Influence of glioma tumour microenvironment on the transport of ANG1005 via low-density lipoprotein receptor-related protein 1.

BACKGROUND: ANG1005 consists of three molecules of paclitaxel conjugated via ester bonds to the 19-amino-acid peptide Angiopep-2. The new chemical agent has been shown to cross the blood-brain barrier (BBB) by receptor-mediated transcytosis via low-density lipoprotein receptor-related protein 1 (LRP1). The experiments here examined the role of LRP1 in the subsequent endocytosis of drug into cancer cells. METHODS: Localisation of ANG1005 and Angiopep-2 was examined by immunohistochemistry and in-vivo near-infrared fluorescence imaging in mice carrying orthotopic glioma tumours. Transport of ANG1005 and Angiopep-2 was examined in U87 glioblastoma cell lines. RESULTS: Systemically administered ANG1005 and Cy5.5Angiopep-2 localised to orthotopic glioma tumours in mice. The glioma transplants correlated with high expression levels of LRP1. Decreasing LRP1 activity, by RNA silencing or LRP1 competitors, decreased uptake of ANG1005 and Angiopep-2 into U87 glioblastoma cells. Conversely, LRP1 expression and endocytosis rates for ANG1005 and Angiopep-2 increased in U87 cells under conditions that mimicked the microenvironment near aggressive tumours, that is, hypoxic and acidic conditions. CONCLUSION: ANG1005 might be a particularly effective chemotherapeutic agent for the wide array of known LRP1-expressing brain and non-brain cancers, in particular those with an aggressive phenotype.

Antitumour activity of ANG1005, a conjugate between paclitaxel and the new brain delivery vector Angiopep-2.

BACKGROUND AND PURPOSE: Paclitaxel is highly efficacious in the treatment of breast, head and neck, non-small cell lung cancers and ovarian carcinoma. For malignant gliomas, paclitaxel is prevented from reaching its target by the presence of the efflux pump P-glycoprotein (P-gp) at the blood-brain barrier. We investigated the utilization of a new drug delivery system to increase brain delivery of paclitaxel. EXPERIMENTAL APPROACH: Paclitaxel molecules were conjugated to a brain peptide vector, Angiopep-2, to provide a paclitaxel-Angiopep-2 conjugate named ANG1005. We determined the brain uptake capacity, intracellular effects and antitumour properties of ANG1005 in vitro against human tumour cell lines and in vivo in human xenografts. We then determined ANG1005 activity on brain tumours with intracerebral human tumour models in nude mice. KEY RESULTS: We show by in situ brain perfusion that ANG1005 enters the brain to a greater extent than paclitaxel and bypasses the P-gp. ANG1005 has an antineoplastic potency similar to that of paclitaxel against human cancer cell lines. We also demonstrate that ANG1005 caused a more potent inhibition of human tumour xenografts than paclitaxel. Finally, ANG1005 administration led to a significant increase in the survival of mice with intracerebral implantation of U87 MG glioblastoma cells or NCI-H460 lung carcinoma cells. CONCLUSIONS AND IMPLICATIONS: These results demonstrate the antitumour potential of a new drug, ANG1005, and establish that conjugation of anticancer agents with the Angiopep-2 peptide vector could increase their efficacy in the treatment of brain cancer.

Stimulation of tPA-dependent provisional extracellular fibrin matrix degradation by human recombinant soluble melanotransferrin.

Tissue-type plasminogen activator (tPA) and its substrate plasminogen (Plg) are key components in the fibrinolytic system. We have recently demonstrated, that truncated human recombinant soluble melanotransferrin (sMTf) could stimulate the activation of Plg by urokinase plasminogen activator and inhibit angiogenesis. Since various angiogenesis inhibitors were shown to stimulate tPA-mediated plasminogen activation, we examined the effects of sMTf on tPA-dependent fibrinolysis. This study demonstrated that sMTf enhanced tPA-activation of Plg by 6-fold. sMTf also increased the release of [125I]-fibrin fragments by tPA-activated plasmin. Moreover, we observed that the interaction of sMTf with Plg provoked a change in the fibrin clot structure by cleaving the fibrin alpha and beta chains. Overall, the present study shows that sMTf modulates tPA-dependent fibrinolysis by modifying the clot structure. These results also suggest that sMTf properties could involve enhanced dissolution of the provisional extracellular fibrin matrix.

Activation of the extracellular signal-regulated protein kinase (ERK) cascade by membrane-type-1 matrix metalloproteinase (MT1-MMP).

The mechanisms underlying membrane-type-1 matrix metalloproteinase (MT1-MMP)-dependent induction of cell migration were investigated. Overexpression of MT1-MMP induced a marked increase in cell migration, this increase being dependent on the presence of the cytoplasmic domain of the protein. MT1-MMP-dependent migration was inhibited by a mitogen-activated protein kinase kinase 1 inhibitor, suggesting the involvement of the extracellular signal-regulated protein kinase (ERK) cascade in the induction of migration. Accordingly, MT1-MMP overexpression induced the activation of ERK, this process being also dependent on the presence of its cytoplasmic domain. MT1-MMP-induced activation of both migration and ERK required the catalytic activity of the enzyme as well as attachment of the cells to matrix proteins. The MT1-MMP-dependent activation of ERK was correlated with the activation of transcription through the serum response element, whereas other promoters were unaffected. Taken together, these results indicate that MT1-MMP trigger important changes in cellular signal transduction events, leading to cell migration and to gene transcription, and that these signals possibly originate from the cytoplasmic domain of the protein.

Calmodulin inhibitors trigger the proteolytic processing of membrane type-1 matrix metalloproteinase, but not its shedding in glioblastoma cells.

Most transmembrane proteins are subjected to limited proteolysis by cellular proteases, and stimulation of cleavage of membrane proteins by calmodulin (CaM) inhibitors was recently shown. The present study investigated the ability of several CaM inhibitors to induce the proteolytic cleavage of the membrane type-1 matrix metalloproteinase (MT1-MMP) from the cell surface of highly invasive U-87 glioblastoma cells. Although no shedding of a soluble MT1-MMP form was induced by CaM inhibitors in the conditioned media, we showed that these inhibitors induced MT1-MMP proteolytic processing to the 43 kDa membrane-bound inactive form that was not correlated with an increase in proMMP-2 activation but rather with an increase in tissue inhibitor of MMPs (TIMP)-2 expression levels. Moreover, this proteolytic processing was sensitive to marimastat suggesting the involvement of MMPs. Interestingly, CaM inhibitors antagonized concanavalin A- and cytochalasin D-induced proMMP-2 activation, and affected the cytoskeletal actin organization resulting in the loss of migratory potential of U-87 glioblastoma cells. Cytoplasmic tail-truncated MT1-MMP constructs expressed in COS-7 cells were also affected by CaM inhibitors suggesting that these inhibitors stimulated MT1-MMP proteolytic processing by mechanisms independent of the CaM-substrate interaction. We also propose that TIMP-2 acts as a negative regulator of MT1-MMP-dependent activities promoted by the action of CaM inhibitors in U-87 glioblastoma cells.

RhoB expression is induced after the transient upregulation of RhoA and Cdc42 during neuronal differentiation and influenced by culture substratum and microtubule integrity.

RhoGTPases are important intracellular signalling switches in the regulation of cytoskeleton organization. They likely have an important role in ontogenesis because cytoskeletal rearrangements accompany cell differentiation and specialization. Western blotting showed that protein expression of RhoA, RhoB and Cdc42 RhoGTPases dramatically increased, in a programmed manner, during neuronal differentiation of P19 mouse embryonal carcinoma cells with retinoic acid. RhoA and Cdc42 expression were sequentially upregulated and peaked during the commitment period while that of RhoB was induced in post-mitotic neurons. Although RhoB had a higher expression on matrices allowing cell spreading and neurite elongation, it was distributed throughout cell volume by immunocytofluorescence and associated with various cell compartments by centrifugal subfractionation, suggesting a role not restricted at neurites at this stage of differentiation. RhoA and Cdc42 were mainly cytosolic and RhoB particulate in the P19 cell model. Treatment of cells with cytoskeleton disruptors showed that poisons of microtubules but not of actin filaments or neurofilaments increased the cytosolic level of RhoB. The results indicate that RhoA, Cdc42 and RhoB must intervene at specific stages of neuronal development and there exists a relationship between RhoB expression/distribution, the microtubule network and the extracellular matrix during this process.

Glycosphingolipids modulate renal phosphate transport in potassium deficiency.

BACKGROUND: Potassium (K) deficiency (KD) and/or hypokalemia have been associated with disturbances of phosphate metabolism. The purpose of the present study was to determine the cellular mechanisms that mediate the impairment of renal proximal tubular Na/Pi cotransport in a model of K deficiency in the rat. METHODS: K deficiency in the rat was achieved by feeding rats a K-deficient diet for seven days, which resulted in a marked decrease in serum and tissue K content. RESULTS: K deficiency resulted in a marked increase in urinary Pi excretion and a decrease in the V(max) of brush-border membrane (BBM) Na/Pi cotransport activity (1943 +/- 95 in control vs. 1184 +/- 99 pmol/5 sec/mg BBM protein in K deficiency, P < 0.02). Surprisingly, the decrease in Na/Pi cotransport activity was associated with increases in the abundance of type I (NaPi-1), and type II (NaPi-2) and type III (Glvr-1) Na/Pi protein. The decrease in Na/Pi transport was associated with significant alterations in BBM lipid composition, including increases in sphingomyelin, glucosylceramide, and ganglioside GM3 content and a decrease in BBM lipid fluidity. Inhibition of glucosylceramide synthesis resulted in increases in BBM Na/Pi cotransport activity in control and K-deficient rats. The resultant Na/Pi cotransport activity in K-deficient rats was the same as in control rats (1148 +/- 52 in control + PDMP vs. 1152 +/- 61 pmol/5 sec/mg BBM protein in K deficiency + PDMP). These changes in transport activity occurred independent of further changes in BBM NaPi-2 protein or renal cortical NaPi-2 mRNA abundance. CONCLUSION: K deficiency in the rat causes inhibition of renal Na/Pi cotransport activity by post-translational mechanisms that are mediated in part through alterations in glucosylceramide content and membrane lipid dynamics.

Permeability of the peptidic GH secretagogues hexarelin and EP 51389, across rat jejunum.

The intestinal permeability of hexarelin and EP 51389, two growth hormone releasing hexa- and tri- peptide analogues, was assessed in vitro with side-by-side diffusion chambers in the apical-to-basolateral (AP-to-BL) and in the basolateral-to-apical (BL-to-AP) direction using excised rat jejunal segments. The effect of EP 51389 on P-glycoprotein (P-gp) was evaluated by rhodamine 123 accumulation on monolayers of CH(R)C5 cells with increasing concentrations of EP 51389. Hexarelin and EP 51389 permeability were found to be < 1%. Permeability coefficients (P(app)) were 18.87 +/- 2.86 (x10(-7) cm/s) and 5.87 +/- 0.45 (x10(-7) cm/s) for hexarelin and EP 51389, respectively. Bidirectional studies revealed that hexarelin transport was similar in both directions. EDTA did not influence hexarelin permeability. Permeability was predominantly secretory for EP 51389 as P(app) in the BL-to-AP direction [32.56 +/- 6.11 (x10(-7) cm/s)] was greater than AP-to-BL. Confirming involvement of a secretory transport system, chlorpromazine inhibited EP 51389 transport across the jejunum. EP 51389 inhibited P-gp in a dose dependent manner resulting in the intracellular accumulation of rhodamine in CH(R)C5 cells. These results suggest that: 1) the intestinal permeability of hexarelin and EP 51389 is poor; 2) the passage of hexarelin is mainly via a transcellular passive pathway since the contribution of paracellular permeability to the overall permeability is rather low; 3) P-gp may act as a potential barrier for the intestinal absorption of EP 51389.

Expression of multidrug-resistance P-glycoprotein (MDR1) in human brain tumors.

Multidrug resistance (MDR) is associated with the expression of P-glycoprotein (P-gp), an ATP-dependent transporter which expels anti-cancer drugs from cells. In the present study, MDR1 P-gp was immunodetected by Western blot analysis in 60 human brain tumors, including meningiomas, schwannomas, low-grade gliomas (astrocytomas, pilocytic astrocytomas) and high-grade gliomas (anaplastic astrocytomas, glioblastomas and anaplastic oligodendrogliomas). Most samples from primary tumors expressed P-gp at the same levels as normal brain tissue except for schwannomas, in which levels were reduced by 65%, and meningiomas, in which levels were more than 10-fold higher in 7 of 10 samples. P-gp levels were 70% and 95% lower in brain metastases from melanomas and lung adenocarcinomas, respectively, than in normal brain tissue. These results indicate that the majority of primary brain tumors express MDR1 P-gp and that its high expression levels in meningiomas may be a marker for this type of brain tumor.

Effect of ischemia-reperfusion on the renal brush-border membrane sodium-dependent phosphate cotransporter NaPi-2.

To understand the mechanisms underlying ischemia-reperfusion-induced renal proximal tubule damage, we analyzed the expression of the Na+-dependent phosphate (Na+/Pi) cotransporter NaPi-2 in brush border membranes (BBM) isolated from rats which had been subjected to 30 min renal ischemia and 60 min reperfusion. Na+/Pi cotransport activities of the BBM vesicles were also determined. Ischemia caused a significant decrease (about 40%, P < 0.05) in all forms of NaPi-2 in the BBM, despite a significant increase (31+/-3%, P < 0.05) in the Na+/Pi cotransport activity. After reperfusion, both NaPi-2 expression and Na+/Pi cotransport activity returned to control levels. In contrast with Na+/Pi cotransport, ischemia significantly decreased Na+-dependent glucose cotransport but did not affect Na+-dependent proline cotransport. Reperfusion caused further decreases in both Na+/glucose (by 60%) and Na+/proline (by 33%) cotransport. Levels of NaPi-2 were more reduced in the BBM than in cortex homogenates, suggesting a relocalization of NaPi-2 as a result of ischemia. After reperfusion, NaPi-2 levels returned to control values in both BBM and homogenates. These data indicate that the NaPi-2 protein and BBM Na+/Pi cotransport activity respond uniquely to reversible renal ischemia and reperfusion, and thus may play an important role in maintaining and restoring the structure and function of the proximal tubule.

Matrix proteinase inhibition by AE-941, a multifunctional antiangiogenic compound.

BACKGROUND: Matrix metalloproteinases (MMPs) play an important role in tissue remodeling under normal physiological and pathological conditions and are thus attractive targets for both diagnostic and therapeutic purposes. Here, we examined the effect of AE-941, an orally bioavailable standardized extract made of cartilage that shows significant antiangiogenic and antimetastatic properties in vivo, on the activity of various members of the MMP family. MATERIALS AND METHODS: The effect of AE-941 on the activity of MMPs was assessed by fluorimetric assays and by substrate gel zymography. RESULTS: AE-941 markedly inhibits the gelatinolytic activity of MMP-2 and to a lesser extent those of MMP-1, MMP-7, MMP-9 and MMP-13. AE-941 also inhibited the elastinolytic activities of MMP-2 and MMP-9 as well as MMP-12 (metalloelastase), porcine pancreatic elastase (PPE), and human leukocyte elastase (HLE). Western blot analysis revealed the presence within AE-941 of immunoreactive TIMP-like proteins, suggesting that these proteins may be at least partly responsible for the observed MMP inhibition. CONCLUSIONS: Taken together, these results demonstrate that AE-941 contains TIMP-like proteins that could be responsible for the specific inhibition of MMPs. Given the recent studies suggesting the presence within this compound of specific inhibitor(s) of endothelial cell proliferation, AE-941 appears as a pleotropic agent able to interfere with several biochemical steps leading to angiogenesis and to other physiopathological conditions. Since AE-941 is currently under Phase III clinical investigations, these findings are also of considerable importance for our understanding of its anticancer properties.

Isolation of endothelial cells from brain, lung, and kidney: expression of the multidrug resistance P-glycoprotein isoforms.

Endothelial cells (EC) were isolated from brain, lung, and renal cortex using magnetic microbeads cross-linked to an antibody directed against the platelet-endothelial cell adhesion molecule-1 (PECAM-1). Levels of endothelial nitric oxide synthase (eNOS) and PECAM-1 were measured by Western blots and both were enriched in the positively selected EC fractions. The multidrug resistance P-glycoprotein (P-gp) was strongly enriched (59-fold) in the EC fraction from brain and was absent in the negative fraction, in which the glial fibrillary acidic protein (GFAP), an astrocyte marker, was present. Lower P-gp levels were detected in EC from renal cortex and lung. Reverse transcription-polymerase chain reaction analysis showed that the mdr1a gene was preferentially expressed in EC fraction from the brain. The mdr1b gene was found in EC from renal cortex whereas both mdr1 genes were detected in EC from lung. Our results indicate that EC can be isolated using microbeads and that the isoform of P-gp found in brain is mostly mdr1a, associated with EC.

Localization of membrane-type 1 matrix metalloproteinase in caveolae membrane domains.

Membrane-type 1 matrix metalloproteinase (MT1-MMP) is a membrane-associated MMP that has been recently reported to have a central role in tumour cell invasion. Here we report that both the native and overexpressed recombinant forms of MT1-MMP are highly enriched in low-density Triton X-100-insoluble membrane domains that contain the caveolar marker protein caveolin 1. Moreover, the MT1-MMP-dependent activation of proMMP-2 induced by concanavalin A and cytochalasin D was correlated with the processing of MT1-MMP to its proteolytically inactive 43 kDa fragment in U-87 glioblastoma and HT-1080 fibrosarcoma tumour cell lines; this processing was also preferentially observed within the caveolar fraction. Interestingly, whereas the expression of caveolin 1 had no effect on the MT1-MMP-dependent activation of proMMP-2, its co-expression with MT1-MMP antagonized the MT1-MMP-increased migratory potential of COS-7 cells. Taken together, our results provide evidence that MT1-MMP is preferentially compartmentalized and proteolytically processed in caveolae of cancer cells. The inhibition of MT1-MMP-dependent cell migration by caveolin 1 also suggests that the localization of MT1-MMP to caveolin-enriched domains might have an important function in the control of its enzymic activity.

AE-941 (Neovastat): a novel multifunctional antiangiogenic compound.

AE-941 (Neovastat) is a naturally occurring product extracted from cartilage and has antiangiogenic properties. It has reached Phase III clinical trial evaluation for the treatment of solid tumors (non-small cell lung cancer and renal cell carcinoma) and a pivotal Phase II clinical trial in multiple myeloma is ongoing. AE-941 inhibits several steps of the angiogenesis process, including matrix metalloproteinase activities and VEGF signaling pathways. Moreover, AE-941 induces endothelial cell apoptosis and tissue-type plasminogen activator activity, thus suggesting that it is a multifunctional antiangiogenic drug. Results from Phase I/II clinical trials indicate that AE-941, given orally, is well tolerated. Moreover, the median survival time in patients with renal cell carcinoma and non-small cell lung cancer was significantly longer in patients receiving high doses of AE-941 compared to low doses.

Multidrug resistance in brain tumors: roles of the blood-brain barrier.

Malignant brain tumors and brain metastases present a formidable clinical challenge against which no significant advances have been made over the last decade. Multidrug resistance (MDR) is one of the main factors in the failure of chemotherapy against central nervous system tumors. The MDR1 gene encoding P-glycoprotein (P-gp), a drug efflux pump which plays a significant role in modulating MDR in a wide variety of human cancers, is highly expressed in the blood-brain barrier (BBB). The BBB controls central nervous system exposure to many endogenous and exogenous substances. The exact molecular mechanisms by which the BBB is involved in the resistance of brain tumors to chemotherapy remain to be identified. The purpose of this review is to summarize reports demonstrating that P-gp, one of the most phenotypically important markers of the BBB, is present in primary brain tumors and thus plays a crucial role in their clinical resistance to chemotherapy.

Rapid activation of matrix metalloproteinase-2 by glioma cells occurs through a posttranslational MT1-MMP-dependent mechanism.

Matrix metalloproteinase-2 (MMP-2) has been suggested to play a crucial role in tumor invasion and angiogenesis. In order to understand the mechanisms underlying proMMP-2 activation, we compared the biochemical and cellular events triggered by two potent MMP-2 activators, the lectin concanavalin A (ConA) and the cytoskeleton disrupting agent cytochalasin D (CytoD). Incubation of U87 human glioma cells for 24 h in the presence of ConA or CytoD induced a marked activation of proMMP-2 and this activation was correlated in both cases with an increase in the mRNA levels of MT1-MMP. At the protein level, proMMP-2 activation induced by CytoD or ConA strongly correlated with the appearance of a 43-kDa MT1-MMP proteolytic breakdown product in cell lysates. Interestingly, CytoD also induced a very rapid (2 h) activation of proMMP-2 that was independent of protein synthesis. Under these conditions, CytoD also promoted the rapid proteolytic breakdown of the 63 kDa pro form of MT1-MMP, resulting in the appearance of the 43 kDa MT1-MMP processed form. Overexpression of a recombinant full-length MT1-MMP protein in glioma cells resulted in the activation of proMMP-2 that was correlated with the generation of the 43 kDa fragment of the protein. By contrast, overexpression of the protein in COS-7 cells promoted proMMP-2 activation without inducing the production of the 43 kDa fragment. These results thus suggest that activation of proMMP-2 occurs through both translational and post-translational mechanisms, both involving proteolytic processing of membrane-associated MT1-MMP. This processing of MT1-MMP is, however, not essential to proMMP-2 activation but may represent a regulatory mechanism to control the activity of MT1-MMP.

Tyrosine phosphorylation of the vascular endothelial-growth-factor receptor-2 (VEGFR-2) is modulated by Rho proteins.

The effects of Rho-specific modifying toxins on the tyrosine phosphorylation of endothelial cell proteins were investigated. Incubation of the cells with the Rho-activating toxin cytotoxic necrotizing factor 1 (CNF1) induced a marked increase in the tyrosine phosphorylation of a number of signalling intermediates of the vascular endothelial growth factor (VEGF)-mediated cascade, including focal adhesion kinase, paxillin, phospholipase Cgamma1 and a Shc-associated protein of 195 kDa. Both CNF1- and VEGF-dependent tyrosine phosphorylation of these proteins were significantly reduced by prior incubation with C3 transferase, a known inhibitor of RhoA function, suggesting a Rho-dependent mechanism. The stimulation of endothelial cells with CNF1 resulted in a marked increase in the tyrosine phosphorylation of the VEGF receptor (VEGFR)-2, which was correlated with a stimulation of its kinase activity and with its association with downstream tyrosine phosphorylated proteins. The stimulatory effect of CNF1 was specific for VEGFR-2 since the phosphotyrosine content of VEGFR-1 was not affected by the toxin. Transient overexpression of a dominant-active RhoA mutant also induced an increase in the tyrosine phosphorylation of the VEGFR-2, whereas overexpression of a dominant-inactive form of the protein was without effect. Taken together, these results indicate that Rho proteins may play an important role in angiogenesis by modulating the tyrosine phosphorylation levels of VEGFR-2.

Modulation of Rho and cytoskeletal protein attachment to membranes by a prenylcysteine analog.

The GTPases Rho regulate the assembly of polymerized actin structures. Their C-terminal sequences end with the CAAX motif that undergo a lipidation of the cysteine residue. Analogs to the C-terminal ends of Rho proteins, N-acetyl-S-all-trans, trans-farnesyl-L-cysteine and N-acetyl-S-all-trans-geranylgeranyl-L-cysteine, wereused to analyze the role of prenylation in their membrane association. Silver-stained gels indicated that N-acetyl-S-all-trans-geranylgeranyl-L-cysteine treatment released only a few proteins of 20, 46, and 60 kDa. Western blot analysis showed that N-acetyl-S-all-trans-geranylgeranyl-L-cysteine released RhoB (10%), RhoA (28%), and Cdc42 (95%) from membranes, whereas N-acetyl-S-all-trans and trans-farnesyl-L-cysteine did not. Rab1, which possesses two geranylgeranyl groups, was also strongly extracted by N-acetyl-S-all-trans-geranylgeranyl-L-cysteine, whereas Ras, which is farnesylated, was not. Furthermore, N-acetyl-S-all-trans-geranylgeranyl-L-cysteine was very efficient (95%) in dissociating actin and tubulin from membranes but not integral membrane protein P-glycoprotein and sodium/phosphate cotransporter NaP(i)-2. The extraction of Rho and cytoskeletal proteins occurred below the critical micellar concentration of N-acetyl-S-all-trans-geranylgeranyl-L-cysteine. Membrane treatments with 0.7 m KI totally extracted actin, whereas 70% of Cdc42 was released. Actin was, however, insoluble in Triton X-100-treated membranes, whereas this detergent extracted (80%) Cdc42. These data show that Rho proteins and actin are not physically bound together and suggest that their extraction from membranes by N-acetyl-S-all-trans-geranylgeranyl-L-cysteine likely occurs via different mechanisms.

Association of cyclophilin A with renal brush border membranes: redistribution by cyclosporine A.

BACKGROUND: Administration of the immunosuppressive agent cyclosporine A (CsA) is associated with nephrotoxicity. The main target for CsA, cyclophilin A (CypA), was found in high levels in epithelial cells of renal proximal tubules. In the present study, CypA was immunodetected and characterized following CsA treatment in subcellular fractions of renal cortex. METHOD: The renal content and distribution of CypA was evaluated in untreated rats and in rats treated with a subcutaneous injection of CsA (10 mg. kg-1. day-1) for 10 days. RESULTS: In untreated rats, membrane-bound CypA represents 0.25% of total brush border membrane (BBM) proteins, similar to the proportion found in the soluble fraction. High ionic strength treatment was unable to extract CypA from BBMs, whereas alkaline treatment (Na2CO2, pH 11) and detergent 3 - [(3 - cholamidopropyl) - dimethyl - ammonio] - 1 - propanesulfate (CHAPS) released it from BBMs. These results indicate that CypA is associated with renal BBMs, and that hydrophobic interactions are involved in this association. The CypA distribution was strongly modified in both BBMs and the soluble fraction after CsA treatment, but its affinity for CsA estimated by photoaffinity labeling was unaffected. The CypA expression level decreased by 45% in BBMs, while it increased by 33% in the soluble fraction, compared with control rats. CypA remained associated with the membranes following in vitro incubation of renal BBMs with CsA. However, incubation of CypA with one of its substrates released CypA from renal BBMs. CONCLUSIONS: These experiments suggest that renal BBMs contain a significant amount of CypA and chronic exposure to CsA, and acute exposure to one of CypA substrates may modify its subcellular distribution.