Properties of Wilms' tumor line (TuWi) and pig kidney line (LLC-PK1) typical of normal kidney tubular epithelium

Renal ciliopathies: promising drug targets and prospects for clinical trials

INTRODUCTION

Renal ciliopathies represent a collection of genetic disorders characterized by deficiencies in the biogenesis, maintenance, or functioning of the ciliary complex. These disorders, which encompass autosomal dominant polycystic kidney disease (ADPKD), autosomal recessive polycystic kidney disease (ARPKD), and nephronophthisis (NPHP), typically result in cystic kidney disease, renal fibrosis, and a gradual deterioration of kidney function, culminating in kidney failure.

AREAS COVERED

Here we review the advances in basic science and clinical research into renal ciliopathies which have yielded promising small compounds and drug targets, within both preclinical studies and clinical trials.

EXPERT OPINION

Tolvaptan is currently the sole approved treatment option available for ADPKD patients, while no approved treatment alternatives exist for ARPKD or NPHP patients. Clinical trials are presently underway to evaluate additional medications in ADPKD and ARPKD patients. Based on preclinical models, other potential therapeutic targets for ADPKD, ARPKD, and NPHP look promising. These include molecules targeting fluid transport, cellular metabolism, ciliary signaling and cell-cycle regulation. There is a real and urgent clinical need for translational research to bring novel treatments to clinical use for all forms of renal ciliopathies to reduce kidney disease progression and prevent kidney failure.

Transcriptomes of Major Proximal Tubule Cell Culture Models

BACKGROUND

Cultured cell lines are widely used for research in the physiology, pathophysiology, toxicology, and pharmacology of the renal proximal tubule. The lines that are most appropriate for a given use depend upon the genes expressed. New tools for transcriptomic profiling using RNA sequencing (RNA-Seq) make it possible to catalog expressed genes in each cell line.

METHODS

Fourteen different proximal tubule cell lines, representing six species, were grown on permeable supports under conditions specific for the respective lines. RNA-Seq followed standard procedures.

RESULTS

Transcripts expressed in cell lines variably matched transcripts selectively expressed in native proximal tubule. Opossum kidney (OK) cells displayed the highest percentage match (45% of proximal marker genes [TPM threshold =15]), with pig kidney cells (LLC-PK1) close behind (39%). Lower-percentage matches were seen for various human lines, including HK-2 (26%), and lines from rodent kidneys, such as NRK-52E (23%). Nominally, identical OK cells from different sources differed substantially in expression of proximal tubule markers. Mapping cell line transcriptomes to gene sets for various proximal tubule functions (sodium and water transport, protein transport, metabolic functions, endocrine functions) showed that different lines may be optimal for experimentally modeling each function. An online resource (https://esbl.nhlbi.nih.gov/JBrowse/KCT/) has been created to interrogate cell line transcriptome data. Proteomic analysis of NRK-52E cells confirmed low expression of many proximal tubule marker proteins.

CONCLUSIONS

No cell line fully matched the transcriptome of native proximal tubule cells. However, some of the lines tested are suitable for the study of particular metabolic and transport processes seen in the proximal tubule.

Comparative Cytotoxicity Rankings of Four Aminoglycoside Antibiotics in the Chang, SIRC and LLC-PK1 Cell Lines

A series of structurally related aminoglycosides — neomycin, gentamicin, amikacin, and streptomycin — were screened for cytotoxicity in three cell lines, Chang (liver), SIRC (corneal epithelial), and LLC-PK1 (kidney). The main objectives of this study were: firstly, to determine whether the proximal tubule origin of the LLC-PK1 cell line conferred increased sensitivity to this class of xenobiotic when compared to cell lines derived from organs other than the kidney; and secondly, to determine whether any of the cell lines would rank the in vitro cytotoxic potential of the compounds in an order consistent with their in vivo toxicities. LDH leakage and cell proliferative effects (CP) were the endpoints used to measure cytotoxicity.

The proximal tubule derivation of the LLC-PK1 cell line did not appear to confer significantly increased sensitivity to any of the aminoglycosides tested using LDH release and cell proliferation as endpoints of cytotoxicity. The relative cytotoxicity rankings were as follows: Chang — gentamicin>neomycin>amikacin>streptomycin (LDH), neomycin∼gentamicin∼streptomycin >amikacin (CP); SIRC — neomycin∼gentamicin∼streptomycin>amikacin (LDH and CP); and LLC-PK1 — gentamicin∼streptomycin>neomycin>amikacin (LDH), and streptomycin >neomycin>gentamicin∼amikacin (CP). The results suggest that the Chang line provides a cytotoxicity ranking consistent with in vivo nephrotoxicity data. The SIRC line ranks amikacin the least cytotoxic, but fails to discriminate between the cytotoxicities of gentamicin, neomycin and streptomycin. The LLC-PK1 cell line ranks the compounds in an order which is inconsistent with in vivo results. The LLC-PK1 cell line appears to be the most sensitive to streptomycin, which is the only agent tested that is not accumulated in the kidney in vivo. The results may reflect basal cytotoxicity, since relatively non-specific endpoints were used. Perhaps the LLC-PK1 cell line would rank the cytotoxic potential of this class of compounds more accurately if parameters which are more renal-specific were measured as endpoints.

Unique Triterpenoid of Jujube Root Protects Cisplatin-induced Damage in Kidney Epithelial LLC-PK1 Cells via Autophagy Regulation

Chronic exposure to cisplatin is associated with irreversible kidney impairment. In this present study, we explored the protective effects of 3-dehydroxyceanothetric acid 2-methyl ester (3DC2ME) isolated from roots of jujube (Ziziphus jujuba, Rhamnaceae) against cisplatin-induced damage in vitro. In kidney epithelial LLC-PK1 cells, western blotting and staining with specific autophagy epifluorescent dye CytoID were used to determine the molecular pathways involving autophagy. Treatment with 3DC2ME reduced the increased Cyto-ID-stained autophagic vesicles and reversed the protein expressions of 5' AMP-activated protein kinase subunit β-1 (AMPK)/mammalian target of rapamycin (mTOR)-dependent signaling pathway in cisplatin-induced cell death. Additionally, treatment with autophagy inhibitor 3-methyladenine (3-MA) and with or without 3DC2ME attenuated the cisplatin-induced apoptosis. Although further research is necessary to substantiate the effects, we evaluated the potential mechanism of action of 3DC2ME as an adjuvant for cancer patients.

Structural Insights into Escherichia coli Shiga Toxin (Stx) Glycosphingolipid Receptors of Porcine Renal Epithelial Cells and Inhibition of Stx-Mediated Cellular Injury Using Neoglycolipid-Spiked Glycovesicles

Shiga toxin (Stx) producing Escherichia coli (STEC) cause the edema disease in pigs by releasing the swine-pathogenic Stx2e subtype as the key virulence factor. Stx2e targets endothelial cells of animal organs including the kidney harboring the Stx receptor glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer, Galα1-4Galβ1-4Glcβ1-1Cer) and globotetraosylceramide (Gb4Cer, GalNAcβ1-3Galα1-4Galβ1-4Glcβ1-1Cer). Since the involvement of renal epithelial cells in the edema disease is unknown, in this study, we analyzed the porcine kidney epithelial cell lines, LLC-PK1 and PK-15, regarding the presence of Stx-binding GSLs, their sensitivity towards Stx2e, and the inhibitory potential of Gb3- and Gb4-neoglycolipids, carrying phosphatidylethanolamine (PE) as the lipid anchor, towards Stx2e. Immunochemical and mass spectrometric analysis revealed various Gb3Cer and Gb4Cer lipoforms as the dominant Stx-binding GSLs in both LLC-PK1 and PK-15 cells. A dihexosylceramide with proposed Galα1-4Gal-sequence (Gal₂Cer) was detected in PK-15 cells, whereas LLC-PK1 cells lacked this compound. Both cell lines were susceptible towards Stx2e with LLC-PK1 representing an extremely Stx2e-sensitive cell line. Gb3-PE and Gb4-PE applied as glycovesicles significantly reduced the cytotoxic activity of Stx2e towards LLC-PK1 cells, whereas only Gb4-PE exhibited some protection against Stx2e for PK-15 cells. This is the first report identifying Stx2e receptors of porcine kidney epithelial cells and providing first data on their Stx2e-mediated damage suggesting possible involvement in the edema disease.

Opportunities and Challenges for Molecular Understanding of Ciliopathies-The 100,000 Genomes Project

Cilia are highly specialized cellular organelles that serve multiple functions in human development and health. Their central importance in the body is demonstrated by the occurrence of a diverse range of developmental disorders that arise from defects of cilia structure and function, caused by a range of different inherited mutations found in more than 150 different genes. Genetic analysis has rapidly advanced our understanding of the cell biological basis of ciliopathies over the past two decades, with more recent technological advances in genomics rapidly accelerating this progress. The 100,000 Genomes Project was launched in 2012 in the UK to improve diagnosis and future care for individuals affected by rare diseases like ciliopathies, through whole genome sequencing (WGS). In this review we discuss the potential promise and medical impact of WGS for ciliopathies and report on current progress of the 100,000 Genomes Project, reviewing the medical, technical and ethical challenges and opportunities that new, large scale initiatives such as this can offer.

Type III Interferon Restriction by Porcine Epidemic Diarrhea Virus and the Role of Viral Protein nsp1 in IRF1 Signaling

Type III interferons (IFNs) play a vital role in maintaining the antiviral state of the mucosal epithelial surface in the gut, and in turn, enteric viruses may have evolved to evade the type III IFN responses during infection. To study the possible immune evasion of the type III IFN response by porcine epidemic diarrhea virus (PEDV), a line of porcine intestinal epithelial cells was developed as a cell model for PEDV replication. IFN-λ1 and IFN-λ3 inhibited PEDV replication, indicating the anti-PEDV activity of type III IFNs. Of the 21 PEDV proteins, nsp1, nsp3, nsp5, nsp8, nsp14, nsp15, nsp16, open reading frame 3 (ORF3), E, M, and N were found to suppress type III IFN activities, and IRF1 (interferon regulatory factor 1) signaling mediated the suppression. PEDV specifically inhibited IRF1 nuclear translocation. The peroxisome is the innate antiviral signaling platform for the activation of IRF1-mediated IFN-λ production, and the numbers of peroxisomes were found to be decreased in PEDV-infected cells. PEDV nsp1 blocked the nuclear translocation of IRF1 and reduced the number of peroxisomes to suppress IRF1-mediated type III IFNs. Mutational studies showed that the conserved residues of nsp1 were crucial for IRF1-mediated IFN-λ suppression. Our study for the first time provides evidence that the porcine enteric virus PEDV downregulates and evades IRF1-mediated type III IFN responses by reducing the number of peroxisomes.IMPORTANCE Porcine epidemic diarrhea virus (PEDV) is a highly contagious enteric coronavirus that emerged in swine in the United States and has caused severe economic losses. PEDV targets intestinal epithelial cells in the gut, and intestinal epithelial cells selectively induce and respond to the production of type III interferons (IFNs). However, little is known about the modulation of the type III IFN response by PEDV in intestinal epithelial cells. In this study, we established a porcine intestinal epithelial cell model for PEDV replication. We found that PEDV inhibited IRF1-mediated type III IFN production by decreasing the number of peroxisomes in porcine intestinal epithelial cells. We also demonstrated that the conserved residues in the PEDV nsp1 protein were crucial for IFN suppression. This study for the first time shows PEDV evasion of the type III IFN response in intestinal epithelial cells, and it provides valuable information on host cell-virus interactions not only for PEDV but also for other enteric viral infections in swine.

Inhibition of NF-κB activity by the porcine epidemic diarrhea virus nonstructural protein 1 for innate immune evasion

Porcine epidemic diarrhea virus emerged in the US is known to suppress the type I interferons response during infection. In the present study using porcine epithelial cells, we showed that PEDV inhibited both NF-κB and proinflammatory cytokines. PEDV blocked the p65 activation in infected cells and suppressed the PRD II-mediated NF-κB activity. Of the total of 22 viral proteins, nine proteins were identified as NF-κB antagonists, and nsp1 was the most potent suppressor of proinflammatory cytokines. Nsp1 interfered the phosphorylation and degradation of IκBα, and thus blocked the p65 activation. Mutational studies demonstrated the essential requirements of the conserved residues of nsp1 for NF-κB suppression. Our study showed that PEDV inhibited NF-κB activity and nsp1 was a potent NF-κB antagonist for suppression of both IFN and early production of pro-inflammatory cytokines.

•

PEDV inhibits type I IFNs and NF-κB-mediated pro-inflammatory cytokines.

•

PEDV blocks p65 nuclear translocation in virus-infected cells.

•

Among 22 viral proteins, nsp1, nsp3, nsp5, nsp7, nsp14, nsp15, nsp16, ORF3, and E are NF-κB antagonists.

•

Nsp1 suppresses pro-inflammatory cytokines and p65 activation by blocking IκBα phosphorylation.

•

The conserved residues of nsp1 are crucial for NF-κB suppression.

Palladin is upregulated in kidney disease and contributes to epithelial cell migration after injury

Recovery from acute kidney injury involving tubular epithelial cells requires proliferation and migration of healthy cells to the area of injury. In this study, we show that palladin, a previously characterized cytoskeletal protein, is upregulated in injured tubules and suggest that one of its functions during repair is to facilitate migration of remaining cells to the affected site. In a mouse model of anti-neutrophilic cytoplasmic antibody involving both tubular and glomerular disease, palladin is upregulated in injured tubular cells, crescents and capillary cells with angiitis. In human biopsies of kidneys from patients with other kidney diseases, palladin is also upregulated in crescents and injured tubules. In LLC-PK1 cells, a porcine proximal tubule cell line, stress induced by transforming growth factor-β1 (TGF-β1) leads to palladin upregulation. Knockdown of palladin in LLC-PK1 does not disrupt cell morphology but does lead to a defect in cell migration. Furthermore, TGF-β1 induced increase in the 75 kDa palladin isoform occurs in both the nucleus and the cytoplasm. These data suggest that palladin expression is induced in injured cells and contributes to proper migration of cells in proximal tubules, possibly by regulation of gene expression as part of the healing process after acute injury.

Interaction of Isoflavones with the BCRP/ABCG2 Drug Transporter

This review will provide a comprehensive overview of the interactions between dietary isoflavones and the ATP-binding cassette (ABC) G2 efflux transporter, which is also named the breast cancer resistance protein (BCRP). Expressed in a variety of organs including the liver, kidneys, intestine, and placenta, BCRP mediates the disposition and excretion of numerous endogenous chemicals and xenobiotics. Isoflavones are a class of naturallyoccurring compounds that are found at high concentrations in commonly consumed foods and dietary supplements. A number of isoflavones, including genistein and daidzein and their metabolites, interact with BCRP as substrates, inhibitors, and/or modulators of gene expression. To date, a variety of model systems have been employed to study the ability of isoflavones to serve as substrates and inhibitors of BCRP; these include whole cells, inverted plasma membrane vesicles, in situ organ perfusion, as well as in vivo rodent and sheep models. Evidence suggests that BCRP plays a role in mediating the disposition of isoflavones and in particular, their conjugated forms. Furthermore, as inhibitors, these compounds may aid in reversing multidrug resistance and sensitizing cancer cells to chemotherapeutic drugs. This review will also highlight the consequences of altered BCRP expression and/or function on the pharmacokinetics and toxicity of chemicals following isoflavone exposure.

Protective effects of methanolic extract form fruits of Lycium ruthenicum Murr on 2,2'-azobis (2-amidinopropane) dihydrochloride-induced oxidative stress in LLC-PK1 cells

Background:

Fruits of Lycium ruthenicum Murr is a health food and also used as a folk to treat heart disease, abnormal menstruation and menopause in Tibetan, China. However; whether L. ruthenicum Murr fruits methanolic extracts (LFME) protect LLC-PK1 porcine renal tubules cells from AAPH-induced oxidative damage has not been investigated.

Objective:

To investigate the protective effects of L. ruthenicum Murr fruits methanolic extracts (LFME) against 2, 2’- azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidative damage in renal proximal tubule LLC-PK1 cells.

Materials and Methods:

LLC-PK1 cells were co-incubated with AAPH (1mM) and different concentrations of LFMW together for 24 h. Cell viability was determined by MTT assay. Total intercellular reactive oxygen species (ROS) levels and lipid peroxidation were measured using a fluorescent probe 2’, 7’-dichlorfluorescein-diacetate (DCFH-DA) and the TBA reactive substance (TBARS) assay, respectively. The endogenous antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GSH-px) and intercellular glutathione (GSH) levels were determined using commercial assay kits according to the manufacturer's instructions.

Results:

LFME did not show a significant cytotoxic effect and increased the viability of LLC-PK1 cells in a concentration-dependent manner. LFME also decreased the total intercellular levels of ROS, reduced lipid peroxidation and increased the GSH levels as well as the activities of endogenous antioxidant enzymes to protect LLC-PK1 cells against AAPH-induced oxidative damage.

Conclusion:

The results from the present study indicated that LFME is an effective ROS scavenger to protect LLC-PK1 cells against AAPH-induced oxidative damage through decreasing ROS generation, reducing lipid peroxidation and up-regulation of endogenous GSH levels and antioxidant enzymes.

Effects of serum lipoproteins on cyclosporine A cellular uptake and renal toxicity in vitro

In-vitro studies were performed to shed light on previous findings that showed increased uptake of cyclosporine A in the kidneys and liver of hyperlipidemic rats, and increased signs of kidney toxicity. Hepatocytes were obtained from rats, cultured, and exposed to a diluted serum from hyperlipidemic rats. Some cells were also exposed to lipid-lowering drugs. After washing out the rat serum or lipid-lowering drugs, cells were exposed to cyclosporine A embedded in serum lipoproteins. Pretreatment with hyperlipidemic serum and lipid-lowering drugs was associated with an increased uptake of cyclosporine A. As expected, atorvastatin caused an increase in low density lipoprotein receptor and a decrease in MDR1A mRNA in the hepatocytes. A decrease in NRK-52E rat renal tubular cellular viability caused by cyclosporine A was noted when cells were preincubated with diluted hyperlipidemic serum. This was matched with evidence of hyperlipidemic-serum-associated increases in the NRK-52E cellular uptake of cyclosporine A and rhodamine-123. The findings of these experiments suggested that in hyperlipidemia the expression and (or) the functional activity of P-glycoprotein was diminished, leading to greater hepatic and renal uptake of cyclosporine A, and renal cellular toxicity.

Antioxidative effects of fermented sesame sauce against hydrogen peroxide-induced oxidative damage in LLC-PK1 porcine renal tubule cells

BACKGROUND/OBJECTIVES

This study was performed to investigate the in vitro antioxidant and cytoprotective effects of fermented sesame sauce (FSeS) against hydrogen peroxide (H2O2)-induced oxidative damage in renal proximal tubule LLC-PK1 cells.

MATERIALS/METHODS

1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl radical ((•)OH), and H2O2 scavenging assay was used to evaluate the in vitro antioxidant activity of FSeS. To investigate the cytoprotective effect of FSeS against H2O2-induced oxidative damage in LLC-PK1 cells, the cellular levels of reactive oxygen species (ROS), lipid peroxidation, and endogenous antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-px) were measured.

RESULTS

The ability of FSeS to scavenge DPPH, (•)OH and H2O2 was greater than that of FSS and AHSS. FSeS also significantly inhibited H2O2-induced (500 µM) oxidative damage in the LLC-PK1 cells compared to FSS and AHSS (P < 0.05). Following treatment with 100 µg/mL of FSeS and FSS to prevent H2O2-induced oxidation, cell viability increased from 56.7% (control) to 83.7% and 75.6%, respectively. However, AHSS was not able to reduce H2O2-induced cell damage (viability of the AHSS-treated cells was 54.6%). FSeS more effectively suppressed H2O2-induced ROS generation and lipid peroxidation compared to FSS and AHSS (P < 0.05). Compared to the other sauces, FSeS also significantly increased cellular CAT, SOD, and GSH-px activities and mRNA expression (P < 0.05).

CONCULUSIONS

These results from the present study suggest that FSeS is an effective radical scavenger and protects against H2O2-induced oxidative damage in LLC-PK1 cells by reducing ROS levels, inhibiting lipid peroxidation, and stimulating antioxidant enzyme activity.

Do you know the sex of your cells?

Do you know the sex of your cells? Not a question that is frequently heard around the lab bench, yet thanks to recent research is probably one that should be asked. It is self-evident that cervical epithelial cells would be derived from female tissue and prostate cells from a male subject (exemplified by HeLa and LnCaP, respectively), yet beyond these obvious examples, it would be true to say that the sex of cell lines derived from non-reproductive tissue, such as lung, intestine, kidney, for example, is given minimal if any thought. After all, what possible impact could the presence of a Y chromosome have on the biochemistry and cell biology of tissues such as the exocrine pancreatic acini? Intriguingly, recent evidence has suggested that far from being irrelevant, genes expressed on the sex chromosomes can have a marked impact on the biology of such diverse tissues as neurons and renal cells. It is also policy of AJP-Cell Physiology that the source of all cells utilized (species, sex, etc.) should be clearly indicated when submitting an article for publication, an instruction that is rarely followed (http://www.the-aps.org/mm/Publications/Info-For-Authors/Composition). In this review we discuss recent data arguing that the sex of cells being used in experiments can impact the cell's biology, and we provide a table outlining the sex of cell lines that have appeared in AJP-Cell Physiology over the past decade.

Culturing primary rat inner medullary collecting duct cells

Arginine-vasopressin (AVP) facilitates water reabsorption by renal collecting duct principal cells and thereby fine-tunes body water homeostasis. AVP binds to vasopressin V2 receptors (V2R) on the surface of the cells and thereby induces synthesis of cAMP. This stimulates cellular signaling processes leading to changes in the phosphorylation of the water channel aquaporin-2 (AQP2). Protein kinase A phoshorylates AQP2 and thereby triggers the translocation of AQP2 from intracellular vesicles into the plasma membrane facilitating water reabsorption from primary urine. Aberrations of AVP release from the pituitary or AVP-activated signaling in principal cells can cause central or nephrogenic diabetes insipidus, respectively; an elevated blood plasma AVP level is associated with cardiovascular diseases such as chronic heart failure and the syndrome of inappropriate antidiuretic hormone secretion. Here, we present a protocol for cultivation of primary rat inner medullary collecting duct (IMCD) cells, which express V2R and AQP2 endogenously. The cells are suitable for elucidating molecular mechanisms underlying the control of AQP2 and thus to discover novel drug targets for the treatment of diseases associated with dysregulation of AVP-mediated water reabsorption. IMCD cells are obtained from rat renal inner medullae and are used for experiments six to eight days after seeding. IMCD cells can be cultured in regular cell culture dishes, flasks and micro-titer plates of different formats, the procedure only requires a few hours, and is appropriate for standard cell culture laboratories.

Hydroxytyrosol glucuronides protect renal tubular epithelial cells against H(2)O(2) induced oxidative damage

Hydroxytyrosol (2-(3',4'-dihydroxyphenyl)ethanol; HT), the most active ortho-diphenolic compound, present either in free or esterified form in extravirgin olive oil, is extensively metabolized in vivo mainly to O-methylated, O-sulfated and glucuronide metabolites. We investigated the capacity of three glucuronide metabolites of HT, 3'-O-β-d-glucuronide and 4'-O-β-d-glucuronide derivatives and 2-(3',4'-dihydroxyphenyl)ethanol-1-O-β-d-glucuronide, in comparison with the parent compound, to inhibit H(2)O(2) induced oxidative damage and cell death in LLC-PK1 cells, a porcine kidney epithelial cell line. H(2)O(2) treatment exerted a toxic effect inducing cell death, interacting selectively within the pro-death extracellular-signal relate kinase (ERK 1/2) and the pro-survival Akt/PKB signaling pathways. It also produced direct oxidative damage initiating the membrane lipid peroxidation process. None of the tested glucuronides exhibited any protection against the loss in renal cell viability. They also failed to prevent the changes in the phosphorylation states of ERK and Akt, probably reflecting their inability to enter the cells, while HT was highly effective. Notably, pretreatment with glucuronides exerted a protective effect at the highest concentration tested against membrane oxidative damage, comparable to that of HT: the formation of malondialdehyde, fatty acid hydroperoxides and 7-ketocholesterol was significantly inhibited.

cDNA cloning of porcine PKD2 gene and RNA interference in LLC-PK1 cells

Mutations in the PKD2 gene cause autosomal dominant polycystic kidney disease (ADPKD), a common, inherited disease that frequently leads to end-stage renal disease (ESRD). Swine show substantial similarity to humans physiologically and anatomically, and are therefore a good model system in which to decipher the structure and function of the PKD2 gene and to identify potential therapeutic targets. Here we report the cloning and characterization of the porcine PKD2 cDNA showing that the full-length gene (3370 bases) is highly expressed in kidney, with minimal expression in the liver. RNA interference (RNAi) is a promising tool to enable identification of the essential components necessary for exploitation of the pathway involved in cellular processes. We therefore designed four shRNAs and nine siRNAs targeting the region of the porcine PKD2 gene from exons 3 to 9, which is supposed to be a critical region contributing to the severity of ADPKD. The results from HeLa cells with the dual-luciferase reporter system and porcine kidney cells (LLC-PK1) showed that sh12 could efficiently knock down the PKD2 gene with an efficiency of 51% and P1 and P2 were the most effective siRNAs inhibiting 85% and 77% respectively of PKD2 expression compared with untreated controls. A subsequent functional study of the transient receptor potential polycystic (TRPP) 2 channel protein indicated that the decreased expression of TRPP2 induced by siRNA P1 and P2 could release the arrest of the cell cycle from G0/G1 promoting progression to S and G2 phases. Our data, therefore, provides evidence of potential knock-down target sites in the PKD2 gene and paves the way for the future generation of transgenic ADPKD knock-down animal models.

The effect of acyclovir on the tubular secretion of creatinine in vitro

Background

While generally well tolerated, severe nephrotoxicity has been observed in some children receiving acyclovir. A pronounced elevation in plasma creatinine in the absence of other clinical manifestations of overt nephrotoxicity has been frequently documented. Several drugs have been shown to increase plasma creatinine by inhibiting its renal tubular secretion rather than by decreasing glomerular filtration rate (GFR). Creatinine and acyclovir may be transported by similar tubular transport mechanisms, thus, it is plausible that in some cases, the observed increase in plasma creatinine may be partially due to inhibition of tubular secretion of creatinine, and not solely due to decreased GFR. Our objective was to determine whether acyclovir inhibits the tubular secretion of creatinine.

Methods

Porcine (LLC-PK1) and human (HK-2) renal proximal tubular cell monolayers cultured on microporous membrane filters were exposed to [2-¹⁴C] creatinine (5 μM) in the absence or presence of quinidine (1E+03 μM), cimetidine (1E+03 μM) or acyclovir (22 - 89 μM) in incubation medium.

Results

Results illustrated that in evident contrast to quinidine, acyclovir did not inhibit creatinine transport in LLC-PK1 and HK-2 cell monolayers.

Conclusions

The results suggest that acyclovir does not affect the renal tubular handling of creatinine, and hence, the pronounced, transient increase in plasma creatinine is due to decreased GFR, and not to a spurious increase in plasma creatinine.

Comparison of the novel HK-2 human renal proximal tubular cell line with the standard LLC-PK1 cell line in studying drug-induced nephrotoxicity

Established cell lines are widely used as in vitro models in toxicology studies. The choice of an appropriate cell line is critical when performing studies to elucidate drug-induced toxicity in humans. The porcine renal proximal tubular cell line LLC-PK1 is routinely used to study the nephrotoxic effects of drugs in humans. However, there are significant interspecies differences in drug pharmacokinetics and pharmacodynamics. The objective of this study was to determine whether the human renal proximal tubular cell line HK-2 is an acceptable model to use when performing in vitro toxicity studies to predict effects in humans. We examined 2 nephrotoxic agents, ifosfamide (IFO) and acyclovir, that exhibit different clinical nephrotoxic patterns. HK-2 cells metabolized IFO to its nephrotoxic metabolite, chloroacetaldehyde (CAA). Acyclovir induced a concentration-dependent decrease in HK-2 cell viability, suggesting that acyclovir may induce direct insult to renal proximal tubular cells. The results support clinical pathology data in humans and suggest that HK-2 cells are a suitable model to use in in vitro toxicity studies to determine drug-induced nephrotoxicity in humans.

The effect of risperidone on D-amino acid oxidase activity as a hypothesis for a novel mechanism of action in the treatment of schizophrenia

D-Amino acid oxidase (DAO) has been established to be involved in the oxidation of D-serine, an allosteric activator of the N-methyl-D-aspartate-type glutamate receptor in the brain, and to be associated with the onset of schizophrenia. The effect of risperidone, a benzisoxazole derivative, atypical antischizophrenic drug, on the activity of human DAO was tested using an in-vitro oxygraph system and rat C6, stable C6 transformant cells overexpressing mouse DAO (designated as C6/DAO) and pig kidney epithelial cells (LLC-PK(1)). Risperidone has a hyperbolic mixed-type inhibition, designated as 'partial uncompetitive inhibition effect', with K(i) value of 41 microM on human DAO. Risperidone exhibited a protective effect from D-amino acid induced cell death in both C6/DAO and LLC-PK(1) cells with 10% increase in viability. These data indicate the involvement of DAO activity in D-serine metabolism and also suggest a new mechanism of action to risperidone as antischizophrenic drug.

Protective effect of hydroxytyrosol and tyrosol against oxidative stress in kidney cells

Bioavailability studies in animals and humans fed with extravirgin olive oil demonstrated that hydroxytyrosol and tyrosol, the major simple phenolic compounds in extravirgin olive oil, are dose-dependently absorbed and excreted. Once absorbed, they undergo extensive metabolism; hydroxytyrosol and tyrosol concentrate mainly in the kidney, where they may exert an important role in the prevention of oxidative stress induced renal dysfunction. In this study we monitored the ability of hydroxytyrosol and tyrosol to protect renal cells (LLC-PK1) following oxidative damage induced by H2O2. Oxidative stress was evaluated by monitoring the changes of the membrane lipid fraction. Hydroxytyrosol exerted a significant antioxidant action, inhibiting the production of MDA, fatty acids hydroperoxides and 7-ketocholesterol, major oxidation products of unsaturated fatty acids and cholesterol, and thus protecting the cells from H2O2-induced damage. Tyrosol, instead, in this experimental model, did not exert any protective effect.

Juxtacrine activation of epidermal growth factor (EGF) receptor by membrane-anchored heparin-binding EGF-like growth factor protects epithelial cells from anoikis while maintaining an epithelial phenotype

Loss of cell-matrix adhesion is often associated with acute epithelial injury, suggesting that "anoikis" may be an important contributor to cell death. Resistance against anoikis is a key characteristic of transformed cells. When nontransformed epithelia are injured, activation of the epidermal growth factor (EGF) receptor (EGFR) by paracrine/autocrine release of soluble ligands can induce a prosurvival program, but there is generally evidence for concomitant dedifferentiation. The EGFR ligand, heparin-binding EGF-like growth factor (HB-EGF), is synthesized as a membrane-anchored precursor that can activate the EGFR via juxtacrine signaling or can be released and act as a soluble growth factor. In Madin-Darby canine kidney cells, expression of membrane-anchored HB-EGF increases cell-cell and cell-matrix adhesion. Therefore, these studies were designed to test the effects of juxtacrine HB-EGF signaling upon cell survival and epithelial integrity when cells are denied proper cell-matrix interactions. Cells expressing a noncleavable mutated form of membrane-anchored HB-EGF demonstrated increased survival from anoikis, formed larger cell aggregates, and maintained epithelial characteristics even following prolonged detachment from the substratum. Physical association between membrane-anchored HB-EGF and EGFR was observed. Signaling studies indicated synergistic effects of EGFR activation and phosphatidylinositol 3-kinase signaling to regulate apoptotic and survival pathways. In contrast, although administration of exogenous EGF partially suppressed anoikis in wild type cells, it also led to an increased expression of mesenchymal markers, suggesting dedifferentiation. Taken together, we propose a novel role for membrane-anchored HB-EGF in the cytoprotection of epithelial cells.

Experimental strategies to improve in vitro models of renal ischemia

Ischemia has elicited a great deal of interest among the scientific community due to its role in life-threatening pathologies such as cancer, stroke, acute renal failure, and myocardial infarction. Oxygen deprivation (hypoxia) associated with ischemia has recently become a subject of intense scrutiny. New investigators may find it challenging to induce hypoxic injury in vitro. Researchers may not always be aware of the experimental barriers that contribute to this phenomenon. Furthermore, ischemia is associated with other major insults, such as excess carbon dioxide (hypercapnia), nutrient deprivation, and accumulation of cellular wastes. Ideally, these conditions should also be incorporated into in vitro models. Therefore, the motivation behind this review is to: i. delineate major in vivo ischemic insults; ii. identify and explain critical in vitro parameters that need to be considered when simulating ischemic pathologies; iii. provide recommendations to improve experiments; and as a result, iv. enhance the validity of in vitro results for understanding clinical ischemic pathologies. Undoubtedly, it is not possible to completely replicate the in vivo environment in an ex vivo model system. In fact, the primary goal of many in vitro studies is to elucidate the role of specific stimuli during in vivo pathological events. This review will present methodologies that may be implemented to improve the applicability of in vitro models for understanding the complex pathological mechanisms of ischemia. Finally, although these topics will be discussed within the context of renal ischemia, many are pertinent for cellular models of other organ systems and pathologies.

Anti-inflammatory and antinecrotic effects of the volatile anesthetic sevoflurane in kidney proximal tubule cells

Renal ischemia-reperfusion (IR) injury is a major clinical problem without effective therapy. We recently reported that volatile anesthetics protect against renal IR injury, in part, via their anti-inflammatory properties. In this study, we demonstrate the anti-inflammatory and antinecrotic effects of sevoflurane in cultured kidney proximal tubule cells and probed the mechanisms of sevoflurane-induced renal cellular protection. To mimic inflammation, human kidney proximal tubule (HK-2) cells were treated with tumor necrosis factor-α (TNF-α; 25 ng/ml) in the presence or absence of sevoflurane. In addition, we studied the effects of sevoflurane pretreatment on hydrogen peroxide (H2O2)-induced necrotic cell death in HK-2 or porcine proximal tubule (LLC-PK1) cells. We demonstrate that sevoflurane suppressed proinflammatory effects of TNF-α evidenced by attenuated upregulation of proinflammatory cytokine mRNA (TNF-α, MCP-1) and ICAM-1 protein and reduced nuclear translocation of the proinflammatory transcription factors NF-κB and AP-1. Sevoflurane reduced necrotic cell death induced with H2O2in HK-2 cells as well as in LLC-PK1cells. Sevoflurane treatment resulted in phosphorylation of prosurvival kinases, ERK and Akt, and increased de novo HSP-70 protein synthesis without affecting the synthesis of HSP-27 or HSP-32. We conclude that sevoflurane has direct anti-inflammatory and antinecrotic effects in vitro in a renal cell type particularly sensitive to injury following IR injury. These mechanisms may, in part, account for volatile anesthetics' protective effects against renal IR injury.

Calcitonin receptor-stimulating peptide-1 regulates ion transport and growth of renal epithelial cell line LLC-PK1

Calcitonin receptor-stimulating peptide-1 (CRSP-1) is a peptide recently identified from porcine brain by monitoring the cAMP production through an endogenous calcitonin (CT) receptor in the renal epithelial cell line LLC-PK(1). Here we investigated the effects of CRSP-1 on the ion transport and growth of LLC-PK(1) cells. CRSP-1 inhibited the growth of LLC-PK(1) cells with a higher potency than porcine CT. CRSP-1 enhanced the uptake of (22)Na(+) into LLC-PK(1) cells more strongly than did CT and slightly reduced the (45)Ca(2+) uptake. The enhancement of the (22)Na(+) uptake was abolished by 5-(N-ethyl-N-isopropyl) amiloride, a strong Na(+)/H(+) exchanger (NHE) inhibitor for NHE1, even at a concentration of 1x10(-8)M, although other ion transporter inhibitors did not affect the (22)Na(+) uptake. These results indicate that CRSP-1 enhances the (22)Na(+) uptake by the specific activation of NHE1. Taken together, CRSP-1 is considered to be a new regulator for the urinary ion excretion and renal epithelial cell growth.

Suitability of LLC-PK1 pig kidney cells for the study of drug action on renal cell cholesterol uptake: Identification and characterization of low-density lipoprotein receptors

INTRODUCTION

The purpose of this study was to identify and characterize the presence of low-density lipoprotein receptors (LDLr) in LLC-PK(1) cells.

METHODS

LLC-PK(1) cells were assessed for the presence of LDLr by conducting dose-response, LDL specific binding and competitive studies with DiI-LDL, and Western blot and RT-polymerase chain reaction (PCR) analyses. Assay conditions with IgG-C7, a monoclonal antibody (mAb) to the LDLr, were optimized, including temperature, preincubation time, and concentration in LLC-PK(1) cells.

RESULTS

LLC-PK(1) cells express LDL receptors as determined by LDL specific and competitive binding studies and Western blot and RT-PCR analysis (specific binding 0.5 ng DiI-LDL/mug of cellular protein).

DISCUSSION

Taken together, these findings confirm the presence of LDL receptors on LLC-PK1 cells and support the appropriateness of using these cells in studies involving renal cell cholesterol uptake and metabolism.

HPAF-II, a cell culture model to study pancreatic epithelial cell structure and function

OBJECTIVES

Epithelial cells have distinct apical and basolateral plasma membrane domains separated by tight junctions. This phenotype is essential for the directional transport functions of epithelial cells. Here we characterized a well-differentiated pancreatic epithelial cell line to establish a useful model for understanding the mechanisms involved in the regulation of junctional complexes, polarity, and disease processes in the pancreas.

METHODS

Immunofluorescence of cell junction marker proteins and electron microscopy were used to determine the presence of tight junctions, adherens junctions, and desmosomes. The functionality of tight junctions was tested by transepithelial resistance measurements and transepithelial permeability studies of nonionic molecules. Tight junction function in polarity was determined by laser scanning confocal microscopy.

RESULTS

Immunofluorescence analysis in HPAF-II cells revealed tight junction localization of ZO-1, occludin, and claudin-4; adherens junction localization of E-cadherin and beta-catenin; and desmosomal localization of desmocollin. Transmission electron microscopy showed the presence of tight junctions, adherens junctions, and des-mosomes, and freeze-fracture electron microscopy revealed the presence of distinct anastomosing tight junction strands. Transepithelial electrical resistance and permeability measurements revealed functional tight junctions. In addition, 3-dimensional images of the monolayer generated by laser scanning confocal microscopy revealed that HPAF-II cells show polarity. Immunoblotting and RT-PCR analyses revealed high expression levels of E-cadherin and Na,K-ATPase beta-subunit but low levels of the transcription factor Snail in HPAF-II cells compared with MiaPaCa-2 cells.

CONCLUSION

The HPAF-II cell line is a well-differentiated human pancreatic carcinoma cell line that should be useful as a model for studies aimed at understanding epithelial polarity, regulation of junctional complexes, and disease processes in pancreas.

Cellular pharmacokinetics and pharmacodynamics of the glycopeptide antibiotic oritavancin (LY333328) in a model of J774 mouse macrophages

The intracellular pharmacokinetics and pharmacodynamics of oritavancin (LY333328) were studied in cultured cells. Oritavancin was avidly accumulated by J774 and THP-1 macrophages and rat fibroblasts and to a lesser extent by LLC-PK1 and Caco-2 cells. In J774 macrophages, the level of accumulation reached a plateau (at 370-fold the extracellular concentration) within 24 h and was partly defeated by a rise in serum protein levels. Efflux was incomplete (with a plateau at two-thirds of the original level at 6 h). In short-term kinetic studies, oritavancin uptake was linear for up to 4 h (as was the case for horseradish peroxidase and small latex beads, used as markers of the fluid phase and adsorptive endocytosis, respectively), which was in contrast to azithromycin and chloroquine uptake (which accumulate in cells by diffusion and segregation). The rates of clearance of oritavancin and latex beads were comparable (150 and 120 microl x mg of protein(-1) x h(-1), respectively) and were approximately 200 times higher than that of horseradish peroxidase. Oritavancin accumulation was partially reduced by monensin but was unaffected by acidic pH (these conditions abolished chloroquine accumulation). Cell-associated oritavancin was found in lysosomal fractions after homogenization of J774 macrophages and fractionation by isopycnic centrifugation. Oritavancin was bactericidal against intracellular Staphylococcus aureus (phagolysosomal infection) but was unable to control the intracellular growth of Listeria monocytogenes (cytosolic infection), even though its cellular concentration largely exceeded the MIC (0.02 mg/liter) and minimal bactericidal concentration (2 mg/liter). We conclude that oritavancin enters cells by adsorptive endocytosis (favored by its lipophilic side chain and/or the presence of three protonatable amines), which drives it to lysosomes, where it exerts antibiotic activity.

Differential toxic effects of gentamicin on cultured renal epithelial cells (LLC-PK1) on application to the brush border membrane or the basolateral membrane

Aminoglycoside antibiotics are generally accepted to accumulate in renal proximal tubule cells from the luminal surface and show toxic effects on the cells. The binding affinity and membrane permeability of aminoglycoside antibiotics are different at the brush border membrane (BBM) and the basolateral membrane (BLM) of proximal tubule cells. This study was performed, therefore, to investigate the differential effects of the aminoglycoside antibiotic gentamicin (GM) on cultured LLC-PK1 cells, a pig kidney proximal epithelial cell line, after addition to the BBM or the BLM side. LLC-PK1 cells were cultured on microporous membranes until forming confluent monolayers, and then GM was added to either the BBM or the BLM side. GM caused release of enzymes from the organelles, with a higher level of release observed following addition to the BBM side than that to the BLM side. Patterns of [3H]GM uptake by the cells differed in a manner dependent on whether it was added to the BBM or the BLM side. That is, the cellular uptake from the BBM side increased with incubation time, while that from the BLM side showed rapid saturation. These results suggested that aminoglycoside antibiotics show differential effects on cultured proximal epithelial cells and have differential patterns of cellular uptake when added to the BBM or the BLM side.

Use of a renal tubule cell line (LLC-PK1) to study the nephrotoxic potential of a kappa-type Bence-Jones protein

The cytotoxicity of a Bence-Jones protein was assessed using a porcine renal tubule cell line (LLC-PK1), with the aim of developing a model for studying the potential nephrotoxicity of these proteins. The effects of a kappa Bence-Jones protein on cell viability were studied by means of biochemical methods (supravital dye uptake and measurement of cellular enzyme activities) and morphological electron microscopy. After a 24-h-treatment with Bence-Jones protein, a moderate cytotoxicity (about 15%) was noted but only a minor difference compared to treatment with bovine albumin in the same conditions. The morphological study showed a few cells in the process of lysis, but their numbers were insufficient for the demonstration of a clear cytotoxic effect. Immunocytochemical studies showed Bence-Jones protein fixation on some cells, especially on the outer membrane. Labeling of the hyaloplasm and basal pole of a few cells pointed to internalization of protein by LLC-PK1 cells. Although the cytotoxicity of the Bence-Jones protein tested here was only moderate, the use of this model enabled its cytotoxic effect to be distinguished from that of beta-lactoglobulin. This isolate could serve as a "moderate control" for a later study with a BJP having caused acute renal failure.

Virus infection of polarized epithelial cells

This chapter focuses on the interaction of viruses with epithelial cells. The role of specific pathways of virus entry and release in the pathogenesis of viral infection is examined together with the mechanisms utilized by viruses to circumvent the epithelial barrier. Polarized epithelial cells in culture, which can be grown on permeable supports, provide excellent systems for investigating the events in virus entry and release at the cellular level, and much information is being obtained using such systems. Much remains to be learned about the precise routes by which many viruses traverse the epithelial barrier to initiate their natural infection processes, although important information has been obtained in some systems. Another area of great interest for future investigation is the process of virus entry and release from other polarized cell types, including neuronal cells.

Expression of plasmolipin in the developing rat brain

Plasmolipin is an hydrophobic plasma membrane proteolipid present in both kidney and brain. The protein consists of two subunits of 17-18.5 kD, which together form K+ selective voltage-dependent channels. In this report, we define the embryonic and postnatal expression of plasmolipin in the developing rat brain. Plasmolipin was found to be essentially restricted to the postnatal period increasing eight-fold between the first to fourth week after birth. A fetal plasmolipin immunoreactive protein (FPIP) was identified in embryonic brain and also during the early postnatal development of the cerebellum. The expression of FPIP was biphasic with an initial transient increase between E15-E20 followed by a decrease in its levels. FPIP was not detected in the developed rat CNS. FPIP was found in a variety of dividing and immature cells including cultured astrocytes and embryonic neurons, neuroblastoma cells, and rat thymus. In contrast, plasmolipin was restricted to oligodendrocytes of the neural cells tested and to renal tubular epithelial cells.

Renal proximal tubular cells in suspension or in primary culture as in vitro models to study nephrotoxicity

The kidney forms a frequent target for xenobiotic toxicity. The complex biochemical mechanisms underlying nephrotoxicity are best studied in vitro provided that reliable and relevant in vitro models are available. Since most nephrotoxicants affect primarily the cells of the proximal tubules (PTC), much effort has been directed towards the development of in vitro models of PTC. This review focuses on the preparation of PTC and the use of these cells. Discussed are important criteria such as the viability (survival time) of the cells and the parameters to assess toxicity. Recent studies have shown that isolated PTC in suspension are especially suitable for studies on the biochemical mechanisms of 'acute' nephrotoxicity, whereas PTC in primary culture may be used to investigate mechanisms of nephrotoxic damage at very low concentrations, upon prolonged exposure. PTC cultured on porous filter membranes provide new possibilities to study toxicity in relation to cell and transport polarity. Primary cell cultures of human PTC have been set up. Although a further characterization of these systems is needed, recent data indicate their usefulness.

Secretion of endothelin and related peptides from renal epithelial cell lines

Using specific radioimmunoassays (RIAs) for endothelin (ET) and big ET, we have studied whether ET and related peptides are secreted from renal epithelial cell lines (LLCPK1 and MDCK) of non-endothelial origin. Dilution curves of extracts of conditioned media from both LLCPK1 and MDCK cell lines were parallel to those of standard porcine (p) ET and big pET in each RIA. Both cell lines incubated in serum-free medium secreted ET- and C-terminal fragment (CTF)-like immunoreactivity (LI) of big ET as a function of time. Reverse-phase HPLC coupled with both RIAs of the extracted media from both cell lines revealed a single component with ET-LI coeluting with pET(1-21) and several components with CTF-LI, one corresponding to the elution position of big pET(1-39), one to its CTF(22-39), and the others eluting earlier than CTF. These data indicate that endothelin and related peptides are synthesized by and secreted from cells other than endothelial cells.

Characterization of primary cell cultures derived from rat renal proximal tubules

Proximal tubules were prepared from rat kidney cortex by collagenase digestion and purified by Percoll gradient centrifugation. Their enrichment was estimated by comparing the specific activities of various cell-specific enzymes in homogenates of renal cortex and of the isolated tubules. The tubules were cultured in a 50:50 mixture of Dulbecco's modified Eagle's and Ham's F12 media supplemented with insulin, transferrin, epidermal growth factor, hydrocortisone, and prostaglandin E1. After 2 to 3 d an extensive outgrowth of epithelial cells developed from the attached tubules. After 5 to 7 d near confluent monolayers were obtained. Hormonal responsiveness, marker enzyme activities, and transport properties were determined to further characterize the primary cultures. The cultured cells exhibited increased cyclic AMP production in response to parathyroid hormone but not calcitonin or vasopressin, consistent with the absence of cells derived from distal and collecting tubules. The cells also retained significant levels of 25-hydroxyvitamin D3-1 alpha-hydroxylase, alkaline phosphatase, and gamma-glytamyl-transpeptidase, three enzymes that are primarily associated with the proximal tubule. The cultured epithelial cells also exhibit a Na+-dependent phosphate and glucose transport systems. Therefore, the cells retain many functional properties that are characteristic of proximal tubules. Thus, the primary cultures should be suitable for the study of processes that occur specifically within this segment of the rat nephron.

Na+-sugar cotransport system as a polarization marker during organization of epithelial membrane

The present study analyzed the changes in Na+-dependent sugar transport and transepithelial electrical resistance as LLC-PK1 cells reorganize into epithelial membranes. Sugar influx increased to reach a maximum 9 h after plating. The increase in the transepithelial electrical resistance, however, showed a significant delay, reaching steady state 15 h after plating. No changes in the electrochemical Na+ gradient were observed during the reorganization of the epithelial membranes. Kinetic analysis and [3H]phlorizin-binding studies showed that the increase in sugar influx resulted from an increase in the number of carriers. Unidirectional sugar influx measurements indicated that the sugar transporters were primarily located at the apical surface of the epithelial cells. These observations are consistent with the hypothesis that the sorting of native proteins occurs intracellularly before their insertion in the apical membrane, or as an alternative that they are randomly inserted, but then immediately sorted such as any carrier could be detected in the basolateral side during the reorganization process. In addition, the results suggest that the functional development of the apical membrane may occur before the complete sealing of the intercellular space during the development of the occluding junctions. Furthermore, development of the sugar transport system and occluding junctions was inhibited by cycloheximide and puromycin but not by actinomycin D, suggesting that the expression of epithelial cell polarization is probably a posttranslational event in the protein synthesis.

A 13C-NMR study on the influxes into the tricarboxylic acid cycle of a renal epithelial cell line, LLC-PK1/Cl4: the metabolism of [2-13C]glycine, L-[3-13C]alanine and L-[3-13C]aspartic acid in renal epithelial cells

Perchloric acid extracts of LLC-PK1/Cl4 cells, a renal epithelial cell line, incubated with either [2-13C]glycine L-[3-13C]alanine, or D,L-[3-13C]aspartic acid were investigated by 13C-NMR spectroscopy. All amino acids, except labelled glycine, gave rise to glycolytic products and tricarboxylic acid cycle (TCA) intermediates. For the first time we also observed activity of gamma-glutamyltransferase activity and glutathione synthetase activity in LLC-PK1 cells, as is evident from enrichment of reduced glutathione. Time courses showed that only 6% of the labelled glycine was utilized in 30 min, whereas 31% of L-alanine and 60% of L-aspartic acid was utilized during the same period. 13C-NMR was also shown to be a useful tool for the determination of amino acid uptake in LLC-PK1 cells. These uptake experiments indicated that glycine, alanine and aspartic acid are transported into Cl4 cells via a sodium-dependent process. From the relative enrichment of the glutamate carbons, we calculated the activity of pyruvate dehydrogenase to be about 61% when labelled L-alanine was the only carbon source for LLC-PK1/Cl4 cells. Experiments with labelled D,L-aspartic, however, showed that about 40% of C-3-enriched oxaloacetate (arising from a de-amination of aspartic acid) reached the pyruvate pool.

Differential toxicity as a result of apical and basolateral treatment of LLC-PK1 monolayers with S-(1,2,3,4,4-pentachlorobutadienyl)glutathione and N-acetyl-S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine

Monolayers of LLC-PK1 cells, a cell line with features typical of proximal tubular epithelial cells, were treated at the apical and basolateral side with S-(1,2,3,4,4-pentachlorobutadienyl)glutathione (PCBD-GSH) and N-acetyl-S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine (PCBD-NAC). Apical treatment with PCBD-GSH (greater than 20 microM) resulted in cytotoxicity, which could be inhibited by acivicin and aminooxyacetic acid (AOAA), inhibitors of gamma-glutamyltranspeptidase (gamma GT) and beta-lyase respectively. In contrast apical treatment with PCBD-NAC was only toxic at high concentrations (greater than 850 microM), and this effect could hardly be inhibited by AOAA. Basolateral treatment of confluent LLC-PK1 monolayers, grown on porous membranes, with PCBD-GSH gave a much smaller response than apical treatment, consistent with the fact that gamma GT is predominantly present at the apical side. Basolateral treatment even with high concentrations of PCBD-NAC (1.1 mM) did not show an increase in cytotoxicity when compared to the effect after apical treatment. These results suggest the absence of an organic anion transporter, by which these conjugates in vivo are transported into the cells from the basolateral side. This supposition was substantiated in a study of transcellular transport of the model ions tetraethyl ammonium (TEA) and para-aminohippurate (PAH), in LLC-PK1 monolayers, grown as indicated above. No active PAH transport could be demonstrated, whereas an active TEA transport was present. The absence of an organic anion transporter limits the usefulness of LLC-PK1 cells for the study of nephrotoxicity of compounds, like PCBD-NAc, needing this transport to enter the cells. However, the finding of an active basolateral organic cation transporter, together with the presence of gamma GT, dipeptidase and beta-lyase, makes this system especially interesting for testing all compounds that use this transporter or these enzymes in order to elicit toxicity.

Malignant conversion of murine squamous papilloma cell lines by transfection with the fos oncogene

Murine papilloma cell lines 308 and SP-1 have been used as recipients for transfected oncogenes to investigate malignant conversion. These cell lines express an activated c-rasHa gene with a codon 61 mutation and produce squamous papillomas when transplanted as skin grafts onto nude mice. They are not tumorigenic by subcutaneous injection. Both papilloma cell lines were stably transfected with plasmid DNA containing either a rearranged murine plasmacytoma-derived c-myc (minus exon 1), adenovirus 5 E1A, FBJ v-fos or a human c-fos/FBJ v-fos chimera, using cotransfection with the neomycin resistance gene contained in pSV2neo to select for transformants. Southern and northern blotting analysis confirmed the uptake and expression of exogenous DNA in both G418-selected cell lines and in the derived tumors. Unlike the E1A- and myc-containing plasmids, both fos constructs caused malignant conversion in either cell line, as defined by the squamous cell carcinoma histology of tumors from grafted cells and the development of carcinomas after subcutaneous injection into athymic nude mice. Immunofluorescence analysis for specific keratin gene expression indicated that tumors derived by introduction of either of the fos oncogenes were devoid of staining for K1, a 67 kDa epidermal keratin that is expressed in papillomas but not in squamous carcinomas. Tumors from E1A, myc, or pSV2neo transfectants expressed K1, although in a focal distribution. The malignant phenotype induced by the fos oncogene constructs was not associated with the ability to form agar colonies in vitro or to express gamma-glutamyl transpeptidase in the tumors. Since both 308 and SP-1 were sensitive to the fos oncogene for malignant conversion and insensitive to E1A or myc, it is possible that fos may cooperate with the endogenous-activated c-rasHa gene to convert these cells to malignancy. However, since gamma-glutamyl transpeptidase activity is found in the majority of chemically induced mouse skin carcinomas that possess an activated c-rasHa gene, fos activation may not be a common pathway for spontaneous malignant conversion.

A 31P-NMR study on the recovery of intracellular pH in LLC-PK1/Cl4 cells from intracellular alkalinization

The regulation of intracellular pH (pHi) in a renal epithelial cell line, LLC-PK1/Cl4, during re-acidification from an alkaline load was studied by 31P-NMR. Intracellular alkalinization was induced by 10 mM ammonium glucuronate or by preloading with and subsequent removal of 20% CO2; the rate of re-acidification was found to be 0.047 pH units/min and 0.053 pH units/min, respectively. This rate of re-acidification was inhibited by 83% if Cl- was removed from the extracellular medium. A similar inhibition was found in the presence of 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS) (76% inhibition) and 1 mM bumetanide (81% inhibition). No change in recovery was found after removing sodium from the extracellular medium, indicating that LLC-PK1/Cl4 cells recover from an intracellular alkaline load by a Cl-/HCO3- exchanger, which is SITS- and bumetanide-sensitive and has no requirement for sodium. In addition, the steady-state pHi in Cl4 cells was monitored by 31P-NMR. Removal of Cl- from the extracellular medium introduced an increase in pHi by 0.33 pH units, whereas 1 mM SITS and 1 mM bumetanide caused an increase in pHi by 0.14 or 0.13 pH units. In the presence of 1 mM amiloride, an inhibitor of the Na+/H+ exchanger, the steady-state pHi did not change significantly. These results indicate that at pHo 7.4 the steady-state intracellular pH of LLC-PK1/Cl4 cells strongly depends on the activity of the Cl-/HCO3- exchanger. Under the same conditions the activity of the Na+/H+ exchanger seems to be negligible.

Investigations on the mode of action of the fungus toxin orellanine on renal cell cultures

The effects of the fungal nephrotoxin orellanine, of 2,2'-bipyridine and of 4,4'-bipyridine on monolayers of LLPCK1-cells were tested. It is shown by the E.C.50 on growing cells that orellanine is the most toxic of the tested bipyridyls. Orellanine causes disruption of confluent monolayers and decreases the activities of membrane bound alkaline phosphatase and of cytosolic lactate dehydrogenase. Also 3H-leucine and 3H-thymidine incorporation are reduced. In contrast to this, ATP- and NADPH-levels remain constant. The cell membrane is not affected. This indicates an intracellular mechanism of action.

Characterization of Na+-dependent phosphate uptake in cultured kidney cells (JTC-12) from monkey

Phosphate uptake was studied in confluent monolayers of an epithelial-cell line (JTC-12) derived from monkey kidney. Phosphate uptake consisted of a saturable, Na+-dependent, component, which accounted for about 80% of the uptake, and a nonsaturable, Na+-independent, component. The saturable component was specifically dependent on the presence of extracellular Na+ and has an apparent Km value for phosphate of 0.12 mM at 137-mM-Na+, which is close to those reported in the brush-border membranes in mammalian kidneys. The presence of Na+ in the uptake solution decreased the Km for phosphate without affecting the Vmax. Phosphate uptake was inhibited by carbonyl cyanide p-trifluoromethoxyphenylhydrazone and ouabain, suggesting that phosphate transport is an active, energy-dependent, process and is dependent on an Na+ gradient across cell membranes. With respect to the effect of external Na+ concentration, a sigmoid relation was seen between the initial velocity of phosphate uptake and Na+ concentrations, and Hill analysis gave a Hill coefficient of 1.8. In the pH range 6.6-7.4, phosphate uptake declined with increasing pH. Phosphate uptake was stimulated when cells were cultured in the presence of insulin, and was also affected by changes in phosphate concentrations in cultured medium. These results indicate that JTC-12 cells have an Na+-dependent phosphate-transport system with many of the features of phosphate transport in the proximal tubule.

Differentiated properties characteristic of renal proximal epithelium in a cell line derived from a normal monkey kidney (JTC-12)

The JTC-12 cell, an established cell line derived from a normal monkey kidney, was studied in an attempt to characterize the epithelial qualities. Phase contrast microscopy showed dome formation in confluent monolayers and electron microscopic examinations revealed the presence of numerous microvilli on the apical membranes and desmosome between cells. Sonicated cells showed activities of gamma-glutamyl transpeptidase, leucine aminopeptidase, alkaline phosphatase, and trehalase, marker enzymes of renal proximal epithelium. Alkaline phosphatase activity exhibited the characteristics of a renal type isozyme. Furthermore, confluent JTC-12 monolayers exhibited Na+-dependent transport of hexose, amino acid as well as inorganic phosphate. These findings indicate that JTC-12 cells in monolayer culture maintain ultrastructural, biochemical, and physiological properties of renal proximal epithelial cells. This cell line will be useful for further studies on cellular functions of renal proximal epithelium.

The function of gamma-glutamyl transpeptidase as a determinant in cell sensitivity to azaserine toxicity

The enzyme gamma-glutamyl transpeptidase (GGT) is characteristically present at high levels in mammalian cells that are vulnerable in vivo to the selectively toxic and carcinogenic effects of the naturally occurring diazo amino acid L-azaserine. The possible role of GGT as a determinant of cellular sensitivity to azaserine toxicity was investigated. No correlation was found between GGT activity and the abilities of different cell lines or GGT-deficient cell strains of TuWi, a human nephroblastoma-derived line high in GGT, to accumulate azaserine. However, the thiols glutathione and cysteine were found to inhibit the toxicity of azaserine in cultures of TuWi. In addition, maleate lowered both intracellular and extracellular glutathione levels and enhanced sensitivity of TuWi cells to azaserine, while serine-borate, a potent inhibitor of GGT, increased extracellular glutathione levels and inhibited azaserine toxicity. Since extracellular glutathione accumulation, which may reflect the rate of cellular glutathione turnover, is increased in cultures of azaserine-resistant, GGT-deficient strains of TuWi, we propose that GGT enhances cellular sensitivity to azaserine primarily by increasing the rate of glutathione turnover, thus removing the glutathione from detoxification pathways.

Specific membrane receptors for atrial natriuretic factor in renal and vascular tissues

Membranes from rabbit aorta and from rabbit and rat kidney cortex possess high-affinity (Kd = 10(-10) M) specific binding sites for atrial natriuretic factor (ANF). Similar high-affinity sites are present in an established cell line from pig kidney, LLC-PK1. Results of fractionation studies indicate that the receptors are localized in the plasma membrane of these tissues. The binding is time-dependent and saturable. An excellent quantitative correlation was found between the affinity of synthetic ANF and analogs of intermediate activity to aorta membranes and the half-maximal concentration needed for relaxation of rabbit aorta rings contracted by addition of serotonin. Furthermore, the binding affinity of the receptor in kidney membranes is consistent with the concentration required for in vivo natriuresis in the rat. Biologically inactive synthetic ANF fragments and other peptide hormones such as angiotensin II and vasopressin do not significantly inhibit binding. These data suggest that the receptors for ANF in vascular and renal tissues are responsible for mediating the physiological actions of this peptide in these target tissues.