Use of RNA interference to inhibit integrin (alpha6beta4)-mediated invasion and migration of breast carcinoma cells

Integrin α6β4 signals through DNA damage response pathway to sensitize breast cancer cells to cisplatin

Integrin α6β4 is highly expressed in triple negative breast cancer (TNBC) and drives its most aggressive traits; however, its impact on chemotherapeutic efficacy remains untested. We found that integrin α6β4 signaling promoted sensitivity to cisplatin and carboplatin but not to other chemotherapies tested. Mechanistic investigations revealed that integrin α6β4 stimulated the activation of ATM, p53, and 53BP1, which required the integrin β4 signaling domain. Genetic manipulation of gene expression demonstrated that mutant p53 cooperated with integrin α6β4 for cisplatin sensitivity and was necessary for downstream phosphorylation of 53BP1 and enhanced ATM activation. Additionally, we found that in response to cisplatin-induced DNA double strand break (DSB), integrin α6β4 suppressed the homologous recombination (HR) activity and enhanced non-homologous end joining (NHEJ) repair activity. Finally, we discovered that integrin α6β4 preferentially activated DNA-PK, facilitated DNA-PK-p53 and p53-53BP1 complex formation in response to cisplatin and required DNA-PK to enhance ATM, 53BP1 and p53 activation as well as cisplatin sensitivity. In summary, we discovered a novel function of integrin α6β4 in promoting cisplatin sensitivity in TNBC through DNA damage response pathway.

Loss of α6β4 Integrin-Mediated Hemidesmosomes Promotes Prostate Epithelial Cell Migration by Stimulating Focal Adhesion Dynamics

Epithelial cell adhesion is mediated by actin cytoskeleton-linked focal adhesions (FAs) and intermediate filament-associated hemidesmosomes (HDs). HDs are formed by α6β4-integrins and mediate stable anchoring to the extracellular matrix (ECM) while FAs containing β1-integrins regulate cell migration. Loss of HDs has been reported in various cancers such as prostate cancer where it correlates with increased invasive migration. Here we have studied cell migration properties and FA dynamics in genetically engineered prostate epithelial cell lines with intact or disrupted HDs. Disruption of HDs by depleting α6- or β4-integrin expression promoted collective cell migration and modulated migratory activity. Dynamic analysis of fluorescent protein-tagged FA marker proteins revealed faster FA assembly and disassembly kinetics in HD-depleted cells. FRAP analysis showed that loss of HDs correlated with faster diffusion rates of focal adhesion kinase (FAK) and vinculin in and out of FAs. These data suggest that loss of α6β4-mediated HDs promote cell migration and FA assembly dynamics by influencing the molecular diffusion rates of FAK.

Crosstalk between insulin-like growth factor (IGF) receptor and integrins through direct integrin binding to IGF1

It has been generally accepted that integrin cell adhesion receptors are involved in growth factor signaling (integrin-growth factor crosstalk), since antagonists to integrins often suppress growth factor signaling. Partly because integrins have been originally identified as cell adhesion receptors to extracellular matrix (ECM) proteins, current models of the crosstalk between IGF1 and integrins propose that ECM ligands (e.g., vitronectin) bind to integrins and IGF1 binds to IGF receptor type 1 (IGF1R), and two separate signals merge inside the cells. Our research proves otherwise. We discovered that IGF1 interacts directly with integrins, and induces integrin-IGF-IGF1R complex formation on the cell surface. IGF1 signaling can be detected in the absence of ECM (anchorage-independent conditions). Integrin antagonists block both ECM-integrin interaction and IGF-integrin interaction, and do not distinguish the two. This is one possible reason why integrin-IGF1 interaction has not been detected. With these new discoveries, we believe that the direct IGF-integrin interaction should be incorporated into models of IGF1 signaling. The integrin-binding defective mutant of IGF1 is defective in inducing IGF signaling, although the mutant still binds to IGF1R. Notably, the IGF1 mutant is dominant-negative and suppresses cell proliferation induced by wt IGF1, and suppresses tumorigenesis in vivo, and thus the IGF1 mutant has potential as a therapeutic.

Integrin β4 promotes cell invasion and epithelial-mesenchymal transition through the modulation of Slug expression in hepatocellular carcinoma

Integrin β4 (ITGB4) is a transmembrane receptor involved in tumorigenesis and the invasiveness of many cancers. However, its role in hepatocellular carcinoma (HCC), one of the most prevalent human cancers worldwide, remains unclear. Here, we examined the involvement of ITGB4 in HCC and explored the underlying mechanisms. Real-time PCR and immunohistochemical analyses of tissues from 82 patients with HCC and four HCC cell lines showed higher ITGB4 levels in tumor than in adjacent non-tumor tissues and in HCC than in normal hepatic cells. Silencing of ITGB4 repressed cell proliferation, colony forming ability and cell invasiveness, whereas ectopic expression of ITGB4 promoted the proliferation and invasion of HCC cells and induced epithelial to mesenchymal transition (EMT) in parallel with the upregulation of Slug, as shown by transwell assays, WB and immunocytochemistry. Knockdown of Slug reduced cell viability inhibited invasion and reversed the effects of ITBG4 overexpression on promoting EMT, and AKT/Sox2-Nanog may also be involved. In a xenograft tumor model induced by injection of ITGB4-overexpressing cells into nude mice, ITGB4 promoted tumor growth and metastasis to the lungs. Taken together, our results indicate that ITGB4 plays a tumorigenic and pro-metastatic role mediated by Slug and suggest IGTB4 could be a prognostic indicator or a therapeutic target in patients with HCC.

A role for PVRL4-driven cell-cell interactions in tumorigenesis

During all stages of tumor progression, cancer cells are subjected to inappropriate extracellular matrix environments and must undergo adaptive changes in order to evade growth constraints associated with the loss of matrix attachment. A gain of function screen for genes that enable proliferation independently of matrix anchorage identified a cell adhesion molecule PVRL4 (poliovirus-receptor-like 4), also known as Nectin-4. PVRL4 promotes anchorage-independence by driving cell-to-cell attachment and matrix-independent integrin β4/SHP-2/c-Src activation. Solid tumors frequently have copy number gains of the PVRL4 locus and some have focal amplifications. We demonstrate that the transformation of breast cancer cells is dependent on PVRL4. Furthermore, growth of orthotopically implanted tumors in vivo is inhibited by blocking PVRL4-driven cell-to-cell attachment with monoclonal antibodies, demonstrating a novel strategy for targeted therapy of cancer. DOI:http://dx.doi.org/10.7554/eLife.00358.001.

Cross-talk between integrin α6β4 and insulin-like growth factor-1 receptor (IGF1R) through direct α6β4 binding to IGF1 and subsequent α6β4-IGF1-IGF1R ternary complex formation in anchorage-independent conditions

Integrin αvβ3 plays a role in insulin-like growth factor-1 (IGF1) signaling (integrin-IGF1 receptor (IGF1R) cross-talk). The specifics of the cross-talk are, however, unclear. In a current model, "ligand occupancy" of αvβ3 (i.e. the binding of extracellular matrix proteins) enhances signaling induced by IGF1 binding to IGF1R. We recently reported that IGF1 directly binds to αvβ3 and induces αvβ3-IGF1-IGF1R ternary complex formation. Consistently, the integrin binding-defective IGF1 mutant (R36E/R37E) is defective in inducing ternary complex formation and IGF signaling, but it still binds to IGF1R. Like αvβ3, integrin α6β4 is overexpressed in many cancers and is implicated in cancer progression. Here, we discovered that α6β4 directly bound to IGF1, but not to R36E/R37E. Grafting the β4 sequence WPNSDP (residues 167-172), which corresponds to the specificity loop of β3, to integrin β1 markedly enhanced IGF1 binding to β1, suggesting that the WPNSDP sequence is involved in IGF1 recognition. WT IGF1 induced α6β4-IGF1-IGF1R ternary complex formation, whereas R36E/R37E did not. When cells were attached to matrix, exogenous IGF1 or α6β4 expression had little or no effect on intracellular signaling. When cell-matrix adhesion was reduced (in poly(2-hydroxyethyl methacrylate-coated plates), IGF1 induced intracellular signaling and enhanced cell survival in an α6β4-dependent manner. Also IGF1 enhanced colony formation in soft agar in an α6β4-dependent manner. These results suggest that IGF binding to α6β4 plays a major role in IGF signaling in anchorage-independent conditions, which mimic the in vivo environment, and is a novel therapeutic target.

Regulation of apoptosis and autophagy by sphingosylphosphorylcholine in vascular endothelial cells

Sphingosylphosphorylcholine (SPC), an important cardiovascular mediator derived from sphingomyelin that has atheroprotective effects via actions on vascular endothelial cells (VECs) at normal levels in vivo. However, the underlying mechanism is not well known. To clarify this question, we first investigated the effect of SPC on VEC apoptosis and autophagy induced by deprivation of serum and fibroblast growth factor 2 (FGF-2). SPC at 5-20 µM inhibited apoptosis and induced autophagy in vitro. To understand the underlying mechanism, we investigated the role of integrin β4 in SPC-induced autophagy in VECs. SPC significantly decreased the level of integrin β4, whereas overexpression of integrin β4 inhibited SPC-induced autophagy. Moreover, knockdown of integrin β4 promoted VEC autophagy. To understand the downstream factors of integrin β4 in this process, we observed the effects of SPC on phosphatidylcholine-specific phospholipase C (PC-PLC) activity and level of p53. PC-PLC activity and p53 level in cytoplasm was decreased during autophagy induced by SPC, and knockdown of integrin β4 inhibited the activity of PC-PLC and the cytoplasmic level of p53. SPC may promote autophagy via integrin β4. Moreover, PC-PLC and p53 may be the downstream factors of integrin β4 in autophagy of VECs deprived of serum and FGF-2.

The 'chemoinvasion' assay, 25 years and still going strong: the use of reconstituted basement membranes to study cell invasion and angiogenesis

Invasive and metastatic cells must cross basement membranes (BMs) in order to disseminate to distant sites. The 'chemoinvasion assay' using a reconstituted basement membrane, matrigel, in Boyden blind-well chambers was developed 25 years ago as a tool for invasion and metastasis research. Since then, it was adapted for investigation of how different cells types engage with and penetrate basement membrane, including research in angiogenesis, invasive cell migration, protease functions, and preclinical development of anti-invasive and anti-angiogenic agents. As novel mechanisms of metastasis and angiogenesis come to light and old paradigms are challenged, we examine how the assay can still provide innovative insights. We review established applications and variants of the matrigel invasion assay, highlight key findings derived from it and discuss future developments, including roles for accessory and cancer stem cells.

Direct binding of the EGF-like domain of neuregulin-1 to integrins ({alpha}v{beta}3 and {alpha}6{beta}4) is involved in neuregulin-1/ErbB signaling

Integrin-growth factor receptor cross-talk plays a role in growth factor signaling, but the specifics are unclear. In a current model, integrins and growth factor receptors independently bind to their ligands (extracellular matrix and growth factors, respectively). We discovered that neuregulin-1 (NRG1), either as an isolated EGF-like domain or as a native multi-domain form, binds to integrins αvβ3 (with a K(D) of 1.36 × 10(-7) m) and α6β4. Docking simulation predicted that three Lys residues at positions 180, 184, and 186 of the EGF-like domain are involved in integrin binding. Mutating these residues to Glu individually or in combination markedly suppressed integrin binding and ErbB3 phosphorylation. Mutating all three Lys residues to Glu (the 3KE mutation) did not affect the ability of NRG1 to bind to ErbB3 but markedly reduced the ability of NRG1 to induce ErbB3 phosphorylation and AKT and Erk1/2 activation in MCF-7 and T47D human breast cancer cells. This suggests that direct integrin binding to NRG1 is critical for NRG1/ErbB signaling. Notably, stimulation of cells with WT NRG1 induced co-precipitation of ErbB3 with α6β4 and with αvβ3 to a much lower extent. This suggests that WT NRG1 induces integrin-NRG1-ErbB3 ternary complex formation. In contrast, the 3KE mutant was much less effective in inducing ternary complex formation than WT NRG1, suggesting that this process depends on the ability of NRG1 to bind to integrins. These results suggest that direct NRG1-integrin interaction mediates integrin-ErbB cross-talk and that α6β4 plays a major role in NRG-ErbB signaling in these cancer cells.

ARRDC3 suppresses breast cancer progression by negatively regulating integrin beta4

Large-scale genetic analyses of human tumor samples have been used to identify novel oncogenes, tumor suppressors and prognostic factors, but the functions and molecular interactions of many individual genes have not been determined. In this study we examined the cellular effects and molecular mechanism of the arrestin family member, ARRDC3, a gene preferentially lost in a subset of breast cancers. Oncomine data revealed that the expression of ARRDC3 decreases with tumor grade, metastases and recurrences. ARRDC3 overexpression represses cancer cell proliferation, migration, invasion, growth in soft agar and in vivo tumorigenicity, whereas downregulation of ARRCD3 has the opposite effects. Mechanistic studies showed that ARRDC3 functions in a novel regulatory pathway that controls the cell surface adhesion molecule, β-4 integrin (ITGβ4), a protein associated with aggressive tumor behavior. Our data indicates ARRDC3 directly binds to a phosphorylated form of ITGβ4 leading to its internalization, ubiquitination and ultimate degradation. The results identify the ARRCD3-ITGβ4 pathway as a new therapeutic target in breast cancer and show the importance of connecting genetic arrays with mechanistic studies in the search for new treatments.

Integrin targeted drug and gene delivery

IMPORTANCE OF THE FIELD

Recently, there has been substantial progress in the development of integrin targeted pharmaceuticals and drug delivery systems. Integrin is an important member in the cell adhesion molecule family, which is involved in regulation of complex biological conditions, from keeping normal physiological activities to causing cellular dysfunction in diseased cells. Hence, it is timely to summarize the recent developments in integrin targeted drug and gene delivery systems to understand better their advantages and limitations.

AREAS COVERED IN THIS REVIEW

In this review, advances in the discovery and clinical trials of these integrin antagonists against different integrin subunits are summarized and discussed. Besides using integrin inhibitor as a single therapeutic agent, integrin antagonists that were conjugated to cytotoxic drugs by synthetic chemistry or coupled to biomacromolecules by either DNA recombination technology or fusion protein technology for integrin targeted therapy have been explored. Furthermore, nanoparticles with integrin targeting ligands for both drug and gene delivery, typically for antiangiogenesis and anticancer therapy, are highlighted and evaluated.

WHAT THE READER WILL GAIN

This review sheds light on the future development of integrin targeted drug and/or gene delivery systems.

TAKE HOME MESSAGE

Although thus far there are still limitations, integrin targeted delivery systems have already shown their potential as important pharmaceuticals in the near future.

Integrin (alpha6beta4) signals through Src to increase expression of S100A4, a metastasis-promoting factor: implications for cancer cell invasion

Integrin alpha6beta4 is linked to cancer cell motility and invasion in aggressive and metastatic cancer cells. In this study, we showed that expression of the beta4 integrin in MDA-MB-435 cancer cells (MDA-MB-435/beta4) leads to a dramatic increase in expression of a metastasis-promoting factor, S100A4, as determined by affymetrix gene chip microarray, quantitative real-time PCR, and Western blot analysis. Alternatively, knocking down beta4 integrin expression in MDA-MB-231 breast carcinoma cells by shRNA reduced the level of S100A4 expression. The mechanism by which alpha6beta4 enhances S100A4 expression involves Src, Akt, and NFAT. We have further shown that Y1494, a tyrosine residue of the ITIM motif in the cytoplasmic domain of the beta4 integrin subunit, is essential for alpha6beta4-dependent S100A4 expression. Reduction of S100A4 expression by shRNA blocked migration, invasion, and anchorage-independent growth of MDA-MB-435/beta4, SUM-159, and MDA-MB-231 cells. These studies define a novel mechanism by which integrin alpha6beta4 promotes cancer cell motility and invasion, and provides insight into how S100A4 expression is regulated in cancer cells.

A key tyrosine (Y1494) in the beta4 integrin regulates multiple signaling pathways important for tumor development and progression

Expression of the alpha6beta4 integrin is associated with poor patient prognosis and reduced survival in a variety of human cancers. In recent years, a limited number of in vivo studies have examined the contribution of this integrin receptor to cancer progression and they have revealed that the alpha6beta4 integrin plays a multifaceted role in regulating tumor development and progression. In the current study, we investigated the mechanism by which one tyrosine residue in the beta4 subunit cytoplasmic domain, Y1494, contributes to the tumor-promoting functions of the alpha6beta4 integrin in vivo. We show that Y1494 participates in the stimulation of diverse signaling pathways that promote alpha6beta4-dependent tumor growth and invasion. Mutation of Y1494 inhibits the ability of the alpha6beta4 integrin to support anchorage-independent growth in vitro and tumor development and angiogenesis in vivo, a result that mimics the loss of total expression of the beta4 subunit. Our results support the hypothesis that Y1494 regulates alpha6beta4-dependent anchorage-independent growth through activation of the extracellular signal-regulated kinase 1/2 signaling pathway, and invasion through the combined activation of phosphatidylinositol 3-kinase and Src. Collectively, our results identify Y1494 as a major regulatory site for signaling from the alpha6beta4 integrin to promote tumor development and progression.

Integrin alpha6beta4 controls the expression of genes associated with cell motility, invasion, and metastasis, including S100A4/metastasin

The integrin alpha6beta4 is associated with carcinoma progression by contributing to apoptosis resistance, invasion, and metastasis, due in part to the activation of select transcription factors. To identify genes regulated by the alpha6beta4 integrin, we compared gene expression profiles of MDA-MB-435 cells that stably express integrin alpha6beta4 (MDA/beta4) and vector-only-transfected cells (MDA/mock) using Affymetrix GeneChip analysis. Our results show that integrin alpha6beta4 altered the expression of 538 genes (p < 0.01). Of these genes, 36 are associated with pathways implicated in cell motility and metastasis, including S100A4/metastasin. S100A4 expression correlated well with integrin alpha6beta4 expression in established cell lines. Suppression of S100A4 by small interference RNA resulted in a reduced capacity of alpha6beta4-expressing cells to invade a reconstituted basement membrane in response to lysophosphatidic acid. Using small interference RNA, promoter analysis, and chromatin immunoprecipitation, we demonstrate that S100A4 is regulated by NFAT5, thus identifying the first target of NFAT5 in cancer. In addition, several genes that are known to be regulated by DNA methylation were up-regulated dramatically by integrin alpha6beta4 expression, including S100A4, FST, PDLIM4, CAPG, and Nkx2.2. Notably, inhibition of DNA methyltransferases stimulated expression of these genes in cells lacking the alpha6beta4 integrin, whereas demethylase inhibitors suppressed expression in alpha6beta4 integrin-expressing cells. Alterations in DNA methylation were confirmed by bisulfate sequencing, thus suggesting that integrin alpha6beta4 signaling can lead to the demethylation of select promoters. In summary, our data suggest that integrin alpha6beta4 confers a motile and invasive phenotype to breast carcinoma cells by regulating proinvasive and prometastatic gene expression.

Integrin alpha(v)beta(3)-Targeted Cancer Therapy

Anti-angiogenesis is a promising strategy for the treatment of cancer. Integrins, consisting of two noncovalently bound transmembrane alpha and beta subunits, are an important molecular family involved in tumor angiogenesis. The blockade of integrin signaling has been demonstrated to be efficient to inhibit tumor growth, angiogenesis, and metastasis. Among all the integrins, alpha(v)beta(3) seems to be the most important one during tumor angiogenesis. The inhibition of integrin alpha(v)beta(3) signaling with antibodies, peptides, peptidomimetics, and other antagonists has great potential in the treatment of cancer. In addition, integrin alpha(v)beta(3) is highly expressed on activated endothelial cells, new-born vessels as well as some tumor cells, but is not present in resting endothelial cells and most normal organ systems, making it a suitable target for anti-angiogenic therapy. In this article we will review the role of integrin alpha(v)beta(3) in angiogenesis, present recent progress in the use of integrin alpha(v)beta(3) antagonists and integrin-targeted delivery systems as potential cancer therapeutics, and discuss future perspectives.

The Role of Integrins in Cancer and the Development of Anti-Integrin Therapeutic Agents for Cancer Therapy

Integrins have been reported to mediate cell survival, proliferation, differentiation, and migration programs. For this reason, the past few years have seen an increased interest in the implications of integrin receptors in cancer biology and tumor cell aggression. This review considers the potential role of integrins in cancer and also addresses why integrins are present attractive targets for drug design. It discusses of the several properties of the integrin-based chemotherapeutic agents currently under consideration clinically and provides an insight into cancer drug development using integrin as a target.

Suppressing phosphatidylcholine-specific phospholipase C and elevating ROS level, NADPH oxidase activity and Rb level induced neuronal differentiation in mesenchymal stem cells

In the previous research, we found that D609 (tricyclodecan-9-yl-xanthogenate) could induce human marrow stromal cell (hMSC) differentiation to neuron-like cells. In this study, to understand the possible mechanism, we sequentially investigated the changes of phosphatidylcholine-specific phospholipase C (PC-PLC) activity, the expression of Rb, the intracellular reactive oxygen species (ROS) levels, NADPH oxidase and superoxide dismutase (SOD) activities when D609 induced neuronal differentiation in rat mesenchymal stem cells (MSCs). The results showed that D609 obviously inhibited the activity of PC-PLC when it induced neuronal differentiation in rat MSCs. Simultaneously, ROS level and the activity of NADPH oxidase increased significantly, but the MnSOD and Cu/ZnSOD activities were not altered. Furthermore, the level of Rb protein was evidently elevated. Our data suggested that PC-PLC mediated neuronal differentiation of rat MSCs by elevating NADPH oxidase activity, ROS level, and up-regulating the expression of Rb protein.

Increased cell survival, migration, invasion, and Akt expression in PTHrP-overexpressing LoVo colon cancer cell lines

Parathyroid hormone-related protein (PTHrP) has been localized in human colon cancer tissue and cell lines. We have previously shown that PTHrP increases colon cancer cell proliferation, extracellular matrix adhesion, and cell-surface integrin alpha6beta4 expression. Since cancer cell migration, invasion, and survival are crucial components of metastasis, and colon cancer has a high metastatic potential, in this study we used the human colon cancer cell line LoVo as a model system to study the effects of PTHrP on these parameters. PTHrP expression was modulated by stable transfection with a construct expressing PTHrP (-36 to +139). We report that PTHrP increases cell migration, invasion, and survival. PTHrP altered cell morphology, with PTHrP-overexpressing cells exhibiting increased spreading and several long protrusions. PTHrP also increased the steady-state mRNA levels of the integrin alpha6 and beta4 subunits, indicating a direct and/or indirect effect of PTHrP on the transcriptional and/or post-transcriptional regulation of integrin alpha6 and beta4 expression. Integrin alpha6beta4 activates the phosphoinositol 3-kinase (PI3-K)/Akt pathway, leading to glycogen synthase kinase-3 (GSK-3) deactivation. PTHrP overexpression also led to an increase in active Akt and inactive GSK-3 levels, indicating that the PTHrP-mediated upregulation of integrin alpha6beta4 expression may activate the PI3-K pathway, resulting in increased cell survival, migration and invasion.

PTH-related protein upregulates integrin alpha6beta4 expression and activates Akt in breast cancer cells

Breast cancer is the most common carcinoma that metastasizes to bone. Tumor-produced parathyroid hormone-related protein (PTHrP), a known stimulator of osteoclastic bone resorption, is a major mediator of the osteolytic process in breast cancer. We have previously shown that PTHrP increases breast cancer cell proliferation, survival, migration, and pro-invasive integrin alpha6beta4 expression. To determine the role of integrin alpha6beta4 in these PTHrP-mediated effects, we utilized two strategies to modulate expression of the alpha6 and beta4 subunits in parental and PTHrP-overexpressing MDA-MB-231 and MCF-7 cells: overexpression of alpha6beta4 by transfection with constructs encoding the alpha6 and beta4 subunits, and suppression of endogenous alpha6beta4 expression by transfection with siRNAs targeting these subunits. We now show that the effects of PTHrP are mediated via upregulation of integrin alpha6beta4 expression. We also show that integrin alpha6beta4 expression is modulated at the mRNA level, indicating a transcriptional and/or post-transcriptional mechanism of action for PTHrP. PTHrP expression also increased the levels of phosphorylated Akt, with a consequent increase in the levels of phosphorylated (inactive) glycogen synthase kinase-3 (GSK-3). The role of PTHrP in breast cancer growth and metastasis may thus be mediated via upregulation of integrin alpha6beta4 expression and Akt activation, with consequent inactivation of GSK-3.

Prospects of RNA interference therapy for cancer

RNA interference (RNAi) is a powerful gene-silencing process that holds great promise in the field of cancer therapy. The discovery of RNAi has generated enthusiasm within the scientific community, not only because it has been used to rapidly identify key molecules involved in many disease processes including cancer, but also because RNAi has the potential to be translated into a technology with major therapeutic applications. Our evolving understanding of the molecular pathways important for carcinogenesis has created opportunities for cancer therapy employing RNAi technology to target the key molecules within these pathways. Many gene products involved in carcinogenesis have already been explored as targets for RNAi intervention, and RNAi targeting of molecules crucial for tumor-host interactions and tumor resistance to chemo- or radiotherapy has also been investigated. In most of these studies, the silencing of critical gene products by RNAi technology has generated significant antiproliferative and/or proapoptotic effects in cell-culture systems or in preclinical animal models. Nevertheless, significant obstacles, such as in vivo delivery, incomplete suppression of target genes, nonspecific immune responses and the so-called off-target effects, need to be overcome before this technology can be successfully translated into the clinical arena. Significant progress has already been made in addressing some of these issues, and it is foreseen that early phase clinical trials will be initiated in the very near future.

Absence of p300 induces cellular phenotypic changes characteristic of epithelial to mesenchyme transition

p300 is a transcriptional cofactor and prototype histone acetyltransferase involved in regulating multiple cellular processes. We generated p300 deficient (p300⁻) cells from the colon carcinoma cell line HCT116 by gene targeting. Comparison of epithelial and mesenchymal proteins in p300⁻ with parental HCT116 cells showed that a number of genes involved in cell and extracellular matrix interactions, typical of ‘epithelial to mesenchyme transition’ were differentially regulated at both the RNA and protein level. p300⁻ cells were found to have aggressive ‘cancer’ phenotypes, with loss of cell–cell adhesion, defects in cell–matrix adhesion and increased migration through collagen and matrigel. Although migration was shown to be metalloproteinase mediated, these cells actually showed a downregulation or no change in the level of key metalloproteinases, indicating that changes in cellular adhesion properties can be critical for cellular mobility.

Safrole oxide induces apoptosis by up-regulating Fas and FasL instead of integrin β4 in A549 human lung cancer cells

Previously, we found that 3,4-(methylenedioxy)-1-(2',3'-epoxypropyl)-benzene (safrole oxide) induced a typical apoptosis in A549 human lung cancer cells by activating caspase-3, -8, and -9. In this study, we further investigated which upstream pathways were activated by safrole oxide during the apoptosis. Immunofluorescence assay combined with laser scanning confocal microscopy revealed that both Fas and Fas ligand (FasL) were up-regulated by the small molecule. In addition, Fas protein distribution was altered, showing a clustering distribution instead of a homogeneous one. Subsequently, Western blot analysis confirmed the up-regulations of Fas and its membrane-binding form of FasL (m-FasL), as well as P53 protein. Conversely, safrole oxide hardly affected integrin beta4 subunit expression or distribution, which was reflected from the data obtained by immunofluorescence assay combined with laser scanning confocal microscopy. The results suggested that Fas/FasL pathway might be involved in safrole oxide-induced apoptosis of A549 cells, while integrin beta4 might be irrelevant to the apoptosis. Nevertheless, we first found the strong expression of integrin beta4 in A549 cells. The study first suggested that safrole oxide might be used as a small molecular promoter of Fas/FasL pathway to elicit apoptosis in A549 cells, which would lay the foundation for us to insight into the new strategies for lung cancer therapy.

A Novel Mechanism for Integrin-Mediated Ras Activation in Breast Carcinoma Cells: The α6β4 Integrin Regulates ErbB2 Translation and Transactivates Epidermal Growth Factor Receptor/ErbB2 Signaling

ErbB2 (HER2, Neu) and Ras play key roles in tumor invasion and metastasis. We identified a novel mechanism by which integrin alpha(6)beta(4) regulates ErbB2 expression, Ras activation, and the invasion of breast carcinoma cells. Here we show that integrin alpha(6)beta(4) regulates Ras activity especially in serum-depleted condition. Down-regulation of beta(4) integrin by beta(4) short hairpin RNA (shRNA) decreased Ras activity and carcinoma invasion whereas reexpression of this integrin restored Ras activity. ErbB2, a binding partner of epidermal growth factor receptor (EGFR), and EGFR modulated Ras activity, and integrin alpha(6)beta(4) regulated phospho-EGFR level without affecting EGFR expression. We also found that integrin alpha(6)beta(4) is involved in ErbB2 expression. Depletion of beta(4) by shRNA reduced ErbB2 protein level without affecting ErbB2 mRNA level and reexpression of beta(4) increased ErbB2 protein level. Reduction of eukaryotic initiation factor 4E, a rate-limiting factor for cap-dependent translation, decreased ErbB2 protein level, and beta(4) shRNA cells exhibited a shift in ErbB2 mRNA to light polysomes compared with control cells. These results show that integrin alpha(6)beta(4) regulates ErbB2 through translational control. In summary, we propose a novel mechanism for ErbB2 up-regulation and Ras activation in serum-depleted breast cancer cells; integrin alpha(6)beta(4) regulates the expression of ErbB2 and the subsequent phosphorylation of EGFR and activation of Ras. These findings provide a mechanism that substantiates the reported role of alpha(6)beta(4) in carcinoma invasion.

Safrole oxide induced human umbilical vein vascular endothelial cell differentiation into neuron-like cells by depressing the reactive oxygen species level at the low concentration

Previously, we found that 5-25 microg/ml safrole oxide could inhibit apoptosis and dramatically make a morphological change in human umbilical vein vascular endothelial cells (HUVECs). But the possible mechanism by which safrole oxide function is unknown. To answer this question, in this study, we first investigated the effects of it on the activity of nitric oxide synthetase (NOS), the expressions of Fas and integrin beta4, which play important roles in HUVEC growth and apoptosis, respectively. The results showed that, at the low concentration (10 microg/ml), safrole oxide had no effects on NOS activity and the expressions of Fas and integrin beta4. Then, we investigated whether HUVECs underwent differentiation. We examined the expressions of neuron-specific enolase (NSE) and neurofilament-L (NF-L). Furthermore, we analyzed the changes of intracellular reactive oxygen species (ROS). After 10 h of treatment with 10 microg/ml safrole oxide, some HUVECs became neuron-like cells in morphology, and intensively displayed positive NSE and NF-L. Simultaneously, ROS levels dramatically decreased during HUVECs differentiation towards neuron-like cells. At the low concentration, safrole oxide induced HUVECs differentiation into neuron-like cells. Furthermore, our data suggested that safrole oxide might perform this function by depressing intracellular ROS levels instead of by affecting cell growth or apoptosis signal pathways.

The alpha6beta4 integrin maintains the survival of human breast carcinoma cells in vivo

The alpha6beta4 integrin has been widely implicated in carcinoma function in vitro; however, in vivo data are scarce. To determine the importance of alpha6beta4 in tumor progression, a SUM-159 breast carcinoma cell line that is essentially devoid of alpha6beta4 expression was generated using an RNA interference strategy. Loss of alpha6beta4 expression inhibits colony formation in soft agar assays, suggesting a vital role for alpha6beta4 in survival signaling and anchorage-independent growth. Orthotopic injection of the beta4-deficient cell line into the mammary fat pad of immunocompromised mice yielded significantly fewer and smaller tumors than the control cell line, revealing a role for the alpha6beta4 integrin in tumor formation. Under conditions that mimicked the in vivo environment, decreased expression of the alpha6beta4 integrin led to enhanced apoptosis as determined by the percentage of Annexin V-FITC+, PI- cells and the presence of caspase-3 cleavage products. Recombinant vascular endothelial growth factor (VEGF) significantly inhibited the cell death observed in the beta4-deficient cell line, demonstrating the importance of VEGF expression in this survival pathway. Furthermore, loss of alpha6beta4 expression leads to enhanced apoptosis and reduced expression of VEGF in breast carcinoma cells in vivo. Importantly, the specificity of alpha6beta4 in both the in vitro and in vivo assays showed that reexpression of the beta4 subunit into the beta4-deficient cell line could rescue the functional phenotype. Taken together, these data implicate the alpha6beta4 integrin in tumor formation by regulating tumor cell survival in a VEGF-dependent manner.

Altered localization of p120 catenin during epithelial to mesenchymal transition of colon carcinoma is prognostic for aggressive disease

We examined the expression and localization of p120 catenin (p120ctn) as a consequence of the epithelial to mesenchymal transition (EMT) of highly differentiated colon carcinoma cells (LIM1863 cells). This unique line grows in suspension as spheroids and undergoes an EMT within 24 hours following stimulation with transforming growth factor-beta and tumor necrosis factor-alpha. Although p120ctn expression remains stable during the EMT, its localization shifts from cell-cell junctions to the cytoplasm. Interestingly, a marked decrease in RhoA activation coincident with E-cadherin loss occurs during the EMT and correlates with the formation of a p120ctn/RhoA complex. Use of RNA interference showed that p120ctn reduction results in increased RhoA activity and a significant decrease in the motility of post-EMT cells. To determine the relevance of these findings to colorectal cancer progression, we assessed p120ctn expression by immunohistochemistry in 557 primary tumors. Of note, we observed that 53% of tumors presented cytoplasmic staining for p120ctn, and statistical analysis revealed that this localization is predictive of poor patient outcome. Cytoplasmic p120ctn correlated with later-stage tumors, significantly reduced 5- and 10-year survival times and a greater propensity for metastasis to lymph nodes compared with junctional p120ctn. We also confirmed that altered localization of p120ctn corresponded with loss or cytoplasmic localization of E-cadherin. These alterations in E-cadherin are also associated with a significant reduction in patient survival time and an increase in tumor stage and lymph node metastasis. These data provide a compelling argument for the importance of both p120ctn and the EMT itself in the progression of colorectal carcinoma.

RNA interference: from gene silencing to gene-specific therapeutics

In the past 4 years, RNA interference (RNAi) has become widely used as an experimental tool to analyse the function of mammalian genes, both in vitro and in vivo. By harnessing an evolutionary conserved endogenous biological pathway, first identified in plants and lower organisms, double-stranded RNA (dsRNA) reagents are used to bind to and promote the degradation of target RNAs, resulting in knockdown of the expression of specific genes. RNAi can be induced in mammalian cells by the introduction of synthetic double-stranded small interfering RNAs (siRNAs) 21–23 base pairs (bp) in length or by plasmid and viral vector systems that express double-stranded short hairpin RNAs (shRNAs) that are subsequently processed to siRNAs by the cellular machinery. RNAi has been widely used in mammalian cells to define the functional roles of individual genes, particularly in disease. In addition, siRNA and shRNA libraries have been developed to allow the systematic analysis of genes required for disease processes such as cancer using high throughput RNAi screens. RNAi has been used for the knockdown of gene expression in experimental animals, with the development of shRNA systems that allow tissue-specific and inducible knockdown of genes promising to provide a quicker and cheaper way to generate transgenic animals than conventional approaches. Finally, because of the ability of RNAi to silence disease-associated genes in tissue culture and animal models, the development of RNAi-based reagents for clinical applications is gathering pace, as technological enhancements that improve siRNA stability and delivery in vivo, while minimising off-target and nonspecific effects, are developed.

Mobilization and activation of a signaling competent α6β4integrin underlies its contribution to carcinoma progression

This review examines the hypothesis that the function of the alpha 6beta 4 integrin is altered substantially as normal epithelia undergo malignant transformation and progress to invasive carcinoma and that the functions of this integrin contribute to the behavior of aggressive carcinoma cells. Specifically, alpha 6beta 4 functions primarily as an adhesion receptor in normal epithelia, often as a component of hemidesmosomes and associated with intermediate filaments. Factors in the host-tumor microenvironment have the potential to mobilize alpha 6beta 4 from hemidesmosomes and promote its association with F-actin in lamellae and filopodia, a process that is mediated by PKC-dependent phosphorylation of the beta 4 cytoplasmic domain. Importantly, this altered localization of alpha 6beta 4 appears to be coupled to an activation of its signaling potential, which may occur through its association with growth factor receptors or lipid rafts, possibilities that are not mutually exclusive. The primal signaling event triggered by alpha 6beta 4 appears to be activation of PI3-K and this activation has profound consequences on the migration, invasion and survival of carcinoma cells. Arguably, the ability of alpha 6beta 4 to stimulate the PI3-K-dependent translation of VEGF and possibly other growth factors may be the most significant contribution of this integrin to carcinoma because of the potential autocrine and paracrine effects of these factors.

Modulation of angiogenesis with siRNA inhibitors for novel therapeutics

Cancer and many other serious diseases are characterized by the uncontrolled growth of new blood vessels. Recently, RNA interference (RNAi) has reinvigorated the therapeutic prospects for inhibiting gene expression and promises many advantages over binding inhibitors, including high specificity, which is essential for targeted therapeutics. This article describes the latest developments using small-interfering RNA (siRNA) inhibitors to downregulate various angiogenic and tumor-associated factors, both in cell-culture assays and in animal disease models. The majority of research efforts are currently focused on understanding gene function, as well as proof-of-concept for siRNA-mediated anti-angiogenesis. The prospects for siRNA therapeutics, both advantages and looming hurdles, are evaluated.

The role of small RNAs in human diseases: potential troublemaker and therapeutic tools

Small RNAs, including short interfering RNAs (siRNAs) and microRNAs (miRNAs), are ubiquitous, versatile repressors of gene expression in plants, animals, and many fungi. They can trigger destruction of homologous mRNA or inhibition of cognate mRNA translation and play an important role in maintaining the stable state of chromosome structure and regulating the expression of protein-coding genes. Furthermore, the recent research showed that there exists close relationship between small RNAs and human diseases. Several human diseases have surfaced in which miRNAs or their machinery might be implicated, such as some neurological diseases and cancers. The specificity and potency of small RNAs suggest that they might be promising as therapeutic agents. This article will review the role of small RNAs in some human diseases etiology and investigations of taking siRNAs as therapeutic tools for treating viral infection, cancer, and other diseases. We also discuss the potential of miRNAs in gene therapy.

Discovery of a novel small molecule, 1-ethoxy-3-(3,4-methylenedioxyphenyl)-2-propanol, that induces apoptosis in A549 human lung cancer cells

A novel small molecule, 1-ethoxy-3-(3,4-methylenedioxyphenyl)-2-propanol (EOD), was synthesized in our laboratory. Previously, we reported pharmacological properties of EOD, triggering apoptosis in Human umbilical vein endothelial cells (HUVECs). Here, we further investigated the effects of EOD on the growth of A549 human lung cancer cells. EOD treatment induced apoptosis in A549 cells via up-regulating the expression of P53 protein, blocking cell cycle partly at G1 phase, and ultimately activating caspase-3. In contrast, caspase-8 might be irrelevant to EOD-triggered apoptosis. This study indicated that EOD might be a potential chemopreventive agent for lung cancer. The work would encourage us to add more novel compounds to our 'library' of small molecules derived through modern synthetic organic chemistry, and would drive us to determine the proteins that the compounds target.

Integrin α6β4 promotes expression of autotaxin/ENPP2 autocrine motility factor in breast carcinoma cells

In advanced breast carcinomas, the alpha6beta4 integrin is associated with a migratory and invasive phenotype. In our current study, we show that expression of the alpha6beta4 integrin in MDA-MB-435 breast carcinoma cells leads to increased expression of the autocrine motility factor autotaxin, as determined by Affymetrix gene chip, real-time quantitative RT-PCR and immunoblot analyses. We further demonstrate that increased autotaxin secretion from integrin alpha6beta4 expressing cells acts to enhance chemotaxis through its ability to convert lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA) and accounts for 80% of the motogenic activity of the conditioned medium. We determine that integrin alpha6beta4-dependent overexpression of autotaxin in MDA-MB-435 cells is mediated by NFAT1, but not NFAT5, through the use of siRNAs that specifically target autotaxin, integrin beta4, NFAT1 and NFAT5. Finally, we show by electrophoretic mobility shift assays that two consensus NFAT binding sites found in the autotaxin promoter strongly and specifically bind NFAT1 from integrin alpha6beta4 expressing cells. In summary, we find that the alpha6beta4 integrin potentiates autotaxin expression through the upregulation and activation of NFAT1. These observations highlight for the first time a mechanism by which NFAT transcription factors can facilitate an invasive and motile phenotype downstream of integrin alpha6beta4 signaling.

Overexpression of beta1-chain-containing laminins in capillary basement membranes of human breast cancer and its metastases

INTRODUCTION

Laminins are the major components of vascular and parenchymal basement membranes. We previously documented a switch in the expression of vascular laminins containing the alpha4 chain from predominantly laminin-9 (alpha4beta2gamma1) to predominantly laminin-8 (alpha4beta1gamma1) during progression of human brain gliomas to high-grade glioblastoma multiforme. Here, differential expression of laminins was studied in blood vessels and ductal epithelium of the breast.

METHOD

In the present study the expressions of laminin isoforms alpha1-alpha5, beta1-beta3, gamma1, and gamma2 were examined during progression of breast cancer. Forty-five clinical samples of breast tissues including normal breast, ductal carcinomas in situ, invasive ductal carcinomas, and their metastases to the brain were compared using Western blot analysis and immunohistochemistry for various chains of laminin, in particular laminin-8 and laminin-9.

RESULTS

Laminin alpha4 chain was observed in vascular basement membranes of most studied tissues, with the highest expression in metastases. At the same time, the expression of laminin beta2 chain (a constituent of laminin-9) was mostly seen in normal breast and carcinomas in situ but not in invasive carcinomas or metastases. In contrast, laminin beta1 chain (a constituent of laminin-8) was typically found in vessel walls of carcinomas and their metastases but not in those of normal breast. The expression of laminin-8 increased in a progression-dependent manner. A similar change was observed from laminin-11 (alpha5beta2gamma1) to laminin-10 (alpha5beta1gamma1) during breast tumor progression. Additionally, laminin-2 (alpha2beta1gamma1) appeared in vascular basement membranes of invasive carcinomas and metastases. Chains of laminin-5 (alpha3beta3gamma2) were expressed in the ductal epithelium basement membranes of the breast and diminished with tumor progression.

CONCLUSION

These results suggest that laminin-2, laminin-8, and laminin-10 are important components of tumor microvessels and may associate with breast tumor progression. Angiogenic switch from laminin-9 and laminin-11 to laminin-8 and laminin-10 first occurs in carcinomas in situ and becomes more pronounced with progression of carcinomas to the invasive stage. Similar to high-grade brain gliomas, the expression of laminin-8 (and laminin-10) in breast cancer tissue may be a predictive factor for tumor neovascularization and invasion.

Hypoxia stimulates carcinoma invasion by stabilizing microtubules and promoting the Rab11 trafficking of the alpha6beta4 integrin

Hypoxia plays a key role in tumor cell survival, invasion, and metastasis. Here we show that hypoxia increases tumor cell invasion by the modulation of Rab11, an important molecule for vesicular trafficking, especially membrane protein recycling and translocation of proteins from trans-Golgi network to plasma membrane. Dominant-negative Rab11 dramatically decreased hypoxia-induced invasion of MDA-MB-231 breast carcinoma cells without affecting cell apoptosis. Hypoxia-induced Rab11 trafficking is regulated by microtubule stability, as evidenced by the findings that hypoxia increases Glu tubulin and that colchicine blocks Rab11 trafficking and invasion. Inhibition of GSK-3beta activity by hypoxia seems to be central to microtubule stabilization and invasion. In fact, expression of a dominant-negative GSK-3beta was sufficient to stimulate invasion in normoxia. One target of Rab11-mediated trafficking that contributes to invasion is the integrin alpha6beta4. Hypoxia induced a significant increase in alpha6beta4 surface expression but it had no effect on the surface expression of alpha3beta1. This increase is dependent on Rab11 and stable microtubules. In summary, we identify vesicle trafficking as a novel target of hypoxic stimulation that is important for tumor invasion.

Role of ICAM1 in invasion of human breast cancer cells

We identified previously a region on chromosome 19p13.2 spanning the genes encoding the intercellular adhesion molecules (ICAM), ICAM1, ICAM4 and ICAM5 as a breast cancer susceptibility locus. Genetic variants in this region were also associated with indicators of disease severity, including higher rates of metastases to other organs. Based on this association, we set out to explore the role of ICAM1 in proliferation and invasion of human breast cancer cells. We observed that ICAM1 downregulation at the mRNA and protein levels led to a strong suppression of human breast cell invasion through a matrigel matrix. Under the same conditions, no significant effect on cell proliferation in vitro was seen. Incubation of cells with an antibody against ICAM1 blocked invasion of the highly metastatic MDA-MB-435 cell line in a dose-dependent manner without affecting cell migration. We also demonstrated that the level of ICAM1 protein expression on the cell surface positively correlated with metastatic potential of five human breast cancer cell lines and that ICAM1 mRNA levels were elevated in breast tumor compared with adjacent normal tissue. These results corroborate our previous genetic finding that variations in the ICAM region are associated with the occurrence of metastases and establish a causal role of ICAM1 in invasion of metastatic human breast carcinoma cell lines.

Antiangiogenic gene therapy of cancer: recent developments

With the role of angiogenesis in tumor growth and progression firmly established, considerable effort has been directed to antiangiogenic therapy as a new modality to treat human cancers. Antiangiogenic agents have recently received much widespread attention but strategies for their optimal use are still being developed. Gene therapy represents an attractive alternative to recombinant protein administration for several reasons. This review evaluates the potential advantages of gene transfer for antiangiogenic cancer therapy and describes preclinical gene transfer work with endogenous angiogenesis inhibitors demonstrating the feasibility of effectively suppressing and even eradicating tumors in animal models. Additionally, we describe the advantages and disadvantages of currently available gene transfer vectors and update novel developments in this field. In conclusion, gene therapy holds great promise in advancing antiangiogenesis as an effective cancer therapy and will undoubtedly be evaluated in human clinical trials in the near future.

The Met receptor and alpha 6 beta 4 integrin can function independently to promote carcinoma invasion

It has been proposed that a constitutive, physical association of the Met receptor and the alpha(6)beta(4) integrin exists on the surface of invasive carcinoma cells and that hepatocyte growth factor (HGF)-mediated invasion is dependent on alpha(6)beta(4) (Trusolino, L., Bertotti, A., and Comoglio, P. M. (2001) Cell 107, 643-654). The potential significance of these results prompted us to re-examine this hypothesis. Using three different carcinoma cell lines that express both Met and alpha(6)beta(4), we were unable to detect the constitutive association of these receptors by co-immunoprecipitation. Moreover, carcinoma cells that lacked expression of alpha(6)beta(4) exhibited Met-dependent invasion toward HGF, and increasing Met expression by viral infection of these cells enhanced invasion without inducing alpha(6)beta(4) expression. Although expression of alpha(6)beta(4) in such cells enhanced their invasion to HGF, it also enhanced their ability to invade toward other chemoattractants such as lysophosphatidic acid, and this latter invasion was not inhibited by a function-blocking Met antibody. Finally, depletion of beta(4) by RNA interference in invasive carcinoma cells that express both receptors reduced the ability of these cells to invade toward HGF by approximately 25%, but it did not abrogate their invasion. These data argue that the invasive function of Met can be independent of alpha(6)beta(4) and that alpha(6)beta(4) has a generic influence on the invasion of carcinoma cells that is not specific to Met.