Bauhinia forficata lectin (BfL) induces cell death and inhibits integrin-mediated adhesion on MCF7 human breast cancer cells

BACKGROUND

Plant lectins have attracted great interest in cancer studies due to their antitumor activities. These proteins or glycoproteins specifically and reversibly bind to different types of carbohydrates or glycoproteins. Breast cancer, which presents altered glycosylation of cell surface glycoproteins, is one of the most frequent malignant diseases in women. In this work, we describe the effect of the lectin Bauhinia forficata lectin (BfL), which was purified from B. forficata Link subsp. forficata seeds, on the MCF7 human breast cancer cellular line, investigating the mechanisms involved in its antiproliferative activity.

METHODS

MCF7 cells were treated with BfL. Viability and adhesion alterations were evaluated using flow cytometry and western blotting.

RESULTS

BfL inhibited the viability of the MCF7 cell line but was ineffective on MDA-MB-231 and MCF 10A cells. It inhibits MCF7 adhesion on laminin, collagen I and fibronectin, decreases α1, α6 and β1 integrin subunit expression, and increases α5 subunit expression. BfL triggers necrosis and secondary necrosis, with caspase-9 inhibition. It also causes deoxyribonucleic acid (DNA) fragmentation, which leads to cell cycle arrest in the G2/M phase and a decrease in the expression of the regulatory proteins pRb and p21.

CONCLUSION

BfL shows selective cytotoxic effect and adhesion inhibition on MCF7 breast cancer cells.

GENERAL SIGNIFICANCE

Cell death induction and inhibition of cell adhesion may contribute to understanding the action of lectins in breast cancer.

Nuclear localization of aldolase A correlates with cell proliferation

Muscle fructose 1,6-bisphosphate aldolase (ALDA) is a glycolytic enzyme which may localize both in nuclei and cytoplasm of cells, however its role in the nuclei is unclear. Here, we demonstrate the links between subcellular localization of ALDA and the cell cycle progression as well as the availability of energetic substrates. Results of our studies indicate that nuclear localization of ALDA correlates with the proliferative activity of the cells and with the expression of Ki-67, a marker of proliferation, both in the KLN-205 (mouse lung cancer cells) and human squamous cell lung cancer cells (hSCC). Chemically-induced block of cell cycle entry in S phase and the inhibition of transcription stimulate removal of ALDA from cells nuclei suggesting that nuclear ALDA is involved in cells proliferation. On the other hand, subcellular distribution of the enzyme also depends on the stress and pro-survival signals mediated by the Akt and the p38 pathways and, in non-proliferating cells, on the availability of glucose and lactate. The results presented here point to ALDA as a factor involved in the regulation of cells proliferation.

Cell cycle-dependent expression and subcellular localization of fructose 1,6-bisphosphatase

Recently a gluconeogenic enzyme was discovered—fructose 1,6-bisphosphatase (FBPase)—that localizes in the nucleus of a proliferating cell, but its physiological role in this compartment remains unclear. Here, we demonstrate the link between nuclear localization of FBPase and the cell cycle progression. Results of our studies indicate that in human and mouse squamous cell lung cancer, as well as in the HL-1 cardiomyocytes, FBPase nuclear localization correlates with nuclear localization of S and G2 phase cyclins. Additionally, activity and expression of the enzyme depends on cell cycle stages. Identification of FBPase interacting partners with mass spectrometry reveals a set of nuclear proteins involved in cell cycle regulation, mRNA processing and in stabilization of genomic DNA structure. To our knowledge, this is the first experimental evidence that muscle FBPase is involved in cell cycle events.

Differential expression of FAK and Pyk2 in metastatic and non-metastatic EL4 lymphoma cell lines

The murine EL4 lymphoma cell line exists in variants that are either sensitive or resistant to phorbol 12-myristate 13-acetate (PMA). In sensitive cells, PMA causes Erk MAPK activation and Erk-mediated growth arrest. In resistant cells, PMA induces a low level of Erk activation, without growth arrest. A relatively unexplored aspect of the phenotypes is that resistant cells are more adherent to culture substrate than are sensitive cells. In this study, the roles of the protein tyrosine kinases FAK and Pyk2 in EL4 phenotype were examined, with a particular emphasis on the role of these proteins in metastasis. FAK is expressed only in PMA-resistant (or intermediate phenotype) EL4 cells, correlating with enhanced cell-substrate adherence, while Pyk2 is more highly expressed in non-adherent PMA-sensitive cells. PMA treatment causes modulation of mRNA for FAK (up-regulation) and Pyk2 (down-regulation) in PMA-sensitive but not PMA-resistant EL4 cells. The increase in Pyk2 mRNA is correlated with an increase in Pyk2 protein expression. The roles of FAK in cell phenotype were further explored using transfection and knockdown experiments. The results showed that FAK does not play a major role in modulating PMA-induced Erk activation in EL4 cells. However, the knockdown studies demonstrated that FAK expression is required for proliferation and migration of PMA-resistant cells. In an experimental metastasis model using syngeneic mice, only FAK-expressing (PMA-resistant) EL4 cells form liver tumors. Taken together, these studies suggest that FAK expression promotes metastasis of EL4 lymphoma cells.

‘In vivo’ and ‘in vitro’ activity of Larrea divaricata Cav. on EL-4 cells

Larrea divaricata is a plant widely used in folk medicine in Argentina. It has been demonstrated that an aqueous extract of L. divaricata possesses a biphasic effect on cell proliferation, at low concentrations exerts a stimulatory action and at high concentrations exerts anti-proliferative effects upon the T lymphoma BW 5147; therefore, we propose in this paper to test the effect of the extract ‘in vitro’ and ‘in vivo’ in another T-cell lymphoma named EL-4. It was analyzed ‘in vitro’ cell proliferation by tritiated thymidine uptake and the effect of the extract on tumors induced in mice analyzing tumor progression and survival.The results showed that the aqueous extract induced the proliferation of tumor cells at all the concentrations studied. The results ‘in vivo’ showed that the aqueous extract stimulated significantly the size of tumors and that untreated mice lived longer than those treated. It is important to be very careful when plant extracts are selected for the treatment of several diseases. Consequently, before using a plant extract, specific scientific studies must be undertaken on different models to certificate therapeutic and adverse effects. Moreover, it can be said that L. divaricata has a specific anti-tumor mechanism of action depending on the targets.

Growth inhibitory activity of a novel lectin from Cliona varians against K562 human erythroleukemia cells

PURPOSE

In this study, the antitumoral potential of a novel lectin (CvL) purified from the marine sponge Cliona varians was studied in different cancer cell lines.

METHODS

CvL cytotoxicity was evaluated in mammalian tumor cells and in normal human peripheral blood lymphocytes by the MTT assay using the same range of concentrations (1-150 microg ml(-1)). The mechanisms involved in K562 cell death were investigated by confocal fluorescence microscopy, flow cytometry and immunoblot.

RESULTS

CvL inhibited the growth of human leukemia cells, with IC(50) values of 70 and 100 microg ml(-1) for K562 and JURKAT cells, respectively, but it was ineffective on blood lymphocytes and solid tumor cell lines. K562 cell death occurred 72 h after exposure to the lectin and with signs of apoptosis, as analyzed by DAPI and annexin V/PI staining. Investigation of the possible mediators of this process showed that cell death occurred via a caspase-independent pathway. Confocal fluorescence microscopy indicated a pivotal role for the lysosomal protease cathepsin B in mediating cell death. Accordingly, pre-incubation of K562 cells with the cathepsin inhibitor L-trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E-64) abolished CvL cytotoxic effect. Furthermore, we found upregulation of tumor necrosis factor receptor 1 (TNFR1) and down-modulation of p65 subunit of nuclear factor kappa B (NFkappaB) expression in CvL-treated cells. These effects were accompanied by increased levels of p21 and reduced expression of pRb, suggesting that CvL can induce cell cycle arrest.

CONCLUSIONS

Collectively, these findings indicate an antileukemic effect for CvL and suggest that cathepsin B acts as a death mediator in CvL-induced cytotoxicity possibly in an uncharacterized connection with the membrane death receptor pathway.

A Novel Role for p73 in the Regulation of Akt-Foxo1a-Bim Signaling and Apoptosis Induced by the Plant Lectin, Concanavalin A

Virtually all human cancers encounter disruption of the "p53 network." From a therapeutic point of view, it is important to devise strategies that eliminate cancer cells, which are often defective in functional p53 and protect p53-expressing normal cells. By comparing the response of a pair of isogenic cell lines, we identify a plant-derived compound, Concanavalin A (Con A), which differentially kills p53-null cells. Further, we find that p53 family member, p73, plays a critical role that is unmasked in the absence of p53. Con A treatment leads to induction of p73 and several others that are important mediators of apoptosis and act downstream, such as p21, Bax, Foxo1a, and Bim. Inactivation of p73 reverses the expression of these proteins and apoptosis. Inhibition of Akt activation sensitizes otherwise resistant cells. These observations thus reveal a novel role for p73 in the regulation of Akt-Foxo1a-Bim signaling and apoptosis especially when p53 is absent.

Wheat germ lectin induces G2/M arrest in mouse L929 fibroblasts

Wheat germ lectin (WGA) is a cytotoxic lectin for many cell lines [Wang et al., 2000], but its underlying mechanism is not clear. In this report, we found that incubation of synchronized mouse L929 fibroblasts with WGA resulted in a dose-dependent reduction of intracellular incorporation of 3H-thymidine and MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide)-conversion activity (IC50 congruent with 0.4 microM). Fluorescein-conjugated WGA was demonstrated to transport from the cell surface into the paranuclear region of cultured L929 cells within 30 min, and subsequently evoked lipid peroxidation of plasma membrane and vacuolation in the cytoplasm of these cells. Studies with tritiated thymidine incorporation, immunofluorescence microscopy, immunoblotting analysis and flow cytometry revealed that WGA inhibited cell cycle progression after one replication, resulting in G2/M arrest and alteration of cell cycle regulatory proteins, particularly activation of p21Cip1/WAF1 and suppression of cyclin B and cdc 2. Although there was an increase of cytosolic caspase 3 and bax protein expression, no apoptotic bodies were observed by both fluorescence and transmission electron microscopy. These results suggest that WGA arrested L929 proliferation after one cell cycle in the G2/M phase through activation of the p21Cip1/WAF1 and suppression of Cyclin B-Cdc2.

The importance of drug scheduling and recovery phases in determining drug activity. Improving etoposide efficacy in BCR-ABL-positive CML cells

K562 leukaemic cells are known to be less sensitive to etoposide than other cell lines, despite having similar topo II mRNA levels and cleavable complex formation. We have investigated the effect of etoposide schedule on cell cycle distribution, apoptosis and p21(waf1) and cdk1(p34) status in two bcr-abl-positive chronic myeloid leukaemia (CML) cell lines (K562 and KU812) and two small cell lung cancer (SCLC) cell lines (H69 and GLC4). During a continuous 5-day exposure, the SCLC cell lines showed a time and concentration-dependent loss of cell viability, with an initial block in the G2/M phase of the cell cycle followed by apoptosis. In contrast, the two CML cell lines showed no significant apoptosis or loss of viability after a similar block in G2/M. However, when K562 or KU812 cells were placed in drug-free medium following a 3-day drug exposure there was marked, concentration-dependent apoptosis (% apoptosis after release at 1 microM etoposide in K562, 10% at 24 h, 30% at 48 h). Our data also show that p21(waf1) does not increase after etoposide treatment in either H69 or GLC4 (both with mutated-p53). Although K562 and KU812 cells are null-p53, the arrest in G2/M during drug exposure was associated with increased p21(waf1) and a decrease in cdk1 (both P<0.001 compared with controls). Upon release of these cells from drug-medium, p21(waf1) gradually returned to control levels, which was associated with an easing of the block at G2/M and an induction of apoptosis. This study highlights the importance of cell cycle regulatory proteins in drug sensitivity and resistance, and suggests that in cells such as K562 and KU812, a pulsed schedule may be more active than a single prolonged exposure.

Modulation of protein kinase C in antitumor treatment

PKC isoenzymes were found to be involved in proliferation, antitumor drug resistance and apoptosis. Therefore, it has been tried to exploit PKC as a target for antitumor treatment. PKC alpha activity was found to be elevated, for example, in breast cancers and malignant gliomas, whereas it seems to be underexpressed in many colon cancers. So it can be expected that inhibition of PKC activity will not show similar antitumor activity in all tumors. In some tumors it seems to be essential to inhibit PKC to reduce growth. However, for inhibition of tumor proliferation it may be an advantage to induce apoptosis. In this case an activation of PKC delta should be achieved. The situation is complicated by the facts that bryostatin leads to the activation of PKC and later to a downmodulation and that the PKC inhibitors available to date are not specific for one PKC isoenzyme. For these reasons, PKC modulation led to many contradicting results. Despite these problems, PKC modulators such as miltefosine, bryostatin, safingol, CGP41251 and UCN-01 are used in the clinic or are in clinical evaluation. The question is whether PKC is the major or the only target of these compounds, because they also interfere with other targets. PKC may also be involved in apoptosis. Oncogenes and growth factors can induce cell proliferation and cell survival, however, they can also induce apoptosis, depending on the cell type or conditions in which the cells or grown. PKC participates in these signalling pathways and cross-talks. Induction of apoptosis is also dependent on many additional factors, such as p53, bcl-2, mdm2, etc. Therefore, there are also many contradicting results on PKC modulation of apoptosis. Similar controversial data have been reported about MDR1-mediated multidrug resistance. At present it seems that PKC inhibition alone without direct interaction with PGP will not lead to successful reversal of PGP-mediated drug efflux. One possibility to improve chemotherapy would be to combine established antitumor drugs with modulators of PKC. However, here also very contrasting results were obtained. Many indicate that inhibition, others, that activation of PKC enhances the antiproliferative activity of anticancer drugs. The problem is that the exact functions of the different PKC isoenzymes are not clear at present. So further investigations into the role of PKC isoenzymes in the complex and interacting signalling pathways are essential. It is a major challenge in the future to reveal whether modulation of PKC can be used for the improvement of cancer therapy.

Phosphorylation of paxillin via the ERK mitogen-activated protein kinase cascade in EL4 thymoma cells

Intracellular signals can regulate cell adhesion via several mechanisms in a process referred to as "inside-out" signaling. In phorbol ester-sensitive EL4 thymoma cells, phorbol-12-myristate 13-acetate (PMA) induces activation of extracellular signal-regulated kinase (ERK) mitogen-activated protein kinases and promotes cell adhesion. In this study, clonal EL4 cell lines with varying abilities to activate ERKs in response to PMA were used to examine signaling events occurring downstream of ERK activation. Paxillin, a multifunctional docking protein involved in cell adhesion, was phosphorylated on serine/threonine residues in response to PMA treatment. This response was correlated with the extent and time course of ERK activation. PMA-induced phosphorylation of paxillin was inhibited by compounds that block the ERK activation pathway in EL4 cells, primary murine thymocytes, and primary murine splenocytes. Paxillin was phosphorylated in vitro by purified active ERK2. Two-dimensional electrophoresis revealed that PMA treatment generated a complex pattern of phosphorylated paxillin species in intact cells, some of which were generated by ERK-mediated phosphorylation in vitro. An ERK pathway inhibitor interfered with PMA-induced adhesion of sensitive EL4 cells to substrate. These findings describe a novel inside-out signaling pathway by which the ERK cascade may regulate events involved in adhesion.

Cyclin D3 compensates for loss of cyclin D2 in mouse B-lymphocytes activated via the antigen receptor and CD40

Cyclin D2 is the only D-type cyclin expressed in mature mouse B-lymphocytes, and its expression is associated with retinoblastoma protein (pRB) and pRB-related protein phosphorylation and induction of E2F activity, as B-cells enter the cell cycle following stimulation via surface IgM and/or CD40. Cyclin D-dependent kinase activity is required for cell proliferation, yet cyclin D2(-/-) mice have normal levels of mature B-lymphocytes. Here we show that B-lymphocytes from cyclin D2(-/-) mice can proliferate in response to anti-IgM and anti-CD40, but the time taken to enter S-phase is longer than for the corresponding cyclin D2(+/+) cells. This is due to the compensatory induction of cyclin D3, but not cyclin D1, which causes pRb phosphorylation on CDK4-specific sites. This is the first demonstration that loss of a D-type cyclin causes specific expression and functional compensation by another member of the family in vivo and provides a rationale for the presence of mature B-lymphocytes in cyclin D2(-/-) mice.

Expression of p34(cdc2) and cyclins A and B compared to other proliferative features of non-Hodgkin's lymphomas: a multivariate cluster analysis

In view of recent knowledge on proteins regulating the cell cycle, we re-evaluated proliferative features of 98 diffusely growing non-Hodgkin's lymphomas. The combined use of 5 proliferation-associated variables (mitotic indices and percentages of Ki-67(+), p34(cdc2+), cyclin A(+) and cyclin B(+) cells) and their entry into a multivariate cluster analysis separated, without overlaps, the entire cohort into 3 groups (clusters) with (1) low, (2) intermediate and (3) high proliferative activity. Conversely, bivariate plots exposed considerable cluster overlaps. Multivariate stepwise discriminant analysis of all cases revealed a decreasing order of discriminant power for % Ki-67(+) cells > % p34(cdc2+) cells > mitotic index > % cyclin A(+) cells > % cyclin B(+) cells. The combined use of 2 variables only, mitotic index and % p34(cdc2+) cells, allowed a clear-cut separation of clusters 2 and 3. In bivariate plots, correlations were best between % Ki-67(+) cells and % cyclin A(+) cells and between mitotic indices and % cyclin B(+) cells. Except for chronic lymphocytic leukemias, immunocytomas and marginal zone lymphomas (all in cluster 1), individual lymphoma entities were distributed among at least 2 clusters. There was, however, a marked preponderance of mantle cell lymphomas and diffuse follicular center lymphomas in cluster 1 and of diffuse large B-cell lymphomas and peripheral T-cell lymphomas in cluster 2. Anaplastic large-cell lymphomas predominated in cluster 3 and responded best to therapy.

Lymphocyte stimulation by CD3-CD28 enables detection of low T cell interferon-gamma and interleukin-4 production in rheumatoid arthritis

The analysis of cytokine production is increasingly important in defining the course of an immune response and in evaluating specific therapies of immune diseases. In rheumatoid arthritis (RA), a dysregulation in T1/T2 cell balance, as defined by the production of their specific cytokines, IFN-gamma and IL-4, respectively, is suggested. A predominance of T1-cell mediated macrophage activity in the joint plays a key role in the destruction of articular cartilage and subchondral bone, whereas local T2 cell activity, mitigating disease, fails. However, analysis of the cytokines defining both T cell subsets is difficult and spontaneous production is often below detection limits. Several stimuli are therefore used to increase cytokine production. In the present study we examined whether stimulation of peripheral blood T cells in the context of mononuclear cells (PB MNC) by CD3-CD28 is a reliable method for assessing IFN-gamma and IL-4 production and is representative for the spontaneous production of these cytokines. The production of IFN-gamma and IL-4 following CD3-CD28 stimulation of RA PB MNC correlated significantly in a ratio 1 : 1 with production following ionomycin-PMA stimulation. In samples with detectable spontaneous production of IFNgamma and IL-4, production following CD3-CD28 stimulation was significantly higher than in stimulated samples with undetectable spontaneous production. Moreover, in the case of spontaneous production there was a significant positive linear correlation between the CD3-CD28 stimulated and spontaneous IFNgamma and IL-4 production, although production of both cytokines was not equally enhanced. Serial sampling did not show significant daily or weekly variation in stimulated cytokine production. The results demonstrate that a pecific T-cell stimulation by CD3-CD28 is a reliable way to enhance IFN-gamma and IL-4 production above the detection limit and so measure the T1/T2 cell balance in RA.

Cyclin E in human cancers

Regulators of the cell cycle such as cyclin E play an important part in neoplasia. The cyclin E protein forms a partnership with a specific protein kinase. This complex phosphorylates key substrates to initiate DNA synthesis. Cyclin-dependent kinase inhibitors (CKIs) are able to suppress the activity of cyclin E. Various substances (including proteins produced by oncogenic viruses) affect cyclin E directly or indirectly through an interaction with CKIs. These interactions are important in elucidating the mechanisms of neoplasia. They may also provide prognostic information in a wide range of common cancers. Cyclin E may even be a target for treatment of cancers in the future.

Differential downstream functions of protein kinase Ceta and -theta in EL4 mouse thymoma cells

Sensitive EL4 mouse thymoma cells (s-EL4) respond to phorbol esters with growth inhibition, adherence to substrate, and production of cytokines including interleukin 2. Since these cells express several of the phorbol ester-sensitive protein kinase C (PKC) isozymes, the function of each isozyme remains unclear. Previous studies demonstrated that s-EL4 cells expressed substantially more PKCeta and PKCtheta than did EL4 cells resistant to phorbol esters (r-EL4). To examine potential roles for PKCeta and PKCtheta in EL4 cells, wild type and constitutively active versions of the isozymes were transiently expressed using a Sindbis virus system. Expression of constitutively active PKCeta, but not PKCtheta, in s- and r-EL4 cells altered cell morphology and cytoskeletal structure in a manner similar to that of phorbol ester treatment, suggesting a role for PKCeta in cytoskeletal organization. Prolonged treatment of s-EL4 cells with phorbol esters results in inhibition of cell cycling along with a decreased expression of most of the PKC isozymes, including PKCtheta. Introduction of virally expressed PKCtheta, but not PKCeta, overcame the inhibitory effects of the prolonged phorbol ester treatment on cell cycle progression, suggesting a possible involvement of PKCtheta in cell cycle regulation. These results support differential functions for PKCeta and PKCtheta in T cell activation.

The generation of 1H-NMR-detectable mobile lipid in stimulated lymphocytes: relationship to cellular activation, the cell cycle, and phosphatidylcholine-specific phospholipase C

Mobile lipids detected using 1H-NMR in stimulated lymphocytes were correlated with cell cycle phase, expression of the interleukin-2 receptor alpha and proliferation to assess the activation status of the lymphocytes. Mobile lipid levels, IL-2R alpha expression and proliferation increased after treatment with PMA and ionomycin. PMA or ionomycin stimulation alone induced increased IL-2R alpha expression but not proliferation. PMA- but not ionomycin-stimulation generated mobile lipid. Treatment with anti-CD3 antibody did not increase IL-2R alpha expression or proliferation but did generate increased amounts of mobile lipid. The cell cycle status of thymocytes treated with anti-CD3, PMA or ionomycin alone indicated an accumulation of the cells in the G1 phase of the cell cycle. The generation of mobile lipid was abrogated in anti-CD3 antibody-stimulated thymic lymphocytes but not in splenic lymphocytes, using a phosphatidylcholine-specific phospholipase C (PC-PLC) inhibitor which blocked cells in the G1/S phase of the cell cycle. This suggests that the 1H-NMR-detectable mobile lipid may be generated in anti-CD3 antibody-stimulated thymic lymphocytes by the action of PC-PLC activity via the catabolism of PC, in the absence of classical signs of activation.