Thapsigargin, Inhibitor of Sarco-Endoplasmic Ca2+-ATPase, Effectively Suppresses the Expression of S100A4 Protein in Human Breast Cancer Cell Line

Thapsigargin (SERCA ATPase inhibitor) inhibited the S100A4 metastatic marker expression in MDA-MB231 breast cancer cells. We found that S100A4 gene transcription is regulated by Ca²⁺ signaling pathways. We found that the synthesis of S100A4 mRNA and S100A4 protein in MDA-MB231 cells was effectively suppressed by thapsigargin at a concentration of 0.4-4 μM with retaining cell viability. We assume that the change in the gene transcription in response to disturbance of Ca²⁺ homeostasis is directly involved in the remodeling of Ca²⁺ signaling pathways.

The Expression Level of S100A4 Protein Affects the Migration Activity of Breast Cancer Cells

Reduced expression of metastatic marker protein S100A4 in triple-negative breast cancer cells MDA-MB-231 leads to a decrease in the migration ability of cells and increases the sensitivity of the modified cells to docetaxel therapy. Cells capable of migration differ from the immotile cells in the content of the S100A4 protein in the cell, and this difference persists after the treatment of cells with the agents that reduce the intracellular level of S100A4. The presence of exogenous S100A4 protein in culture medium reduces the content of this protein in breast cancer cells. The results of the study show that the ability of breast cancer cells to migrate depends on the S100A4 protein concentration in the cell.

Combined Action of PGRPs-Hsp70 Cytotoxic Complex with Paclitaxel Improves Outcomes of Melanoma Treatment in Mice

We studied the effect of PGRPs-Hsp70 cytotoxic complex that is analogous to natural complex secreted by cytotoxic lymphocytes and the antitumor drug paclitaxel on the development of M3 melanoma in DBA mice. Significant inhibition of tumor growth was observed in all experimental groups by days 20 and 35 of observation; paclitaxel monotherapy was less effective than administration of PGRPs-Hsp70 cytotoxic complex and its combination with paclitaxel. Pairwise comparison of Kaplan-Meier curves showed that survival was maximum in the group receiving combined therapy with PGRPs-Hsp70 cytotoxic complex and paclitaxel in comparison with groups receiving monotherapy.

The role of S100A4 protein in anticancer cytotoxicity: its presence is required on the surface of CD4+CD25+PGRPs+S100A4+ lymphocyte and undesirable on the surface of target cells

S100A4 is a Ca²⁺-binding protein that performs an important role in metastasis. It is also known for its antitumor functions. S100A4 is expressed by a specialized subset of CD⁴⁺CD²⁵⁺ lymphocytes and is present on those cell's membranes along with peptidoglycan recognition proteins (PGRPs). There, by interacting with major heat shock protein Hsp70, S100A4 plays an important cytotoxic role. The resulting stably formed complex of PGRPs, S100A4 and Hsp70 is required for the identification and binding between a lymphocyte and a target cell. Here, we investigated the S100A4 functions in CD⁴⁺CD²⁵⁺PGRPs⁺S100A4⁺ lymphocyte cytotoxicity against target cells. We demonstrated that those lymphocytes do not form a stable complex with the tumor target cells that themselves have S1004A on their surface. That observation can be explained by our finding that S100A4 precludes the formation of a stable complex between PGRPs, S100A4 (on the lymphocytes' surface), and Hsp70 (on the target cells' surface). The decrease in S100A4 level in CD⁴⁺CD²⁵⁺PGRPs⁺S100A4⁺ lymphocytes inhibits their cytotoxic activity, while the addition of S100A4 in the medium restores it. Thus, the resistance of target cells to CD⁴⁺CD²⁵⁺PGRPs⁺ S100A4⁺ lymphocyte cytotoxicity depends on their S100A4 expression level and can be countered by S100A4 antibodies.

Lymphocytes incubated in the presence of IL-2 lose the capacity for chemotaxis but acquire antitumor activity

Naïve non-activated lymphocytes are capable of releasing the chemoattractant complex Tag7-Mts1 and can migrate along the gradient of its concentration. After activation of these cells by IL-2, they acquire the abilities to kill tumor cells and to release the cytotoxic Tag7-Hsp70 complex, which is accompanied by a loss of both the Tag7-Mts1-mediated lymphocyte chemotaxis and the ability to release this chemoattractant into the conditioned medium.

A new role for PGRP-S (Tag7) in immune defense: lymphocyte migration is induced by a chemoattractant complex of Tag7 with Mts1

PGRP-S (Tag7) is an innate immunity protein involved in the antimicrobial defense systems, both in insects and in mammals. We have previously shown that Tag7 specifically interacts with several proteins, including Hsp70 and the calcium binding protein S100A4 (Mts1), providing a number of novel cellular functions. Here we show that Tag7-Mts1 complex causes chemotactic migration of lymphocytes, with NK cells being a preferred target. Cells of either innate immunity (neutrophils and monocytes) or acquired immunity (CD4(+) and CD8(+) lymphocytes) can produce this complex, which confirms the close connection between components of the 2 branches of immune response.

Transcription factor Oct-1 stimulates the release of Mts1/S100A4 protein by the cancer cells

The effect of the transcription factor Oct-1 (POU2F1) on the expression of the tumor cell marker metastasin (Mts1/S100A4) was studied. Comparative analysis of various tumor lines showed no clear correlation between the expression level of Mts1/S100A4 and the content of Oct-1. However, at stable transfection of tumor cells with Oct-1A, Oct-1L, and Oct-1X isoforms we detected an elevated level of Oct-1, which stimulated Mts1/S100A4 secretion. These findings extend our understanding of the molecular mechanisms of the tumorigenic effect of Oct-1.

Molecular mechanisms of different sensitivity of tumor cells to dexamethasone

The response of two cell lines, CSML-0 (does not express metastasin) and CSML-100 (high expression of metastasin) to cytolytic action of glucocorticoid was studied. Dexamethasone (1 microM) induced apoptosis of CSML-0 cells, while CSLM-100 cells were resistant to its cytolytic action. Apoptotic death of CSLM-100 cells was induced by incubation with dexamethasone in the presence of Ca-ATPase inhibitors, vanadate or thapsigargin. Metastasin, a proteins of the S-100 family, activated Ca-ATPase and ATP-dependent Ca2+ transport in plasmolemmal fraction of CSML-100 cells. Experiments showed that metastasin-induced activation of Ca-ATPase is a possible mechanisms of CSML-100 cell resistance to cytolytic dexamethasone action.

Nonlymphoid cultured cells possess a system controlling cellular compatibility

We show that various nonlymphoid cultured cells can activate the production of cytotoxic factors in response to direct contact with cells of a different kind. Accumulation of cytotoxic factors in the medium was detected 1 h after contact of K562 and L929 cells or after contact of L929 cells with purified membranes of K562 cells. TNF-alpha or immunologically related proteins, or both, but not Fas-ligand or lymphotoxin, were also accumulated in membranes of K562 and L929 cells shortly after these cells had been allowed to contact each other. The cytotoxic factors expressed by nonlymphoid cells trigger apoptosis of target cells. These observations strongly suggest that nonlymphoid cells possess molecular mechanisms controlling cellular compatibility.

Spectral studies on the calcium-binding properties of Mts1 protein and its interaction with target protein

Two calcium-binding sites of the Mts1 protein, a member of S-100 protein family, were distinguished with the Fluo-3 fluorescent technique. The geometric mean of the apparent dissociation constant (Kd) for these two sites is 2.6 microM; the Hill coefficient (nH) is 0.98. In the presence of a novel target protein p37, isolated from the mouse adenocarcinoma cell line CSML-100, Mts1 binds Ca2+ ions with higher affinity and with strong positive cooperativity (Kd = 0.2 microM, nH = 1.91). Interaction of Mts1 with p37 is confirmed by the fluorescent probe 2-p-toluidinylnaphthalene-6-sulfonate (TNS). Reaction with TNS shows that p37 interacts with the hydrophobic site of Mts1 which is exposed due to the binding of Ca2+ ions.

Calcium-binding characteristics and conformational changes in metastasin, a member of S-100 protein family

Investigation of Ca(2+)-binding characteristics of metastasin (Mts-1) by competition with Fluo-3 revealed two types of Ca(2+)-binding sites in Mts-1 with the geometric mean of their dissociation constant (Kd) value of 2.6 microM for the two EF-sites. The Hill coefficient (nH) is 0.98. A substantial increase in the affinity of Mts-1 for Ca2+ and strong cooperative character of binding (kd = 0.2 microM, nH = 1.91) is observed in the presence of the target protein p37 isolated from mouse adenocarcinoma cell lines CSML-100 and CSML-0. Two different hydrophobic sites of binding with the fluorescent probe 2-(p-toludino)naphthalene-6-sulfonate (TNS) per Mts-1 molecule have been determined. The exposure of the hydrophobic binding sites of the first type are shown to be Ca(2+)-dependent and the hydrophobic binding sites of the second type are exposed independently of Ca2+ concentration. A decrease in the number of Ca(2+)-dependent hydrophobic centers in the presence of p37 protein was detected by measurements of TNS fluorescence.

[Study of calcium-binding properties of the Mts-1 protein and its recombinant analog using the fluorescent probe Fura-2]

A procedure based on the ability of Mts-1 to competitively inhibit the formation of Fura-2 complexes with Ca(2+)-ions is described. It has been shown that Mts-I reversibly inhibits the complex formation between Fura-2 and calcium. The efficiency of natural Mts-I isolated from cells of the CSML-100 line and of its recombinant analog on the formation of the Fura-2+Ca complex is different. The inhibition constant, Ki, for the native protein is equal to 2,4 microM, that for the recombinant form is 8.5 microM. The data obtained are suggestive of posttranslational modification of Mts-I in cells under in vivo conditions.

[Oxidative inactivation of angiotensin-converting enzyme]

Hydrogen peroxide inactivates the purified human angiotensin-converting enzyme (ACE) in vitro; the inactivating effect of H2O2 is eliminated by an addition of catalase. The lung and kidney ACE are equally sensitive to the effect of hydrogen peroxide. After addition of oxidants (H2O2 alone or H2O2 + ascorbate or H2O2 + Fe2+ mixtures) to the membranes or homogenates of the lung, the inactivation of membrane-bound ACE is far less pronounced despite the large-scale accumulation of lipid peroxidation products. The marked inactivation of ACE in the membrane fraction (up to 55% of original activity) was observed during ACE incubation with a glucose:glucose oxidase:Fe2+ mixture. Presumably the oxidative potential of H2O2 in tissues in consumed, predominantly, for the oxidation of other components of the membrane (e.g., lipids) rather than for ACE inactivation.

Atriopeptin 2 is hydrolysed by cardiac but not pulmonary isozyme of angiotensin-converting enzyme

Hydrolysis of Bz-Gly-Ser-Phe-Arg, C-terminal fragment of atriopeptin 2, by human cardiac angiotensin-converting enzyme has been studied. The KM for the reaction was 10(-4) M. The effect of concentration of NaCl on activity of cardiac angiotensin-converting enzyme has been determined, which allowed to regard Bz-Gly-Ser-Phe-Arg as bradykinin-like substrates. It was demonstrated that cardiac, but not pulmonary isozyme of angiotensin-converting enzyme specifically hydrolyses atriopeptin 2.

[Various properties of angiotensin-converting enzyme from the seal Phoca groenlandica]

It was found that the molecular mass of the angiotensin-converting enzyme from seal (Phoca groenlandica) lungs determined by electrophoresis in 7.5% PAAG in the presence of sodium dodecyl sulfate is 150 kD. The enzyme has a pH optimum with respect to hippuryl-L-histidyl-L-leucine at 7.3--7.5; KM is 1.2 mM. The enzyme is inhibited by the substrate to form a nonproductive ES2 complex with the dissociation constant (Ks') of 4.8 mM. The activation of the seal angiotensin-converting enzyme in the presence of NaCl was studied. The bradykinin-potentiating factor (SQ 20881) inhibits the seal enzyme with a high efficiency (IC50 = 2.5.10(-8) M). Monoclonal antibodies to the angiotensin-converting enzyme from human lungs do not interact with its seal lung counterpart, which points to the species specificity of the angiotensin-converting enzyme.

Monoclonal antibody to human lung angiotensin-converting enzyme

The hybridoma producing monoclonal antibody (IgG1) to human angiotensin-converting enzyme (ACE) has been prepared by fusion of murine myeloma P3O1 with spleen cells of BALB/c mice immunized with a purified human lung ACE preparation. A high specificity of monoclonal antibody (MAb) binding to immobilized ACE has been demonstrated by enzyme-linked immunosorbent assay and that of soluble ACE by an immunoadsorption test. The latter technique permits the use of impure ACE preparations for the screening procedure. This MAb did not affect ACE activity. We believe this antibody will be useful not only for immunoassay and immunopurification of ACE, but also as a tool for the investigation of the tissue distribution of the enzyme as well as for the study of the structure and mechanism of action of ACE.

[Monoclonal antibodies to the angiotensin-converting enzyme from the human lung]

The hybridoma producing monoclonal antibody (IgG1) to human angiotensin-converting enzyme (ACE) has been prepared by fusion of murine myeloma P3O1 with spleen cells of BALB/c mice immunised with a purified human lung ACE preparation. A high specificity of monoclonal antibody (MAb) binding to immobilized ACE has been demonstrated by ELISA; that of soluble ACE--by immunoadsorption test. The latter technique permits the use of impure ACE preparations for the screening procedure. This MAb did not effect ACE activity. This antibody is believed useful not only for immunoassay and immunopurification of ACE, but also as a tool for investigation of enzyme distribution in tissue as well as for studying the structure and mechanism of ACE action.

Affinity chromatography and some properties of the angiotensin-converting enzyme from human heart

Human heart angiotensin-converting enzyme has been purified by affinity chromatography on immobilized N-[1(S)-carboxy-5-aminopentyl]-Gly-Gly. The isolation procedure permitted a 1650-fold-purified enzyme to be obtained. The specific activity of angiotensin-converting enzyme was 38 units per mg protein. The molecular weight of enzyme determined by polyacrylamide gel electrophoresis in denaturing conditions was 150,000. The isoelectric point (5.3) of the enzyme was determined by chromatofocusing. The Km values of the enzyme for Bz-Gly-His-Leu and angiotensin I are 1.2 mM and 10 microM, respectively. Substrate inhibition of heart angiotensin-converting enzyme with a K's of 14 mM has been shown. The human heart enzyme is inhibited by SQ 20881 (IC50 = 40 nM). It was shown that NaCl, CaCl2 as well as Na2SO4 in the absence of Cl- are activators of the heart angiotensin-converting enzyme, whereas CH3COONa and NaNO3 have no effect on a catalytic activity of the enzyme.

[Isolation and molecular kinetic properties of the angiotensin-converting enzyme from the human heart]

An angiotensin-converting enzyme was isolated from human heart using N[-1(S)-carboxy-5-aminopentyl]glycyl-glycine as an affinity adsorbent. The isolation procedure resulted in an enzyme purified 1650-fold. The enzyme specific activity was 38.0 u./mg protein, Mr = 150 kD. The pH optimum for the angiotensin-converting enzyme towards Hip-His-Leu lies at 7.8, Km = 1.2 mM. The enzyme was inhibited by the substrate (Ks' = 14 mM). The enzyme effectively catalyzed the hydrolysis of angiotensin I (Km = 10 microM; kcat = 250 s-1). NaCl, CaCl2 as well as Na2SO4 in the absence of Cl- activated the enzyme, whereas CH3COONa and NaNO3 did not influence the enzyme activity. It was found that the bradykinin-potentiating factor inhibited the cardiac angiotensin-converting enzyme with IC50 = 4.0 X 10(-8) M.

[Isolation and properties of the angiotensin-converting enzyme from human lungs]

Using chromatofocusing, an angiotensin-converting enzyme (EC 3.4.15.1) has been isolated from human lung. The procedure allows for 24 300-fold purification of the enzyme. The enzyme specific activity is 36.3 u. per mg protein; Mr as determined by polyacrylamide gel electrophoresis is 150 000. The lung enzyme after solubilization by trypsin treatment was found to be heterogeneous. Four isoforms of the enzyme with pI 5.3, 4.9, 4.8 and 4.6 were identified. The pH-optimum for the enzyme with respect to hippuryl-L-histidyl-L-leucine hydrolysis lies at 8.3; Km = 2.8 mM. The effect of Cl- on the enzyme activity was studied. It was found that the bradykinin-potentiating factor (SQ 20 881) inhibits the human lung angiotensin-converting enzyme (I50 = 1.6 X 10(-8) M).