Use of an immobilized human endogenous lectin for the purification of complementary ligands

Capsaicin binds the N-terminus of Hsp90, induces lysosomal degradation of Hsp70, and enhances the anti-tumor effects of 17-AAG (Tanespimycin)

Heat shock protein 90 (Hsp90) and its co-chaperones promote cancer, and targeting Hsp90 holds promise for cancer treatment. Most of the efforts to harness this potential have focused on targeting the Hsp90 N-terminus ATP binding site. Although newer-generation inhibitors have shown improved efficacy in aggressive cancers, induction of the cellular heat shock response (HSR) by these inhibitors is thought to limit their clinical efficacy. Therefore, Hsp90 inhibitors with novel mechanisms of action and that do not trigger the HSR would be advantageous. Here, we investigated the mechanism by which capsaicin inhibits Hsp90. Through mutagenesis, chemical modifications, and proteomic studies, we show that capsaicin binds to the N-terminus of Hsp90 and inhibits its ATPase activity. Consequently, capsaicin and its analogs inhibit Hsp90 ATPase-dependent progesterone receptor reconstitution in vitro. Capsaicin did not induce the HSR, instead, it promoted the degradation of Hsp70 through the lysosome-autophagy pathway. Remarkably, capsaicin did not induce degradation of the constitutively expressed cognate Hsc70, indicating selectivity for Hsp70. Combined treatments of capsaicin and the Hsp90 inhibitor 17-AAG improved the anti-tumor efficacy of 17-AAG in cell culture and tridimensional tumor spheroid growth assays using breast and prostate cancer models. Consistent with this, in silico docking studies revealed that capsaicin binding to the ATP binding site of Hsp90 was distinct from classical N-terminus Hsp90 inhibitors, indicating a novel mechanism of action. Collectively, these findings support the use of capsaicin as a chemical scaffold to develop novel Hsp90 N-terminus inhibitors as well as its ability to be a potential cancer co-therapeutic.

Interaction of pepsin with aromatic amino acids and their derivatives immobilized to Sepharose

The interaction of porcine pepsin A with immobilized derivatives of aromatic amino acids was investigated. Divinyl sulfone-activated Sepharose was used to immobilize N-acetyl-l-phenylalanine and 3,5-diiodo-l-tyrosine via their free carboxyl groups and l-tyrosine via its amino group. Immobilized l-tyrosine was iodinated after coupling. The optimum conditions for the separation of porcine pepsin A using the prepared affinity carriers were studied and the following parameters were established: enzyme recovery, reproducibility of analyses, capacity and dependence of the elution peak area on the concentration of the loaded enzyme. The ability of the prepared affinity carriers to retain various types of proteins was compared under optimum conditions for porcine pepsin A separation. While immobilized 3,5-diiodo-l-tyrosine and iodinated l-tyrosine-Sepharose adsorbed relatively high amounts of bovine serum albumin and ovalbumin, only negligible amounts of these proteins were adsorbed to immobilized N-acetyl-l-phenylalanine. The behavior of porcine pepsin A was the same as its complex with pepstatin A on the prepared affinity carriers, indicating that the enzyme active site is not involved in the studied interaction.

GCUNC-45 is a novel regulator for the progesterone receptor/hsp90 chaperoning pathway

The hsp90 chaperoning pathway is a multiprotein system that is required for the production or activation of many cell regulatory proteins, including the progesterone receptor (PR). We report here the identity of GCUNC-45 as a novel modulator of PR chaperoning by hsp90. GCUNC-45, previously implicated in the activities of myosins, can interact in vivo and in vitro with both PR-A and PR-B and with hsp90. Overexpression and knockdown experiments show GCUNC-45 to be a positive factor in promoting PR function in the cell. GCUNC-45 binds to the ATP-binding domain of hsp90 to prevent the activation of its ATPase activity by the cochaperone Aha1. This effect limits PR chaperoning by hsp90, but this can be reversed by FKBP52, a cochaperone that is thought to act later in the pathway. These findings reveal a new cochaperone binding site near the N terminus of hsp90, add insight on the role of FKBP52, and identify GCUNC-45 as a novel regulator of the PR signaling pathway.

Immobilization of L-glyceryl phosphorylcholine: isolation of phosphorylcholine-binding proteins from seminal plasma

The preparation of an affinity sorbent containing immobilized L-glyceryl phosphorylcholine for affinity chromatography of phosphorylcholine-binding proteins from seminal plasma is described. The ligand was coupled either after its maleinylation to poly(acrylamide-allyl amine) copolymer or directly to divinyl sulfone-activated Sepharose. The prepared phosphorylcholine derivative coupled to Sepharose was used for affinity chromatography of phosphorylcholine-binding proteins from bull and boar seminal plasma. Adsorbed proteins were specifically eluted with phosphorylcholine solution. Isolated phosphorylcholine-binding proteins were characterized by SDS electrophoresis and HPLC with reversed phase. Composition of the boar phosphorylcholine-binding fraction obtained by affinity chromatography on immobilized L-glyceryl phosphorylcholine was compared with that eluted from immobilized heparin by the phosphorylcholine solution. No phosphorylcholine-binding proteins were found in human seminal plasma.

Affinity chromatography of porcine pepsin on different types of immobilized 3,5-diiodo-L-tyrosine

The preparation of affinity sorbents containing immobilized iodinated derivatives of L-tyrosine for the affinity chromatography of porcine pepsin is described. The ligand was coupled either to Sepharose 4B or bead cellulose after the divinylsulfone activation or to Sepharose 4B after the activation with 2,4,6-trichloro-1,3,5-triazine. The highest capacity for porcine pepsin was found in the case of 3,5-diiodo-L-tyrosine coupled to divinylsulfone-activated Sepharose.

Analysis of galectin 1-mediated cell signaling by combined precipitation and electrophoresis techniques

Galectin-1 (GAL1) is a beta-galactoside-binding protein that has been implicated in the regulation of viability of lymphoid cells. However, the signaling pathway governed by the binding of GAL1 to the cell membrane is not understood yet. As a first step toward the elucidation of GAL1-initiated signaling events, electrophoresis techniques such as sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and two-dimensional electrophoresis (2-DE) were used together with precipitation techniques. This allowed us to identify the membrane receptor of GAL1, and to characterize the signal resulting from the binding of GAL1 to this receptor. Our results demonstrate that the tyrosine phosphatase CD45 is the receptor for GAL1, and that the src-type tyrosine kinase Lyn is a target for the effects of GAL1/CD45 interactions in B-cells. Furthermore, these results show the usefulness of combined precipitation and electrophoresis techniques to analyze phosphotyrosine-dependent mechanisms during the study of cell functions.

Heat-induced oligomerization of the molecular chaperone Hsp90. Inhibition by ATP and geldanamycin and activation by transition metal oxyanions

It has been previously reported that heat shock protein 90 (Hsp90) oligomerizes at high temperatures and displays concomitantly a novel chaperone activity (Yonehara, M., Minami, Y., Kawata, Y., Nagai, J., and Yahara, I. (1996) J. Biol. Chem., 271, 2641-2645). In order to better define these oligomerization properties at high temperatures and to know whether they are influenced by modulators of Hsp90 function, heat-induced oligomerization of highly purified dimeric Hsp90 has been investigated over a wide range of temperature and protein concentrations by native polyacrylamide gel electrophoresis and size exclusion chromatography. Whereas below 50 degreesC, the dimeric form is maintained over a large range of concentrations, at the critical temperature of 50 degreesC, a sharp transition from dimeric to higher order oligomeric species takes place within minutes, in a highly ordered process, suggesting that a conformational change, leading to the appearance of a new oligomerization site, occurs in Hsp90 dimer. Moreover, at and above the critical temperature, the extent of oligomerization increases with Hsp90 concentration. Formation of high order oligomers at high temperatures is sensitive to modulators of Hsp90 function. ATP and geldanamycin, both known to bind to the same pocket of Hsp90, are inhibitors of this process, whereas molybdate, vanadate, and Nonidet P-40, which are thought to increase surface hydrophobicity of the protein, are activators. Thus, oligomerization of Hsp90 at high temperatures may be mediated through hydrophobic interactions that are hindered by ligands and favored by transition metal oxyanions. The fact that the heat-induced oligomerization of Hsp90 is affected by specific ligands that modulate its properties also suggests that this process may be involved in cell protection during heat shock.

Glycoaffinity chromatography and biological recognition

The potential of bioaffinity chromatography as a tool for study of biological recognition mechanisms is gaining increasing recognition. Biochromatographic methods allow the separation of proteins according to both the structure of their polypeptidic chain and their post-translational modifications. Among the various post-translational modifications which proteins undergo, glycosylation has conducted to the development of original methods (glycotechnologies). This review discusses the applications of glycotechnologies in bioaffinity chromatography, and particularly the use of biochromatography to elucidate mechanisms involved in glycobiology.

Galectin-1 is a major receptor for ganglioside GM1, a product of the growth-controlling activity of a cell surface ganglioside sialidase, on human neuroblastoma cells in culture

Cell density-dependent inhibition of growth and neural differentiation in the human neuroblastoma cell line SK-N-MC are associated with a ganglioside sialidase-mediated increase of GM1 and lactosylceramide at the cell surface. Because these glycolipids expose galactose residues, we have initiated the study of the potential role of galectins in such cellular events. Using specific antibodies, galectin-1 but not galectin-3 was found to be present at the cell surface. Assessment of carbohydrate-dependent binding revealed a saturable amount of ligand sites approaching 2.6 x 10(6) galectin-1 molecules bound/cell. Presence during cell culture of the sialidase inhibitor 2-deoxy-2,3-dehydro-N-acetylneuraminic acid or of the GM1-binding cholera toxin B subunit effected a decrease of the presentation of galectin-1 ligands by 30-50%. The assumption that GM1 is a major ligand for galectin-1 was reinforced by the correlation between the number of carbohydrate-dependent 125I-iodinated GM1-neoganglioprotein binding sites and the amount of immunoreactive surface galectin-1, the marked sensitivity of probe binding to the presence of anti-galectin-1 antibody, and the inhibition of cell adhesion to surface-immobilized GM1 by the antibody. The results open the possibility that the carbohydrate-dependent interaction between ganglioside GM1 and galectin-1 may relay sialidase-dependent alterations in this cell system.

Cell calcium signalling induced by endogenous lectin carbohydrate interaction in the Jurkat T cell line

The effects of the beta-galactoside-binding lectin from human placenta (HPL14) on intracellular calcium concentration ([Ca2+]i) were examined in the human Jurkat T cell line. The lectin induces a concentration dependent increase in [Ca2+]i. This calcium signalling effect is clearly mediated through complementary cell surface galactoglycoconjugates because it can be blocked by beta-galactosides. The observed Ca2+ - response involves both the release of calcium from intracellular stores and a calcium influx from the extracellular space. It is sustained in the presence of 1 mM extracellular calcium whereas it becomes transient when the influx of extracellular calcium was blocked by calcium chelation to EGTA. Voltage-sensitive calcium channel blockers like verapamil and prenylamine were without effect on the action of HPL14. Protection of the sugar binding activity of HPL14 in the absence of a thiol-reducing reagent by carboxamidomethylation (CM-HPL14) or by substitution Cys2 with serine (C2S) results in lectin proteins with considerably decreased calcium signalling efficiency. The recombinant lectin (Rec H) and the mutant protein obtained by substitution of highly conservative Trp68 with tyrosine (W68Y) induce lower levels of [Ca2+]i compared to wild type lectin.

Purification and characterization of natural antibodies that recognize a human brain lectin

We have recently identified oligoclonal IgG antibodies that are related to a human brain lectin (HBL14) from serum and cerebrospinal fluid of patients with neurological disorders. They were termed lectin-like IgG (L-IgG) (Joubert-Caron et al., 1994a,b). In this paper, the occurrence of antibodies reactive both towards HBL14 and L-IgG was investigated. Binding of antibodies to HBL14 was demonstrated by solid-phase ELISA and chromatography on immobilized HBL14. Fab fragments of these antibodies were also shown to bind to HBL14. The specificity of the antibodies towards HBL14 was studied using a panel of different antigens. Our data show that individual sera from healthy people as well as a pool of immunoglobulins from 80 blood donors contain an IgG autoreactivity to HBL14, while no IgM autoreactivity was detected. Anti-HBL14 antibodies from sera were purified using affinity chromatography on immobilized HBL14. Affinity chromatography further allowed us to demonstrate that the binding of anti-HB14 antibodies was mediated through their Fab fragments. A higher amount of anti-HBL14 antibodies was purified using a L-IgG-depleted fraction of sera. The binding of anti-HBL14 antibodies to L-IgG was confirmed by ELISA. Finally, anti-HBL14 antibodies were found to be polyreactive. These results indicate the occurrence of a novel class of natural antibodies reactive towards a human brain lectin and suggest that these antibodies may participate in immunoregulatory mechanisms probably though idiotypic/anti-idiotypic interaction.

Oligoclonal beta-galactoside-binding immunoglobulins antigenically related to 14 kDa lectin in human serum and cerebrospinal fluid: purification and characterization

1. An antiserum raised against a 14 kDa beta-galactoside specific lectin from human brain (HBL14) was used to probe blots from samples of serum and cerebrospinal fluid. The only HBL14-immunoreactive material detected was heavy and light chains of a beta-galactoside-binding IgG fraction (lectin-like IgG). 2. Lectin-like IgG, as well as IgG Fab fragments, compete with HBL14 for binding either to anti-HBL14 antibody or to a lactosyl polyacrylamide-based copolymer. 3. Purification of lectin-like IgG was obtained by affinity chromatography on immobilized rabbit anti-lectin immunoglobulins. The carbohydrate-binding specificity of the purified molecules was restricted to beta-Gal-containing structures and close to the HBL14 one.