Lack of cardiac differentiation in c-kit-enriched porcine bone marrow and spleen hematopoietic cell cultures using 5-azacytidine.

The adult spleen is a source of early hematopoietic stem cells (HSC). We therefore studied whether culturing spleen or bone marrow (BM) HSC in medium containing 5-azacytidine could induce a cardiac phenotype. c-kit enrichment and depletion of adult pig spleen and BM mononuclear cells were obtained by magnetic bead separation using biotinylated pig stem cell factor (c-kit ligand). Cells were incubated with 5-azacytidine for 24 h and refreshed with 5-azacytidine-free medium every 48 h. Western blot was used to detect cardiac troponin and myosin heavy chains. Although 5-azacytidine treatment led to the formation of ball-like cell clusters in both c-kit-enriched populations, these clusters showed no rhythmic contractions (beating), as observed by others. Furthermore, neither cardiac troponin nor myosin was detected in cells derived from either source. Our methodology and treatment with 5-azacytidine did not induce cardiac gene expression in porcine HSC derived from either pig spleen or BM.

Persistence of dominant T cell clones in accepted solid organ transplants.

Donor/recipient MHC class II matching is beneficial to the survival of allogeneic kidneys in humans and swine. In the latter, tolerance to class I-disparate grafts can be induced by a short course of immunosuppression, a peripheral mechanism that implicates regulatory T cells. Absence of treatment will lead to prompt rejection. Rejected grafts are infiltrated by dominant alloaggressive T cells, whereas there is still speculation on the specificity and function of T cells invading accepted tissues. To characterize the TCR repertoire of graft-infiltrating T cells (GITC) in accepted kidneys, we have used the RT-PCR-based spectratyping technique to assess the length polymorphism of the porcine TCRbeta chain complementary-determining region 3 (CDR3). Results show that T cells infiltrating accepted kidneys (n = 5) express a restricted polymorphism of the CDR3 length, whereas PBL from the same animal have the polymorphic distribution of CDR3 lengths found in naive animals; that the skewed Vbeta repertoire in accepted grafts involved distinct Vbeta subfamilies in otherwise MHC-identical recipient animals; that GITC clonal dominance is not caused by immunosuppression because a second kidney, accepted without drug treatment, exhibits the same TCR Vbeta CDR3 profiles than those detected in the first graft; and that intragraft clonal dominance intensifies with time, indicating progressive preeminence of nonaggressive GITC clones. Collectively, these data represent the first example, in a preclinical model, of the emergence of nonaggressive intragraft clones, which may be involved in the induction/maintenance of local tolerance to allogeneic tissues.

Heterogeneity of human anti-pig natural antibodies cross-reactive with the Gal(alpha1,3)Galactose epitope.

BACKGROUND: The cell surface carbohydrate moiety, Gal(alpha1,3)Galactose (alphaGal), has been implicated as the major determinant recognized by more than 80% of human anti-porcine natural antibodies (NAb). An ELISA system was developed for the detection of this subpopulation of porcine cell-reactive NAb using synthetic alphaGal conjugated to bovine serum albumin. METHODS: A screen of 95 human serum samples by this method demonstrated marked variability in the alphaGal reactivity of unrelated donors. The percentage of alphaGal-reactive NAb relative to total immunoglobulin was determined for 10 donors. RESULTS: alphaGal-reactive NAb comprised 1.0-2.4% of total serum IgG, whereas the range was from 3.9% to 8.0% for IgM. CONCLUSIONS: The higher level of alphaGal-reactive IgM suggests that xenoreactive NAbs may be the product of germ-line genes. Two-dimensional gel analysis of affinity-purified alphaGal-reactive NAb from two donors provided evidence suggesting that IgM from this subpopulation of NAb were restricted in protein charge heterogeneity.

Relationship between ABO blood group and levels of Gal alpha,3Galactose-reactive human immunoglobulin G.

BACKGROUND: The terminal Gal alpha1,3Galactose (alphaGal) determinant is present on all porcine glycoproteins and glycolipids, but is not expressed by human cells. Consequently human sera contain anti-alphaGal natural antibodies. The human blood group B antigen [Gal alpha1,3(Fuc1,2)Galactose] is differentiated from the alphaGal epitope by the presence of a fucosyl group. METHODS: To determine whether the expression of the B antigen has any effect on the level of alphaGal-reactive natural antibodies, equal numbers (n=12) of A, B, AB, and O serum samples were evaluated by ELISA and flow cytometry. RESULTS: A significant reduction in IgG alphaGal reactivity was observed with serum samples from B antigen-expressing donors (B, AB) relative to non-B antigen-expressing donors (A, O). CONCLUSIONS: These results are consistent with the possibility that anti-alphaGal antibodies in non-B antigen-expressing individuals include a subset that is reactive with the structurally related B antigen and that this subset is absent in B and AB individuals.

Interactions and three-dimensional localization of a group of nuclear pore complex proteins.

We have used antibodies directed against a number of nuclear pore complex (NPC) proteins to determine their mutual interactions and location within the three-dimensional structure of the NPC. A monoclonal antibody, termed QE5, recognized three NPC polypeptides, p250, NUP153, and p62 on Western blots, and labeled the nuclear envelope of several cultured cell lines by immunofluorescence microscopy. These three polypeptides contained O-linked N-acetylglucosamine residues and were released from the NPC by detergent/high-salt treatment as discrete high molecular weight complexes. p250 was found in association with a novel 75 kD protein, NUP153 was released as a homo-oligomer of about 1 megadalton, and p62 was associated with polypeptides of 58 and 54 kD (previously reported by Finlay, D. R., E. Meier, P. Bradley, J. Horecka, and D. J. Forbes. 1991. J. Cell Biol. 114:169-183). p75, p58, and p54 were not galactosylated in vitro. Xenopus oocyte NEs were labeled with gold-conjugated QE5 and prepared for electron microscopy by quick freezing/freeze drying/rotary metal shadowing. This EM preparation method enabled us to more precisely localize the epitopes of this antibody to the cytoplasmic filaments and the nuclear basket of the NPC. Since QE5 recognizes three O-linked NPC glycoproteins, its labeling was compared with that of the lectin wheat germ agglutinin which recognizes O-linked N-acetylglucosamine moieties. The two probes were found to yield similar, although not identical, distributions of label. To identify the individual proteins with particular NPC components, we have used an anti-peptide antibody against NUP153 and a monospecific anti-p250 polyclonal antibody. Labeling with these two antibodies has documented that NUP153 is a constituent of the nuclear basket with at least one of its epitopes residing in its terminal ring, whereas p250 is a constituent of the cytoplasmic filaments.

Sequence analysis of a cDNA encoding a human nuclear pore complex protein, hnup153.

Nuclear pore complexes represent the channels for the the bi-directional movement of macromolecules between the nucleus and cytoplasm, and are thought to contain upwards of 100 different polypeptide subunits. Many of these subunits belong to a growing family of polypeptides termed nucleoporins which are characterized by the presence of O-linked N-acetylglucosamine moieties and a distinctive pentapeptide repeat (XFXFG). This paper reports the primary structure of hnup153, the human homologue of the rat nucleoporin, nup153, with which it shares 82% amino acid identity. In addition to 33 copies of the XFXFG repeat, hnup153 exhibits four repeats of 37-38 amino acids each containing an apparent 'zinc finger motif'. These zinc fingers are most closely related to those found in the mouse oncoprotein mdm-2 and a product of Drosophila small optic lobes (sol) gene.

Independent expression and assembly properties of heterologous lamins A and C in murine embryonal carcinomas.

The majority of cells derived from adult mammalian tissues contain three major species of nuclear lamin proteins, A, B and C. In contrast, embryonic cells including undifferentiated murine embryonal carcinomas, contain only B-type lamins, A and C appearing only after differentiation. Human lamins A or C have been introduced by transfection into undifferentiated P19 embryonal carcinomas. Twenty-four hours after transfection, both of these proteins were found to independently associate with the nuclear envelope as judged by immunofluorescence microscopy and at the same time were associated with a salt-resistant structure having solubility properties similar to those of the nuclear lamina. Biosynthetic experiments indicated that heterologous lamin A underwent processing to its mature molecular weight, an event which in adult type cells occurs after assembly into the lamina. Observations on mitotic cells demonstrate that either of the two human lamins will, independent of the other, become dispersed throughout the cytoplasm during prophase and subsequently reassemble at the nuclear periphery during telophase. Nuclear lamins A and C are not, however, equivalent in their abilities to incorporate into the nuclear lamina in these cells. Experiments involving cells arrested in S phase using thymidine suggest that lamin C, but not lamin A, requires progression through the cell cycle and probably mitosis for assembly into the nuclear lamina of P19 EC cells.

Identification of a 200-kD, brefeldin-sensitive protein on Golgi membranes.

A mAb AD7, raised against canine liver Golgi membranes, recognizes a novel, 200-kD protein (p200) which is found in a wide variety of cultured cell lines. Immunofluorescence staining of cultured cells with the AD7 antibody produced intense staining of p200 in the juxtanuclear Golgi complex and more diffuse staining of p200 in the cytoplasm. The p200 protein in the Golgi complex was colocalized with other Golgi proteins, including mannosidase II and beta-COP, a coatomer protein. Localization of p200 by immunoperoxidase staining at the electron microscopic level revealed concentrations of p200 at the dilated rims of Golgi cisternae. Biochemical studies showed that p200 is a peripheral membrane protein which partitions to the aqueous phase of Triton X-114 solutions and is phosphorylated. The p200 protein is located on the cytoplasmic face of membranes, since it was accessible to trypsin digestion in microsomal preparations, and is recovered in approximately equal amounts in membrane pellets and in the cytosol of homogenized cells. Immunofluorescence staining of normal rat kidney cells exposed to the toxin brefeldin A (BFA), showed that there was very rapid redistribution of p200, which was dissociated from Golgi membranes in the presence of this drug. The effect of BFA was reversible, since upon removal of the toxin, AD7 rapidly reassociated with the Golgi complex. In the BFA-resistant cell line PtK1, BFA failed to cause redistribution of p200 from Golgi membranes. Taken together, these results indicate that the p200 Golgi membrane-associated protein has many properties in common with the coatomer protein, beta-COP.

Identification of a Golgi-associated protein that undergoes mitosis dependent phosphorylation and relocation.

By means of a monoclonal antibody (BH3), we have identified a 57-kD protein (p57) that in interphase is restricted largely to the perinuclear region of the cell. Double label immunofluorescence microscopy suggests localization of p57 to the Golgi complex and associated membranous structures. Protease protection experiments and chemical extractability indicate that p57 is a peripheral membrane protein exposed to the cytoplasm. p57 displays unique behavior during mitosis. At the end of G2 or in early prophase, p57 leaves the perinuclear region and accumulates very rapidly within the nucleus, at a time when the nuclear envelope is still intact and before nuclear lamina disassembly. This relocation of p57 coincides with its hyperphosphorylation on serine and threonine residues. After nuclear envelope breakdown p57 becomes uniformly distributed throughout the mitotic cytoplasm until in late telophase when it returns to its perinuclear location and is once again excluded from the nucleus. The behavior of p57 during mitosis suggests that it may play a role in the cellular reorganization evident during mitotic prophase.

The regulation of glucose transporter gene expression by cyclic adenosine monophosphate in NIH3T3 fibroblasts.

The effect of cAMP on glucose transport was studied in fibroblastic cells. Incubation of confluent NIH3T3 cells for 6 h in the presence of cholera toxin (10 ng/ml) and 3-isobutyl-1-methylxanthine [(IBMX) 0.2 mM] or 8-bromo-cAMP (0.3 mM) and IBMX resulted in a 4-fold increase in the rate of deoxyglucose uptake; no change in hexose transport could be detected after treatment for 30 min. Either cholera toxin (0.3 ng/ml-30 ng/ml) or 8-bromo-cAMP (30 microM-3 mM) increased the expression of the mRNA encoding the glucose transporter (GT) protein, as determined by hybridization of size-fractionated total RNA to a rat brain GT cDNA. Activation of adenylate cyclase by forskolin also rapidly induced a 4- to 10-fold increase in GT mRNA. The rise in the level of GT mRNA was maximal 3-4 h after addition of the drug, and returned to basal values by 16 h. The stimulation was concentration dependent, with forskolin producing a maximal effect at 30 microM. The effect of a submaximal concentration (1 microM) of forskolin was greatly enhanced in the presence of IBMX (0.2 mM), which alone had little effect on GT mRNA levels. The forskolin-stimulated increase in GT mRNA was not blocked by inhibition of protein synthesis by cycloheximide (10 micrograms/ml) or anisomycin (100 microM). The involvement of GT gene transcription was assessed by the nuclear run-on assay. Treatment of the cells with 30 microM forskolin increased transcription 10-fold within 30 min; the activation was not blocked by cycloheximide.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium/proton antiport is required for growth of Escherichia coli at alkaline pH.

Evidence is presented indicating that Escherichia coli requires the Na+/H+ antiporter and external sodium (or lithium) ion to grow at high pH. Cells were grown in plastic tubes containing medium with a very low Na+ content (5-15 microM). Normal cells grew at pH 7 or 8 with or without added Na+, but at pH 8.5 external Na was required for growth. A mutant with low antiporter activity failed to grow at pH 8.5 with or without Na+. On the other hand, another mutant with elevated antiporter activity grew at a higher pH than normal (pH 9) in the presence of added Na+ or Li+. Amiloride, an inhibitor of the antiporter, prevented cells from growing at pH 8.5 (plus Na+), although it had no effect on growth in media of lower pH values.

The lactose carrier of Klebsiella pneumoniae M5a1; the physiology of transport and the nucleotide sequence of the lacY gene.

A comparison has been made between the physiology and amino acid sequence of the lactose carriers of Klebsiella pneumoniae M5a1 and Escherichia coli K-12. The membrane transport of lactose was much weaker in Klebsiella than in E. coli. On the other hand o-nitrophenylgalactoside uptake by Klebsiella was distinctly greater than with E. coli. In spite of the differences in sugar transport between the two organisms, the amino acid sequences of the respective lactose carriers were remarkably similar (60% of the amino acids are identical).