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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To explore mechanisms of gut-mucosal IgA immune response, we have established Con A-induced cloned T cell lines originating from PP and spleen. These cloned cells expressed Thy-1.2+, Lyt-1+2-, Ia (I-A and I-E) and H-2 (K/D) surface antigens. Cloned T cells derived from PP were found to suppress LPS-induced IgM and IgG synthesis and secretion of co-cultured PP B cells; in addition, whereas the PP cloned T cells did not bring about IgA production, they did cause the appearance of large numbers of cells expressing sIgA. In contrast, cloned T cells derived from spleen had little or no effect on LPS-induced IgM synthesis and secretion by PP B cells; in addition, whereas they did suppress IgG production, they neither brought about IgA production nor the appearance of cells expressing sIgA. These studies provide evidence for the existence of a new type of T cell in PP, a switch T cell, which is able to induce B cells to undergo class-specific switches from IgM to IgA; the PP switch T cells appear to govern the pathway of DNA recombination (or RNA splicing) rather than cellular events resulting in terminal differentiation. Thus, these switch T cells are probably responsible for the fact that PP are a major source of mucosal IgA B cells. In additional studies, we show that post-switch IgA B cells, i.e. cells precultured with PP cloned T cells, have the capacity to undergo terminal differentiation into IgA producing plasma cells. provided they are exposed to helper T cells (uncloned) and an appropriate mitogenic stimulus (staphylococcal protein A). We can conclude, therefore, that the development of PP B cells into IgA-producing plasma cells in gut-associated lymphoid tissues (GALT) appears to require at least two steps: one which involves heavy chain switching to IgA and which is governed by IgA class-specific switch T cells in PP, and one which involves differentiation of post-switch B cells and which is governed by helper T cells in lymphoid tissues outside of PP (such as MLN and spleen).
Mol Immunol 1983 Sep
PMID:T cell regulation of IgA immunoglobulin production in gut-associated lymphoid tissues. 660 14

Maximal binding (Bmax) of the lectin, wheat germ agglutinin, by small intestinal brush border membrane is significantly reduced in rats infected with Trichinella spiralis. Wheat germ agglutinin specificity is for N-acetylglucosamine and sialic acid. Whereas total hexosamine and N-acetylglucosaminidase-labile N-acetylglucosamine were comparable in membranes from uninfected as compared with infected rats, the total sialic acid content and neuraminidase-released sialic acid were significantly higher in BBM from uninfected hosts. N-Acetylglucosaminidase treatment of membranes reduced Bmax for wheat germ agglutinin in both hosts. Neuraminidase treatment reduced Bmax in uninfected hosts, but tended to increase it in infected rats. Membranes from uninfected rats incorporated more N-acetylglucosamine from UDP-N-[14C]acetylglucosamine into oligosaccharide-lipid than did membranes from infected hosts. However, lipid and protein fractions were labeled at the same rate in both sets of membranes. Sialic acid was incorporated into protein at a slightly faster rate in brush border membrane from uninfected rats, indicative of a higher level of sialotransferase activity. These results suggest that the reduction in Bmax for wheat germ agglutinin in gut epithelial cell membranes from infected rats is related to a reduced level of sialic acid available for lectin binding as well as specific interactions between N-acetylglucosamine and sialic acid.
Mol Biochem Parasitol 1983 Sep
PMID:Sialic acid deficiency in lectin-resistant intestinal brush border membranes from rats following the intestinal phase of trichinellosis. 666 61

A murine BALB/c IgG2a (lambda 3) myeloma immunoglobulin SAPC-15 with binding activity for negatively charged polysaccharides has been purified by affinity chromatography, and its interaction with heparin and various other polyanionic antigens has been studied. The antigen-binding activity has been demonstrated to reside in the Fab part of the immunoglobulin. The S15 myeloma protein in 0.05 M Tris buffer at pH 7.4 precipitated dextran sulfate, heparin, chondroitin sulfate A, B and C, hyaluronic acid, H. influenzae type b polysaccharide, calf thymus DNA, Klebsiella polysaccharide K63 and poly-L glutamic acid. Of these antigens only dextran sulfate was precipitated in 0.01 M phosphate buffered saline (0.15M), pH 7.4. The pepsin S15 Fab fragment did not precipitate with any of these antigens. The intrinsic tryptophanyl fluorescence of S15 was changed maximally by the addition of heparin, and the binding affinity of the immunoglobulin for this antigen was high (greater than 10(6) L/M). S15 may resemble antibody molecules that react with antigens under non-physiological conditions or in pathological conditions or in the external environment as in the lumen of the gut. All the above interactions of S15 with antigens persisted in 0.05 M Tris buffer made physiologically isotonic by the addition of sucrose, and S15 could thus be used to identify these antigens on cell surfaces.
Mol Immunol 1982 Jul
PMID:The interaction of mouse myeloma immunoglobulin S15 with negatively charged polysaccharide antigens. 681 62

In situ hybridization studies reveal novel sites of expression of cholesterol side-chain cleavage cytochrome P450 (P450scc) during murine embryonic development. In addition to fetal adrenals and testes, P450scc transcripts localize in situ to the primitive gut and to a subset of unidentified cells in the dermal mesenchyme of embryonic skin. In the gut, transcripts are most abundant in luminal epithelia of the hindgut, which will form the colon. P450scc transcript abundance at these novel sites is a fraction of that in fetal adrenals or testes, suggesting a local rather than an endocrine function. Immunocytochemical analyses localize P450scc protein to the fetal hindgut, indicating that the transcripts are translated in vivo. RNA isolated from microdissected embryonic hindgut and skin was reverse transcribed and amplified by polymerase chain reaction. DNA sequence analyses of polymerase chain reaction products confirmed that specific hybridization in situ represents authentic P450scc gene (Cyp11A) transcripts and that 3 beta-hydroxysteroid dehydrogenase/delta 5-->delta 4-isomerase transcripts are also present, demonstrating the potential of these fetal tissues to produce pregnenolone and progesterone. P450scc transcripts are also detectable by in situ hybridization in primitive gut and skin of Fushi tarazu factor 1 null mice, which lack the nuclear receptor steroidogenic factor 1, proving that steroidogenic factor 1 is not required for steroid hydroxylase gene expression at these sites. The capacity for C21 steroid biosynthesis in primitive gut and skin during organogenesis raises the question whether local production of steroid hormones may be required for normal cellular growth and differentiation of these tissues during embryogenesis.
Mol Endocrinol 1995 Aug
PMID:Cholesterol side-chain cleavage cytochrome P450 gene expression in the primitive gut of the mouse embryo does not require steroidogenic factor 1. 747 82

The endocrine pancreas consists of several differentiated cell types that are distinguished by their selective expression of peptide hormones such as insulin, glucagon, and somatostatin. Although a number of homeobox-type factors have been proposed as key regulators of individual peptide genes in the pancreas, their cellular distribution and relative abundance remain uncharacterized. Also, their overlapping DNA binding specificities have further obscured the regulatory functions these factors perform during development. In this report we characterize a novel homeobox-type somatostatin transactivating factor termed STF-1, which is uniformly expressed in cells of the endocrine pancreas and small intestine. The 283-amino acid STF-1 protein binds to tissue-specific elements within the somatostatin promoter and stimulates somatostatin gene expression both in vivo and in vitro. Remarkably, STF-1 comprises the predominant tissue-specific element-binding activity in nuclear extracts from somatostatin-producing pancreatic islet cells, suggesting that this protein may have a primary role in regulating peptide hormone expression and specifying endocrine cell lineage in the developing gut.
Mol Endocrinol 1993 Oct
PMID:Characterization of somatostatin transactivating factor-1, a novel homeobox factor that stimulates somatostatin expression in pancreatic islet cells. 750 93

The mouse alpha-fetoprotein (AFP) gene is expressed at high levels in the yolk sac and fetal liver and at low levels in the fetal gut. AFP synthesis decreases dramatically shortly after birth to low levels that are maintained in the adult liver and gut. AFP expression can be reactivated in the adult liver upon renewed cell proliferation such as during liver regeneration or in hepatocellular carcinomas. Previously, two unlinked genetic loci that modulate postnatal AFP levels were identified. The raf locus controls, at least in part, basal steady-state AFP mRNA levels in adult liver. Rif influences the extent of AFP mRNA induction during liver regeneration. Transgenic mice were used to examine the role of 5' AFP regulatory regions in raf- and Rif-mediated control. A fragment of the AFP 5' region containing enhancer element I, the repressor, and the promoter was linked to the mouse class I H-2Dd structural gene. We demonstrate that this hybrid AFP-Dd transgene is expressed in the appropriate tissues. In addition, it is postnatally repressed and reactivated during liver regeneration in parallel with the endogenous AFP gene. Therefore, proper transcriptional control does not require the AFP structural gene. Furthermore, the AFP 5' control region is sufficient to confer raf and Rif responsiveness to the linked H-2Dd structural gene, suggesting that raf and Rif act at the level of transcriptional initiation.
Mol Cell Biol 1994 Oct
PMID:Mouse alpha-fetoprotein gene 5' regulatory elements are required for postnatal regulation by raf and Rif. 752 52

The mouse alpha-fetoprotein (AFP) gene is transcribed at high levels in the visceral endoderm of the yolk sac and fetal liver and at much lower rates in the endoderm of the fetal gut. Expression of the gene in vivo requires the presence of at least one of three enhancers which lie in its 5' flanking region. In this report, we establish that the most distal AFP enhancer directed consistent expression of a linked AFP minigene in all three endodermal tissues in transgenic mice. The enhancer is composed of three domains, each of which is essential for full enhancer function by transient transfection assays. DNase I footprinting identified three regions of the enhancer which are protected by human hepatoma nuclear extracts, one of which corresponded to a consensus site for HNF-3 binding. Site-directed mutations in this site caused a 10-fold reduction in enhancer function by transient transfection. In transgenic mice, however, the mutation resulted in sporadic expression of the transgene, dependent on the site of integration. A similar acquisition of position-dependent sporadic expression of the transgene was observed with a mutation in a second protein binding site, despite the fact that this mutation had very little effect on enhancer function as assessed by transient transfection. These studies underscore the value of examining the functions of specific protein binding sites in vivo.
Mol Cell Biol 1995 Jul
PMID:Molecular analysis of the distal enhancer of the mouse alpha-fetoprotein gene. 754 Jul 20

A new class of acidic glycans isolated from marine sponges and sea urchin embryos was shown to mediate cell adhesion via carbohydrate-carbohydrate interactions. Cell aggregation blocking monoclonal antibodies (Block 1 and Block 2 mAbs) directed against these polysaccharides localized functional epitopes in embryonic sea urchin gut. Immunofluorescence light microscopy of human colon carcinomas and healthy colon samples with Block 1 and Block 2 mAbs established that the carbohydrate structures similar to the invertebrate acidic glycan adhesion molecules are also expressed in humans. The Block 1 mAb labeled basal and apical lamina of tumor cells, whereas the Block 2 bound exclusively to the apical part of the epithelium. In normal tissue whole goblet cell membrane was stained with both antibodies indicating that transformation leads to spatial rearrangement of glycan antigens. Acidic glycans from human colon carcinomas and normal colon were isolated after delipidation, and complete pronase and DNase digestion, by gel filtration and adsorption to anion exchange membranes. Immunodot assay with Block 1 and Block 2 mAbs revealed that tumor cells have elevated expression of both carbohydrate structures. These results suggest that the acidic glycan adhesion molecules, originally found in sponges and sea urchin embryos, may represent a new class of carbohydrate carcino-embryonal antigens involved in cellular interactions associated with morphogenesis, metastasis and renewal of adult tissue.
J Mol Recognit
PMID:A novel class of embryonic cell adhesion glycan epitopes is expressed in human colon carcinomas. 754 Dec 24

Transcription of the mouse alpha-fetoprotein (AFP) gene, which is expressed at high levels in the visceral endoderm of the yolk sac and fetal liver and at low levels in the fetal gut, is regulated by three distinct upstream enhancer regions. To investigate the activities of these regions, each enhancer was individually linked to a heterologous human beta-globin promoter fused to the mouse class I H-2Dd structural gene. When tested in transgenic mice, the beta-globin promoter alone has minimal activity. We find that all three enhancers activate the beta-globin promoter in an AFP-like pattern; i.e., activity is detected in the yolk sac, fetal liver, and fetal gut. The enhancers remain active in the livers and guts of adult mice, consistent with previous studies showing that postnatal AFP repression is due not to the loss of enhancer activity but to a dominant repressor region. Enhancer III also functions in the brain. In addition, these studies reveal that the three enhancers exhibit different position-dependent activities in the adult liver. Enhancers I and II are most active in hepatocytes surrounding the central vein, with a gradual decrease in activity along the hepatic plates toward the portal triad. Enhancer III is active exclusively in hepatocytes surrounding the central vein. These data represent the first examples of individual control elements exhibiting positionally regulated activity in adult liver.
Mol Cell Biol 1995 Sep
PMID:Individual mouse alpha-fetoprotein enhancer elements exhibit different patterns of tissue-specific and hepatic position-dependent activities. 754 36

We investigated the oxidative degradation pathway of 5CH3-H4PteGlu, the main extracellular folate and the predominant form of the vitamin found in food and blood. 5CH3-H4PteGlu is oxidized to 5CH3-5,6-H2PteGlu which subsequently undergoes C9-N10 bond cleavage yielding a pteridine residue and P-ABG, the latter step resulting in irreversible loss of vitamin activity. Under moderately acid conditions typical of the postprandial gut (pH 3.5) 5CH3-H4PteGlu is fairly stable (t1/2 = 273.6 min), while 5CH3-5,6-H2PteGlu is rapidly degraded (t1/2 = 16.9 min). In a neutral environment (pH 6.4) stability is reversed; 5CH3-H4PteGlu t1/2 = 12.0 mins, 5CH3-5,6-H2PteGlu t1/2 = 1504.6 min. Ascorbic acid was efficacious in the facile salvage of 5CH3-H4PteGlu from 5CH3-5,6-H2PteGlu which occurred rapidly and with significant efficiency (100% conversion) under acid (pH 3.5) conditions, t1/2 = 1.3 min (1 mmol/liter ascorbate), but was less efficient under neutral (pH 6.4) conditions t1/2 = 273.6 min (36% conversion). The presence of zinc and iron broadly maintains the pattern of effect, but increases all reaction rates. PteGlu was stable under all conditions studied. These results obtained in an artificial environment were supported by findings in human gastric juice: at a gastric pH of 1.47 with low endogenous ascorbate (7.0 mumol/liter), 5CH3-5,6-H2PteGlu and 5CH3-H4PteGlu both degrade instantly via C9-N10 bond cleavage to yield an equimolar amount of P-ABG. If the same gastric juice is spiked at 58.0 mumol/liter ascorbate (moderate endogenous concentration), 5CH3-H4PteGlu is stable (t1/2 = 334.7 min), while 5CH3-5,6-H2PteGlu is instantly salvaged to 5CH3-H4PteGlu with 43.3% efficiency, and the remaining 5CH3-5,6-H2PteGlu is degraded to P-ABG. In gastric juice with an elevated pH of 7.0 and no endogenous ascorbate, 5CH3-5,6-H2PteGlu and 5CH3-H4PteGlu are both stable, with no C9-N10 bond cleavage. This, for 5CH3-H4PteGlu, is in apparent contrast to findings at pH 6.4 in an artificial environment. The same gastric juice spiked to 50 mumol/liter ascorbate did not result in 5CH3-H4PteGlu salvage from 5CH3-5,6-H2PteGlu.(ABSTRACT TRUNCATED AT 400 WORDS)
Biochem Mol Med 1995 Jun
PMID:Nonenzymatic degradation and salvage of dietary folate: physicochemical factors likely to influence bioavailability. 755 25


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