Biomedical subjects

O Blaschuk

Publications and source records attributed to O Blaschuk.

10 recordsLinked to original sources

PubMed2001

Calreticulin affects beta-catenin-associated pathways.

Calreticulin, a Ca(2+) storage protein and chaperone in the endoplasmic reticulum, also modulates cell adhesiveness. Overexpression of calreticulin correlates with (i) increased cell adhesiveness, (ii) increased expression of N-cadherin and vinculin, and (iii) decreased protein phosphorylation on tyrosine. Among proteins that are dephosphorylated in cells that overexpress calreticulin is beta-catenin, a structural component of cadherin-dependent adhesion complexes, a member of the armadillo family of proteins and a part of the Wnt signaling pathway. We postulate that the changes in cell adhesiveness may be due to calreticulin-mediated effects on a signaling pathway from the endoplasmic reticulum, which impinges on the Wnt signaling pathway via the cadherin/catenin protein system and involves changes in the activity of protein-tyrosine kinases and/or phosphatases.

Animals↗

PubMed2000

INP, a novel N-cadherin antagonist targeted to the amino acids that flank the HAV motif.

The classical cadherins are homophilic binding molecules that play fundamental roles in several biological processes, including axonal growth and synaptic plasticity. The structures of the amino-terminal homophilic binding domains of N-cadherin and E-cadherin have been resolved. However, the mechanisms that govern cadherin binding and specificity remain contentious. In the present study we have used a peptide competition approach to probe for small linear determinants of cadherin binding. We demonstrate that a linear peptide mimetic of a short sequence in ECD1 of N-cadherin (INPISGQ) functions as a highly specific and potent antagonist of N-cadherin function with an IC(50) value of approximately 15 microM. Peptide mimetics of the corresponding motif in chick R-cadherin also inhibited N-cadherin function, albeit with lower efficacy. In contrast, peptide mimetics of the corresponding motif in E- or P-cadherin failed to inhibit N-cadherin function. A short cyclic peptide that contained only the INP motif from N-cadherin was also a potent N-cadherin antagonist (IC(50) approximately 15 microM). Analysis of existing crystal structures suggests that the peptides are likely to antagonize N-cadherin function by binding to the region that flanks the HAV motif at the adhesion dimer interface.

3T3 Cells↗

PubMed2000

Follicular atresia and luteolysis. Evidence of a role for N-cadherin.

Studies suggest that cell-cell interactions may regulate apoptosis; and, in particular, the calcium-dependent cell adhesion molecule N-cadherin has been shown to be capable of modulating this process. Here, we review the evidence that N-cadherin is expressed by human granulosa cells (GCs) and mediates cell-cell adhesion between GCs. There is strong correlation between N-cadherin expression by granulosa or luteal cells and follicular survival in isolated follicles and archival tissue sections. There exists a strong expression of the molecule by GCs in follicles of the resting pool, of growing antral follicles, and of healthy corpora lutea. In contrast, the molecule is lost in degenerating GCs of atretic follicles and in luteal cells of the late luteal phase. Further, the experimental evidence demonstrates that cell-cell adhesion is critical to the survival of GCs and that N-cadherin-mediated cell-cell adhesion is a critical mediator of survival signals and inhibits apoptosis in these cells. Possible mechanisms by which apoptosis may be triggerred in GCs include the downregulation of N-cadherin, which is mediated, at least in part, through the enzymatic cleavage of the extracellular domain of the molecule. Collectively, these observations suggest that downregulation of N-cadherin or the absence of a functional extracellular domain of the molecule prevent GC aggregation and is associated with GC apoptosis. We propose that N-cadherin-mediated GC signaling plays a central role in follicular and luteal cell survival.

Apoptosis↗

PubMed1999

N-cadherin-mediated human granulosa cell adhesion prevents apoptosis: a role in follicular atresia and luteolysis?

Studies suggest that cell-cell interactions may regulate apoptosis, and in particular, the calcium-dependent cell adhesion molecule N-cadherin has been shown to be capable of modulating this process. Rat granulosa cells (GCs) are known to express N-cadherin whereas cAMP is known to induce apoptosis in human and rat GCs. Based on these observations, we hypothesized that N-cadherin regulates human GC apoptosis via a cAMP-dependent mechanism. N-cadherin expression was evaluated in ovarian follicles and corpora lutea utilizing immunohistochemical techniques and in luteinized GCs in culture using immunoblotting, flow cytometric analysis, immunohistochemistry, and indirect immunofluorescence techniques utilizing anti-N-cadherin antibodies directed against both the extracellular and cytoplasmic domains of the molecule. Apoptosis was assessed by TUNEL and DNA fragmentation analysis and confirmed by flow cytometric cell cycle analysis and electron microscopy. The rate of GC apoptosis was found to be two- to three-fold lower among aggregated cells, as compared with single cells. N-cadherin was found to be expressed by aggregating GCs in vitro and GCs cultured in the presence of either N-cadherin function disrupting antibodies or peptides exhibiting enhanced rates of apoptosis. GCs in situ stained intensely for N-cadherin in preantral and normal growing preovulatory follicles as well as early corpora lutea. N-cadherin was weak in atretic follicles and regressing corpora lutea. Exposure of GCs to cAMP increased apoptosis while decreasing N-cadherin protein expression in a dose-dependent manner. Cell culture under serum-free conditions increased apoptosis and decreased N-cadherin expression, in part through cleavage of the extracellular domain of the molecule. The metalloproteinase inhibitor 1-10-phenanthroline inhibited the cleavage of the extracellular domain of N-cadherin and concomitantly inhibited the serum-deprivation-induced apoptosis of aggregated GCs. Collectively, these observations suggest that down-regulation of N-cadherin or the absence of a functional extracellular domain of the molecule prevents cell aggregation and is associated with GC apoptosis. In addition, cAMP induces apoptosis in a dose-dependent manner, and this process is dependent, at least in part, on regulation of the N-cadherin molecule at the surface of the cells. We conclude that N-cadherin-mediated GC signaling plays a central role in follicular and luteal cell survival.

Adult↗

PubMed1998

Activated T-lymphocytes express occludin, a component of tight junctions.

T-lymphocytes routinely traffic from the lymphoid and vascular compartments to the tissues during immune surveillance and inflammatory responses. This egress occurs without compromising endothelial barrier, which is maintained by tight junctions (zonula occludens). We report that T-lymphocytes up-regulate the expression of occludin, a major component of the tight junction in response to stimulation with phorbol ester (PMA) + calcium ionophore, CD3 antibody or T-cell receptor (TCR) antibody. Only activated T-lymphocytes express occludin; this adhesion molecule is nearly absent in resting T-lymphocytes. By immunofluorescence, occludin is seen in lymphocyte aggregates, but does not appear to mediate aggregation since only 50% of the cells in these clusters express occludin. Occludin is expressed between 8 and 24 h following stimulation, and persists for at least 48 h. These data indicate that activated T cells produce occludin which may regulate lymphocyte adhesion and trafficking.

Animals↗

PubMed1992

Fibroblast growth factor receptors contain a conserved HAV region common to cadherins and influenza strain A hemagglutinins: a role in protein-protein interactions?

The first extracellular domain of the cadherins has been shown to exhibit extensive sequence homology with the amino termini of the HA1 chains of influenza strain A hemagglutinins. These regions of homology are known to be functionally important in both the cadherins and the hemagglutinins. The homologous regions harbor the tripeptide HAV, which has been identified as being the cadherin cell adhesion recognition sequence. Here we report that members of the rapidly expanding family of fibroblast growth factor receptors also possess HAV-containing regions. These regions are homologous to the HAV-containing regions present within both the hemagglutinins and the cadherins and appear to be involved in regulating the function of the fibroblast growth factor receptors. We speculate that the HAV motif may represent an evolutionarily conserved amino acid sequence that will prove to be functionally important in a wide variety of proteins.

Amino Acid Sequence↗

PubMed1991

Differentiation and survival of rat olfactory epithelial neurons in dissociated cell culture.

Olfactory epithelial neurons in mammals are unique in that they continue to differentiate from precursor cells in the adult. These neurons extend long axons into the olfactory bulb. Previous attempts to grow these cells in dissociated cell cultures at low density, have not been entirely satisfactory. We report that when plated at very low density, rat olfactory epithelial neurons will differentiate morphologically and biochemically when cultured on astrocytes, but not on non-cellular substrata, such as polylysine, laminin or fibronectin. We demonstrate with antibodies, that these olfactory epithelial neurons require N-CAM, N-cadherin and L1 for neurite extension. Furthermore, synthetic cadherin-peptides containing the tripeptide HAV which is found in the first extracellular domain of N-cadherin, as well as the amino acids flanking this region, appear to be important in cadherin-mediated neurite growth on astrocytes. Astrocytes also appear to enhance the survival and differentiation of olfactory epithelial neurons from embryonic day 15 and 4-5 week post-natal rats, but this effect is not sustained beyond 5 days in cultures of postnatal epithelium.

Amino Acid Sequence↗

PubMed1983

Purification and characterization of a cell-aggregating factor (clusterin), the major glycoprotein in ram rete testis fluid.

Clusterin has been purified from ram rete testis fluid by conventional techniques and by immunoaffinity chromatography. The molecule is characterized as a glycoprotein having a molecular mass of approximately 80,000 Da and an isoelectric point of 3.6. The purified protein retains the capacity to elicit clustering of cells in an in vitro assay. Under reducing conditions in the presence of sodium dodecyl sulfate, clusterin dissociates into subunits of about 40,000 Da. Heterogeneities in apparent molecular mass were eliminated after treatment of clusterin with neuraminidase. Gel filtration chromatography revealed that clusterin exists in dimeric and tetrameric forms under conditions of neutral pH and low salt concentrations. In the presence of 6 M urea, only the monomeric form is evident, with an apparent molecular mass of approximately 85,000 Da. Clusterin, which was found to contain 4.5% glucosamine, binds to concanavalin A-Sepharose and also to wheat germ agglutinin Sepharose. The amino acid composition of clusterin is reported. The possible cellular source of clusterin in rete testis fluid is discussed. It is shown that Sertoli cells in the seminiferous tubule are one potential source, since primary cultures of rat Sertoli cells secrete a protein having the same immunochemical and physical properties as clusterin isolated from ram rete testis fluid. Possible functions of clusterin are discussed.

Amino Acids↗

PubMed1983

Ram rete testis fluid contains a protein (clusterin) which influences cell-cell interactions in vitro.

Ram rete testis fluid is shown to elicit clustering of suspensions of Sertoli cells from testes of immature rats, TM-4 cells derived from mouse testis, and erythrocytes from several species. Details of bioassay procedures and characteristics of the phenomenon are reported. Concanavalin A and wheat germ agglutinin prevent aggregation elicited by rete testis fluid, and this inhibition is specifically prevented by alpha-methylmannoside and N-acetyl-glucosamine, respectively. Influences of rete testis fluid on cell aggregation are not dependent on exogenous calcium, but clustering is blocked by various metabolic inhibitors such as dinitrophenol. Rete testis fluid addition to mixed suspensions of erythrocytes and TM-4 cells is followed by separate aggregation of each cell types. Using aggregation of TM-4 cells suspended in simple medium at low density in rotation as a bioassy, we have determined which fractions in rete testis fluid retain activity. We have shown that a heat-stable, trypsin-sensitive protein, having an isoelectric point below pH 4.0, retains the capacity to aggregate cells. We discuss the possible functions of this protein, named clusterin, in cell interactions.

Animals↗

PubMedDate not supplied

Reproductive tract secretions and bull spermatozoa contain different clusterin isoforms that cluster cells and inhibit complement-induced cytolysis.

Clusterin from bull rete testis fluid (RTF), cauda epididymal fluid (CEF), and octyl-beta-D-glucopyranoside extract of cauda epididymal sperm (CES) was identified and characterized using monoclonal and polyclonal antibodies (Abs) developed against ram clusterin and a beta-subunit-specific oligopeptide of porcine clusterin. One-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis and western blotting showed that bovine RTF clusterin had dimeric and monomeric molecular weights (M(r)s) of approximately 94 kDa and of 42 and 43 kDa, respectively. Clusterin in CEF and CES had similar dimeric M(r)s (74 kDa). Reduced CEF clusterin appeared as three monomers (M(r)=40, 39, and 38 kDa), whereas reduced CES clusterin appeared only at M(r)40 kDa. Enzymatic deglycosylation resulted in similar M(r)s of clusterin from RTF, CEF, and CES. The M(r) of RTF clusterin decreased from 94 kDa to 51 kDa, indicating a carbohydrate content of 45%. After deglycosylation, the M(r) of the CEF clusterin decreased from 74 kDa to two distinct bands at 51 and 50 kDa (with carbohydrate contents of 31 and 32%, respectively), suggesting that two isoforms of the heterodimeric protein are present because of the two isoforms of the alpha-subunit. Under nonreduced conditions, a beta-subunit-specific Ab reacted with M(r) of 36-38 kDa, indicating the existence of free clusterin beta-subunits in CES. RTF, CEF, and CES extracts all caused mouse fibroblastic L-cell aggregation. CEF cell aggregation was inhibited by Hyb-17 Ab but not by other Abs. Both RTF and CEF caused a dose-dependent inhibition of complement-induced cytolysis, although RTF clusterin was more potent than CEF clusterin. We conclude that several isoforms of clusterin occur in the bull reproductive tract and that the variation in carbohydrate content among these isoforms may affect the biological or functional activity of the protein.

Animals↗