Phorbol 12,13-dibutyrate (P(Bu)2)-treated human blood mononuclear cells bind to each other

Treatment of human blood mononuclear cells with nanomolar concentrations of phorbol 12,13-dibutyrate (P(Bu)2) induced their aggregation. The phenomenon was seen within a few minutes and reached its maximum manifestation after 20 min. At this time, 20-30% of unfractionated and nylon wool-passed mononuclear leukocytes were in the aggregates. The influence of pretreatment with 2-deoxyglucose, NaN3, EDTA, cyclohexamide, or incubation at 4 degrees C on the phenomenon indicated that it is energy and temperature dependent, requires the presence of extracellular divalent cations, and is independent of protein synthesis. Nonaggregating 2-deoxyglucose-and NaN3-pretreated cells could still bind [3H]P(Bu)2 which rules out the possibility that the phorbol ester molecule acts as a bridge between the aggregated cells. Seventeen percent of the P(Bu)2-treated T-cell population bound untreated autologous and allogeneic cells. The binding property has a certain species specificity because only 4% of the cells interacted with mouse lymphocytes. At the ultrastructural level, the intercellular binding showed broad areas of surface contact (both between lymphocytes and lymphocyte-monocyte) and "trapping" by surface processes was not seen. Aggregated cells did not show cytopathogenic changes.     

ICAM-2 peptides mediate lymphocyte adhesion by binding to CD11a/CD18 and CD49d/CD29 integrins.

Three fifteen-amino-acid polypeptides designated peptides 1, 2 and 3 were synthesised as likely candidates for mimicking the role of ICAM-2 as a ligand. The ability of each peptide to bind lymphoid cells was tested. Peptide 2 largely mediated cell attachment of unstimulated cells and this binding was only marginally increased by stimulating the cells with phorbol dibutyrate (P(Bu)2). Peptide 3 mediated minimal spontaneous cell attachment, but this binding was significantly enhanced following P(Bu)2 stimulation. Peptide 1 had no effect on cell attachment with or without stimulation. The cell attachment to peptide 2 was both temperature- and cation-dependent. Studies using specific monoclonal antibodies showed that with unstimulated cells, anti-VLA-4 alpha(CD49d) or beta chain (CD29) antibodies (KD4-13 and 4B4) and anti-CD18 (1B4) each partially inhibited the cell binding. Monoclonal antibodies against CD54 (ICAM-1; 84H10 or LB2), MHC class 1 (W6/32) and control mouse IgG had no effect. When anti-CD29 and anti-CD18 monoclonal antibodies were used concurrently, there was almost complete inhibition of the cell attachment. These observations indicated that cell adhesion via ICAM-2 is mediated: (i) predominantly by peptide 2 in unstimulated and P(Bu)2-stimulated cells, and also, to some extent, by peptide 3 in P(Bu)2-stimulated cells and (ii) by binding to both CD11/CD18 and CD49d/CD29 integrins.     

Modulation of human blood lymphocyte cytotoxicity by the phorbol ester tumor promoter P(Bu)2: Increase of target binding,impairment of effector recycling,and activation of lytic potential which is independent of IL-2

Treatment of lymphocytes with the tumor promoter P(Bu)₂ enhanced their target-binding capacity. In the conventional ⁵¹Cr-release assay, the cytotoxic potential of lymphocytes pretreated with P(Bu)₂ for a short time was reduced while after prolonged treatment their function was increased. The peak of lytic potential was attained after 15 hr of exposure. Comparison of the cytotoxic results obtained in suspension and immobilized conjugate assays suggested that P(Bu)₂ treatment causes an impairment of the recycling capacity of lymphocytes. After prolonged exposure, the lytic machinery became activated as reflected by the reduced time elapsing after contact between effectors and targets and the delivery of lethal hit. The activation was also observed in the immobilized agarose assay. It was reflected by the elevated proportion of damaged targets that were bound to the treated lymphocytes. The P(Bu)₂- and interferon-induced augmentation of lytic potential is achieved through different mechanims. Combination treatment applied to the effectors in sequence (first P(Bu)₂ followed by interferon), resulted in an additive effect. Similarly, simultaneous treatment with IL-2 and P(Bu)₂ also gave an additive increase in cytotoxicity. Addition of antibodies directed against IL-2 did not abrogate the P(Bu)₂ effect. Consequently, neither interferon nor IL-2 are involved in the phorbol ester-induced cytotoxic function.     

A human intercellular adhesion molecule (ICAM-1) distinct from LFA-1

Homotypic adhesion by phorbol ester-stimulated lymphocytes requires LFA-1 and Mg+2 and does not involve like-like interactions between LFA-1 molecules on adjacent cells. The latter finding suggested that a second molecule, distinct from LFA-1, also participates in LFA-1-dependent adhesion. The identification of such a molecule was the object of this investigation. After immunization with LFA-1-deficient EBV-transformed lymphoblastoid cells, a MAb was obtained that inhibits phorbol ester-stimulated aggregation of LFA-1+ EBV lines. This MAb defines a novel cell surface molecule, which is designated intercellular adhesion molecule 1 (ICAM-1). ICAM-1 is distinct from LFA-1 in both cell distribution and structure. In SDS-PAGE, ICAM-1 isolated from JY cells is a single chain of Mr = 90,000. As shown by MAb inhibition, ICAM-1 participates in phorbol ester-stimulated adhesion reactions of B lymphocyte and myeloid cell lines and T lymphocyte blasts. However, aggregation of one T lymphocyte cell line (SKW-3) was inhibited by LFA-1 but not ICAM-1 MAb. It is proposed that ICAM-1 may be a ligand in many, but not all, LFA-1-dependent adhesion reactions.     

Antigen Binding Lymphocytes in Congenitally Athymic (Nude) Mice

THE autoradiographic detection of the binding of various radiolabelled antigens to a proportion of lymphocytes from animals not exposed to those antigens (“nonprimed” lymphocytes) is well documented^1–4. Such lymphocytes are thought to have patches of surface immunoglobulin, primarily IgM, which act as specific receptors for antigen^5,6. A proportion at least of these unprimed lymphocytes are immunologically competent as shown in vivo^7,8 and hence are true antigen reactive cells. Most assays have used peripheral lymphocyte suspensions from tissues of man, mouse, rat and chicken, not enriched or fractionated in any way for the two distinct lines of lymphocytes, thymic derived (T) and non-thymic derived (B)⁹. It is not clear whether antigen-binding cells (ABC), detected in routine assays where autoradiographs are exposed for 1–2 weeks, are of both T and B cell type or are predominantly of only one type. Experiments using unlabelled and radiolabelled immunoglobulin antisera with isolated T and B cells have inferred specific antigen binding on both populations although T cells seem to have far fewer antigen binding receptors than B cells¹⁰.     

CD40 signaling activates CD11a/CD18 (LFA-1)-mediated adhesion in B cells.

Cell-cell adhesion events play critical roles in the sequential migrations and multiple specific cell-cell interactions which B cells undergo during normal development and function. We have observed that mAb to several B cell-associated molecules, including mAb to CD19, CD37, and CD40, induce homotypic aggregation of freshly isolated human B cells. The aggregation of B cells induced by CD40 mAb was due to activation of a cell-cell adhesion system, and not due to agglutination by mAb, because 1) in addition to being energy dependent and cation dependent, the aggregation was blocked by inhibitors of messenger RNA and protein synthesis; and 2) a mouse B cell line transformed with intact human CD40 aggregated in response to CD40 mAb, whereas a line expressing surface CD40, but lacking the cytoplasmic tail and previously shown incapable of transmitting a signal from the cell surface, did not aggregate. The aggregation, although of slow onset, was persistent and of high avidity. In addition, CD40 mAb induced increased surface expression of intercellular adhesion molecule-1 (CD54), a ligand for CD11a/CD18 (LFA-1), and CD18 mAb blocked aggregation. CD40 mAb also augmented the ability of dense B cells to stimulate the proliferation of allogeneic T cells via a CD18-dependent process. We conclude that signaling through CD40, elicited by cross-linking the CD40 protein on the cell surface, activates the CD18/intercellular adhesion molecule adhesion system; in addition, CD40 cross-linking may activate a second adhesion system since CD40 mAb induced aggregation of the B cell line Ramos, which does not express surface CD18. B cell adhesion may be triggered by signaling through multiple surface proteins, thereby lending specificity of activation to adhesion systems which are broadly expressed.     

Modulation of the adherence of human lymphocytes to measles-infected cells by prostaglandin E1: A differential effect on lymphocyte subpopulations

Prostaglandins of the E series (PGE) may serve as important regulators of human immune responsiveness. The present study was designed to examine the possibility that PGE may effect human lymphocyte function by the modulation of surface receptors. The presence of surface binding sites on human lymphocytes for measles virus antigens was studied using a rosette adherence assay. We observed that the addition of PGE₁ increased the proportion of measles-infected cells (Hela-Kll) with adherent lymphocytes (75% increase at 3 × 10⁻⁶ M PGE₁). PGE was observed to enhance the adherence of purified normal peripheral T cells (87%) and T lymphoid cells (Molt 3) (27%). In contrast, no significant change in normal peripheral B cell or B lymphoid cell (Raji) adherence was observed with the addition of PGE. These results are consistent with a selective modulation of surface measles virus binding sites by PGE₁ on T and not B lymphoid cells.     

The (2′S,7′S)-O-(2-methylbutanoyl)-columbianetin as a novel allergic rhinitis-control agent

Aims

The (2′S,7′S)-O-(2-methylbutanoyl)-columbianetin (OMC) is a novel secondary metabolite extracted from Corydalis heterocarpa, which has long been used as a folk medicine for various inflammatory diseases in Korea. We examined the effect of OMC on allergic rhinitis (AR).

Main methods

We assessed the therapeutic effects and regulatory mechanisms of OMC on the phorbol 12-myristate 13-acetate plus A23187-stimulated mast cell line, HMC-1 cells and ovalbumin (OVA)-induced AR models.

Key findings

OMC significantly decreased the releases of histamine and tryptase from stimulated HMC-1 cells. The degranulation process, characterized by morphological extension of the filopodia on the surface and membrane ruffling, was strongly induced in the stimulated-HMC-1 cell, however OMC suppressed the morphological changes in stimulated-HMC-1 cells. OMC reduced the production and mRNA expression of inflammatory cytokines. These inhibitory actions by OMC were dependent on the regulation of mitogen-activated protein kinases, nuclear factor-κB, and caspapase-1 signaling pathways. In the AR animal model, the increased rub scores and AR biomarkers (histamine and IgE) in ovalbumin (OVA)-sensitized mice were significantly reduced by the administration of OMC. Furthermore, eosinophils and mast cell infiltrations in nasal mucosa tissue were also blocked through the regulation of macrophage-inflammatory protein and intercellular adhesion molecule-1 levels.

Significance

OMC showed the possibility to regulate AR in activated mast cells and OVA-induced AR models. Hence, we suggest that OMC is a powerful and feasible new agent to suppress AR.     

Binding of alpha 1 antitrypsin (alpha 1 protease inhibitor) to human lymphocytes

Radioiodinated α₁ antitrypsin has been found to bind to human lymphocytes. This binding is fast and reversible, and the cells can be saturated. Each lymphocyte can bind a maximum of approximately 1.2 × 10⁶ molecules of α₁ antitrypsin with an association constant of 0.7 × 10⁶ M^?1×l. The binding is inhibited by the addition of cold α₁ antitrypsin or Soybean trypsin inhibitor, and partially by α₂ macroglobulin. The data suggest that α₁ antitrypsin is likely to bind to a cell surface-associated protease. The addition of cell-free supernatants from lymphocytes incubated at 37°C was found to decrease the binding of α₁ antitrypsin, suggesting that the receptor is released from the cell surface.     

Enhancement of phorbol ester induced cell aggregation after alterations in asparagine-linked oligosaccharides

Summary— Human erythroleukemia (K-562) cells grown in the presence of phorbol 12,13-dibutyrate formed aggregates of cells not seen in untreated control cultures. Furthermore, the proportion of cells in aggregates and the size of the aggregates both increased dramatically in cultures treated with both phorbol ester and kifunensine, an inhibitor of asparagine-linked oligosaccharide processing. Relative to control cells, phorbol ester treated cells exhibited a greater proportion of N-linked oligosaccharides of the complex-type. Kifunensine prevented this change and caused an accumulation of Man₉GlcNAc₂. The enhanced aggregation of cells treated with phorbol ester plus kifunensine depended on phorbol ester concentration and was blocked by inhibitors of protein kinase C (H7, sphinganine and sangivamycin). In flow cytometry analysis, phorbol ester treated K-562 cells showed an increase in CD44, a glycoprotein involved in cell adhesion. Moreover, monoclonal antibody to CD44 augmented reaggregation of phorbol ester treated cells. The results implicate phorbol ester induction of CD44 in aggregation of K-562 cells and demonstrate that the presence of high mannose-type asparagine-linked oligosaccharides on cell glycoproteins correlates with increased aggregation of phorbol ester treated cells.     

Induction by IL 1 and interferon-gamma: tissue distribution, biochemistry, and function of a natural adherence molecule (ICAM-1)

ICAM-1 is a cell surface glycoprotein originally defined by a monoclonal antibody (MAb) that inhibits phorbol ester-stimulated leukocyte aggregation. Staining of frozen sections and immunofluorescence flow cytometry showed intercellular adhesion molecule-1 (ICAM-1) is expressed on non-hematopoietic cells such as vascular endothelial cells, thymic epithelial cells, certain other epithelial cells, and fibroblasts, and on hematopoietic cells such as tissue macrophages, mitogen-stimulated T lymphocyte blasts, and germinal center dendritic cells in tonsils, lymph nodes, and Peyer's patches. ICAM-1 staining on vascular endothelial cells is most intense in T cell areas in lymph nodes and tonsils showing reactive hyperplasia. ICAM-1 is expressed in low amounts on peripheral blood leukocytes. Phorbol ester-stimulated differentiation of myelomonocytic cell lines greatly increases ICAM-1 expression. ICAM-1 expression on dermal fibroblasts is increased threefold to fivefold by either interleukin 1 (IL 1) or interferon-gamma at 10 U/ml over a period of 4 or 10 hr, respectively. The induction is dependent on protein and mRNA synthesis and is reversible. ICAM-1 displays Mr heterogeneity in different cell types with a Mr of 97,000 on fibroblasts, 114,000 on the myelomonocytic cell line U937, and 90,000 on the B lymphoblastoid cell JY. ICAM-1 biosynthesis involves a Mr approximately 73,000 intracellular precursor. The non-N-glycosylated form resulting from tunicamycin treatment has a Mr of 55,000. ICAM-1 isolated from phorbol myristic acetate (PMA) stimulated U937 and from fibroblasts yields an identical major product of Mr = 60,000 after chemical deglycosylation. ICAM-1 MAb interferes with the adhesion of phytohemagglutinin blasts, and the adhesion of the cell line SKW3 to human dermal fibroblast cell layers. Pretreatment of fibroblasts but not lymphocytes with ICAM-1 MAb, and of lymphocytes but not fibroblasts with lymphocyte function-associated antigen 1 MAb inhibits adhesion. Intercellular adhesion is increased by prior exposure of fibroblasts to IL 1, and correlates with induction of ICAM-1.     

PH-DEPENDENCE OF CHLORTETRACYCLINE(CTC)-INDUCED PLUG FORMATION IN NITELLA FLEXILIS (CHARACEAE)1

The formation of chlortetracycline(CTC)-induced wall appositions (callose plugs) in Nitella flexilis (L.)Ag. was pH-dependent in the range between 4.3-8.3. Plug number and plug diameter increased with the pH of the CTC solution. At pH 4.3 plug formation was light-dependent and occurred below the alkaline regions of the cell surface which form during photo synthetic assimilation of HCO₃^?. Inhibition of photosynthesis by 3–(3′,4′-dichlorophenyl)-1, 1-dimethylurea prevented plug formation in the light. Dark-treated cells could be induced to form plugs by raising the pH of the CTC solution. The formation of large but incomplete plugs in the presence of cytochalasin B is explained by the formation of numerous weak alkaline sites. I suggest that CTC enhances locally the Ca²⁺content at the cytoplasm near the plasmamembrane. The ionophoric character of CTC is probably more pronounced at high pH mainly because of a weaker binding with cations and a closer contact with the membrane.     

LFA-1- and ICAM-1-dependent homotypic aggregation of human thymocytes induced by JL1 engagement

Cell-cell adhesion is essential for the appropriate immune response, differentiation, and migration of lymphocytes. This important physiological event is reflected in vitro by homotypic cell aggregation. We have previously reported that a 120 kDa cell surface glycoprotein, JL1, is a unique protein specifically expressed by immature double positive (DP) human thymocytes which are in the process of positive and negative selections through the interaction between thymocyte and antigen-presenting cells (APCs). The function of the JL1 molecule, however, is yet to be identified. We show here that anti-JL1 monoclonal antibody (mAb) induced the homotypic aggregation of human thymocytes in a temperature- and Mg2+-dependent manner. It required an intact cytoskeleton and the interaction between leucocyte function associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) since it was blocked by cytochalasin B and D, and mAb against LFA-1 and ICAM-1 which are known to be involved in the aggregation of thymocytes. Translocation of phosphatidylserine (PtdSer) through the cell membrane was not detected, implying that the molecular mechanism of JL-1-induced homotypic aggregation is different from that of CD99-induced homotypic aggregation. In summary, JL1 is a cell surface molecule that induces homotypic adhesion mediated by the LFA-1 and ICAM-1 interaction and cytoskeletal reorganization. These findings suggest that JL1 may be an important regulator of thymocyte development and thymocyte-APC interaction.     

Association of mouse adenovirus-induced cell surface antigen(s) with histocompatibility antigens

The topological relationship on the mouse adenovirus (M-Ad)-infected cell surface between virus-induced specific cell surface(s) antigens and serologically defined major histocompatibility antigens (H-2) was analyzed by the cap formation technique. Rhodamine-isothiocyanate (RITC)-labeled anti-S serum failed to stain the surface of virus-infected lymphoid cells which were pretreated with anti-H-2 serum and fluorescein isothiocyanate (FITC)-labeled anti-mouse immunoglobulin serum (anti-M-Ig) to cap the appropriate H-2 antigens. Conversely, the capping of the S antigens by pretreatment with anti-S followed by FITC anti-M-Ig serum induced cocapping of H-2 antigens. The β₂ microglobulins (β₂m) were also shown to be cocapped with S antigens by anti-β₂m or by anti-S serum. The S antigens, however, did not cocap with mouse-immunoglobulins or Thyl. 2 antigens on virus-infected B or T lymphocytes, respectively. To further elucidate the molecular relationship between S and H-2 antigens, radio-iodinated virus-infected cells were solubilized with Nonidet P40 (NP40) and S antigens were precipitated with anti-S serum. When the precipitates were analysed with sodium dodecyl sulfate Polyacrylamide gel electrophoresis, two major peaks were seen at positions of molecules of about 45,000 and 12,000 daltons both of which corresponded with molecules which were observed when NP40 extracts of virus-infected or uninfected cells were precipitated with anti-H-2 serum. Sequential immunoprecipitation analysis of infected cell extracts showed that S antigens were coprecipitated with either H-2K or H-2D antigens. These results suggest that the S antigens are somehow associated with H-2K or H-2D antigens separately.     

Analysis of selected blood and immune cell responses to carbohydrate-dependent surface binding of proto- and chimera-type galectins

Cell surface glycans present docking sites to endogenous lectins. With growing insight into the diversity of lectin families it becomes important to answer the question on the activity profiles of individual family members. Focusing on galectins (-galactoside-binding proteins without Ca²⁺-requirement sharing the jelly-roll-like folding pattern), this study was performed to assess the potency of proto-type galectins (galectins-1 and -7 and CG-16) and the chimera-type galectin-3 to elicit selected cell responses by carbohydrate-dependent surface binding and compare the results. The galectins, except for galectin-1, were found to enhance detergent (SDS)-induced hemolysis of human erythrocytes to different degrees. Their ability to confer increased membrane osmofragility thus differs. Aggregation of neutrophils, thymocytes and platelets was induced by the proto-type galectin-1 but not -7, by CG-16 and also galectin-3. Cell-type-specific quantitative differences and the importance of the fine-specificity of the galectin were clearly apparent. In order to detect cellular responses based on galectin binding and bridging of cells the formation of haptenic-sugar-resistant (HSR) intercellular contacts (an indicator of post-binding signaling) was monitored. It was elicited by CG-16 and galectin-1 but not galectin-3, revealing another level at which activities of individual galectins can differ. Acting as potent elicitor of neutrophil aggregation, CG-16-dependent post-binding effects were further analyzed. Carbohydrate-dependent binding to the neutrophils' surface led to a sustained increase of cytoplasmic Ca²⁺ concentration in a dose-dependent manner. The ability of CG-16 to activate H₂O₂ generation by human peripheral blood neutrophils was primed by the Ca²⁺-ionophor ionomycin and by cytochalasin B. In a general context, these results emphasize that – besides plant lectins as laboratory tools – animal lectins can trigger cell reaction cascades, implying potential in vivo relevance for the measured activities. Within the family of galectins, the activity profiles depend on the target cell type and the individual galectin. Notably, proto-type galectins do not necessarily share a uniform capacity as elicitor.     

Solution and solid-state structures of lanthanide nitrate complexes with [(MeO)2P(O)]2C(OH)R (R=Me,tBu)

The complexes Ln(NO₃)₃L^a ₂ (L^a=[(MeO)₂P(O)]₂C(OH)Me; Ln=La–Er) and Ln(NO₃)₃L^b ₂ (L^b=[(MeO)₂P(O)]₂C(OH)^tBu); Ln=La–Lu) have been synthesised. The solid-state structures examined by IR spectroscopy, single crystal X-ray diffraction and extended X-ray absorption fine structure show uniformity across the series up to Dy, the metal being ten coordinate. Solution structures have been examined by ³¹P NMR spectroscopy, conductivity, electrospray mass spectrometry and EXAFS, and results indicate that solution structures fall into two groups, one for the lighter (La–Sm) and one for the heavier (Eu–Lu) lanthanides. This structural change involves the diphosphonate ligands, which appear to be monodenate for the heavier metals, affording these a coordination number of eight.     

Binding of hyaluronic acid to lymphoid cell lines is inhibited by monoclonal antibodies against Pgp-1

Recent biochemical and sequence data suggest a possible relationship between Pgp-1 (identical to CD44/Hermes 1/p85) and a hyaluronic acid-binding function. Here, we have studied the hyaluronic acid-binding activity of a series of murine hematopoietic cell lines using several assays: cell aggregation by hyaluronic acid, binding of fluorescein-conjugated hyaluronic acid, and cell adhesion to hyaluronic acid-coated dishes. Certain Pgp-1-positive T and B cell lines show hyaluronic acid binding that is highly specific and is not competed for by other glycosaminoglycans. Monoclonal antibodies against Pgp-1, but not antibodies against other major cell surface glycoproteins, inhibited hyaluronic acid-induced cell aggregation and cell adhesion to hyaluronic acid-coated dishes. Additionally, some anti-Pgp-1 antibodies inhibited binding of fluorescein-hyaluronic acid to hyaluronic acid-binding lines. We found no Pgp-1-negative lines that bound, but many Pgp-1-positive cell lines did not bind hyaluronic acid. Two Pgp-1-positive thymomas that did not bind hyaluronic acid were induced by phorbol ester to bind hyaluronic acid with the same specificity as other hyaluronic acid-binding lines. Normal hematopoietic cells, including those which express high levels of Pgp-1, such as bone marrow myeloid cells and splenic lymphocytes, showed no detectable hyaluronic acid-binding activity. We discuss several models that might account for these observations: (1) the hyaluronic acid receptor is Pgp-1, but it normally exists in an inactive state; (2) hyaluronic acid receptors are a subset of a family of molecules recognized by anti-Pgp-1 antibodies; (3) the hyaluronic acid receptor is not Pgp-1, but is closely associated with Pgp-1 on the surface of cells which express hyaluronic acid-binding activity.     

P nuclear magnetic resonance study of the interaction of multidentate amines with zinc(II) bis(O,O′-di-iso-butyldithiophosphate)

³¹P NMR has been employed to study the interaction between zinc(II) bis(O,O′-di-iso-butyldithiophosphate), Zn[S₂P(OⁱBu)₂]₂, and four multidentate amines (diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine) in chloroform at 294 K. The major interaction of Zn[S₂P(OⁱBu)₂]₂ and these polyamines involves displacement of the {S₂P(OⁱBu)₂} ligands from the zinc giving [Zn(amine)]²⁺ and [S₂P(OⁱBu)₂]⁻ ions in solution. The magnitudes of the equilibrium constants, K₁ (=[{Zn(amine)}²⁺][{DDP}⁻]₂/[Zn(DDP)₂][amine]), have been evaluated in the cases of triethylenetetramine (20.0 l mol⁻¹), tetraethylenepentamine (19.1 l mol⁻¹) and pentaethylenehexamine (1.58 l mol⁻¹). Crystalline 1:1 ionic complexes have also been isolated from these systems and characterised.     

Negative Cooperativity between α3β1and α2β1Integrins in Human Mammary Carcinoma MDA MB 231 Cells

The α₃β₁integrin has been implicated as a receptor for several matrix components, including collagen, fibronectin, and laminins. The function of α₃β₁seems to be very versatile involving cell adhesion to or migration on ECM, establishment of cell–cell contacts in aggregates, as well as linkage to intracellular tyrosine phosphorylation cascades. Here we report a strong induction of attachment of α₃β₁integrin expressing human breast carcinoma cell line MDA MB 231 to matrix proteins by two α₃integrin subunit function-blocking monoclonal antibodies (P1B5 and ASC-1). In contrast, stimulation of adhesion to ECM by inhibitory α₃integrin-specific antibodies was not observed in the α₃β₁integrin-expressing nonmalignant human mammary epithelial cell line MCF-10A or the human breast carcinoma cell line MDA MB 468 that expressed relatively low amounts of α₃β₁integrin at the cell surface. This increase was specific for collagens and not observed on fibronectin or laminin. Physiological concentrations of bivalent cations were not required. MAb P1B5 did not induce homotypic aggregation of MDA MB 231 cells. The P1B5-induced increase in cell attachment to collagens could be prevented but not reduced below control levels by blocking mAb to the α₂integrin subunit. Function blocking anti-α₅integrin subunit mAb was without effect while anti-β₁-mAb completely abolished adhesion. Our data indicate that negative cooperativity between integrins results in transdominant inhibition of α₂β₁function by α₃β₁in human MDA MB 231 but not MDA MB 468 tumor cells or nonmalignant MCF-10A cells.