Integrin alphavbeta3 promotes anchorage-dependent apoptosis in human intestinal carcinoma cells

αv-Class integrin binding to fibronectin is solely mediated by RGD and unaffected by an RGE mutation

Fibronectin (FN) is an essential glycoprotein of the extracellular matrix; binds integrins, syndecans, collagens, and growth factors; and is assembled by cells into complex fibrillar networks. The RGD motif in FN facilitates cell binding- and fibrillogenesis through binding to α5β1 and αv-class integrins. However, whether RGD is the sole binding site for αv-class integrins is unclear. Most notably, substituting aspartate with glutamate (RGE) was shown to eliminate integrin binding in vitro, while mouse genetics revealed that FNRGE preserves αv-class integrin binding and fibrillogenesis. To address this conflict, we employed single-cell force spectroscopy, engineered cells, and RGD motif-deficient mice (Fn1ΔRGD/ΔRGD) to search for additional αv-class integrin-binding sites. Our results demonstrate that α5β1 and αv-class integrins solely recognize the FN-RGD motif and that αv-class, but not α5β1, integrins retain FN-RGE binding. Furthermore, Fn1ΔRGD/ΔRGD tissues and cells assemble abnormal and dysfunctional FNΔRGD fibrils in a syndecan-dependent manner. Our data highlight the central role of FN-RGD and the functionality of FN-RGE for αv-class integrins.

Integrin α6β4 in Colorectal Cancer: Expression, Regulation, Functional Alterations and Use as a Biomarker

Integrin α6β4 is one of the main laminin receptors and is primarily expressed by epithelial cells as an active component of hemidesmosomes. In this article, after a brief summary about integrins in the gut epithelium in general, I review the knowledge and clinical potential of this receptor in human colorectal cancer (CRC) cells. Most CRC cells overexpress both α6 and β4 subunits, in situ in primary tumours as well as in established CRC cell lines. The mechanisms that lead to overexpression have not yet been elucidated but clearly involve specific transcription factors such as MYC. From a functional point of view, one key element affecting CRC cell behaviour is the relocalization of α6β4 to the actin cytoskeleton, favouring a more migratory and anoikis-resistant phenotype. Another major element is its expression under various molecular forms that have the distinct ability to interact with ligands (α6β4 ± ctd) or to promote pro- or anti-proliferative properties (α6Aβ4 vs. α6Bβ4). The integrin α6β4 is thus involved in most steps susceptible to participation with CRC progression. The potential clinical significance of this integrin has begun to be investigated and recent studies have shown that ITGA6 and ITGB4 can be useful biomarkers for CRC early detection in a non-invasive assay and as a prognostic factor, respectively.

KRAS and BRAF mutations induce anoikis resistance and characteristic 3D phenotypes in Caco‑2 cells

In a number of types of cancer, anoikis, a form of apoptosis induced by loss of extracellular matrix (ECM) attachment, is disturbed. Anoikis resistance is essential in the formation of metastases. A recent study identified carcinoma cell subpopulations surviving without ECM contact in pathological specimens of colorectal cancer. The occurrence of these subpopulations indicated anoikis resistance. In the present study, it is demonstrated that KRAS and BRAF mutations induce anoikis resistance in colon cancer (Caco-2) cells. In 3D cultures, Caco-2 cells transfected with mutated KRAS or BRAF formed multicellular structures analogous to anoikis-resistant subpopulations in actual carcinomas, and serve as an in vitro model for anoikis resistance. Caco-2 cell lines were constructed, with KRAS or BRAF mutations, using retroviral delivery. The current study investigated anoikis resistance using an Annexin V apoptosis test from suspension cultures. 3D in vitro cultures, which were generated in collagen-matrigel mixtures, were assessed using confocal microscopy. 3D cultures embedded in paraffin were analyzed using conventional histopathology. In suspension cultures, Caco-2 cells with KRAS or BRAF mutations indicated a significantly lower proportion of Annexin positivity than the native Caco-2 cells, indicating that these mutations induce anoikis resistance in Caco-2 cells. 3D cultures displayed native Caco-2 cells forming polarized cysts with a single layer thick epithelium, whereas Caco-2 cells with KRAS or BRAF mutations formed partially filled cystic structures or solid round structures where only the outermost layer was in contact with the ECM. Additionally, KRAS mutations induced reversed polarity to Caco-2 cells along with the emergence of solid growth. The present study demonstrated that KRAS and BRAF mutations induce anoikis resistance in Caco-2 colorectal cancer cells. The growth patterns generated from the KRAS and BRAF mutated cells in 3D cultures revealed a resemblance to the putative anoikis-resistant subpopulations in actual carcinomas, including micropapillary structures and solid tumor cell islands. Additionally, KRAS mutation induced the emergence of inverted polarity. In conclusion, 3D cultures with modified Caco-2 cells serve as a valid in vitro model for anoikis resistance and inverted polarity.

Implication of α2β1 integrin in anoikis of MCF-7 human breast carcinoma cells

Silencing of α2β1 integrin expression significantly promoted anchorage-dependent apoptosis (anoikis) and drastically reduced clonal activity of MCF-7 human breast carcinoma cells. Depletion of α2β1 enhanced the production of apoptotic protein p53 and of inhibitor of cyclin-dependent protein kinases, p27, while downregulating antiapoptotic protein Bcl-2 and multifunctional protein cMyc. Blocking the expression of α2β1 had no effect on activity of protein kinase Akt, but it sharply increased the kinase activity of Erk1/2. Pharmacological inhibition of Erk1/2 had a minor effect on anoikis of control cells, while it reduced anoikis of cells with downregulated α2β1 to the level of control cells. The data show for the first time that integrin α2β1 is implicated in the protection of tumor cells from anoikis through a mechanism based on the inhibition of protein kinase Erk.

Lewis y enhances CAM-DR in ovarian cancer cells by activating the FAK signaling pathway and upregulating Bcl-2/Bcl-XL expression

Oligosaccharides on the surface of adhesion molecules may contribute to the process of CAM-DR. To investigate the role of the Lewis y antigen in this process, we established a cell adhesion model mediated by the integrin α5β1-FN interaction in the ovarian cancer cell line, RMG-1-hFUT, which highly expresses Lewis y by transfection with α1,2-fucosyltransferase into RMG-1 cells. Our results indicate that the rates of carboplatin-induced apoptosis and necrosis are reduced in FN-adhered tumor cells, and carboplatin resistance is significantly decreased in the presence of anti-Lewis y antibody. CAM-DR in tumor cells has been correlated with elevated expression of the nuclear anti-apoptotic proteins Bcl-2 and Bcl-XL. Lewis y promotes the expression of the Bcl-2 and Bcl-XL genes by activating the focal adhesion kinase signaling pathway and accelerating their transcription. Thus, Lewis y leads to inhibition of apoptosis and enhancement of CAM-DR by activation of the FAK signaling pathway and upregulation of Bcl-2/Bcl-XL expression in ovarian cancer cell lines.

Modulation of endogenous Cysteine Protease Inhibitor (ICP) 1 expression in Entamoeba histolytica affects amoebic adhesion to Extracellular Matrix proteins

Entamoeba histolytica is an enteric tissue-invading protozoan parasite that causes amoebic colitis and occasionally liver abscess in humans. During tissue invasion, amoebic adhesion to host components is an important event for host cell death leading to successful invasion and infection. Among amoebic virulence factors, Gal/GalNAc lectin is known to be major adhesion factor to host cells. In this study, we investigated the role of amoebic secreted CP (Cysteine Proteases) in amoebic adhesion to extracellular matrix (ECM) protein using CP inhibitor and E. histolytica strains in which the endogenous inhibitor of cysteine protease (ICP) 1 gene was overexpressed (ICP1(+)) or repressed by antisense small RNA-mediated gene silencing (ICP1(-)). We found that pretreatment of wild-type amoebae with CP inhibitor E64, or thiol-group modifiers such as diamide and N-Ethylmaleimide resulted in a significant decrease in adhesion to laminin and collagen ECM proteins. Furthermore, ICP1(+) strain, with a reduction of secreted CP activity, exhibited reduced ability by 40% to adhere to laminin. In contrast, ICP1(-) strain, with a 1.9-fold increase of secreted CP activity, showed a two-fold increase in amoebic adherence to laminin compared to the control strain. In addition, total amount of secreted CP5 was decreased in ICP1(+) amoeba. Conversely, total amount of secreted CP1 and mature-form CP5 were increased in ICP1(-) amoeba. We also found that ICP1 was secreted into extracellular milieu. These results suggest that secreted CP activity by E. histolytica may be an important factor affecting adhesion to host proteins, and regulation of CP secretion by ICP plays a major role in pathogenesis. This study provides insight into the CP-mediated tissue pathogenesis in amoeba-invaded lesions during human amoebiasis.

Elevated autocrine EDIL3 protects hepatocellular carcinoma from anoikis through RGD-mediated integrin activation

BACKGROUND

A remolded microenvironment in hepatocellular carcinoma (HCC) caused by abnormally expressed matricellular proteins could promote HCC progression. The cell-matrix interactions mediated by integrins play an important role in tumor microenvironment. Epidermal Growth Factor-like repeats and Discoidin I-Like Domains 3 (EDIL3), an extracellular matrix (ECM) protein with angiogenic and anti-inflammatory effects, is abnormally highly expressed in HCC. Here we aim to analyze its expression in liver and HCC tissues, investigate the underlined mechanisms accounted for HCC progression.

METHODS

EDIL3 expression level is examined in normal liver, cirrhotic liver and HCC at both mRNA and protein level. The association between EDIL3 and clinical outcomes is analyzed. The pattern of EDIL3 expression and location is examined using Immunofluorescence and ELISA. Overexpression or knock-down of EDIL3 in a panel of cell lines are subjected to assays related to proliferation, invasion, and anoikis to investigate the mechanisms of this matrix protein in HCC progression. Recombinant EDIL3 treatment is applied to confirm the results.

RESULTS

Compared with normal liver and cirrhotic liver, EDIL3 is elevated in HCC. High level of EDIL3 protein is much more commonly in patients with larger tumor or portal vein tumor thrombus (PVTT) formation, associated with poor prognosis. EDIL3 is abundantly expressed in HCC cells and secreted by cancer cells. In vitro and in vivo studies indicate that EDIL3, probably in an autocrine manner, inhibits anoikis and promotes anchorage-independent growth of HCC cells. Further mechanistic studies suggest integrin ligation by EDIL3 and thus that the sustained activation of the FAK-Src-AKT signal is responsible for the anoikis resistance and anchorage independence. Both the administration of cilengitide, a RGD-containing integrin antagonist, and silencing of integrin αV, an important RGD-binding integrin, results in the blockade of anoikis-resistance induced by EDIL3.

CONCLUSION

Our study suggests that high levels of autocrine EDIL3 may contribute to a receptive microenvironment for the survival of detached HCC cells and may involve in cancer cell spreading. We also highlight the importance of interaction between EDIL3 and integrin αV and suggest disrupting the ligation of EDIL3 to integrins via RGD-blocking in selected patients may bear potential therapeutic value.

[Integrins as a potential target for targeted anticancer therapy]

The review briefly summarizes information of structure of integrins and their involvement in the development and malignant progression of tumors. Special attention is paid to approaches based on modification of functional properties of integrins that prevent/antagonize tumor growth and progression; these approaches developed in modem experimental biology have certain perspective in clinical application.

Bioresorbable polymersomes for targeted delivery of cisplatin

Nontoxic bioresorbable polymersomes have been developed that efficiently and site-selectively tether targeting peptides under mild conditions with no toxic catalysts. The binding and release properties of these polymersomes have been evaluated when targeting DLD-1 human colon cancer cells overexpressing the α(5)β(1) integrin. The delivery efficacy to these cells is markedly improved over commonly used RGD targeting peptides by use of an α(5)β(1)-specific targeting peptide, PR_b. Release profiles in buffered solution from pH 7.4 to 4.5 were evaluated and compared to release after binding to cells, and enzymatic degradation was identified as a major cause of rapid payload release in the cell. Intracellular trafficking and release were imaged via confocal microscopy in live cells and colocalization with organelles was evaluated quantitatively over time. Finally, the anticancer drug cisplatin was encapsulated in the PR_b functionalized polymersomes and the presence of PR_b greatly improved delivery efficacy, with increased cisplatin-induced losses to targeted DLD-1 colon cancer cell viability. When delivered to CACO-2 model human epithelial cells expressing low levels of α(5)β(1) integrin, low toxicity was maintained, suggesting that targeting was specific to α(5)β(1) overexpressing cells. These results demonstrate that PR_b-functionalized bioresorbable polymersomes may be an attractive route to minimizing the dose-limiting side effects associated with existing approaches to cisplatin chemotherapy.

Integrin signaling, cell survival, and anoikis: distinctions, differences, and differentiation

Cell survival and apoptosis implicate an increasing complexity of players and signaling pathways which regulate not only the decision-making process of surviving (or dying), but as well the execution of cell death proper. The same complex nature applies to anoikis, a form of caspase-dependent apoptosis that is largely regulated by integrin-mediated, cell-extracellular matrix interactions. Not surprisingly, the regulation of cell survival, apoptosis, and anoikis furthermore implicates additional mechanistic distinctions according to the specific tissue, cell type, and species. Incidentally, studies in recent years have unearthed yet another layer of complexity in the regulation of these cell processes, namely, the implication of cell differentiation state-specific mechanisms. Further analyses of such differentiation state-distinct mechanisms, either under normal or physiopathological contexts, should increase our understanding of diseases which implicate a deregulation of integrin function, cell survival, and anoikis.

[Implication of integrin alpha5beta1 in human breast carcinoma apoptosis and drug resistance]

Doxorubicin-resistant MCF-7Dox line, which is a derivative of the drug-sensitive MCF-7 human breast carcinoma line, differs from the latter by a strongly reduced expression of the alpha2beta1 integrin and a highly increased expression of the alpha5beta1 receptor. Silencing of this integrin in the MCF-7Dox cells by transfection with alpha5-specific siRNA markedly stimulated anoikis and increased sensitivity of the cells to doxorubicin. Alpha5beta1 silencing also leads to significant inhibition of the activity of kinases Akt and Erk2 in MCF-7Dox cells. Our results suggest that integrins alpha5beta1-induced signals, controlling distinct aspects of cell behavior, are conducted through the common signal pathways.

The integrin alpha(v)beta(3-5) ligand MFG-E8 is a p63/p73 target gene in triple-negative breast cancers but exhibits suppressive functions in ER(+) and erbB2(+) breast cancers

The progression from preinvasive lesion to invasive carcinoma is a critical step contributing to breast cancer lethality. We identified downregulation of milk fat globule-EGF factor 8 (MFG-E8) as a contributor to breast cancer progression using microarray analysis of laser capture microdissected (LCM) tissues. We first identified MFG-E8 downregulation in invasive lesions in transgenic mammary tumor models, which were confirmed in LCM-isolated human invasive ductal carcinomas compared with patient-matched normal tissues. In situ analyses of MFG-E8 expression in estrogen receptor (ER) positive cases confirmed its downregulation during breast cancer progression and small inhibitory MFG-E8 RNAs accelerated ER(+) breast cancer cell proliferation. MFG-E8 also decreased in erbB2(+) human cancers and erbB2 transgenic mice lacking MFG-E8 showed accelerated tumor formation. In contrast, MFG-E8 expression was present at high levels in triple-negative (ER(-), PgR(-), erbB2(-)) breast cancers, cell lines, and patient sera. Knockdown, chromatin immunoprecipitation, and reporter assays all showed that p63 regulates MFG-E8 expression, and MFG-E8 knockdowns sensitized triple-negative breast cancers to cisplatin treatment. Taken together, our results show that MFG-E8 is expressed in triple-negative breast cancers as a target gene of the p63 pathway, but may serve a suppressive function in ER(+) and erbB2(+) breast cancers. Its potential use as a serum biomarker that contributes to the pathogenesis of triple-negative breast cancers urges continued evaluation of its differential functions.

Identification of subtilase cytotoxin (SubAB) receptors whose signaling, in association with SubAB-induced BiP cleavage, is responsible for apoptosis in HeLa cells

Subtilase cytotoxin (SubAB), which is produced by certain strains of Shiga-toxigenic Escherichia coli (STEC), causes the 78-kDa glucose-regulated protein (GRP78/BiP) cleavage, followed by induction of endoplasmic reticulum (ER) stress, leading to caspase-dependent apoptosis via mitochondrial membrane damage by Bax/Bak activation. The purpose of the present study was to identify SubAB receptors responsible for HeLa cell death. Four proteins, NG2, α2β1 integrin (ITG), L1 cell adhesion molecule (L1CAM), and hepatocyte growth factor receptor (Met), were identified to be SubAB-binding proteins by immunoprecipitation and purification, followed by liquid chromatography-tandem mass spectrometry analysis. SubAB-induced Bax conformational change, Bax/Bak complex formation, caspase activation, and cell death were decreased in β1 ITG, NG2, and L1CAM small interfering RNA-transfected cells, but unexpectedly, BiP cleavage was still observed. Pretreatment of cells with a function-blocking β1 ITG antibody (monoclonal antibody [MAb] P5D2) enhanced SubAB-induced caspase activation; MAb P5D2 alone had no effect on caspase activation. Furthermore, we found that SubAB induced focal adhesion kinase fragmentation, which was mediated by a proteasome-dependent pathway, and caspase activation was suppressed in the presence of proteasome inhibitor. Thus, β1 ITG serves as a SubAB-binding protein and may interact with SubAB-signaling pathways, leading to cell death. Our results raise the possibility that although BiP cleavage is necessary for SubAB-induced apoptotic cell death, signaling pathways associated with functional SubAB receptors may be required for activation of SubAB-dependent apoptotic pathways.

A previously unreported function of β(1)B integrin isoform in caspase-8-dependent integrin-mediated keratinocyte death

Integrins regulate adhesive cell-matrix interactions and mediate survival signals. On the other hand, unligated or free cytoplasmic fragments of integrins induce apoptosis in many cell types (integrin-mediated death). We have previously shown that β(1) integrin expression protects keratinocyte stem cells from anoikis, whereas the role of the β(1)B integrin isoform has not been clarified. In this study we report that suspended keratinocytes undergo apoptosis through the activation of caspase-8, independently of the Fas/Fas ligand system. Indeed, anti-β(1) integrin-neutralizing antibodies induced apoptosis in short hairpin RNA Fas-associated death domain-treated cells. Moreover, before and during suspension, caspase-8 directly associated with β(1) integrin, which in turn internalized and progressively degraded, shedding the cytoplasmic domain. β(1)B was expressed only in the cytoplasm in a perinuclear manner and remained unaltered during suspension. At 24 hours, as β(1)A was located close to the nucleus, β(1)B colocalized with β(1)A and coimmunoprecipitated with caspase-8. Caspase-8 was activated earlier in β(1)B integrin-transfected keratinocytes, and these cells underwent a higher rate of apoptosis than mock cells. In contrast, caspase-8 was not activated in small interfering RNA (siRNA) β(1)B-transfected cells. These results indicate that when β(1)A is unligated, β(1)B is responsible for "integrin-mediated death" in human keratinocytes.

Proapoptotic function of integrin beta(3) in human hepatocellular carcinoma cells

PURPOSE

This study evaluates the proapoptotic function of integrin beta(3) in human hepatocellular carcinoma (HCC).

EXPERIMENTAL DESIGN

The expression of integrin beta(3) in 67 HCC specimens paired with corresponding neighboring nontumorous tissue was studied by quantitative real-time PCR and Western blot. The proapoptotic function of integrin beta(3) in SMMC-7721 human hepatoma cells overexpressing ITGB3 (gene coding integrin beta(3)) was determined through colony formation, serum starvation, and anoikis assay.

RESULTS

Compared with neighboring pathologically normal liver tissue, approximately 60% of the HCC specimens showed a significant down-regulated level of integrin beta(3) expression. Transient expression of integrin beta(3) in SMMC-7721 resulted in an enhanced level of apoptosis and suppression of colony formation. Cell growth inhibition on serum/ligand deprivation and incidences of anoikis were remarkably increased in SMMC-7721 with stable expression of integrin beta(3) in comparison with vector control transfectants. In addition, expression of fibrinogen and vitronectin, two native ligands for integrin alpha(v)beta(3) in liver, was inhibited, which was correlated with the decreased integrin beta(3) expression. Replenishing these ligands to the starved SMMC-7721 stable transfectants effectively restored the proapoptotic function of integrin beta(3).

CONCLUSIONS

Down-regulation of integrin beta(3) and its ligands in liver is related to the aggressive growth of HCC. Thus, reconstitution of integrin beta(3) in HCC may be a potential therapeutic approach to inhibit aggressive growth of liver cancer.

alpha(v)beta(3) Integrin-mediated drug resistance in human laryngeal carcinoma cells is caused by glutathione-dependent elimination of drug-induced reactive oxidative species

As a model for determination of the role of integrins in drug resistance, we used alpha(v)beta(3) integrin-negative human laryngeal carcinoma cell line (HEp2) and three HEp2-derived cell clones with a gradual increase of alpha(v)beta(3) integrin expression. The alpha(v)beta(3) integrin expression protects cells from cisplatin, mitomycin C, and doxorubicin. In HEp2-alpha(v)beta(3) integrin-expressing cells, the constitutive expression of Bcl-2 protein and the level of glutathione (GSH) were increased compared with HEp2 cells. Pretreatment of HEp2-alpha(v)beta(3) integrin-expressing cells with an inhibitor of GSH synthesis, buthionine sulfoximine (BSO), decreased the level of GSH and partially reverted drug resistance to all above-mentioned drugs, but it did not influence the expression of Bcl-2. Sensitivity to selected anticancer drugs did not change with overexpression of Bcl-2 in HEp2 cells, nor with silencing of Bcl-2 in HEp2-alpha(v)beta(3) integrin-expressing cells, indicating that Bcl-2 is not involved in resistance mechanism. There was no difference in DNA platination between HEp2 and HEp2-alpha(v)beta(3) integrin-expressing cells, indicating that the mechanism of drug resistance is independent of cisplatin detoxification by GSH. A strong increase of reactive oxidative species (ROS) formation during cisplatin or doxorubicin treatment in HEp2 cells was reduced in HEp2-alpha(v)beta(3) integrin-expressing cells. Since this increased elimination of ROS could be reverted by GSH depletion, we concluded that multidrug resistance is the consequence of GSH-dependent increased ability of alpha(v)beta(3)-expressing cells to eliminate drug-induced ROS.

Role of the alpha v-integrin subunit in cell proliferation, apoptosis and tumor metastasis of laryngeal and hypopharyngeal squamous cell carcinomas: a clinical and in vitro investigation

The objective of this study was to investigate the role of alpha v-integrin subunit (ITGAV, CD51) in invasion and metastasis of the laryngeal and hypopharyngeal squamous cell carcinomas and to evaluate whether an antisense oligonucleotide sequence (ASONs) targeting ITGAV gene can result in proliferative inhibition and induce to apoptosis of laryngeal carcinoma cell lines (Hep-2). Firstly, a tissue microarray contained 75 primary carcinomas, 29 non-cancerous normal tissues and 20 metastatic lymph nodes was constructed and used to detect the expression of ITGAV by immunohistochemistry. The changes of ITGAV expression from each group were assessed and correlated to the clinical parameters of the patients. Secondly, the ASONs targeting ITGAV gene was transfected into Hep-2 cells in vitro. The proliferative ability of the cells after transfection was measured by MTT assay and the apoptosis was detected using flow cytometry. Results showed that the expression of ITGAV was significantly correlated with differentiation and lymph node metastasis of these cancers. In vitro test showed that the proliferative ability of Hep-2 cells was significantly inhibited by ASONs in a way of concentration- and time-depending mode, and a significant apoptosis of Hep-2 cells was also observed after ASONs transfection. In conclusion, the expression of ITGAV was significantly correlated with differentiation and metastasis of the laryngeal and hypopharyngeal carcinomas; down-regulation of ITGAV gene could inhibit proliferation of Hep-2 cells and induce to its apoptosis. These results suggest that ITGAV gene may become a promising prognostic marker and new treatment target for these cancers.

Rotavirus replication in intestinal cells differentially regulates integrin expression by a phosphatidylinositol 3-kinase-dependent pathway, resulting in increased cell adhesion and virus yield

Changes in the interactions between intestinal cells and their surrounding environment during virus infection have not been well documented. The growth and survival of intestinal epithelial cells, the main targets of rotavirus infection, are largely dependent on the interaction of cell surface integrins with the extracellular matrix. In this study, we detected alterations in cellular integrin expression following rotavirus infection, identified the signaling components required, and analyzed the subsequent effects on cell binding to the matrix component collagen. After rotavirus infection of intestinal cells, expression of alpha2beta1 and beta2 integrins was up-regulated, whereas that of alphaVbeta3, alphaVbeta5, and alpha5beta1 integrins, if present, was down-regulated. This differential regulation of integrins was reflected at the transcriptional level. It was unrelated to the use of integrins as rotavirus receptors, as both integrin-using and integrin-independent viruses induced integrin regulation. Using pharmacological agents that inhibit kinase activity, integrin regulation was shown to be dependent on phosphatidylinositol 3-kinase (PI3K) but independent of the activities of the mitogen-activated protein kinases p38 and ERK1/2, and cyclooxygenase-2. Replication-dependent activation of the PI3K/Akt pathway was observed following infection of intestinal and nonintestinal cell lines. Rotavirus activation of PI3K was important for regulation of alpha2beta1 expression. Blockade of integrin regulation by PI3K inhibition led to decreased adherence of infected intestinal cells to collagen and a concomitant decrease in virus titer. These findings indicate that rotavirus-induced PI3K activation causes regulation of integrin expression in intestinal cells, leading to prolonged adherence of infected cells to collagen and increased virus production.

Flow cytometric immunophenotyping of cancer cells in effusion specimens: Diagnostic and research applications

Flow cytometry (FCM) immunophenotyping is frequently used as an ancillary technique for the diagnosis of hematological malignancies or for measurement of DNA content. In recent years, we applied FCM to the diagnosis of metastatic adenocarcinoma and malignant mesothelioma in effusions. We established a panel of antibodies that allows for rapid and effective differentiation between epithelial cells, mesothelial cells, and leukocytes. FCM was subsequently used for quantitative analysis of integrin subunits. Recently, we studied different parameters of the immune response, including HLA molecules and chemokine receptors, using this method. Our data suggest that FCM is an effective method for the characterization of cancer cells in clinical effusion specimens in both the diagnostic and research setting, and that this method is comparable to immunohistochemistry in terms of sensitivity and specificity, with the additional advantage of providing quantitative data. This review discusses previous work in this area and the future potential of this method in the characterization of tumor cells in serous effusions.

Purification and characterization of Ophiophagus hannah cytotoxin-like proteins

Three cytotoxin-like proteins from the venom of Ophiophagus hannah were isolated by a combination of ion exchange chromatography and reverse phase HPLC. Amino acid sequence analysis revealed that these proteins all consisted of 63 amino acids and shared approximate 50% and 56% sequence identity with Naja naja atra cardiotoxins and cardiotoxin-like basic proteins (CLBPs), respectively. CD spectra revealed that their secondary structure was dominated with beta-sheet as those noted with cardiotoxins and CLBPs. O. hannah cytotoxin-like protein exhibited a cell-lytic activity on SK-N-SH cells, but its activity was more weak than that noted for N. naja atra cardiotoxin 3. Alternatively, apoptotic cell death was induced by the addition of N. naja atra CLBP. Based on the sequence information with the toxin molecules, the functional residues and regions related to the differential activity with O. hannah cytotoxin-like protein, cardiotoxin and CLBP are discussed.

The role of beta1 integrin subfamily in anchorage-dependent apoptosis of breast carcinoma cells differing in multidrug resistance

Integrin expression was investigated in MCF-7 human breast adenocarcinoma line and in the MCF-7Dox line, which was selected from MCF-7 by a resistance to multiple antitumor drugs (MDR). We have shown that acquisition of MDR was accompanied by a drastically reduced expression of some integrins of the beta1-subfamily (alpha2beta1, alpha3beta1, alpha6beta1) and of alpha vbeta5 intergin in the adenocarcinoma cells. In contrast, expression of alpha5beta1 integrin was markedly increased in the MDR cells. Along with multiple antitumor drug resistance, MCF-7Dox cells demonstrate elevated resistance to anchorage-dependent apoptosis (anoikis) and enhanced in vitro invasive activity. To elucidate the implication of beta1-integrins in the above phenotypic modifications, the effect of beta1-integrin signaling was assayed. Stimulation of beta1-mediated signaling was accomplished by treating of the cells with antibodies to the beta1-subunit common for members of the beta1-subfamily. These data show that activation of beta1-integrin signaling markedly upregulated anoikis of the adenocarcinoma cells.

Extracellular Matrix Metalloproteinase Inducer (CD147) Confers Resistance of Breast Cancer Cells to Anoikis through Inhibition of Bim

Overexpression of extracellular matrix metalloproteinase inducer (EMMPRIN or CD147), a member of the immunoglobulin family and a glycoprotein enriched on the surface of tumor cells, promotes invasion, metastasis, and growth and survival of malignant cells and confers resistance to some chemotherapeutic drugs. However, the molecular mechanisms underlying the actions of EMMPRIN are not fully understood. In this study we sought to determine whether EMMPRIN contributes to the malignant phenotype of breast cancer by inhibiting anoikis, a form of apoptosis induced by loss or alteration of cell-cell or cell-matrix anchorage, and to explore the signaling pathways involved. We found that in the absence of attachment, human breast carcinoma cells expressing high levels of EMMPRIN formed less compact aggregates with larger surface area and less fibronectin matrix assembly, had higher viability, and were resistant to anoikis. Knockdown of EMMPRIN expression by RNA interference (small interfering RNA or short hairpin RNA) sensitized cancer cells to anoikis, as demonstrated by activation of caspase-3, increased DNA fragmentation, and decreased cellular viability. Furthermore, we observed that the accumulation of Bim, a proapoptotic BH3-only protein, was reduced in EMMPRIN-expressing cells and that silencing of EMMPRIN expression elevated Bim protein levels and enhanced cellular sensitivity to anoikis. Treatment of cells with a MEK inhibitor (U0126) or proteasome inhibitor (epoxomicin) also up-regulated Bim accumulation and rendered cells more sensitive to anoikis. These results indicated that expression of EMMPRIN protects cancer cells from anoikis and that this effect is mediated at least in part by a MAP kinase-dependent reduction of Bim. Because anoikis deficiency is a key feature of neoplastic transformation and invasive growth of epithelial cancer cells, our study on the role of EMMPRIN in anoikis resistance and the mechanism involved underscores the potential of EMMPRIN expression as a prognostic marker and novel target for cancer therapy.

Resensitization of breast cancer cells to anoikis by Tropomyosin-1: role of Rho kinase-dependent cytoskeleton and adhesion

Two most common properties of malignant cells are the presence of aberrant actin cytoskeleton and resistance to anoikis. Suppression of several key cytoskeletal proteins, including tropomyosin-1 (TM1), during neoplastic transformation is hypothesized to contribute to the altered cytoskeleton and neoplastic phenotype. Using TM1 as a paradigm, we have shown that cytoskeletal proteins induce anoikis in breast cancer (MCF-7 and MDA MB 231) cells. Here, we have tested the hypothesis that TM1-mediated cytoskeletal changes regulate integrin activity and the sensitivity to anoikis. TM1 expression in MDA MB 231 cells promotes the assembly of stress fibers, induces rapid anoikis via caspase-dependent pathways involving the release of cytochrome c. Further, TM1 inhibits binding of MDA MB 231 cells to collagen I, but promotes adhesion to laminin. Inhibition of Rho kinase disrupts TM1-mediated cytoskeletal reorganization and adhesion to the extracellular matrix components, whereas the parental cells attach to collagen I, spread and form extensive actin meshwork in the presence of Rho kinase inhibitor, underscoring the differences in parental and TM1-transduced breast cancer cells. Further, treatment with the cytoskeletal disrupting drugs rescues the cells from TM1-induced anoikis. These new findings demonstrate that the aberrant cytoskeleton contributes to neoplastic transformation by conferring resistance to anoikis. Restoration of stress fiber network through enhanced expression of key cytoskeletal proteins may modulate the activity of focal adhesions and sensitize the neoplastic cells to anoikis.

Increased adenoviral transduction efficacy in human laryngeal carcinoma cells resistant to cisplatin is associated with increased expression of integrin alphavbeta3 and coxsackie adenovirus receptor

In our study, we investigated molecular mechanisms of increased adenoviral transduction efficacy in cisplatin-resistant human laryngeal carcinoma cells CA3ST as compared to parental cells HEp2. Using reverse transcription-PCR, the genes potentially implicated in adenoviral entry were screened. In cisplatin-resistant cells, only upregulation of alphavbeta3 integrin was detected, which was additionally confirmed by flow cytometry. Moderately increased expression of CAR was determined in cisplatin-resistant CA3ST cells using flow cytometry and measurement of wild-type adenovirus Ad5CMVbetagal attachment. In order to test the implication of alphavbeta3 integrin in transduction efficacy, 6 HEp2-derived alphavbeta3-expressing clones with graded expression of alphavbeta3 were isolated. To a certain degree of density, expression of alphavbeta3 positively correlated with Ad5CMVbetagal transduction efficacy (i.e., increased viral transduction), suggesting a role of alphavbeta3 in transduction efficacy. However, HEp2 clones with the highest alphavbeta3) expression were negatively correlated with transduction efficacy (i.e., decreased viral transduction). This was shown to be associated with downregulation of alphavbeta5 integrin, also involved in viral transduction, in clones with the highest alphavbeta3 expression. The implication of CAR in increased adenoviral transduction efficacy in cisplatin resistant CA3ST cells was further assessed by transduction experiments using adenoviral mutant Ad5FbDelta639 whose entry is only to a very small extent dependent on the presence of CAR. Indeed, Ad5FbDelta639 infected 2.5-fold more, in comparison to wild-type adenovirus, which infected 5-fold more efficiently resistant CA3ST cells than parental HEp2 cells, indicating that increased expression of CAR contributes to increased efficacy of adenoviral transduction. Thus, the data presented provide evidence that both alphavbeta3 integrin and CAR are involved in increased adenoviral transduction efficacy in cisplatin resistant CA3ST cells. These findings may have significant implications in human gene therapy using adenoviruses, especially in patients after unsuccessful cisplatin treatment.

Multidrug-resistant tumor cells with decreased malignancy: a role for integrin αvβ3

We studied whether acquisition of multidrug resistance (MDR) by tumor cells can alter their integrin profile and malignant behavior. Hamster fibroblast cell line HET-SR-2SC-LNM was selected for MDR, yielding the 2SC/20 subline. Compared with the parental cells, the 2SC/20 subline weakly adhered to denatured collagen (dCol) which correlated with decreased expression of alphavbeta3, a dCol receptor. Importantly, 2SC/20 subline demonstrated significantly decreased activity of collagenase MMP-2, lower ability to invade Matrigel, and attenuated metastasis in syngeneic animals. We provide evidence for the first time that selection for MDR can be associated with down-regulation of alphavbeta3 integrin, supporting our recent proof of the pro-apoptotic role of this integrin (Oncogene 20 (2001) 4710). Lack of alphavbeta3 expression may link cell survival under toxic conditions with decreased malignancy of the resulting drug resistant tumor.

Mitochondrial dysfunction in CD47-mediated caspase-independent cell death: ROS production in the absence of cytochrome c and AIF release

Ligation of CD47 by its natural ligand thrombospondin (TSP), or cross-linking by CD47 antibodies, triggers caspase-independent cell death in normal and leukemic cells. This kind of cell death is characterised by the cytoplasmic events of apoptosis including externalisation of phosphatidylserines and mitochondria swelling. We report herein selective mitochondrial changes in CD47-dependent cell death of T cells. After T cell stimulation via CD47, a rapid mitochondrial transmembrane potential (deltapsi(m)) disruption is accompanied by the production of reactive oxygen species (ROS) and phosphatidylserine exposure. Surprisingly, mitochondrial dysfunction does not induce cytochrome c or AIF release. Moreover, the dying cells do not exhibit caspase-3 activation and display intact nuclei without any large-scale, or oligonucleosomal DNA fragmentation. We conclude that DeltaPsi(m) loss and ROS production are an early step in CD47-dependent killing and neither cytochrome c, nor AIF are implicated in this new cell death pathway.

Decrease in survival threshold of quiescent colon carcinoma cells in the presence of a small molecule integrin antagonist

The role of adhesion molecules, such as alphav integrins, in the control of the survival of quiescent tumor cells is unclear. We used S 34961, a novel small molecule alphav integrin antagonist, to investigate the role of integrin-signaling in the survival of populations of quiescent human HT-29 and HCT 116 colon carcinoma cells. S 34961 at 1 microM induced detachment, but cells retained viability, existing as clusters. Nonligated beta-integrins may recruit and activate caspase-8 [J Cell Biol 155:459-470, 2001]. However, congruent with the absence of apoptosis, no activation of caspase-8 in these cells was detected after incubation with S 34961. A rapid (2 h) change in conformation of the N terminus of proapoptotic Bak was observed before detachment, together with a decrease in phosphorylation of focal adhesion kinase (2 h) and subsequent (8 h) decreases in phosphorylation of extracellular signal-regulated kinase-1/2 and Akt. Together, these results suggested that although treatment with S 34961 has no effect on survival per se, it may reduce the survival threshold of the tumor cells, with Bak in an activated state. Indeed, concomitant incubation of S 34961 with 10 microM U-0126 (a mitogen-activated protein kinase kinase inhibitor) was found to lead to apoptosis (at 24 h), whereas U-0126 alone had no effect. Together, these observations could guide the use of combination therapy with integrin antagonists in the clinic.

Specific beta1 integrin site selectively regulates Akt/protein kinase B signaling via local activation of protein phosphatase 2A

Integrin transmembrane receptors generate multiple signals, but how they mediate specific signaling is not clear. Here we test the hypothesis that particular sequences along the beta(1) integrin cytoplasmic domain may exist that are intimately related to specific integrin-mediated signaling pathways. Using systematic alanine mutagenesis of amino acids conserved between different beta integrin cytoplasmic domains, we identified the tryptophan residue at position 775 of human beta(1) integrin as specific and necessary for integrin-mediated protein kinase B/Akt survival signaling. Stable expression of a beta(1) integrin mutated at this amino acid in GD25 beta(1)-null cells resulted in reduction of Akt phosphorylation at both Ser(473) and Thr(308) activation sites. As a consequence, the cells were substantially more sensitive to serum starvation-induced apoptosis when compared with cells expressing wild type beta(1) integrin. This inactivation of Akt resulted from increased dephosphorylation by a localized active population of protein phosphatase 2A. Both Akt and protein phosphatase 2A were present in beta(1) integrin-organized cytoplasmic complexes, but the activity of this phosphatase was 2.5 times higher in the complexes organized by the mutant integrin. The mutation of Trp(775) specifically affected Akt signaling, without effects on other integrin-activated pathways including phosphoinositide 3-kinase, MAPK, JNK, and p38 nor did it influence activation of the integrin-responsive kinases focal adhesion kinase and Src. The identification of Trp(775) as a specific site for integrin-mediated Akt signaling supports the concept of specificity of signaling along the integrin cytoplasmic domain.

Regulation of the intestinal epithelial response to cyclic strain by extracellular matrix proteins

Repetitive mechanical deformation may stimulate intestinal epithelial proliferation. Because the extracellular matrix modulates static intestinal epithelial biology, we examined whether matrix proteins influence intestinal epithelial responses to deformation. Human Caco-2BBE cells and nontransformed human enterocytes (HIPEC) were subjected to 10% average cyclic strain at 10 cycles/min on flexible membranes precoated with matrix proteins without or with plasma fibronectin or functional anti-integrin antibodies in the medium. Strain stimulated proliferation, focal adhesion kinase, extracellular signal-regulated protein kinase (ERK), p38, and Jun N-terminal kinase similarly on collagen I or IV, and more weakly on laminin, but had no effect on fibronectin. MEK blockade (PD98059) prevented strain-stimulated proliferation on collagen but did not affect proliferation on fibronectin. Adding tissue fibronectin to a collagen substrate or plasma fibronectin to the media suppressed strain s mitogenic and signal effects, but not those of epidermal growth factor. Functional antibodies to the alpha5 or alpha(v) integrin subunit blocked strain's effects on Caco-2 proliferation and ERK activation, although ligation of the alpha2 or alpha6 subunit did not. Repetitive strain also stimulated, and fibronectin inhibited, human intestinal primary epithelial cell proliferation. Repetitive deformation stimulates transformed and nontransformed human intestinal epithelial proliferation in a matrix-dependent manner. Tissue or plasma fibronectin may regulate the intestinal epithelial response to strain via integrins containing alpha5 or alpha(v).

Engineered fibronectin type III domain with a RGDWXE sequence binds with enhanced affinity and specificity to human alphavbeta3 integrin

Fibronectin is an extracellular matrix protein with broad binding specificity to cell surface receptors, integrins. The tenth fibronectin type III domain (FNfn10) is a small, autonomous domain of fibronectin containing the RGE sequence that is directly involved in integrin binding. However, in isolation FNfn10 only weakly bind to integrins. We reasoned that high-affinity and high-specificity variants of FNfn10 to a particular integrin could be engineered by optimizing residues surrounding the integrin-binding RGD sequence in the flexible FG loop. Affinity maturation of FNfn10 to alphavbeta3 integrin, an integrin up-regulated in angiogenic endothelial cells and in some metastatic tumor cells, yielded alphavbeta3-binding FNfn10 mutants with a novel RGDWXE consensus sequence. We characterized one of the RGDWXE-modified clones, FNfn10-3JCLI4, as purified protein. FNfn10-3JCLI4 binds with high affinity and specificity to purified alphavbeta3 integrin. Alanine scanning mutagenesis suggested that both the tryptophan and glutamic acid residues following the RGD sequence are required for maximal affinity and specificity for alphavbeta3. FNfn10-3JCLI4 specifically stained alphavbeta3-positive cells as detected with flow cytometry and it inhibited alphavbeta3-dependent cell adhesion. As with the anti-alphavbeta3 antibody LM609, FNfn10-3JCLI4 can interfere with in vitro capillary formation. Taken together, these data show that FNfn10-3JCL14 is a specific, high-affinity alphavbeta3-binding protein that can inhibit alphavbeta3-dependent cellular processes similar to an anti-alphavbeta3 monoclonal antibody. These properties, combined with the small, monomeric, cysteine-free and highly stable structure of FNfn10-3JCLI4, may make this protein useful in future applications involving detection and targeting of alphavbeta3-positive cells.

Alpha6beta1 integrin induces proteasome-mediated cleavage of erbB2 in breast cancer cells

ErbB2 and alpha6 integrin have been implicated in malignancy of breast cancer cells. Here we have determined the influence of alpha6beta1 integrin on erbB2 signaling in anchorage-independent growth, using MDA-MB435 breast cancer cells. Firstly, we transfected the cells with erbB2 cDNA, and isolated cells with high or low levels of alpha6beta1 integrin by cell sorting (alpha6H-ErbB and alpha6L-ErbB). We found that an erbB ligand, heregulin beta1, enhanced growth activity of alpha6L-ErbB cells, but not alpha6H-ErbB cells. Secondly, we established cells expressing a beta4 integrin deletion mutant (beta4-deltacyt), which selectively inhibited alpha6beta1 integrin expression and adhesion to laminin-1. Again, heregulin beta1 enhanced the growth of erbB2 cDNA-transfected beta4-deltacyt cells, but not mock cells. Western blot analysis revealed that heregulin beta1 stimulated phosphorylation of Akt and its downstream molecules, GSK3beta and p70S6kinase, and that the extent of phosphorylation was greater in ErbB2/beta4-deltacyt cells than ErbB2/mock cells. Furthermore, we found that the erbB2 cytoplasmic domain was truncated in ErbB2/mock cells, which was independent of ligand stimulation and adhesion, and was suppressed by proteasome inhibitors. These results suggest that alpha6beta1 integrin inhibits erbB2 signals by inducing proteasome-dependent proteolytic cleavage of the erbB2 cytoplasmic domain, and may thereby contribute to the regulation of tumor growth.

Get a ligand, get a life: integrins, signaling and cell survival

Programmed cell death is crucial for the development and maintenance of multicellular organisms. The decision to live, or to die, depends, at the cellular level, upon the cell's interaction with extracellular cues that trigger cell signaling pathways promoting survival or death. The extracellular matrix (ECM) influences the execution of the apoptotic program through the actions of adhesion receptors. Among these, integrins initiate a variety of downstream signaling events in response to ECM ligation. Integrins directly activate survival pathways via the PI 3-kinase and MAPK pathways and act as essential cofactors for their stimulation by growth factors. Conversely, elevated integrin expression in the absence of appropriate ligands, or in the presence of natural or synthetic antagonists, can promote apoptosis under otherwise permissive growth conditions. Integrins thus act in a crucial biosensory role, coordinating survival or death responses as a function of ECM composition. This dual function provides an elegant mechanism through which tissue-remodeling events may regulate cell death or survival in a temporal, ECM-governed manner.

Inhibition of angiogenesis in vitro by alphav integrin-directed antisense oligonucleotides

The integrin alpha v beta 3 plays a central role in angiogenesis. In this study, we used antisense oligodeoxyribonucleotides (ONs) directed against the alpha v subunit of alpha v beta 3 to inhibit integrin expression. Ten ON sequences, which were selected by systematic alignment of computer-predicted secondary structures of alpha v mRNA, were transfected into human umbilical vein endothelial cells (HUVECs). Following stimulation by PMA, five antisense ONs significantly inhibited alpha v mRNA and protein expression in activated HUVEC at a concentration of 0.05 mciroM with complete prevention of PMA-induced alpha v up-regulation by the most potent antisense ON. Inhibition of alpha v expression was associated with significant inhibition of migration of HUVEC by 28% and had no effect on proliferation and apoptosis. Moreover, transfection of antisense ON inhibited the formation of tube-like structures of HUVEC in Matrigel by 44%. In a cell culture model of angiogenesis consisting of a co-culture of endothelial cells with fibroblasts, transfection of antisense ONs resulted in an inhibition of tube formation of 61%. In conclusion, alpha v antisense ONs are potent inhibitors of angiogenesis in vitro. They might, therefore, be a therapeutic alternative to antagonists, which directly bind to alpha v integrins, and might be useful for the treatment of malignant tumors and hematological malignancies.

ECM remodeling regulates angiogenesis: endothelial integrins look for new ligands

The process of angiogenesis is a dynamic one. Vascular endothelial cells are changing at the same time the extracellular matrix is being remodeled. Stupack and Cheresh discuss how remodeling of the extracellular matrix (ECM) and changes in the endothelial cell protein production and integrin expression contribute to the complex process of new blood vessel growth from an existing vascular bed.