Biomedical subjects

L Nitsch

Publications and source records attributed to L Nitsch.

At least 19 recordsLinked to original sources

PubMed2006

Bovine papillomavirus E5 oncoprotein binds to the activated form of the platelet-derived growth factor beta receptor in naturally occurring bovine urinary bladder tumours.

Studies regarding the functions of the bovine papillomavirus (BPV) E5 oncoprotein in vivo are lacking and no E5-mediated mechanism underlying epithelial carcinogenesis is known. We have shown that BPV-2 DNA is present in the majority of naturally occurring urinary bladder tumours of cattle and that E5 is expressed in the cancer cells. Here we show that the interaction between the platelet-derived growth factor (PDGF) beta receptor and BPV E5, described in vitro in cultured cells, takes place in vivo in bovine urinary bladder cancers. In these cancers, E5 and PDGF beta receptor colocalize, as shown by confocal microscopy, and physically interact, as shown by coimmunoprecipitation. Furthermore, the PDGF beta receptor associated with E5 is highly phosphorylated, suggesting the functional activation of the receptor upon E5 interaction. Our results demonstrate, for the first time, that E5-PDGF beta receptor interaction occurs during the natural history of bovine urinary bladder tumours, suggesting an important role for E5 in carcinogenesis. Finally, the system provides a suitable animal model of papillomavirus-associated cancer to test therapeutic vaccination against E5. Successful bladder tumour regression would provide a valuable model for therapeutic vaccination against papillomavirus-associated tumours.

Adenocarcinoma↗

PubMed2004

Mild Wolf-Hirschhorn phenotype and partial GH deficiency in a patient with a 4p terminal deletion.

Wolf-Hirschhorn syndrome (WHS) is caused by a variably-sized deletion of chromosome 4 involving band 4p16 whose typical craniofacial features are "Greek warrior helmet appearance" of the nose, microcephaly, and prominent glabella. Almost all patients show mental retardation and pre- and post-natal growth delay. Patient was born at term, after a pregnancy characterized by intra-uterine growth retardation (IUGR). Delivery was uneventful. Developmental delay was evident since the first months of life. At 2 years, he developed generalized tonic-clonic seizures. Because of short stature, low growth velocity and delayed bone age, at 4 years he underwent growth hormone (GH) evaluation. Peak GH after two provocative tests revealed a partial GH deficiency. Clinical observation at 7 years disclosed a distinctive facial appearance, with microcephaly, prominent eyes, and beaked nose. Brain MRI showed left temporal mesial sclerosis. GTG banded karyotype was normal. Because of mental retardation, subtelomeric fluorescence in situ hybridization (FISH) analysis was performed, disclosing a relatively large deletion involving 4p16.2 --> pter (about 4.5 Mb), in the proband, not present in the parents. The smallest deletion detected in a WHS patient thus far includes two candidate genes, WHSC1 and WHSC2. Interestingly, that patient did not show shortness of stature, and that could be due to the haploinsufficiency of other genes localized in the flanking regions. Contribution of GH alterations and possible GH therapy should be further considered in WHS patients.

Abnormalities, Multiple↗

PubMed2002

Hormonal control of the transcription factor Pax8 and its role in the regulation of thyroglobulin gene expression in thyroid cells.

The transcription factor Pax8 plays an important role in the expression of the differentiated phenotype of thyroid follicular cells. It has recently been shown that Pax8 is necessary for thyroglobulin (Tg) gene expression in the fully differentiated rat thyroid cell line PC. We have used the PC model system to investigate the role of Pax8 as a mediator of TSH regulation of Tg gene expression. We have demonstrated that Pax8 expression, as well as Tg expression, is severely reduced in cells grown in the absence of hormones and serum. The re-addition of TSH or forskolin to the culture medium is able to restore to wild-type levels the expression of both Pax8 and Tg. We have determined that the action of TSH/forskolin on Pax8 is at the transcriptional level. However, the re-expression of Pax8 can be observed several hours before that of Tg, suggesting that either another factor is needed or that Pax8 itself must be post-translationally modified by a newly synthesized protein to become active. To distinguish between these two possibilities we have stably transfected into PC cells an exogenous Pax8 that is expressed independently of TSH. Our results indicate that in these cells the Tg promoter is still dependent on TSH despite the constitutive presence of Pax8. Furthermore, we also show that in this condition Tg gene transcription requires de novo protein synthesis. In conclusion, TSH regulates the expression of Pax8 at a transcriptional level and also regulates the activity of Pax8 by controlling the expression of one or more as yet unknown factors.

Animals↗

PubMed2000

Abrogation of nerve growth factor-induced terminal differentiation by ret oncogene involves perturbation of nuclear translocation of ERK.

Oncogenic variants of the receptor tyrosine kinase, Ret, cause formation of tumors of neuroendocrine derivation in the multiple endocrine neoplasia type 2 and, thus, likely interfere with antiproliferative and/or differentiative extracellular signals. Here we took advantage of two rat pheochromocytoma-derived cell lines (PC12/MEN2A and PC12/MEN2B) to investigate whether Ret-induced nerve growth factor (NGF) unresponsiveness might involve impairment of ERK signaling. In fact, these cells, stably transfected with distinct forms of the active ret oncogene, fail to block proliferation, even upon NGF stimulation. In these cells we show the presence of both chronic ERKs activity and high expression levels of MKP-3, an ERK-specific phosphatase. Despite the presence of MKP-3, ERK activity can be further stimulated by NGF, but it fails to translocate into the nucleus and consequently to induce immediate-early gene transcription. Because of the presence of MKP-3, our results suggest the existence of a negative regulatory feedback acting on ERKs as a mechanism responsible for the abrogation of NGF-induced terminal differentiation. Indeed, MKP-3 seems to be implicated in the persistence of ERKs in cell cytoplasm. This interpretation is further supported by the observation that in ret-transfected cells, forced expression of an active form of MEK-1 may overcome this block; it restores transcription from the c-fos promoter, induces translocation of ERKs into the nucleus, and inhibits cell proliferation.

Animals↗

PubMed2000

Detergent insoluble microdomains are not involved in transcytosis of polymeric Ig receptor in FRT and MDCK cells.

In polarized epithelial cells, sorting of proteins and lipids to the apical or basolateral domain of the plasma membrane can occur via direct or indirect (transcytotic) pathways from the trans Golgi network (TGN). The 'rafts' hypothesis postulates that the key event for direct apical sorting of some transmembrane proteins and the majority of GPI-anchored proteins depends on their association with glycosphingolipid and cholesterol enriched microdomains (rafts). However, the mechanism of indirect sorting to the apical membrane is not clear. The polyimmunoglobulin receptor (pIgR) is one of the best studied proteins that follow the transcytotic pathway. It is normally delivered from the TGN to the basolateral surface of polarized Madin-Darby Canine Kidney (MDCK) cells from where it transports dIgA or dIgM to the apical surface. We have studied the intracellular trafficking of pIgR in Fischer rat thyroid cells (FRT), and have investigated the sorting machinery involved in transcytosis of this receptor in both FRT and MDCK cells. We found that, in contrast with MDCK cells, a significant amount (approximately 30%) of pIgR reaches the apical surface by a direct pathway. Furthermore, in both cell lines it does not associate with Triton X-100 insoluble microdomains, suggesting that at least in these cells 'rafts' are not involved in basolateral to apical transcytosis.

Animals↗

PubMed2000

Echistatin inhibits pp125FAK autophosphorylation, paxillin phosphorylation and pp125FAK-paxillin interaction in fibronectin-adherent melanoma cells.

Echistatin, a snake-venom RGD-containing protein, was previously shown to disrupt cell-matrix adhesion by a mechanism that involves the reduction of pp125FAK tyrosine phosphorylation levels. The aim of this study was to establish the sequence of events downstream pp125FAK dephosphorylation that could be responsible for echistatin-induced disassembly of actin cytoskeleton and focal adhesions in fibronectin-adherent B16-BL6 melanoma cells. The results obtained show that echistatin induces a decrease of both autophosphorylation and kinase activity of pp125FAK. One hour of cell exposure to echistatin caused a 39% decrease of pp125FAK Tyr397 phosphorylation and a 31% reduction of pp125FAK autophosphorylation activity as measured by immune-complex kinase assay. Furthermore, 1 h of cell treatment by echistatin produced a 63% decrease of paxillin phosphorylation, as well as a reduction in the amount of paxillin bound to pp125FAK. Immunofluorescence analysis of echistatin treated cells showed the concomitant disappearance of both paxillin and pp125FAK from focal adhesions. The reduction of paxillin phosphorylation may represent a critical step in the pathway by which disintegrins exert their biological activity, including the inhibition of experimental metastasis in vivo.

Animals↗

PubMed2000

Analysis of cadherin/catenin complexes in transformed thyroid epithelial cells: modulation by beta 1 integrin subunit.

We have analysed the expression of cadherin/catenin complex molecules in PC C13 rat thyroid cells transformed in vitro with different oncogenes. No significant downregulation of either E-cadherin, alpha-, beta- and gamma-catenin was detected following the introduction of activated forms of myc, adenovirus E1A, ras, raf, myc + ras, E1A + raf. However, ras- and raf-transformed PC C13 cells showed altered adherens junctions. An altered distribution of cadherin/catenin complexes characterized by radially oriented membrane spikes perpendicular to cell edges was the most prominent feature evidenced by immunofluorescence. No beta1 integrin localization was observed in areas where this altered pattern of E-cadherin expression was detected. However, beta1 integrin subunit expression was detected at areas of cell-cell contact where E-cadherin showed a normal pattern of expression. Furthermore, ras- and raf-transformed PC C13 cells showed the ability to migrate in collagen gels, in contrast to their normal untransformed counterpart. Overexpression of beta1 integrin was found to restore normal E-cadherin localization at cell-cell contacts and to partially inhibit the ability to migrate in collagen gels. Finally, two cell lines obtained by ras transformation in vivo, and derived from a rat primary thyroid carcinoma (TK6) and its lung metastasis (MPTK6), were found to have lost gamma-catenin expression. TK6 lost also E-cadherin expression and membrane localization of alpha-catenin. These results suggest that: i) in vitro thyroid cell transformation is associated to a change in cadherin/catenin complexes distribution rather than to a decrease in expression; ii) in vivo transformation is associated to the loss of expression of some of these molecules likely due to tumor progression; iii) alterations in beta1 integrin subunit expression can result in changes in cadherin/catenin function thus implying that an integrin-cadherin synergy may exist in thyroid cells.

Adenovirus E1A Proteins↗

PubMed2000

Detergent-insoluble GPI-anchored proteins are apically sorted in fischer rat thyroid cells, but interference with cholesterol or sphingolipids differentially affects detergent insolubility and apical sorting.

In contrast to Madin-Darby canine kidney cells, Fischer rat thyroid cells deliver the majority of endogenous glycosylphosphatidyl inositol (GPI)-anchored proteins to the basolateral surface. However, we report here that the GPI proteins Placental Alkaline Phosphatase (PLAP) and Neurotrophin Receptor-Placental Alkaline Phosphatase (NTR-PLAP) are apically localized in transfected Fischer rat thyroid cells. In agreement with the "raft hypothesis," which postulates the incorporation of GPI proteins into glycosphingolipids and cholesterol-enriched rafts, we found that both of these proteins were insoluble in Triton X-100 and floated into the lighter fractions of sucrose density gradients. However, disruption of lipid rafts by removal of cholesterol did not cause surface missorting of PLAP and NTR-PLAP, and the altered surface sorting of these proteins after Fumonisin B1 treatment did not correlate with reduced levels in Triton X-100 -insoluble fractions. Furthermore, in contrast to the GPI-anchored forms of both of these proteins, the secretory and transmembrane forms (in the absence of a basolateral cytoplasmic signal) were sorted to the apical surface without association with lipid microdomains. Together, these data demonstrate that the GPI anchor is required to mediate raft association but is not sufficient to determine apical sorting. They also suggest that signals present in the ectodomain of the proteins play a major role and that lipid rafts may facilitate the recognition of these signals in the trans-Golgi network, even though they are not required for apical sorting.

Animals↗

PubMed1999

Mechanisms of apical protein sorting in polarized thyroid epithelial cells.

The process leading to thyroid hormone synthesis is vectorial and depends upon the polarized organization of the thyrocytes into the follicular unit. Thyrocyte membrane proteins are delivered to two distinct domains of the plasma membrane using apical (AP) and basolateral (BL) sorting signals. A recent hypothesis for AP sorting proposes that apically destined proteins cluster with glycosphingolipids (GSLs) and cholesterol, into microdomains (or rafts) of the Golgi membrane from which AP vesicles originate. In MDCK cells the human neurotrophin receptor, p75hNTR, is delivered to the AP surface through a sorting signal, rich in O-glycosylated sugars, identified in its ectodomain. We have investigated whether this signal is functional in the thyroid-derived FRT cell line and whether p75hNTR clusters into lipid rafts to be sorted to the AP membrane. We found that p75hNTR is apically delivered via a direct pathway and does not associate with rafts during its transport to the surface of FRT cells. Therefore, although the same signal could be recognized by different cell types thyroid cells may possess a tissue-specific sorting machinery.

Binding Sites↗

PubMed1999

RhoA activity is required for fibronectin assembly and counteracts beta1B integrin inhibitory effect in FRT epithelial cells.

FRT thyroid epithelial cells synthesize fibronectin and organize a network of fibronectin fibrils at the basal surface of the cells. Fibronectin fibril formation is enhanced by the overexpression of the ubiquitous beta1A integrin and is inhibited by the expression of the dominant-negative beta1B subunit. We tested the hypotheses that RhoA activity might mediate the integrin-dependent fibronectin fibrillogenesis and might counteract beta1B integrin inhibitory effect. FRT-beta1A cells were transfected with a vector carrying a dominant negative form of RhoA (RhoAN19) or treated with the C3 transferase exoenzyme. Both treatments inhibited fibronectin assembly and caused loss of actin microfilaments and adhesion plaques. On the other hand, FRT-beta1B cells were transfected with the constitutively activated form of RhoA (RhoAV14) or treated with the E. coli cytotoxic necrotizing factor 1, which directly activates RhoA. Either treatment restored microfilament and adhesion plaque assembly and promoted fibronectin fibril organization. A great increase in fibronectin fibril assembly was also obtained by treatment of FRT-beta1B cells with TGF-beta. Our data indicate that RhoA is required to promote fibronectin matrix assembly in FRT cells and that the activation of the signal transduction pathway downstream of RhoA can overcome the inhibitory effect of beta1B integrin.

Actin Cytoskeleton↗

PubMed1998

Caveolin transfection results in caveolae formation but not apical sorting of glycosylphosphatidylinositol (GPI)-anchored proteins in epithelial cells.

Most epithelial cells sort glycosylphosphatidylinositol (GPI)-anchored proteins to the apical surface. The "raft" hypothesis, based on data mainly obtained in the prototype cell line MDCK, postulates that apical sorting depends on the incorporation of apical proteins into cholesterol/glycosphingolipid (GSL) rafts, rich in the cholesterol binding protein caveolin/VIP21, in the Golgi apparatus. Fischer rat thyroid (FRT) cells constitute an ideal model to test this hypothesis, since they missort both endogenous and transfected GPI-anchored proteins to the basolateral plasma membrane and fail to incorporate them into cholesterol/glycosphingolipid clusters. Because FRT cells lack caveolin, a major component of the caveolar coat that has been proposed to have a role in apical sorting of GPI-anchored proteins (Zurzolo, C., W. Van't Hoff, G. van Meer, and E. Rodriguez-Boulan. 1994. EMBO [Eur. Mol. Biol. Organ.] J. 13:42-53.), we carried out experiments to determine whether the lack of caveolin accounted for the sorting/clustering defect of GPI-anchored proteins. We report here that FRT cells lack morphological caveolae, but, upon stable transfection of the caveolin1 gene (cav1), form typical flask-shaped caveolae. However, cav1 expression did not redistribute GPI-anchored proteins to the apical surface, nor promote their inclusion into cholesterol/GSL rafts. Our results demonstrate that the absence of caveolin1 and morphologically identifiable caveolae cannot explain the inability of FRT cells to sort GPI-anchored proteins to the apical domain. Thus, FRT cells may lack additional factors required for apical sorting or for the clustering with GSLs of GPI-anchored proteins, or express factors that inhibit these events. Alternatively, cav1 and caveolae may not be directly involved in these processes.

Animals↗

PubMed1998

Beta1B integrin interferes with matrix assembly but not with confluent monolayer polarity, and alters some morphogenetic properties of FRT epithelial cells.

Beta1B is a beta1 integrin splice variant that differs from the ubiquitous beta1A in the terminal portion of the cytosolic tail. The expression of this variant in CHO cells results in reduced fibroblast adhesion and motility (Balzac, E et al., J. Cell Biol. 127, 557-565 (1994)). We have evaluated the phenotypic changes induced by the expression of beta1B in the FRT epithelial cell line. Stable transfectants of FRT cells expressing beta1B or beta1A human integrins were obtained. The transfected integrins associated with the endogenous alpha subunits and were delivered to the plasma membrane. Beta1B expressing cells attached less efficiently and spread less on fibronectin, laminin or type IV collagen coated dishes. A great reduction of fibronectin fibrils associated to the basal membrane of non-confluent beta1B transfected cells was observed. This was paralleled by the disappearance of microfilament bundles and loss of basally located focal adhesions. On the contrary, upon beta1A transfection, a higher amount of fibronectin fibrils, together with microfilament bundles and focal adhesions, was observed. Expression of beta1B did not significantly modify the ability to manifest the polarized phenotype when cells were grown to confluence on filters in two-chamber-systems. Beta1B-transfected cells showed reduced motile properties when embedded as aggregates in type I collagen gels. Moreover, formation of polarized cysts in suspension culture was impaired. The results show that beta1B, by interfering with focal adhesion organization, microfilament and fibronectin assembly, cell spreading and migration, affects some morphogenetic properties of FRT epithelial cells.

Actin Cytoskeleton↗

PubMed1997

Transfection of TTF-1 gene induces thyroglobulin gene expression in undifferentiated FRT cells.

The thyroglobulin gene, the substrate for thyroid hormone biosynthesis, is not expressed in the FRT cell line, which, even though it manifests the polarised epithelial phenotype, does not express any of the thyroid functional properties. Two transcription factors, TTF-1 and Pax-8, have been implicated in thyroid specific expression of the thyroglobulin gene. FRT cells contain Pax-8 but they lack TTF-1. In this paper, we show that transfection of TTF-1 expression vectors in FRT cells results in activation of thyroglobulin gene expression. If the expression vector encoded for TTF-1-ER, a fusion gene coding for the entire TTF-1 protein fused to the hormone-binding domain of the steroid receptor, under the control of the RSV promoter, thyroglobulin gene expression was controlled by estrogen. These data provide a direct demonstration that TTF-1 activates the chromosomal thyroglobulin promoter. Since transfection of TTF-1 expression vectors in non-thyroid cell types did not result in thyroglobulin gene expression, it is suggested that Pax-8, in addition, perhaps, to a specific cellular environment, might be required for thyroid specific expression of the thyroglobulin gene.

Animals↗

PubMed1997

Echistatin induces decrease of pp125FAK phosphorylation, disassembly of actin cytoskeleton and focal adhesions, and detachment of fibronectin-adherent melanoma cells.

B16-BL6 mouse melanoma cells cultured on fibronectin-coated dishes were detached by treatment with echistatin, an RGD-containing disintegrin. Echistatin was active at micromolar concentrations and was not cytotoxic. Its effect was dose-dependent and reversible. Sequential morphological changes leading to rounding up of the cells were detected by phase-contrast microscopy and by immunofluorescence analysis. A dramatic reduction in the number and size of focal adhesions and loss of cytoplasmic actin filaments were observed well before cell detachment occurred. Echistatin treatment down-regulated the phosphorylation of pp125FAK in fibronectin-adherent cells in a dose- and time-dependent fashion. The reduction of pp125FAK phosphorylation preceded cell detachment and occurred even in the presence of orthovanadate, an inhibitor of protein tyrosine phosphatases. These results suggest that echistatin detaches cells from the fibronectin substratum by inducing a decrease of pp125FAK phosphorylation and that echistatin acts by inhibiting protein tyrosine kinase activity rather than activating protein tyrosine phosphatases.

Actin Cytoskeleton↗

PubMed1996

Human serum immunoglobulin counteracts rotaviral infection in Caco-2 cells.

Oral administration of human serum immunoglobulin reduces the duration of diarrhea and of rotaviral excretion in children. To investigate the in vitro effects of immunoglobulin on virus-enterocyte interaction, Caco-2 cells were infected with Rotavirus strain SA11. Immunoglobulin was added prior to and at various times postinfection. Indirect immunofluorescence was performed with an antibody against VP-6 rotaviral antigen. Cell viability and monolayer transepithelial electrical resistance (TEER) were monitored. Immunofluorescence showed a perinuclear distribution in 90% of cells. Rotavirus infection induced a progressive decrease in TEER and a parallel reduction in cell viability, depending on viral load. Preincubation of the virus with immunoglobulin prevented cell infection as judged by immunofluorescence. Immunoglobulin addition to infected cells partially prevented the decrease in TEER and induced a later shift of TEER toward increasing values, suggesting restoration of monolayer's integrity. The efficacy of immunoglobulin depended on its concentration and on the time of its addition. These results indicate that immunoglobulin is effective in preventing infection and in reducing cell damage, through a direct anti-Rotavirus action and may indicate that immunoglobulin should be administered in the early phase of diarrhea, to reduce the severity of Rotavirus infection.

Administration, Oral↗

PubMed1996

Collagen interaction with apically expressed beta 1 integrins: loss of transepithelial resistance and reorganization of cultured thyroid cell monolayer.

We have cultured FRT rat thyroid cells to confluency on filters in bicameral systems and allowed a type I collagen solution to gel on their apical compartment. A dramatic drop in transepithelial resistance occurred within 2 h after collagen addition. This drop in transepithelial resistance was dependent upon collagen concentration. Cells interacting with the collagen lost their apical microvilli, formed pseudopods and displayed rearrangements in the distribution of actin and uvomorulin. After 24 h the cells had reorganized in two layers, one facing the other, with opposite orientations. We found that in approximately 15 to 20% of the cells within a confluent monolayer alpha 1 and beta 1 integrin subunits were localized in a subdomain of the apical plasma membrane, other than on the basolateral surface, as they normally are. By double immunofluorescence, after addition of diluted collagen solutions, we were able to detect collagen fibers that were bound to these integrin-containing apical subdomains. The addition of anti-beta 1 antibodies to the apical domain significantly delayed the drop in transepithelial resistance induced by the collagen gel. These data suggest that members of the beta 1 integrin family that are expressed on the apical domain may act as receptors for collagen fibers and may play a role in promoting changes in cell orientation.

Actins↗

PubMed1995

Expression of the RET oncogene induces differentiation of SK-N-BE neuroblastoma cells.

Expression of the RET proto-oncogene, a cell surface receptor for an as yet unknown ligand, is associated with tumors, tissues, and cell lines of neural crest origin. Accumulating evidence suggests that RET activity is involved in the process of neuronal differentiation. Moreover, induction of phenotypic differentiation of neuroblastoma cell lines is associated with the rapid accumulation of RET transcripts. To verify the role of RET in neuronal differentiation, we introduced into the human neuroblastoma cell line SK-N-BE four versions of the RET oncogene, activated by different mechanisms: RET/PTC1 and RET/PTC3, which are activated by rearrangement with heterologous genes; and two activated RET mutants, which carry the single amino acid substitution found associated to the inheritance of the multiple endocrine neoplasia type 2A (retMEN2A allele) and type2B (retMEN2B allele), respectively. We demonstrate that, after transfection with the RET oncogenes, SK-N-BE cells display a reduced growth rate and acquire a neurite-bearing phenotype accompanied by enhanced expression of the axonal growth-associated protein, GAP-43, and the high molecular weight neurofilament, NF200. These results indicate that, when activated, RET is able to cause growth inhibition and to promote neuronal differentiation of neuroblastoma cells.

Blotting, Northern↗

PubMed1993

Glycosylphosphatidylinositol-anchored proteins are preferentially targeted to the basolateral surface in Fischer rat thyroid epithelial cells.

Glycosylphosphatidylinositol (GPI) acts as an apical targeting signal in MDCK cells and other kidney and intestinal cell lines. In striking contrast with these model polarized cell lines, we show here that Fischer rat thyroid (FRT) epithelial cells do not display a preferential apical distribution of GPI-anchored proteins. Six out of nine detectable endogenous GPI-anchored proteins were localized on the basolateral surface, whereas two others were apical and one was not polarized. Transfection of several model GPI proteins, previously shown to be apically targeted in MDCK cells, also led to unexpected results. While the ectodomain of decay accelerating factor (DAF) was apically secreted, 50% of the native, GPI-anchored form, of this protein was basolateral. Addition of a GPI anchor to the ectodomain of Herpes simplex gD-1, secreted without polarity, led to basolateral localization of the fusion protein, gD1-DAF. Targeting experiments demonstrated that gD1-DAF was delivered vectorially from the Golgi apparatus to the basolateral surface. These results indicate that FRT cells have fundamental differences with MDCK cells with regard to the mechanisms for sorting GPI-anchored proteins: GPI is not an apical signal but, rather, it behaves as a basolateral signal. The "mutant" behavior of FRT cells may provide clues to the nature of the mechanisms that sort GPI-anchored proteins in epithelial cells.

Animals↗