Molecular events in production and transport of secretory IgA: a basis for design of reagents for passive immune protection.
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Animals↗
Biomedical subjects
E Pringault
Publications and source records attributed to E Pringault.
Experimental approaches to brush border morphogenesis.
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Animals↗
Regulatory sequences on the human villin gene trigger the expression of a reporter gene in a differentiating HT29 intestinal cell line.
To develop a molecular tool for tissue-specific targeting of gene expression in immature and differentiated epithelial cells of the small and large intestinal mucosa, we have isolated the 2-kb 5'-flanking region of the human villin gene. This region contains numerous short sequences that are conserved among other tissue-specific promoters of genes expressed in differentiated enterocytes. This DNA fragment promotes the transcription and expression of the luciferase reporter gene in villin-positive intestinal, renal, and hepatoma cell lines but not in a villin-negative keratinocyte cell line. The pattern of expression corresponds that of the endogenous gene, indicating that this sequence can direct intestine-specific transcription. In the differentiating HT29 intestinal cell line, expression of the reporter gene is already detectable in undifferentiated cells, and dramatically increases when terminal differentiation is induced. Thus, as previously reported for the endogenous gene the isolated 5'-flanking region of the villin gene responds positively to conditions known to stimulate terminal differentiation of these cultured epithelial intestinal cells. The reported results indicate that this genomic fragment contains sufficient regulatory elements to recapitulate the expression pattern of the villin promoter during intestinal differentiation.
Adenocarcinoma↗
Establishment of renal proximal tubule cell lines by targeted oncogenesis in transgenic mice using the L-pyruvate kinase-SV40 (T) antigen hybrid gene.
Targeted oncogenesis allowed us to obtain two cell lines which have been derived from the proximal tubule of kidney from transgenic mice harbouring the simian virus (SV40) large T and small t antigens placed under the control of the 5' regulatory sequence from the rat L-type pyruvate kinase (L-PK) gene. The cell lines (PKSV-PCT and PKSV-PR cells) were derived from early (PCT) and late (Pars Recta, PR) microdissected proximal tubules grown in D-glucose-enriched medium. In such conditions of culture, both cell lines exhibited L-PK transcripts, a stable expression of SV40-encoded nuclear large T antigen, a prolonged life span but failed to induce tumors when injected sub-cutaneously into athymic (nu-nu) mice. Confluent cells, grown on plastic support or porous filters, were organized as monolayers of polarized cuboid cells with well developed apical microvilli and formed domes. Both cell lines exhibited morphological features of proximal tubule cells with villin located in the apical brush-border and substantial amounts of hydrolase activity. By immunofluorescence studies using specific antibodies, aminopeptidase N appeared restricted to the apical microvillar domain, whereas the H2 histocompatibility antigen was distributed in the cytoplasm and lateral membranes. These results demonstrate that the proximal morphological phenotype has been fully preserved in these cultured cells derived from tissue-specific targeted oncogenesis in transgenic mice.
Aminopeptidases↗
Functional properties of proximal tubule cell lines derived from transgenic mice harboring L-pyruvate kinase-SV40 (T) antigen hybrid gene.
This study describes the functional characterization of two cell lines derived from the proximal convoluted (PKSV-PCT cells) and proximal straight (PKSV-PR) tubules microdissected out from kidneys of transgenic mice harboring the simian virus 40 (SV40) large T and small t antigens placed under the control of the rat L-type pyruvate kinase (L-PK) 5' regulatory sequence. Both cell lines exhibited cellular cyclic AMP stimulated by parathormone (PTH) and calcitonin (CT) and a sodium-dependent glucose transporter. Uptake of the fluid-phase marker [3H]inulin showed that both cell lines grown on filters exhibited biphasic apical and basolateral endocytic rates. Results from Northern blot analysis indicate that the expression of the T antigen gene (Tag) is dependent on the concentration of D-glucose in the medium and show that the L-PK construct has maintained its capacity for up- or down-regulation by carbohydrates. Replacement of D-glucose by neoglucogenic substrates (lactate, oxaloacetate) blunted the expression of Tag transcripts and induced arrest of cell growth. Compared to cell grown in D-glucose-enriched medium, the hormonal sensitivities to PTH and CT and the sodium-dependent glucose uptake were unchanged whereas quiescent cells exhibited increased hydrolase content. Thus the proximal function has been preserved in these cultured cells derived from tissue-specific targeted oncogenesis in transgenic mice. As the expression of Tag transcripts is controlled by D-glucose, the structural and physiological characteristics of these cell lines can be studied in either quiescent or active growth conditions.
Animals↗
Developmental regulation of villin gene expression in the epithelial cell lineages of mouse digestive and urogenital tracts.
The expression of villin, an actin-binding protein and major structural component of the brush border of specialized absorptive cells, was studied during mouse embryogenesis. We show that the ontogeny of villin expression is limited to the epithelial cell lineages of the digestive and uro-genital tracts and accounts for the tissue-specific expression observed in adult mice. This spatiotemporal pattern of villin expression is distinctive in sequence, intensity, regional distribution and polarization. During the development of the primitive gut, villin is faintly and discontinuously expressed in the invaginating foregut but it is expressed in every cell bordering the hindgut pocket. Later, villin expression increases along the developing intestine and concentrates in the brush border of the epithelium bordering the villi. In gut derivatives, villin is present in liver and pancreas primordia but only biliary and pancreatic cells maintain a faint villin expression as observed in adults. In the urogenital tract, mesonephric tubules are the first mesodermal derived structures to express villin. This expression is maintained in the ductuli efferents, paradidymis and epoöphoron. Villin then appears in the proximal metanephric tubules and later increases and concentrates in the brush border of the renal proximal tubular epithelial cells. Thus villin expression can be considered as an early marker of the endodermal cell lineage during the development of the digestive system. Conversely, during the development of the excretory and genital system, villin is only expressed after the mesenchyme/epithelium conversion following the appearance of tubular structures. These observations emphasize the multiple levels of regulation of villin gene activity that occur during mouse embryogenesis and account for the strict pattern of tissue-specific expression observed in adults. In the future, regulatory elements of the villin gene may be used to target the early expression of oncogenes to the digestive and urogenital tracts of transgenic mice.
Animals↗
Structure of the human villin gene.
We have isolated and characterized the complete human villin gene. The villin gene is located on chromosome 2q35-36 in humans and on chromosome 1 in mice. Villin belongs to a family of calcium-regulated actin-binding proteins that share structural and functional homologies. The villin gene is expressed mainly in cells that develop a brush border, such as mucosal cells of the small and large intestine and epithelial cells of the kidney proximal tubules. Villin gene expression is strictly regulated during adult life and embryonic development in the digestive and urogenital tracts and, thus, may be used as a marker of the digestive and renal cell lineages. The human villin gene has one copy per haploid genome, encompasses about 25 kilobases, and contains 19 exons. Analysis of the structural organization of this gene shows that the two mRNAs that encode villin in humans arise by alternative choice of one of the two polyadenylylation signals located within the last exon. The overall organization of the exons reflects the gene duplication event from which this family of actin-binding proteins originated.
Actins↗
From the structure to the function of villin, an actin-binding protein of the brush border.
Villin, a calcium-regulated actin-binding protein, modulates the structure and assembly of actin filaments in vitro. It is organized into three domains, the first two of which are homologous. Villin is mainly produced in epithelial cells that develop a brush border and which are responsible for nutrient uptake. Expression of the villin structural gene is precisely regulated during mouse embryogenesis and is restricted in adults, to certain epithelia of the gastrointestinal and urogenital tracts. The function of villin has been assessed by transfecting CV1 cells with a human cDNA encoding wild-type villin or mutant villin. Synthesis of large amounts of villin in cells which do not normally produce this protein induces the growth of microvilli on the cell surface and the redistribution of F-actin, concomitant with the disappearance of stress fibers. The complete villin sequence is required for the morphogenic effect. These results suggest that villin plays a key role in the morphogenesis of microvilli.
Actins↗
Villin expression in the visceral endoderm and in the gut anlage during early mouse embryogenesis.
Villin is an evolutionarily well conserved, Ca2+ regulated actin-binding protein, and a major structural component of the brush border of specialized absorptive cells. Using paraffin sections and an affinity purified polyclonal anti-villin antibody, we have investigated the early expression of villin during mouse embryogenesis. Villin is first detectable at the early post-implantation stage in visceral endodermal cells at the periphery of the egg cylinder. In this extra embryonic layer, the expression of villin increases and then persists until full term gestation. In the embryo, villin first appears in gut anlage during the axial rotation. Using the same methodology, villin expression is also demonstrated in differentiating embryoid bodies from a teratocarcinoma. Both in extra embryonic and embryonic extracts, villin expression is confirmed by immunoblot and Northern blot analysis which reveal, respectively, a single polypeptide of 93 kd and an mRNA of 3.4 kb in length, two well defined parameters for adult mouse villin gene expression. The results presented here show that paraffin sections allow very sensitive and highly resolutive detection of antigens in early embryogenesis. They provide a detailed developmental profile of villin expression and demonstrate the usefulness of villin as a marker for epithelial cells involved in absorptive processes.
Animals↗
Localization of the villin gene on human chromosome 2q35-q36 and on mouse chromosome 1.
A partial cDNA clone coding for the 110 carboxyterminal amino acids of human villin was used for mapping the human villin gene. In situ hybridization experiments on human chromosomes with tritiated probe allowed the regional localization of the villin locus to chromosome 2 at q35-36. Data obtained from restriction fragment length polymorphism analysis of two mouse species demonstrated the assignment of the villin gene to mouse chromosome 1 by assessment of linkage with the fast skeletal isoform of the myosin light-chain gene. These villin gene localizations add a fourth locus to the conserved gene cluster encoding the fast skeletal muscle isoform of the myosin light chain, isocitrate dehydrogenase, and the gamma crystallins and confirm the partial homology of the human chromosome 2 long arm and mouse chromosome 1.
Animals↗
Villin, a specific marker for some epithelia specialized in transport, to study the differentiation of intestinal and kidney cells in vivo and in a human colon adenocarcinoma line HT29 in culture.
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Adenocarcinoma↗
Sequence of human villin: a large duplicated domain homologous with other actin-severing proteins and a unique small carboxy-terminal domain related to villin specificity.
Villin is a calcium-regulated actin-binding protein that caps, severs, and bundles actin filaments in vitro. This 92,500-D protein is a major constituent of the actin bundles within the microvilli of the brush border surface of intestinal and kidney proximal tubule cells. Villin is a very early marker of cells involved in absorption and its expression is highly increased during intestinal cell differentiation. The amino acid sequence deduced from the cDNA sequence revealed that human villin is composed of three domains. The first two domains appear as the result of a duplication: their structural organization is similar. We can then define a basic unit in which a slightly hydrophilic motif is followed by three hydrophobic motifs, similar between themselves and regularly spaced. The duplicated domain is highly homologous to three other actin-severing proteins and this basic structure represents the whole molecule in severin and fragmin, while two basic units compose gelsolin. The third domain which is carboxy terminal is villin specific: it is unique among actin modulating proteins so far known. It could account for its actin-binding properties (dual regulation by calcium of severing and bundling activities). We propose that it may also be related to the subcellular localization of villin in different epithelial cell types.
Actins↗
Differential distribution of villin and villin MRNA in mouse intestinal epithelial cells.
The distribution of the mRNA encoding for villin, the major actin-binding protein of intestinal brush border, was studied during the differentiation of mouse intestinal epithelial cells and compared to the distribution of the protein. In situ hybridization using a cRNA clone specific for villin indicated that the distribution of the mRNA did not fully parallel that of the protein, although the overall labelling pattern for mRNA and protein along the crypt-villus axis was similar. While villin was present in equal amounts in all cells along the villi, villin-specific mRNA was mainly accumulated in the cells at the villus base, the area of the epithelium where terminal differentiation takes place and where the brush border is formed.
Animals↗
A human villin cDNA clone to investigate the differentiation of intestinal and kidney cells in vivo and in culture.
Villin, a Ca2+-regulated actin-binding protein is a major component of microvilli of intestinal epithelial cells and kidney proximal tubule cells. Villin expression during assembly of the brush border can be investigated using a human colon adenocarcinoma cell line HT29-18. This cell line is able to differentiate under nutritional control and develops an enterocyte-like phenotype. A cDNA library from a subclone HT29-18-C1 was constructed in an expression vector and a cDNA specific for human villin was isolated. This cDNA codes for the 110 carboxy-terminal residues of villin. Within that region, the 76 carboxy-terminal residues present 65% homology with the chicken villin 'head piece'. We show that two mRNA species 4.0 kb and 3.2 kb long hybridize with this cDNA probe in humans, whereas in rat and chicken only one mRNA species can be detected. The two villin mRNA species are co-expressed in normal human small and large intestinal mucosa and tumoral HT29-18 cells as well as in normal kidney. No villin mRNAs were detected in other normal or malignant epithelial cell types. Finally, we observed an accumulation of the two mRNA species coding for villin when HT29-18 cells become differentiated, suggesting that control of villin expression during terminal differentiation can occur at the transcription level or by RNA stabilization.
Adenocarcinoma↗
Cell-surface insulin receptor cycling and its implication in the glycogenic response in cultured foetal hepatocytes.
The insulin-receptor cycle was investigated in cultured foetal rat hepatocytes by determining the variations in insulin-binding sites at the cell surface after short exposure to the hormone. Binding of 125I-insulin was measured at 4 degrees C after dissociation of prebound native insulin. Two protocols were used: exchange binding assay and binding after acid treatment; both gave the same results. Cell-surface 125I-insulin-receptor binding decreased sharply (by 40%) during the first 5 min of 10 nM-insulin exposure (t1/2 = 2 min) and remained practically constant thereafter; subsequent removal of the hormone restored the initial binding within 10 min. This fall-rise sequence corresponded to variations in the number of insulin receptors at the cell surface, with no detectable change in receptor affinity. The reversible translocation of insulin receptors from the cell surface to a compartment not accessible to insulin at 4 degrees C was hormone-concentration- and temperature-dependent. SDS/polyacrylamide-gel electrophoresis after cross-linking of bound 125I-insulin to cell-surface proteins with disuccinimidyl suberate showed that these variations were not associated with changes in Mr of binding components, in particular for the major labelled band of Mr 130,000. The insulin-receptor cycle could be repeated after intermittent exposure to insulin. Continuous or intermittent exposure to the hormone gave a similar glycogenic response, contrary to the partial effect of a unique short (5-20 min) exposure. A relationship could be established between the repetitive character of the rapid insulin-receptor cycle and the maximal expression of the biological effect in cultured foetal hepatocytes.
Animals↗
Reutilization of insulin receptor and hormonal response in cultured foetal hepatocytes: the effects of chloroquine and vinblastine.
The effects of chloroquine and vinblastine (10-100 microM) on insulin degradation and biological action were studied in cultured foetal rat hepatocytes. Insulin degradation, as measured by the release of trichloroacetic acid-soluble radioactivity from 125I-insulin into the medium, was strictly cell-associated, saturable with respect to insulin concentrations and linearly related to the amount of cell-associated hormone. The maximal rate of insulin degradation was 4,700 molecules/min per cell, and its KM about 5 nM. Thus, insulin receptors (30,000 sites/cell; half-life close to 13 hr) must be reutilized 450-fold before being degraded with an average time of reutilization inferior to 10 min. In the presence of 70 microM chloroquine or 100 microM vinblastine, insulin degradation was inhibited by 80% and the amount of cell-associated hormone enhanced 2-3-fold. Nearly total inhibition of insulin-stimulated glycogenesis was obtained with 70 microM chloroquine and 45 microM vinblastine. When hepatocytes were preincubated with chloroquine or vinblastine, insulin binding remained high for up to 4 hr, then progressively decreased thereafter. The addition of 10 nM native insulin during preincubation with the drugs resulted in an earlier and more pronounced decrease in insulin binding, whereas native insulin alone did not induce any change. Both the inhibition of insulin degradation and onset of receptor down-regulation suggest a drug-induced impairment in the receptor reutilization. This defect is correlated to a loss of the glycogenic effect of insulin in cultured foetal rat hepatocytes.
Animals↗
Differences in degradation processes for insulin and its receptor in cultured foetal hepatocytes.
Binding and degradation of 125I-labelled insulin were studied in cultured foetal hepatocytes after exposure to the protein-synthesis inhibitors tunicamycin and cycloheximide. Tunicamycin (1 microgram/ml) induced a steady decrease of insulin binding, which was decreased by 50% after 13 h. As the total number of binding sites per hepatocyte was 20000, the rate of the receptor degradation could not exceed 13 sites/min per hepatocyte. Cycloheximide (2.8 micrograms/ml) increased insulin binding by 30% within 6 h, an effect that persisted for up to 25 h. This drug had a specific inhibitory effect on the degradation of proteins prelabelled for 10 h with [14C]glucosamine, without affecting the degradation of total proteins. Chronic exposure to 10 nM-insulin neither decreased insulin binding nor modified the effect of the drugs. The absence of down-regulation of insulin receptors cannot be attributed to rapid receptor biosynthesis in foetal hepatocytes. Cellular insulin degradation, which is exclusively receptor-mediated, was determined by two different parameters. First, the rate of release of degraded insulin into the medium was 600 molecules/min per hepatocyte with 1 nM labelled hormone, and increased (preincubation with cycloheximide) or decreased (tunicamycin) as a function of the amount of cell-bound insulin. Secondly, the percentage of cell-bound insulin degraded was not changed by the presence of protein-synthesis inhibitors (25-30%). The stability of insulin degradation suggested that this process was dependent on long-life proteinase systems. Such differences in degradation rates and cycloheximide sensitivity imply that hormone- and receptor-degradation processes utilize distinct pathways.
Animals↗
[Expression of the glycogenic response to insulin in cultured fetal hepatocytes].
In the present study, we used primary cultures of fetal rat hepatocytes which are highly suitable for studying the glycogenic effect of insulin and its regulation. After a lag in the period of culture in the presence of cortisol, glycogenic response to insulin developed together with a progressive accumulation of glycogen. When insulin was added, the rate of glycogen synthesis increased, becoming maximal after 2-3 h, due to the activation of the glycogen synthase system already present. Modification of glycogen precursors in the medium did not alter the amplitude of the insulin effect. The glycogenic effect of insulin was unrelated to that of glucose load and occurred after the formation of glucose-1-phosphate. This only happened when the cyclic AMP-dependent glycogenolytic system was not stimulated, since it was suppressed by low doses of glucagon. Insulin effect, which was time-dependent, ceased after 4 h. This corresponded to a desensitization of hepatocytes without any alteration in the specific binding of insulin. These variations in the glycogenic effect of insulin were likely due to different causes; one of these could be the first events following the interaction of insulin with its receptor.
Animals↗