TolCV1 inhibition by NPPB renders Vibrio vulnificus less virulent and more susceptible to antibiotics

Bacterial efflux pumps play important roles in the antibiotic resistance and excretion of virulence factors. We previously characterized that TolCV1, a component of efflux pumps, plays critical roles in resistance to antibiotics and bile and also RtxA1 toxin secretion of Vibrio vulnificus. In this context, we speculated that TolCV1 blockers would have a dual effect of enhancing susceptibility to antibiotics and suppressing virulence of V. vulnificus. Here, we show that the chloride channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) increases susceptibility to antibiotics and suppresses cytotoxicity of V. vulnificus through inhibition of TolCV1. NPPB significantly decreased TolCV1 in V. vulnificus cells by liberating the protein from the cell body. Checkerboard assay showed that NPPB enhanced the antimicrobial activities of antibiotics such as kanamycin, tetracycline, erythromycin, and ampicillin against V. vulnificus. Moreover, NPPB inhibited the secretion of RtxA1 toxin and protected host cells from V. vulnificus-induced cytotoxicity. In addition, NPPB markedly suppressed V. vulnificus growth in the presence of bile salts and enhanced the therapeutic effect of tetracycline in V. vulnificus-infected mice. The safety and efficacy of NPPB were confirmed at the cellular and animal levels. Collectively, TolCV1 inhibition by NPPB renders V. vulnificus less virulent and more susceptible to antibiotics.

The role of lysosomal membrane proteins in glucose and lipid metabolism

Lysosomes have long been regarded as the "garbage dump" of the cell. More recently, however, researchers have revealed novel roles for lysosomal membranes in autophagy, ion transport, nutrition sensing, and membrane fusion and repair. With active research into lysosomal membrane proteins (LMP), increasing evidence has become available showing that LMPs are inextricably linked to glucose and lipid metabolism, and this relationship represents mutual influence and regulation. In this review, we summarize the roles of LMPs in relation to glucose and lipid metabolism, and describe their roles in glucose transport, glycolysis, cholesterol transport, and lipophagy. The role of transport proteins can be traced back to the original discoveries of GLUT8, NPC1, and NPC2, which were all found to have significant roles in the pathways involved in glucose and lipid metabolism. CLC-5 and SIDT2-knockout animals show serious phenotypic disorders of metabolism, and V-ATPase and LAMP-2 have been found to interact with proteins related to glucose and lipid metabolism. These findings all emphasize the critical role of LMPs in glycolipid metabolism and help to strengthen our understanding of the independent and close relationship between LMPs and glycolipid metabolism.

Antiproteinuric and Hyperkalemic Mechanisms Activated by Dual Versus Single Blockade of the RAS in Renovascular Hypertensive Rats

This study aimed to investigate the antiproteinuric and hyperkalemic mechanisms activated by dual renin-angiotensin system (RAS) blockade in renovascular hypertensive rats (2-kidney 1-clip model [2K-1C]). Six weeks after clipping the left renal artery or sham operation (2K), rats were treated with losartan, enalapril, or both drugs for two weeks. We found that 2K-1C rats displayed higher tail-cuff blood pressure (BP), increased non-clipped kidney Ang II concentration, and more pronounced urinary albumin excretion than 2K. BP was decreased by the treatment with either enalapril or losartan, and the combination of both drugs promoted an additional antihypertensive effect in 2K-1C rats. Renal Ang II content and albuminuria were reduced by either enalapril or losartan in monotherapy and restored to control levels by dual RAS blockade. Albuminuria in 2K-1C rats was accompanied by downregulation of the glomerular slit protein podocin, reduction of the endocytic receptors megalin and cubilin, and a marked decrease in the expression of the ClC-5 chloride channel, compared to 2K animals. Treatment with losartan and enalapril in monotherapy or combination increased the expression of podocin, cubilin, and ClC-5. However, only the combined therapy normalized podocin, cubilin, and ClC-5 protein abundance in the non-clipped kidney of 2K-1C rats. Renovascular hypertensive 2K-1C rats had a lower concentration of plasma potassium compared to 2K rats. Single RAS blockade normalized potassium plasma concentration, whereas 2K-1C rats treated with dual RAS blockade exhibited hyperkalemia. Hypokalemia in 2K-1C rats was accompanied by an increase in the cleaved activated forms of α-ENaC and γ-ENaC and the expression of β-ENaC. Combined RAS blockade but not monotherapy significantly reduced the expression of these ENaC subunits in 2K-1C rats. Indeed, double RAS blockade reduced the abundance of cleaved-α-ENaC to levels lower than those of 2K rats. Collectively, these results demonstrate that the antiproteinuric effect of dual RAS blockade in 2K-1C rats is associated with the restored abundance of podocin and cubilin, and ClC-5. Moreover, double RAS blockade-induced hyperkalemia may be due, at least partially, to an exaggerated downregulation of cleaved α-ENaC in the non-clipped kidney of renovascular hypertensive rats.

The Angiotensin II Type 1 Receptor-Associated Protein Attenuates Angiotensin II-Mediated Inhibition of the Renal Outer Medullary Potassium Channel in Collecting Duct Cells

Adjustments in renal K⁺ excretion constitute a central mechanism for K⁺ homeostasis. The renal outer medullary potassium (ROMK) channel accounts for the major K⁺ secretory route in collecting ducts during basal conditions. Activation of the angiotensin II (Ang II) type 1 receptor (AT1R) by Ang II is known to inhibit ROMK activity under the setting of K⁺ dietary restriction, underscoring the role of the AT1R in K⁺ conservation. The present study aimed to investigate whether an AT1R binding partner, the AT1R-associated protein (ATRAP), impacts Ang II-mediated ROMK regulation in collecting duct cells and, if so, to gain insight into the potential underlying mechanisms. To this end, we overexpressed either ATRAP or β-galactosidase (LacZ; used as a control), in M-1 cells, a model line of cortical collecting duct cells. We then assessed ROMK channel activity by employing a novel fluorescence-based microplate assay. Experiments were performed in the presence of 10⁻¹⁰ M Ang II or vehicle for 40 min. We observed that Ang II-induced a significant inhibition of ROMK in LacZ, but not in ATRAP-overexpressed M-1 cells. Inhibition of ROMK-mediated K⁺ secretion by Ang II was accompanied by lower ROMK cell surface expression. Conversely, Ang II did not affect the ROMK-cell surface abundance in M-1 cells transfected with ATRAP. Additionally, diminished response to Ang II in M-1 cells overexpressing ATRAP was accompanied by decreased c-Src phosphorylation at the tyrosine 416. Unexpectedly, reduced phospho-c-Src levels were also found in M-1 cells, overexpressing ATRAP treated with vehicle, suggesting that ATRAP can also downregulate this kinase independently of Ang II-AT1R activation. Collectively, our data support that ATRAP attenuates inhibition of ROMK by Ang II in collecting duct cells, presumably by reducing c-Src activation and blocking ROMK internalization. The potential role of ATRAP in K⁺ homeostasis and/or disorders awaits further investigation.

ClC-5 Downregulation Induces Osteosarcoma Cell Apoptosis by Promoting Bax and tBid Complex Formation

Osteosarcoma is the most common malignant bone tumor. Chloride (Cl^-) channels-mediated Cl^- movement plays an important role in regulating the functions of various cancer cells, but its role in osteosarcoma remains unclear. In this study, we found that ClC-5 was increased in osteosarcoma tissues compared with normal bone tissues. Patients with high ClC-5 expression showed poor overall survival relative to those patients with low ClC-5 expression. Higher ClC-5 expression and lower intracellular Cl^- concentration ([Cl^-]_i) were observed in osteosarcoma cells compared with normal osteoblasts. Lowering [Cl^-]_i increased the viability of osteosarcoma cells, which was markedly blocked by ClC-5 downregulation. Knockdown of ClC-5 significantly induced osteosarcoma cell apoptosis and increased the release of cytochrome c from mitochondria to cytosol, concomitantly with cleavage of caspase-9, caspase-3, and PARP. The effect of ClC-5 downregulation on osteosarcoma cell apoptosis and viability was abolished by caspase-3 and caspase-9 inhibitors, but not caspase-8 inhibitor. Furthermore, ClC-5 inhibition promoted Bax translocation from cytosol to mitochondria. Immunoprecipitation showed that ClC-5 interacted with Bax and ClC-5 downregulation enhanced Bax and tBid complex formation. Collectively, we demonstrate that ClC-5 downregulation induces osteosarcoma cell apoptosis via mitochondria-dependent apoptotic pathway activation by promoting Bax and tBid association and subsequent Bax translocation.

Glibenclamide inhibits BK polyomavirus infection in kidney cells through CFTR blockade

BK polyomavirus (BKPyV) is a ubiquitous pathogen in the human population that is asymptomatic in healthy individuals, but can be life-threatening in those undergoing kidney transplant. To-date, no vaccines or anti-viral therapies are available to treat human BKPyV infections. New therapeutic strategies are urgently required. In this study, using a rational pharmacological screening regimen of known ion channel modulating compounds, we show that BKPyV requires cystic fibrosis transmembrane conductance regulator (CFTR) activity to infect primary renal proximal tubular epithelial cells. Disrupting CFTR function through treatment with the clinically available drug glibenclamide, the CFTR inhibitor CFTR₁₇₂, or CFTR-silencing, all reduced BKPyV infection. Specifically, time of addition assays and the assessment of the exposure of VP2/VP3 minor capsid proteins indicated a role for CFTR during BKPyV transport to the endoplasmic reticulum, an essential step during the early stages of BKPyV infection. We thus establish CFTR as an important host-factor in the BKPyV life cycle and reveal CFTR modulators as potential anti-BKPyV therapies.

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BK polyomavirus (BKPyV) is life-threatening in those undergoing kidney transplant.

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BKPyV requires CFTR to infect primary kidney cells.

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Disrupting CFTR function pharmacologically reduces BKPyV infection.

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CFTR is required during BKPyV transport to the endoplasmic reticulum.

β2-adrenergic Agonists Rescue Lysosome Acidification and Function in PSEN1 Deficiency by Reversing Defective ER-to-lysosome Delivery of ClC-7

Lysosomal dysfunction is considered pathogenic in Alzheimer disease (AD). Loss of presenilin-1 (PSEN1) function causing AD impedes acidification via defective vacuolar ATPase (vATPase) V0a1 subunit delivery to lysosomes. We report that isoproterenol (ISO) and related β2-adrenergic agonists reacidify lysosomes in PSEN1 Knock out (KO) cells and fibroblasts from PSEN1 familial AD patients, which restores lysosomal proteolysis, calcium homeostasis, and normal autophagy flux. We identify a novel rescue mechanism involving Portein Kinase A (PKA)-mediated facilitation of chloride channel-7 (ClC-7) delivery to lysosomes which reverses markedly lowered chloride (Cl^-) content in PSEN1 KO lysosomes. Notably, PSEN1 loss of function impedes Endoplasmic Reticulum (ER)-to-lysosome delivery of ClC-7. Transcriptomics of PSEN1-deficient cells reveals strongly downregulated ER-to-lysosome transport pathways and reversibility by ISO, thus accounting for lysosomal Cl^- deficits that compound pH elevation due to deficient vATPase and its rescue by β2-adrenergic agonists. Our findings uncover a broadened PSEN1 role in lysosomal ion homeostasis and novel pH modulation of lysosomes through β2-adrenergic regulation of ClC-7, which can potentially be modulated therapeutically.

ClC-5 alleviates renal fibrosis in unilateral ureteral obstruction mice

Renal fibrosis is the major feature of end-stage renal disease with high mortality. Chloride (Cl^-) moving along Cl^- channels has been suggested to play to an important role in renal function. This study aims to investigate the role of ClC-5 in renal fibrosis in unilateral ureteral occlusion (UUO) mice. C57BL/6 mice received UUO surgery followed by delivery of adeno-associated virus encoding ClC-5 cDNA (AAVClC-5). Western blotting, real-time PCR and histological analysis were used to investigate the effects of ClC-5 on renal fibrosis and underlying mechanisms. The expression of ClC-5 was significantly decreased in renal cortex of UUO mice and transforming growth factor-β1 (TGF-β1)-stimulated HK2 cells. Overexpression of ClC-5 in vivo markedly ameliorated UUO-induced renal injury and fibrosis. The increased expressions of plasminogen activator inhibitor type 1, connective tissue growth factor, collagen III and collagen IV were also inhibited by ClC-5 upregulation. Moreover, UUO-induced immune cell infiltration and inflammatory cytokines release were attenuated in mice infected with AAVClC-5. In addition, the in vivo and in vitro results showed that ClC-5 overexpression prevented epithelial-to-mesenchymal transition (EMT), concomitantly with a restoration of E-cadherin expression and a decrease of vimentin, α-SMA and S100A4 expressions. Furthermore, ClC-5 overexpression inhibited UUO- or TGF-β1-induced increase in nuclear factor kappa B (NF-κB) acetylation and matrix metalloproteinases-9 (MMP-9) expression. However, downregulation of ClC-5 in HK2 cells further potentiated TGF-β1-induced EMT and increase in NF-κB acetylation and MMP-9 expression. ClC-5 upregulation ameliorates renal fibrosis via inhibiting NF-κB/MMP-9 pathway signaling activation, suggesting that ClC-5 may be a novel therapeutic target for treating renal fibrosis and chronic kidney disease.

Precision toxicology shows that troxerutin alleviates ochratoxin A-induced renal lipotoxicity

Lipotoxicity is the most common cause of severe kidney disease, with few treatment options available today. Precision toxicology can improve detection of subtle intracellular changes in response to exogenous substrates; thus, it facilitates in-depth research on bioactive molecules that may interfere with the onset of certain diseases. In the current study, troxerutin significantly relieved nephrotoxicity, increased endurance, and improved systemic energy metabolism and renal inflammation in OTA-induced nephrotic mice. Lipidomics showed that troxerutin effectively reduced the levels of triglycerides, phosphatidylcholines, and phosphatidylethanolamines in nephropathy. The mechanism was partly attributable to troxerutin in alleviating the aberrantly up-regulated expression of sphingomyelinase, the cystic fibrosis transmembrane conductance regulator, and chloride channel 2. Renal tubular epithelial cells, the main site of toxin-induced accumulation of lipids in the kidney, were subjected to transcriptomic profiling, which uncovered several metabolic factors relevant to aberrant lipid and lipoprotein metabolism. Our work provides new insights into the molecular features of toxin-induced lipotoxicity in renal tubular epithelial cells in vivo and demonstrates the function of troxerutin in alleviating OTA-induced nephrosis and associated systemic energy metabolism disorders.-Yang, X., Xu, W., Huang, K., Zhang, B., Wang, H., Zhang, X., Gong, L., Luo, Y., He, X. Precision toxicology shows that troxerutin alleviates ochratoxin A-induced renal lipotoxicity.

Diabetic rats present higher urinary loss of proteins and lower renal expression of megalin, cubilin, ClC-5, and CFTR

Diabetic nephropathy (DN) occurs in around 40% of those with diabetes. Proteinuria is the main characteristic of DN and develops as a result of increased permeability of the glomerulus capillary wall and/or decreased proximal tubule endocytosis. The goal of this work was to evaluate renal function and the expression of megalin, cubilin, CFTR (cystic fibrosis transmembrane conductance regulator), and ClC-5 in the proximal tubule and renal cortex of rats with type 1 diabetes. Male Wistar rats were randomly assigned to control (CTRL) and diabetic (DM) groups for 4 weeks. Renal function was assessed in 24-h urine sample by calculating clearance and fractional excretion of solutes. The RNA and protein contents of ClC-5, CFTR, megalin, and cubilin were determined in the renal proximal tubule and cortex using real-time polymerase chain reaction and western blotting techniques, respectively. The results showed higher creatinine clearance and higher urinary excretion of proteins, albumin, and transferrin in the DM group than in the CTRL group. Furthermore, the renal cortex and proximal tubule of diabetic animals showed downregulation of megalin, cubilin, ClC-5, and CFTR, critical components of the endocytic apparatus. These data suggest dysfunction in proximal tubule low-molecular-weight endocytosis and protein glomerulus filtration in the kidney of diabetic rats.

A pure chloride channel mutant of CLC-5 causes Dent's disease via insufficient V-ATPase activation

Dent's disease is characterized by defective endocytosis in renal proximal tubules (PTs) and caused by mutations in the 2Cl(-)/H(+) exchanger, CLC-5. However, the pathological role of endosomal acidification in endocytosis has recently come into question. To clarify the mechanism of pathogenesis for Dent's disease, we examined the effects of a novel gating glutamate mutation, E211Q, on CLC-5 functions and endosomal acidification. In Xenopus oocytes, wild-type (WT) CLC-5 showed outward-rectifying currents that were inhibited by extracellular acidosis, but E211Q and an artificial pure Cl(-) channel mutant, E211A, showed linear currents that were insensitive to extracellular acidosis. Moreover, depolarizing pulse trains induced a robust reduction in the surface pH of oocytes expressing WT CLC-5 but not E211Q or E211A, indicating that the E211Q mutant functions as a pure Cl(-) channel similar to E211A. In HEK293 cells, E211A and E211Q stimulated endosomal acidification and hypotonicity-inducible vacuolar-type H(+)-ATPase (V-ATPase) activation at the plasma membrane. However, the stimulatory effects of these mutants were reduced compared with WT CLC-5. Furthermore, gene silencing experiments confirmed the functional coupling between V-ATPase and CLC-5 at the plasma membrane of isolated mouse PTs. These results reveal for the first time that the conversion of CLC-5 from a 2Cl(-)/H(+) exchanger into a Cl(-) channel induces Dent's disease in humans. In addition, defective endosomal acidification as a result of insufficient V-ATPase activation may still be important in the pathogenesis of Dent's disease.

Molecular mechanisms and regulation of urinary acidification

The H(+) concentration in human blood is kept within very narrow limits, ~40 nmol/L, despite the fact that dietary metabolism generates acid and base loads that are added to the systemic circulation throughout the life of mammals. One of the primary functions of the kidney is to maintain the constancy of systemic acid-base chemistry. The kidney has evolved the capacity to regulate blood acidity by performing three key functions: (i) reabsorb HCO3(-) that is filtered through the glomeruli to prevent its excretion in the urine; (ii) generate a sufficient quantity of new HCO3(-) to compensate for the loss of HCO3(-) resulting from dietary metabolic H(+) loads and loss of HCO3(-) in the urea cycle; and (iii) excrete HCO3(-) (or metabolizable organic anions) following a systemic base load. The ability of the kidney to perform these functions requires that various cell types throughout the nephron respond to changes in acid-base chemistry by modulating specific ion transport and/or metabolic processes in a coordinated fashion such that the urine and renal vein chemistry is altered appropriately. The purpose of the article is to provide the interested reader with a broad review of a field that began historically ~60 years ago with whole animal studies, and has evolved to where we are currently addressing questions related to kidney acid-base regulation at the single protein structure/function level.

CFTR and TNR-CFTR expression and function in the kidney

The cystic fibrosis transmembrane conductance regulator (CFTR) is abundantly expressed in the kidney. CFTR mRNA is detected in all nephron segments of rats and humans and its expression is higher in the renal cortex and outer medulla than in the inner medulla. CFTR protein is detected at the apical surface of both proximal and distal tubules of rat kidney but not in the outer medullary collecting ducts. The localization of CFTR in the proximal tubules is compatible with that of endosomes, suggesting that CFTR might regulate pH in endocytic vesicles by equilibrating H+ accumulation due to H+-ATPase activity. Many studies have also demonstrated that CFTR also regulates channel pore opening and the transport of sodium, chloride and potassium. The kidneys also express a CFTR splicing variant, called TNR-CFTR, in a tissue-specific manner, primarily in the renal medulla. This splicing variant conserves the functional characteristics of wild-type CFTR. The functional significance of TNR-CFTR remains to be elucidated, but our group proposes that TNR-CFTR may have a basic function in intracellular organelles, rather than in the plasma membrane. Also, this splicing variant is able to partially substitute CFTR functions in the renal medulla of Cftr-/- mice and CF patients. In this review we discuss the major functions that have been proposed for CFTR and TNR-CFTR in the kidney.

Distinct action of flavonoids, myricetin and quercetin, on epithelial Cl⁻ secretion: useful tools as regulators of Cl⁻ secretion

Epithelial Cl⁻ secretion plays important roles in water secretion preventing bacterial/viral infection and regulation of body fluid. We previously suggested that quercetin would be a useful compound for maintaining epithelial Cl⁻ secretion at a moderate level irrespective of cAMP-induced stimulation. However, we need a compound that stimulates epithelial Cl⁻ secretion even under cAMP-stimulated conditions, since in some cases epithelial Cl⁻ secretion is not large enough even under cAMP-stimulated conditions. We demonstrated that quercetin and myricetin, flavonoids, stimulated epithelial Cl⁻ secretion under basal conditions in epithelial A6 cells. We used forskolin, which activates adenylyl cyclase increasing cytosolic cAMP concentrations, to study the effects of quercetin and myricetin on cAMP-stimulated epithelial Cl⁻ secretion. In the presence of forskolin, quercetin diminished epithelial Cl⁻ secretion to a level similar to that with quercetin alone without forskolin. Conversely, myricetin further stimulated epithelial Cl⁻ secretion even under forskolin-stimulated conditions. This suggests that the action of myricetin is via a cAMP-independent pathway. Therefore, myricetin may be a potentially useful compound to increase epithelial Cl⁻ secretion under cAMP-stimulated conditions. In conclusion, myricetin would be a useful compound for prevention from bacterial/viral infection even under conditions that the amount of water secretion driven by cAMP-stimulated epithelial Cl⁻ secretion is insufficient.

Functional vacuolar ATPase (V-ATPase) proton pumps traffic to the enterocyte brush border membrane and require CFTR

Vacuolar ATPases (V-ATPases) are highly conserved proton pumps that regulate organelle pH. Epithelial luminal pH is also regulated by cAMP-dependent traffic of specific subunits of the V-ATPase complex from endosomes into the apical membrane. In the intestine, cAMP-dependent traffic of cystic fibrosis transmembrane conductance regulator (CFTR) channels and the sodium hydrogen exchanger (NHE3) in the brush border regulate luminal pH. V-ATPase was found to colocalize with CFTR in intestinal CFTR high expresser (CHE) cells recently. Moreover, apical traffic of V-ATPase and CFTR in rat Brunner's glands was shown to be dependent on cAMP/PKA. These observations support a functional relationship between V-ATPase and CFTR in the intestine. The current study examined V-ATPase and CFTR distribution in intestines from wild-type, CFTR(-/-) mice and polarized intestinal CaCo-2BBe cells following cAMP stimulation and inhibition of CFTR/V-ATPase function. Coimmunoprecipitation studies examined V-ATPase interaction with CFTR. The pH-sensitive dye BCECF determined proton efflux and its dependence on V-ATPase/CFTR in intestinal cells. cAMP increased V-ATPase/CFTR colocalization in the apical domain of intestinal cells and redistributed the V-ATPase Voa1 and Voa2 trafficking subunits from the basolateral membrane to the brush border membrane. Voa1 and Voa2 subunits were localized to endosomes beneath the terminal web in untreated CFTR(-/-) intestine but redistributed to the subapical cytoplasm following cAMP treatment. Inhibition of CFTR or V-ATPase significantly decreased pHi in cells, confirming their functional interdependence. These data establish that V-ATPase traffics into the brush border membrane to regulate proton efflux and this activity is dependent on CFTR in the intestine.

Progression of microalbuminuria in SHR is associated with lower expression of critical components of the apical endocytic machinery in the renal proximal tubule

Cumulative epidemiological evidence indicates that the presence of microalbuminuria predicts a higher frequency of cardiovascular events, peripheral disease, and mortality in essential hypertension. Microalbuminuria may arise from increased glomerular permeability and/or reduced proximal tubular reabsorption of albumin by receptor-mediated endocytosis. This study aimed to evaluate the temporal pattern of urinary protein excretion and to test the hypothesis that progression of microalbuminuria is associated with decreased protein expression of critical components of the endocytic apparatus in the renal proximal tubule of spontaneously hypertensive rats (SHR). We found that urinary albumin excretion increased progressively with blood pressure in SHR from 6 to 21 wk of age. In addition, SDS-PAGE analysis of urinary proteins showed that microalbuminuric SHR virtually excreted proteins of the size of albumin or smaller (<70 kDa), typical of tubular proteinuria. Moreover, the protein abundance of the endocytic receptors megalin and cubilin as well as of the chloride channel ClC-5 progressively decreased in the renal cortex of SHR from 6 to 21 wk of age. Expression of the vacuolar H⁺-ATPase B2 subunit was also reduced in the renal cortex of 21-wk-old compared with both 6- and 14-wk-old SHR. Collectively, our study suggests that enhanced urinary protein excretion, especially of albumin, may be due, at least in part, to lower expression of key components of the apical endocytic apparatus in the renal proximal tubule. Finally, one may speculate that dysfunction of the apical endocytic pathway in the renal proximal tubule may contribute to the development of microalbuminuria in essential hypertension.

Anti-angiogenic and anti-metastatic activity of synthetic phosphoethanolamine

BACKGROUND

Renal cell carcinoma (RCC) is the most common type of kidney cancer, and represents the third most common urological malignancy. Despite the advent of targeted therapies for RCC and the improvement of the lifespan of patients, its cost-effectiveness restricted the therapeutic efficacy. In a recent report, we showed that synthetic phosphoethanolamine (Pho-s) has a broad antitumor activity on a variety of tumor cells and showed potent inhibitor effects on tumor progress in vivo.

METHODOLOGY/PRINCIPAL FINDINGS

We show that murine renal carcinoma (Renca) is more sensitive to Pho-s when compared to normal immortalized rat proximal tubule cells (IRPTC) and human umbilical vein endothelial cells (HUVEC). In vitro anti-angiogenic activity assays show that Pho-s inhibits endothelial cell proliferation, migration and tube formation. In addition, Pho-s has anti-proliferative effects on HUVEC by inducing a cell cycle arrest at the G2/M phase. It causes a decrease in cyclin D1 mRNA, VEGFR1 gene transcription and VEGFR1 receptor expression. Pho-s also induces nuclear fragmentation and affects the organization of the cytoskeleton through the disruption of actin filaments. Additionally, Pho-s induces apoptosis through the mitochondrial pathway. The putative therapeutic potential of Pho-s was validated in a renal carcinoma model, on which our remarkable in vivo results show that Pho-s potentially inhibits lung metastasis in nude mice, with a superior efficacy when compared to Sunitinib.

CONCLUSIONS/SIGNIFICANCE

Taken together, our findings provide evidence that Pho-s is a compound that potently inhibits lung metastasis, suggesting that it is a promising novel candidate drug for future developments.

Proteoglycan synthesis and Golgi organization in polarized epithelial cells

A large number of complex glycosylation mechanisms take place in the Golgi apparatus. In epithelial cells, glycosylated protein molecules are transported to both the apical and the basolateral surface domains. Although the prevailing view is that the Golgi apparatus provides the same lumenal environment for glycosylation of apical and basolateral cargo proteins, there are indications that proteoglycans destined for the two opposite epithelial surfaces are exposed to different conditions in transit through the Golgi apparatus. We will here review data relating proteoglycan and glycoprotein synthesis to characteristics of the apical and basolateral secretory pathways in epithelial cells.

Natriuresis and diuretic hormone synergism in R. prolixus upper Malpighian tubules is inhibited by the anti-diuretic hormone, RhoprCAPA-α2

Insects contain an array of hormones that coordinate the actions of the excretory system to achieve osmotic and ionic balance. In the hematophagous insect, Rhodnius prolixus, two diuretic hormones have been identified, serotonin (5HT) and a corticotropin releasing factor-related peptide (RhoprDH), and both lead to an increase in fluid secretion by Malpighian tubules (MTs). However, only 5HT activates reabsorption by the lower MTs to recover K(+) and Cl(-). An anti-diuretic hormone (RhoprCAPA-α2) is believed to coordinate the cessation of the rapid diuresis following blood meal engorgement. However, the role of RhoprCAPA-α2 on fluid secretion by MTs stimulated by RhoprDH was previously unknown. Here we demonstrate that, unlike the inhibitory effect on 5HT-stimulated secretion by MTs, RhoprCAPA-α2 does not inhibit secretion stimulated by RhoprDH although it does abolish the synergism that occurs between the two diuretic hormones. In addition, we show that the natriuresis elicited by either diuretic hormone is reduced by RhoprCAPA-α2. Using electrophysiological tools, we investigate the possible mechanism by which this complex regulatory pathway is achieved. Analysis of the pH of secreted fluid as well as the triphasic response in transepithelial potential in MTs treated with diuretic hormones, suggests that RhoprCAPA-α2 does not inhibit the V-type H(+) ATPase. Taken together, these results indicate that RhoprCAPA-α2 functions to reduce the rapid diuresis following blood feeding, and in addition, it inhibits the natriuresis associated with diuretic hormone stimulated MTs. This may reflect an important regulatory mechanism related to the slow diuresis that occurs as the K(+)-rich blood cells are digested.

A new regulator of the vacuolar H(+)-ATPase in the kidney

Xu et al. identify Slc26a11, a novel member of the Slc26 anion exchanger family, as an electrogenic (Cl(-))(n)/HCO(3)(-) exchanger. Functional characterization of this transporter suggests that Slc26a11 mediates classical electroneutral Cl(-)/HCO(3)(-) exchange but also exhibits an electrogenic Cl(-) conductance. In the kidney, Slc26a11 colocalizes with the vacuolar H(+)-ATPase in intercalated cells, emphasizing the cooperation of the proton pump with chloride transporters.