Targeted oncogenesis: A powerful method to derive renal cell lines

Acidosis induces antimicrobial peptide expression and resistance to uropathogenic E. coli infection in kidney collecting duct cells via HIF-1α

Acute pyelonephritis is frequently associated with metabolic acidosis. We previously reported that metabolic acidosis stimulates expression of hypoxia-inducible factor (HIF)-1α-induced target genes such as stromal derived factor-1 and cathelicidin, an antimicrobial peptide. Since the collecting duct (CD) plays a pivotal role in regulating acid-base homeostasis and is the first nephron segment encountered by an ascending microbial infection, we examined the contribution of HIF-1α to innate immune responses elicited by acid loading of an M-1 immortalized mouse CD cell line. Acid loading of confluent M-1 cells was achieved by culture in pH 6.8 medium supplemented with 5-(N-ethyl-N-isopropyl)-amiloride to block Na+/H+ exchange activity for 24 h. Acid loading induced antimicrobial peptide [cathelicidin and β-defensin (Defb2 and Defb26)] mRNA expression and M-1 cell resistance to uropathogenic Escherichia coli infection to an extent similar to that obtained by inhibition of HIF prolyl hydroxylases, which promote HIF-1α protein degradation. The effect of acid loading on M-1 cell resistance to uropathogenic E. coli infection was reduced by inhibition of HIF-1α (PX-478), and, in combination with prolyl hydroxylase inhibitors, acidosis did not confer additional resistance. Thus, metabolic stress of acidosis triggers HIF-1α-dependent innate immune responses in CD (M-1) cells. Whether pharmacological stabilization of HIF prevents or ameliorates pyelonephritis in vivo warrants further investigation.

Transimmortalized proximal tubule and collecting duct cell lines derived from the kidneys of transgenic mice

This review summarizes the strategy of cellular immortalization based on the principle of targeted oncogenesis in transgenic mice, used to establish models of transimmortalized renal proximal tubule cells, referred to as PKSV-PCT and PKSV-PR-cells, and collecting duct principal cells, referred to as mpkCCD(cl4) cells. These cell lines have maintained for long-term passages the main biochemical and functional properties of the parental cells from which they were derived. Proximal tubule PKSV-PCT and PKSV-PR cells have been proved to be suitable cell systems for toxicological and pharmacological studies. They also permitted the establishment of a model of multidrug-resistant (MDR) renal epithelial tubule cells, PKSV-PR(col50), which have served for the study of both MDR-dependent extrusion of chemotherapeutic drugs and inappropriate accumulation of weak base anthracyclines in intracellular acidic organelles. The novel collecting duct cell line mpkCCD(cl4), which has maintained the characteristics of tight epithelial cells, in particular Na(+) absorption stimulated by aldosterone, has been extensively used for pharmacological studies related to the regulation of ion transport. These cells have permitted the identification of several aldosterone-induced proteins playing a key role in the regulation of Na(+) absorption mediated by the epithelial Na(+) channel ENaC. Recent studies have also provided evidence that these cell lines represent valuable cell systems for the study of host-pathogen interactions and the analysis of the role of renal tubule epithelial cells in the induction of inflammatory response caused by uropathogens that may lead to severe renal damage.

Regulation of NaCl transport in the renal collecting duct: lessons from cultured cells

The fine control of NaCl absorption regulated by hormones takes place in the distal nephron of the kidney. In collecting duct principal cells, the epithelial sodium channel (ENaC) mediates the apical entry of Na(+), which is extruded by the basolateral Na(+),K(+)-ATPase. Simian virus 40-transformed and "transimmortalized" collecting duct cell lines, derived from transgenic mice carrying a constitutive, conditionally, or tissue-specific promoter-regulated large T antigen, have been proven to be valuable tools for studying the mechanisms controlling the cell surface expression and trafficking of ENaC and Na(+),K(+)-ATPase. These cell lines have made it possible to identify sets of aldosterone- and vasopressin-stimulated proteins, and have provided new insights into the concerted mechanism of action of serum- and glucocorticoid-inducible kinase 1 (Sgk1), ubiquitin ligase Nedd4-2 (neural precursor cell-expressed, developmentally down-regulated protein 4-2), and 14-3-3 regulatory proteins in modulating ENaC-mediated Na(+) currents. Epidermal growth factor and induced leucine zipper protein have also been shown to repress and stimulate ENaC-dependent Na(+) absorption, respectively, by activating or repressing the mitogen-activated protein kinase externally regulated kinase(1/2). Overall, these findings have provided evidence suggesting that multiple pathways are involved in regulating NaCl absorption in the distal nephron.

Functional IsK/KvLQT1 potassium channel in a new corticosteroid-sensitive cell line derived from the inner ear

Endolymph, a high K(+)/low Na(+) fluid, participates in mechanoelectrical transduction in inner ear. Molecular mechanisms controlling endolymph ion homeostasis remain elusive, hampered by the lack of appropriate cellular models. We established an inner ear cell line by targeted oncogenesis. The expression of SV40 T antigen was driven by the proximal promoter of the human mineralocorticoid receptor (MR) gene, a receptor expressed in the inner ear. The EC5v cell line, microdissected from the semicircular canal, grew as a monolayer of immortalized epithelial cells forming domes. EC5v cells exhibited on filters of high transepithelial resistance and promoted K(+) secretion and Na(+) absorption. Functional MR and the 11beta-hydroxysteroid dehydrogenase type 2, a key enzyme responsible for MR selectivity were identified. Expression of the epithelial sodium channel and serum glucocorticoid-regulated kinase 1 was shown to be up-regulated by aldosterone, indicating that EC5v represents a novel corticosteroid-sensitive cell line. Ionic measurements and (86)Rb transport assays revealed an apical secretion of K(+) at least in part through the I(sK)/KvLQT1 potassium channel under standard culture conditions. However, when cells were exposed to high apically K(+)/low Na(+) fluid, mimicking endolymph exposure, I(sK)/KvLQT1 actually functioned as a strict apical to basolateral K(+) channel inhibited by clofilium. Quantitative reverse transcriptase-PCR further demonstrated that expression of KvLQT1 but not of I(sK) was down-regulated by high K(+) concentration. This first vestibular cellular model thus constitutes a valuable system to further investigate the molecular mechanisms controlling ionic transports in the inner ear and the pathophysiological consequences of their dysfunctions in vertigo and hearing loss.

Phenotypic analysis of conditionally immortalized cells isolated from the BPK model of ARPKD

To study the pathophysiology of autosomal recessive polycystic kidney disease (ARPKD), we sought to develop conditionally immortalized control and cystic murine collecting tubule (CT) cell lines. CT cells were isolated from intercross breedings between BPK mice (bpk(+/-)), a murine model of ARPKD, and the Immorto mice (H-2K(b)-ts-A58(+/+)). Second-generation outbred offspring (BPK x Immorto) homozygous for the BPK mutation (bpk(-/-); Im(+/+/-); cystic BPK/H-2K(b)-ts-A58), were phenotypically indistinguishable from inbred cystic BPK animals (bpk(-/-)). Cystic BPK/H-2K(b)-ts-A58 mice developed biliary ductal ectasia and massively enlarged kidneys, leading to renal failure and death by postnatal day 24. Principal cells (PC) were isolated from outbred cystic and noncystic BPK/H-2K(b)-ts-A58 littermates at specific developmental stages. Epithelial monolayers were under nonpermissive conditions for markers of epithelial cell polarity and PC function. Cystic and noncystic cells displayed several properties characteristic of PCs in vivo, including amiloride-sensitive sodium transport and aquaporin 2 expression. Cystic cells exhibited apical epidermal growth factor receptor (EGFR) mislocalization but normal expression of ZO-1 and E-cadherin. Hence, these cell lines retain the requisite characteristics of PCs, and cystic BPK/H-2K(b)-ts-A58 PCs retained the abnormal EGFR membrane expression characteristic of ARPKD. These cell lines represent important new reagents for studying the pathogenesis of ARPKD.

Vasopressin-stimulated chloride transport in transimmortalized mouse cell lines derived from the distal convoluted tubule and cortical and inner medullary collecting ducts

BACKGROUND

The fine control of NaCl absorption takes place in the distal parts of the renal tubule, but the regulation of Cl(-) transport in this region has not been fully elucidated. We have analysed the effects of dD-arginine vasopressin (dDAVP) on Cl(-) fluxes in cultured mouse distal convoluted tubule (mpkDCT), cortical collecting duct (mpkCCD) and inner medullary collecting duct (mpkIMCD) cell lines.

METHODS

RT-PCR and Western blotting were used to detect the amiloride-sensitive sodium channel (ENaC) and cystic fibrosis transmembrane conductance regulator (CFTR) mRNAs and protein in cultured mpkDCT, mpkCCD and mpkIMCD cells. Cl(-) fluxes were analysed by measuring the short-circuit current (I(sc)) and bidirectional (36)Cl(-) fluxes on confluent cells grown on filters.

RESULTS

All three cell lines expressed ENaC and CFTR and had I(sc) stimulated by dDAVP. The rise in I(sc) caused by dDAVP (10(-8) M) was inhibited by amiloride, and to a lesser extent by 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) in all three cell lines. The dDAVP-dependent I(sc) measured under apical Na(+)-free condition was reduced by Cl(-) channel blockers with a profile (NPPB>glibenclamide>DIDS), similar to that for rat CFTR. dDAVP stimulated the apical-to-basal (36)Cl(-) flux and to a lesser extent the basal-to-apical (36)Cl(-) flux under open-circuit condition in all three cultured cell lines. Adding NPPB to the apical side reduced the basal-to-apical (36)Cl(-) flux but not the opposite (36)Cl(-) flux from dDAVP-treated cells.

CONCLUSION

These results indicate that dDAVP stimulates the bi-directional flux of Cl(-), resulting in net Cl(-)absorption, in these cultured mouse distal and collecting duct cells. I(sc) experiments also suggest the presence of a minor component of electrogenic Cl(-) secretion, possibly mediated by CFTR.

Using Transgenic Mice to Analyze the Mechanisms of Progression of Chronic Renal Failure

Abstract. An understanding of the mechanisms underlying the formation of renal lesions is necessary for the development of strategies aiming to delay the progression of chronic renal failure. The generation of transgenic mice in the past 20 years has contributed significantly to the study of this phenomenon. Overexpression and/or inactivation of single factors in renal tissue demonstrated that molecules such as growth factors, proto-oncogenes, and renin-angiotensin system elements play major roles in renal deterioration. Several mouse models of renal injury have been developed in the past 10 yr. Transgenic mice that exhibit a normal phenotype under physiologic conditions allow analysis of the roles of single factors in the progression of chronic renal failure when renal injury models are used. Using this strategy, it was demonstrated that vascular adaptation, which is a process that involves the endothelin/nitric oxide balance, is essential for the survival of mice after nephron reduction and that the epidermal growth factor/activator protein-1/Bcl-2 pathway is involved in the development of renal lesions after renal injury, possibly via adjustment of the proliferation/apoptosis balance. Moreover, it was demonstrated that selective inhibition of epidermal growth factor signaling in the kidney successfully prevents the progression of chronic renal failure. These results indicate the power of transgenesis for elucidation of the pathogenesis of renal disease.

Targeted oncogenesis reveals a distinct tissue-specific utilization of alternative promoters of the human mineralocorticoid receptor gene in transgenic mice

The human mineralocorticoid receptor (hMR) is a nuclear receptor mediating aldosterone action, whose expression is driven by two alternative promoters, P1 and P2, flanking the two first 5'-untranslated exons. In vivo characterization of hMR regulatory regions was performed by targeted oncogenesis in mice using P1 or P2 directing expression of the large T antigen of SV40 (TAg). While transgenic P1.TAg founders rapidly developed lethal hibernomas from brown fat, cerebral primitive neuroectodermal tumors and facial leiomyosarcomas occurred in P2.TAg mice. Quantitative analyses of mouse MR (mMR) and transgene expression indicate that P1 promoter was transcriptionally active in all MR-expressing tissues, directing strong TAg expression in testis and salivary glands, moderate in lung, brain, uterus, liver, and heart but, unlike mMR, rather low in colon and kidney. Importantly, the renal transgene expression colocalized with mMR in the distal nephron. In contrast, P2 promoter was approximately 10 times less potent than P1, with no activity in the brain and colon. Several immortalized cell lines were established from both neoplastic and normal tissues of transgenic mice. These cells exhibited differentiated characteristics and maintained MR expression, thus providing useful models for further studies exploring the widespread expression and functions of MR. Our results demonstrate that hMR gene expression in vivo is controlled by complex regulatory mechanisms involving distinct tissue-specific utilization of alternative promoters.

Immortalized kidney epithelial cells as tools for hormonally regulated ion transport studies

The development of transgenic mice carrying the simian virus-40 large T antigen gene or the temperature-sensitive simian virus-40 large T antigen gene, either alone or placed under the control of the 5'-regulatory regions of tissue-specific or ubiquitous genes, has permitted the production of differentiated, polarized kidney epithelial cells. This review covers the immortalized cell lines issued from the various parts of the renal tubule and, in particular, the recently established collecting duct cell lines that have been used as ex-vivo cell models to analyze the regulation of ion transport processes by hormones.

Corticosteroid-dependent sodium transport in a novel immortalized mouse collecting duct principal cell line

The final control of sodium balance takes place in the cortical collecting duct (CCD) of the nephron, where corticosteroid hormones regulate sodium reabsorption by acting through mineralocorticoid (MR) and/or glucocorticoid (GR) receptors. A clone of principal CCD cells (mpkCCDc14) has been established that is derived from a transgenic mouse (SV40 large T antigen under the control of the SV40 enhancer/L-type pyruvate kinase promoter). Cells grown on filters form polarized monolayers with high electrical transepithelial resistance (R(T) approximately 4700 ohm x cm2) and potential difference (P(D) approximately -50 mV) and have an amiloride-sensitive electrogenic sodium transport, as assessed by the short-circuit current method (Isc approximately 11 microA/cm2). Reverse transcription-PCR experiments using rat MR primers, [3H]aldosterone, and [3H]dexamethasone binding and competition studies indicated that the mpkCCDc14 cells exhibit specific MR and GR. Aldosterone increased Isc in a dose- (10(-10) to 10(-6) M) and time-dependent (2 to 72 h) manner, whereas corticosterone only transiently increased Isc (2 to 6 h). Consistent with the expression of 11beta-hydroxysteroid dehydrogenase type 2, which metabolizes glucocorticoids to inactive 11-dehydroderivates, carbenoxolone potentiated the corticosterone-stimulated Isc. Aldosterone (5x10(-7) M)-induced Isc (fourfold) was associated with a three- to fivefold increase in alpha-ENaC mRNA (but not in those for beta- or gamma-ENaC) and three- to 10-fold increases in alpha-ENaC protein synthesis. In conclusion, this new immortalized mammalian CCD clonal cell line has retained a high level of epithelial differentiation and sodium transport stimulated by aldosterone and therefore represents a useful mammalian cell system for identifying the genes controlled by aldosterone.

Advances in cell separation: recent developments in counterflow centrifugal elutriation and continuous flow cell separation

Cell separation by counterflow centrifugal elutriation (CCE) or free flow electrophoresis (FFE) is performed at lower frequency than cell cloning and antibody-dependent, magnetic or fluorescence-activated cell sorting. Nevertheless, numerous recent publications confirmed that these physical cell separation methods that do not include cell labeling or cell transformation steps, may be most useful for some applications. CCE and FFE have proved to be valuable tools, if homogeneous populations of normal healthy untransformed cells are required for answering scientific questions or for clinical transplantation and cells cannot be labeled by antibodies, because suitable antibodies are not available or because antibody binding to a cell surface would induce the cell reaction which should be investigated on purified cells or because antibodies bound to the surface hamper the use of the isolated cells. In addition, the methods are helpful for studying the biological reasons for, or effects of, changes in cell size and cellular negative surface charge density. Although the value of the methods was confirmed in recent years by a considerable number of important scientific results, activities to further develop and improve the instruments have, unfortunately, declined.

Stimulated secretion of lysosomal enzymes induced by drugs in transimmortalized proximal tubule mouse kidney cells

We summarize the results of study of the properties of two models of transimmortalized proximal tubule epithelial cells derived from the kidneys of transgenic mice harboring the SV40 large T and little t antigens/L-pyruvate kinase hybrid gene. The two cell lines, referred to as PKSV-PCT and PKSV-PR cells, maintained for long-term passages the main biochemical and functional properties from the convoluted and terminal parts of the proximal tubule, respectively, from which they were derived. In PKSV-PCT cells, gentamicin induced lysosomal alkalinization, decreased the cellular N-acetyl-beta-D-glucuronidase, and stimulated its secretion in a dose-dependent manner. The results indicate that these models of mouse proximal cultured cells could be suitable models for the study of the cellular action of drugs.