040, and troglitazone were markedly greater than those in controls, whereas MRP4-expressing membrane vesicles exhibited significant ATP-dependent uptake of gemfibrozil glucuronide and estradiol glucuronide. MRP3 or MRP4 was expressed in the OATP1B1/MRP2 double transfectants using adenovirus. The expression levels of OATP1B1 and MRP2 proteins were maintained both in the OATP1B1/MRP2/MRP3 and OATP1B1/MRP2/MRP4 triple transfectants, whereas MRP3 and MRP4 were localized in the basal membrane. Significant reductions in the basal-to-apical flux of the glucuronide conjugates of estradiol, gemfibrozil, E3040, and troglitazone were observed in the OATP1B1/MRP2/MRP3 triple transfectants compared with those in the double transfectants, whereas significant reduction was observed only for gemfibrozil glucuronide and estradiol glucuronide in the OATP1B1/MRP2/MRP4 triple transfectants. These results suggest that MRP3- or MRP4-triple transfectants provide a simple and useful in vitro system for evaluating their importance in the hepatobiliary transport of drugs.

Lack of improvement of oral absorption of ME3277 by prodrug formation is ascribed to the intestinal efflux mediated by breast cancer resistant protein (BCRP/ABCG2).

No HeadingPurpose.ME3229, an ester-type prodrug of a hydrophilic glycoprotein IIb/IIIa antagonist (ME3277), failed to show improved oral absorption. Okudaira et al. (J. Pharmacol. Exp. Ther. 294. 580–587, 2000) provided a piece of evidence that this is ascribed to an efflux system, distinct from P-gp and MRP2, that extrudes ME3277 formed from ME3229 in the intestinal epithelial cells. The aim of the present study is to examine the involvement of breast cancer resistant protein (BCRP/ABCG2) as a cause of low oral absorption of ME3229.Methods.The transport activity of ME3277 in the presence and absence of ATP was determined using a rapid filtration method with the membrane vesicles prepared from LLC-PK1 cells expressing BCRP. The plasma concentrations of ME3229 and its metabolites were compared between Bcrp1−/− mice and wild-type mice after a single-pass perfusion of small intestine with ME3229.Results.The ATP-dependent uptake of ME3277 was greater in BCRP-expressing membrane vesicles than that in the control vesicles. Furthermore, it was found that after intestinal perfusion with ME3229 for 60 min, the plasma concentrations of ME3277 and PM-5, a metabolite of ME3229, increased 2-fold and 3-fold, respectively, in Bcrp1 knockout mice. It is possible that BCRP acts synergistically with intestinal carboxylesterases.Conclusion.These results suggest that Bcrp1 plays an important role in the intestinal efflux of ME3277 and, probably, PM-10 and PM-11, metabolites of ME3229, and limits its BA after oral administration of ME3229.

Analysis of a Mitochondrial Apoptotic Pathway Using Bid- Targeted Ribozymes in Human MCF7 Cells in the Absence of a Caspase-3-Dependent Pathway

In normal cells, tumor necrosis factor-alpha (TNF-alpha) activates caspase 8 in both mitochondrion-dependent and mitochondrion-independent apoptotic pathways. It is believed that these two pathways converge, with resultant activation of effector caspases, such as caspase 6 and caspase 7. However, the precise mechanism of the activation of caspases 6 and 7 remains unknown. In this study, in order to focus on the mitochondrion-dependent pathway, we employed MCF7 human breast carcinoma cells, which do not have a functional mitochondrion-independent (caspase 3-dependent) pathway. We specifically targeted the transcript of Bid, a proapoptotic facilitator that is a substrate of caspase 8 in the mitochondrial pathway. In the TNF-alpha-treated MCF7 cells that expressed Bid-targeted ribozymes, the release of cytochrome c and the activation of caspase 9, but not of caspase 8, was delayed. Furthermore, the proteolysis of procaspase 7 was also delayed in Bid ribozyme-expressing cells. Because MCF7 cells are caspase 3 deficient, the direct cross-talk between caspase 8 and caspase 3 does not take place. Therefore, it became clear for the first time that caspase 9 by itself can activate caspase 7 in the absence of the caspase 3-dependent pathway in TNF-alpha-induced apoptosis by the use of specific ribozymes.

Erratum: Retraction Note to: Retraction: Identification of genes that function in the TNF-α-mediated apoptotic pathway using randomized hybrid ribozyme libraries

Nat. Biotechnol. 20, 376–380 (2002) Although the gene discovery technology described in this paper has been demonstrated to have practical utility by several independent researchers, the first author of the paper failed to maintain a proper data notebook to support the results presented. As this constitutes nonadherence to the ethical standards in scientific research, and in accordance with the recommendations from the National Institute of Advanced Industrial Science & Technology (AIST), R.