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

Morphological evidence for the potential protective effects of curcumin and Garcinia kola against diabetes in the rat hippocampus

This research investigated the effects of sciatic nerve transection and diabetes on the hippocampus, and the protective effects of Garcinia kola and curcumin. Thirty-five adults male Wistar albino rats were divided into five groups: a control group (Cont), a transected group (Sham group), a transected + diabetes mellitus group (DM), a transected + diabetes mellitus + Garcinia kola group (DM + GK), and a transected + DM + curcumin group (DM + Cur), each containing seven animals. The experimental diabetes model was created with the intraperitoneal injection of a single dose of streptozotocin. No procedure was applied to the Cont group, while sciatic nerve transection was performed on the other groups. Garcinia kola was administered to the rats in DM + GK, and curcumin to those in DM + Cur. Cardiac perfusion was performed at the end of the experimental period. Brain tissues were dissected for stereological, histopathological, and immunohistochemical evaluations. The volume ratios of hippocampal layers to the entire hippocampus volume were compared between the groups. Anti-S100, anti-caspase 3, and anti-SOX 2 antibodies were used for immunohistochemical analysis. No statistically significant difference was observed in the volume ratios of the four hippocampal layers. However, the volume ratio of the stratum lucidum was higher in the Sham, DM, and DM + Cur groups compared to the Cont group. While curcumin exhibited a protective effect on hippocampal tissue following diabetes induction, Garcinia kola had only a weak protective effect. Increased cell density and nuclear deterioration due to diabetes and nerve transection can be partially ameliorated by treatment with Garcinia kola and curcumin.

New insights into the correlations between circulating tumor cells and target organ metastasis

Organ-specific metastasis is the primary cause of cancer patient death. The distant metastasis of tumor cells to specific organs depends on both the intrinsic characteristics of the tumor cells and extrinsic factors in their microenvironment. During an intermediate stage of metastasis, circulating tumor cells (CTCs) are released into the bloodstream from primary and metastatic tumors. CTCs harboring aggressive or metastatic features can extravasate to remote sites for continuous colonizing growth, leading to further lesions. In the past decade, numerous studies demonstrated that CTCs exhibited huge clinical value including predicting distant metastasis, assessing prognosis and monitoring treatment response et al. Furthermore, increasingly numerous experiments are dedicated to identifying the key molecules on or inside CTCs and exploring how they mediate CTC-related organ-specific metastasis. Based on the above molecules, more and more inhibitors are being developed to target CTCs and being utilized to completely clean CTCs, which should provide promising prospects to administer advanced tumor. Recently, the application of various nanomaterials and microfluidic technologies in CTCs enrichment technology has assisted to improve our deep insights into the phenotypic characteristics and biological functions of CTCs as a potential therapy target, which may pave the way for us to make practical clinical strategies. In the present review, we mainly focus on the role of CTCs being involved in targeted organ metastasis, especially the latest molecular mechanism research and clinical intervention strategies related to CTCs.

Current Advances in 3D Dynamic Cell Culture Systems

The traditional two-dimensional (2D) cell culture methods have a long history of mimicking in vivo cell growth. However, these methods cannot fully represent physiological conditions, which lack two major indexes of the in vivo environment; one is a three-dimensional 3D cell environment, and the other is mechanical stimulation; therefore, they are incapable of replicating the essential cellular communications between cell to cell, cell to the extracellular matrix, and cellular responses to dynamic mechanical stimulation in a physiological condition of body movement and blood flow. To solve these problems and challenges, 3D cell carriers have been gradually developed to provide a 3D matrix-like structure for cell attachment, proliferation, differentiation, and communication in static and dynamic culture conditions. 3D cell carriers in dynamic culture systems could primarily provide different mechanical stimulations which further mimic the real in vivo microenvironment. In this review, the current advances in 3D dynamic cell culture approaches have been introduced, with their advantages and disadvantages being discussed in comparison to traditional 2D cell culture in static conditions.

S100 Calcium Binding Protein Family Members Associate With Poor Patient Outcome and Response to Proteasome Inhibition in Multiple Myeloma

Despite several new therapeutic options, multiple myeloma (MM) patients experience multiple relapses and inevitably become refractory to treatment. Insights into drug resistance mechanisms may lead to the development of novel treatment strategies. The S100 family is comprised of 21 calcium binding protein members with 17 S100 genes located in the 1q21 region, which is commonly amplified in MM. Dysregulated expression of S100 family members is associated with tumor initiation, progression and inflammation. However, the relationship between the S100 family and MM pathogenesis and drug response is unknown. In this study, the roles of S100 members were systematically studied at the copy number, transcriptional and protein level with patients’ survival and drug response. Copy number analysis revealed a predominant pattern of gains occurring in S100 genes clustering in the 1q21 locus. In general, gains of genes encoding S100 family members associated with worse patient survival. However, S100 gene copy number and S100 gene expression did not necessarily correlate, and high expression of S100A4 associated with poor patient survival. Furthermore, integrated analysis of S100 gene expression and ex vivo drug sensitivity data showed significant negative correlation between expression of S100 family members (S100A8, S100A9, and S100A12) and sensitivity to some drugs used in current MM treatment, including proteasome inhibitors (bortezomib, carfilzomib, and ixazomib) and histone deacetylase inhibitor panobinostat. Combined proteomic and pharmacological data exhibited significant negative association of S100 members (S100A4, S100A8, and S100A9) with proteasome inhibitors and panobinostat. Clinically, the higher expression of S100A4 and S100A10 were significantly linked to shorter progression free survival in patients receiving carfilzomib-based therapy. The results indicate an association and highlight the potential functional importance of S100 members on chromosome 1q21 in the development of MM and resistance to established myeloma drugs, including proteasome inhibitors.

Specific and Aspecific Molecular Checkpoints as Potential Targets for Dismantling Tumor Hierarchy and Preventing Relapse and Metastasis Through Shielded Cytolytic Treatments

I have recently theorized that several similarities exist between the tumor process and embryo development. Starting from an initial cancer stem cell (CSC0), similar to an embryonic stem cell (ESC), after implantation in a niche, primary self-renewing CSCs (CSC1s) would arise, which then generate secondary proliferating CSCs (CSC2s). From these epithelial CSCs, tertiary mesenchymal CSCs (CSC3s) would arise, which, under favorable stereotrophic conditions, by asymmetric proliferation, would generate cancer progenitor cells (CPCs) and then cancer differentiated cells (CDCs), thus giving a defined cell heterogeneity and hierarchy. CSC1s-CSC2s-CSC3s-CPCs-CDCs would constitute a defined "tumor growth module," able to generate new tumor modules, forming a spherical avascular mass, similar to a tumor sphere. Further growth in situ of this initial tumor would require implantation in the host and vascularization through the overexpression of some aspecific checkpoint molecules, such as CD44, ID, LIF, HSP70, and HLA-G. To expand and spread in the host tissues, this vascularized tumor would then carry on a real growth strategy based on other specific checkpoint factors, such as those contained in the extracellular vesicles (EVs), namely, microRNAs, messenger RNAs, long non-coding RNAs, and integrins. These EV components would be crucial in tumor progression because they can mediate intercellular communications in the surrounding microenvironment and systemically, dictating to recipient cells a new tumor-enslaved phenotype, thus determining pre-metastatic conditions. Moreover, by their induction properties, the EV contents could also frustrate in time the effects of cytolytic tumor therapies, where EVs released by killed CSCs might enter other cancer and non-cancer cells, thus giving chemoresistance, non-CSC/CSC transition (recurrence), and metastasis. Thus, antitumor cytotoxic treatments, "shielded" from the EV-specific checkpoints by suitable adjuvant agents, simultaneously targeting the aforesaid aspecific checkpoints should be necessary for dismantling the hierarchic tumor structure, avoiding recurrence and preventing metastasis.

Hepatocellular carcinoma-derived exosomes in organotropic metastasis, recurrence and early diagnosis application

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer, despite improvements in the clinical trial and diagnosis, HCC still remains high mortality due to the 70% recurrence and lung metastasis after surgical resection. Exosomes are small membrane vesicles, which are shuttled from donor cells to recipient cells, contributing to the recruitment and reprogramming of constituents via an autocrine or paracrine fashion. HCC derived exosomes could redirect metastasis of tumor cells which lack the capacity to metastasize to a specific organ via generating pre-metastatic niche. These findings emphasize a practical and potentially feasible role of exosomes in the treatment of patients with HCC, both as a target and a vehicle for drug design. We herein summarize recent findings that implicate oncogenes and non-canonical signaling of HCC exosomes, as well as the impact of exosomal bioactive molecules in high recurrence induced by organ-specific metastasis. The aim of review is to illustrate the underlying mechanism of exosomes in tumor metastasis, immune evasion, and the potential application of prognostic biomarker in HCC process.

Molecular networks of FOXP family: dual biologic functions, interplay with other molecules and clinical implications in cancer progression

Though Forkhead box P (FOXP) transcription factors comprising of FOXP1, FOXP2, FOXP3 and FOXP4 are involved in the embryonic development, immune disorders and cancer progression, the underlying function of FOXP3 targeting CD4 + CD25+ regulatory T (Treg) cells and the dual roles of FOXP proteins as an oncogene or a tumor suppressor are unclear and controversial in cancers to date. Thus, the present review highlighted research history, dual roles of FOXP proteins as a tumor suppressor or an oncogene, their molecular networks with other proteins and noncoding RNAs, cellular immunotherapy targeting FOXP3, and clinical implications in cancer progression.

LIN28B increases neural crest cell migration and leads to transformation of trunk sympathoadrenal precursors

The RNA-binding protein LIN28B regulates developmental timing and determines stem cell identity by suppressing the let-7 family of microRNAs. Postembryonic reactivation of LIN28B impairs cell commitment to differentiation, prompting their transformation. In this study, we assessed the extent to which ectopic lin28b expression modulates the physiological behavior of neural crest cells (NCC) and governs their transformation in the trunk region of developing embryos. We provide evidence that the overexpression of lin28b inhibits sympathoadrenal cell differentiation and accelerates NCC migration in two vertebrate models, Xenopus leavis and Danio rerio. Our results highlight the relevance of ITGA5 and ITGA6 in the LIN28B-dependent regulation of the invasive motility of tumor cells. The results also establish that LIN28B overexpression supports neuroblastoma onset and the metastatic potential of malignant cells through let-7a-dependent and let-7a-independent mechanisms.

Long-term Tumor Adaptation after Radiotherapy: Therapeutic Implications for Targeting Integrins in Prostate Cancer

Adaptation of tumor cells to radiotherapy induces changes that are actionable by molecular targeted agents and immunotherapy. This report demonstrates that radiation-induced changes in integrin expression can be targeted 2 months later. Integrins are transmembrane cell adhesion molecules that are essential for cancer cell survival and proliferation. To analyze the short- and long-term effects of radiation on the integrin expression, prostate cancer cells (DU145, PC3, and LNCaP) were cultured in a 3D extracellular matrix and irradiated with either a single dose of radiation (2-10 Gy) or a multifractionated regimen (2-10 fractions of 1 Gy). Whole human genome microarrays, immunoblotting, immunoprecipitation assays, and immunofluorescence staining of integrins were performed. The results were confirmed in a prostate cancer xenograft model system. Interestingly, β1 and β4 integrins (ITGB1 and ITGB4) were upregulated after radiation in vitro and in vivo. This overexpression lasted for more than 2 months and was dose dependent. Moreover, radiation-induced upregulation of β1 and β4 integrin resulted in significantly increased tumor cell death after treatment with inhibitory antibodies. Combined, these findings indicate that long-term tumor adaptation to radiation can result in an increased susceptibility of surviving cancer cells to molecular targeted therapy due to a radiation-induced overexpression of the target. IMPLICATIONS: Radiation induces dose- and schedule-dependent adaptive changes that are targetable for an extended time; thus suggesting radiotherapy as a unique strategy to orchestrate molecular processes, thereby providing new radiation-drug treatment options within precision cancer medicine.

Plectin protects podocytes from adriamycin-induced apoptosis and F-actin cytoskeletal disruption through the integrin α6β4/FAK/p38 MAPK pathway

Podocyte injury is an early pathological change characteristic of various glomerular diseases, and apoptosis and F‐actin cytoskeletal disruption are typical features of podocyte injury. In this study, we found that adriamycin (ADR) treatment resulted in typical podocyte injury and repressed plectin expression. Restoring plectin expression protected against ADR‐induced podocyte injury whereas siRNA‐mediated plectin silencing produced similar effects as ADR‐induced podocyte injury, suggesting that plectin plays a key role in preventing podocyte injury. Further analysis showed that plectin repression induced significant integrin α6β4, focal adhesion kinase (FAK) and p38 MAPK phosphorylation. Mutating Y1494, a key tyrosine residue in the integrin β4 subunit, blocked FAK and p38 phosphorylation, thereby alleviating podocyte injury. Inhibitor studies demonstrated that FAK Y397 phosphorylation promoted p38 activation, resulting in podocyte apoptosis and F‐actin cytoskeletal disruption. In vivo studies showed that administration of ADR to rats resulted in significantly increased 24‐hour urine protein levels along with decreased plectin expression and activated integrin α6β4, FAK, and p38. Taken together, these findings indicated that plectin protects podocytes from ADR‐induced apoptosis and F‐actin cytoskeletal disruption by inhibiting integrin α6β4/FAK/p38 pathway activation and that plectin may be a therapeutic target for podocyte injury‐related glomerular diseases.

Mechanisms and context underlying the role of autophagy in cancer metastasis

Macroautophagy/autophagy is a fundamental cellular degradation mechanism that maintains cell homeostasis, regulates cell signaling, and promotes cell survival. Its role in promoting tumor cell survival in stress conditions is well characterized, and makes autophagy an attractive target for cancer therapy. Emerging research indicates that autophagy also influences cancer metastasis, which is the primary cause of cancer-associated mortality. However, data demonstrate that the regulatory role of autophagy in metastasis is multifaceted, and includes both metastasis-suppressing and -promoting functions. The metastasis-suppressing functions of autophagy, in particular, have important implications for autophagy-based treatments, as inhibition of autophagy may increase the risk of metastasis. In this review, we discuss the mechanisms and context underlying the role of autophagy in metastasis, which include autophagy-mediated regulation of focal adhesion dynamics, integrin signaling and trafficking, Rho GTPase-mediated cytoskeleton remodeling, anoikis resistance, extracellular matrix remodeling, epithelial-to-mesenchymal transition signaling, and tumor-stromal cell interactions. Through this, we aim to clarify the context-dependent nature of autophagy-mediated metastasis and provide direction for further research investigating the role of autophagy in cancer metastasis.

FOXP1 enhances tumor cell migration by repression of NFAT1 transcriptional activity in MDA-MB-231 cells

Until now, forkhead box P1 (FOXP1) has been identified as a tumor suppressor in several correlation studies in breast cancer. Although FOXP1 is defined as a transcriptional repressor that interacts with other transcription factors in various mechanistic studies, there is no study that explains its repressor functions in breast cancer biology. This study demonstrated the repressor function of FOXP1 on nuclear factor of activated T cells (NFAT1) and the migratory effect of this repression in MDA-MB-231 breast cancer cells. Co-immunoprecipitation experiments were performed for the investigation of protein-protein interaction between two transcription factors. Protein-protein interaction on DNA was investigated with EMSA and transcriptional effects of FOXP1 on NFAT1, luciferase reporter assay was performed. Wound healing assay was used to analyze the effects of overexpression of FOXP1 on tumor cell migration. This study showed that FOXP1 has protein-protein interaction with NFAT1 on DNA and enhances breast cancer cell migration by repressing NFAT1 transcriptional activity and FOXP1 shows oncogenic function by regulating breast cancer cell motility.

S100A4 in Cancer Metastasis: Wnt Signaling-Driven Interventions for Metastasis Restriction

The aberrant activity of Wnt signaling is an early step in the transformation of normal intestinal cells to malignant tissue, leading to more aggressive tumors, and eventually metastases. In colorectal cancer (CRC), metastasis accounts for about 90% of patient deaths, representing the most lethal event during the course of the disease and is directly linked to patient survival, critically limiting successful therapy. This review focuses on our studies of the metastasis-inducing gene S100A4, which we identified as transcriptional target of β-catenin. S100A4 increased migration and invasion in vitro and metastasis in mice. In patient CRC samples, high S100A4 levels predict metastasis and reduced patient survival. Our results link pathways important for tumor progression and metastasis: the Wnt signaling pathway and S100A4, which regulates motility and invasiveness. S100A4 suppression by interdicting Wnt signaling has potential for therapeutic intervention. As proof of principle, we applied S100A4 shRNA systemically and prevented metastasis in mice. Furthermore, we identified small molecule inhibitors from high-throughput screens of pharmacologically active compounds employing an S100A4 promoter-driven reporter. Best hits act, as least in part, via intervening in the Wnt pathway and restricted metastasis in mouse models. We currently translate our findings on restricting S100A4-driven metastasis into clinical practice. The repositioned FDA-approved drug niclosamide, targeting Wnt signaling, is being tested in a prospective phase II clinical trial for treatment of CRC patients. Our assay for circulating S100A4 transcripts in patient blood is used to monitor treatment success.

Organotropic metastasis: role of tumor exosomes

A recent paper in Nature shows that tumor exosomes expressing unique integrins can determine organotropic metastasis by preparing pre-metastatic niche through their integrins-mediated fusion with and fertilization of organ-specific resident cells.

Tumour exosome integrins determine organotropic metastasis

Ever since Stephen Paget's 1889 hypothesis, metastatic organotropism has remained one of cancer's greatest mysteries. Here we demonstrate that exosomes from mouse and human lung-, liver- and brain-tropic tumour cells fuse preferentially with resident cells at their predicted destination, namely lung fibroblasts and epithelial cells, liver Kupffer cells and brain endothelial cells. We show that tumour-derived exosomes uptaken by organ-specific cells prepare the pre-metastatic niche. Treatment with exosomes from lung-tropic models redirected the metastasis of bone-tropic tumour cells. Exosome proteomics revealed distinct integrin expression patterns, in which the exosomal integrins α6β4 and α6β1 were associated with lung metastasis, while exosomal integrin αvβ5 was linked to liver metastasis. Targeting the integrins α6β4 and αvβ5 decreased exosome uptake, as well as lung and liver metastasis, respectively. We demonstrate that exosome integrin uptake by resident cells activates Src phosphorylation and pro-inflammatory S100 gene expression. Finally, our clinical data indicate that exosomal integrins could be used to predict organ-specific metastasis.

Tumour exosome integrins determine organotropic metastasis

Ever since Stephen Paget’s 1889 hypothesis, metastatic organotropism has remained one of cancer’s greatest mysteries. Here we demonstrate that exosomes from mouse and human lung-, liver- and brain-tropic tumour cells fuse preferentially with resident cells at their predicted destination, namely lung fibroblasts and epithelial cells, liver Kupffer cells and brain endothelial cells. We show that tumour-derived exosomes uptaken by organ-specific cells prepare the pre-metastatic niche. Treatment with exosomes from lung-tropic models redirected the metastasis of bone-tropic tumour cells. Exosome proteomics revealed distinct integrin expression patterns, in which the exosomal integrins α₆β₄ and α₆β₁ were associated with lung metastasis, while exosomal integrin α_vβ₅ was linked to liver metastasis. Targeting the integrins α₆β₄ and α_vβ₅ decreased exosome uptake, as well as lung and liver metastasis, respectively. We demonstrate that exosome integrin uptake by resident cells activates Src phosphorylation and pro-inflammatory S100 gene expression. Finally, our clinical data indicate that exosomal integrins could be used to predict organ-specific metastasis.

Manganese superoxide dismutase promotes interaction of actin, S100A4 and Talin, and enhances rat gastric tumor cell invasion

It has been demonstrated that cancer cells are under high levels of oxidative stress and express high levels of Manganese superoxide dismutase (MnSOD) to protect themselves and support the anabolic metabolism needed for growth and cell motility. The aim of this study was to identify proteins that may have a correlation with invasion and redox regulation by mitochondrial reactive oxygen species (ROS). MnSOD scavenges superoxide anions generated from mitochondria and is an important regulator of cellular redox status. Oxidative posttranslational modification of cysteine residues is a key mechanism that regulates protein structure and function. We hypothesized that MnSOD regulates intracellular reduced thiol status and promotes cancer invasion. A proteomic thiol-labeling approach with 5-iodoacetamidofluorescein was used to identify changes in intracellular reduced thiol-containing proteins. Our results demonstrate that overexpression of MnSOD maintained the major structural protein, actin, in a reduced state, and enhanced the invasion ability in gastric mucosal cancer cells, RGK1. We also found that the expression of Talin and S100A4 were increased in MnSOD-overexpressed RGK1 cells. Moreover, Talin bound not only with actin but also with S100A4, suggesting that the interaction of these proteins may, in part, contribute to the invasive ability of rat gastric cancer.

Modulation of the cancer cell transcriptome by culture media formulations and cell density

We investigated how varying the composition of cell culture formulations and growing cancer cells at different densities might affect tumor cell genotype. Specifically, we compared gene expression profiles generated by human MDA‑MB‑231 breast cancer cells cultured in different media [minimum essential medium (MEM), Dulbecco's modified Eagle's medium (DMEM), or Roswell Park Memorial Institute (RPMI)‑1640 medium] containing different concentrations of fetal bovine serum (FBS) or different sera (equine or bovine) that were grown at different cell densities. More than 2,000 genes were differentially modulated by at least a 2‑fold difference when MDA‑MB‑231 cancer cells were 90% confluent and compared with cultures that were 50% confluent. Altering the concentration of serum produced an even more pronounced effect on MDA‑MB‑231 cancer cell gene expression in that 2,981 genes were differentially expressed in a comparison between cells cultured in 0.1% FBS and same cell density cultures that were maintained in 10% FBS. A comparison between MDA‑MB‑231 cancer cells that were 90% confluent in MEM, DMEM, or RPMI‑1640 media, all containing 10% FBS, resulted in 8,925 differentially expressed genes. Moreover, one‑quarter (25.6%) of genes from our genome‑wide expression analysis were expressed at significantly different levels by cells grown in MEM, DMEM, or RPMI‑1640 media. Genes associated with epithelial‑mes-enchymal transition (EMT) were among the genes that were differentially modulated by cells grown in different cell culture formulations and these genes were verified at the protein level. Collectively, these results underscore the importance of accurate reporting and maintenance of uniform culture conditions to ensure reproducible results.

Integrin α6β4 and TRPV1 channel coordinately regulate directional keratinocyte migration

The directional migration of epithelial cells is crucial for wound healing. Among integrins, a family of cell adhesion receptors, integrin β4 has been assumed to be a promigratory factor, in addition to its role in stable adhesion. In turn, Ca(2+) signaling is also a key coordinator of migration. Keratinocytes reportedly express transient receptor potential vanilloid channels (TRPV1); however, the function of these channels as a regulator of intracellular Ca(2+) level in cell migration has remained uncharacterized. In the present study, we investigated the role of TRPV1 in directional migration related to integrin β4 using a scratch wound assay on a confluent monolayer sheet of murine keratinocytes (Pam212 cells). Double immunofluorescence staining revealed the de novo expression of integrin β4 and TRPV1 in migrating cells at the wound edge in response to scratch wounding, and both expression levels were almost matched. Epidermal growth factor (EGF) not only promoted keratinocyte migration, but also caused the further up-regulation of both integrin β4 and TRPV1. In addition, the knockdown of the integrin β4 or TRPV1 gene significantly impeded wound closure. The TRPV1 agonist capsaicin significantly promoted migration, while a selective TRPV1 antagonist inhibited it. The gene knockdown of TRPV1 inhibited the expression of the integrin β4 gene and that of β4 protein in migrating cells. These findings suggest that TRPV1 may stimulate directional migration directly by eliciting a Ca(2+) signal or indirectly via integrin β4 expression.

S100A4 negatively regulates β-catenin by inducing the Egr-1-PTEN-Akt-GSK3β degradation pathway

S100A4, also known as the mts1 gene, has been reported as an invasive and metastatic marker for many types of cancers. S100A4 interacts with various target genes that affect tumor cell metastasis; however, little is known about cellular signaling pathways elicited by S100A4. In the current study, we demonstrate an inhibitory effect of S100A4 on β-catenin signaling in breast cancer cells. By overexpressing S100A4 in MCF-7, MDA-MB-231 and MDA-MB-453 breast cancer cells, we observed the down-regulation of β-catenin expression and β-catenin-dependent TCF/LEF transcriptional activities. The activity of GSK3β, which phosphorylates β-catenin and induces proteasomal degradation of β-catenin, was increased in S100A4-overexpressing cell lines. Blocking Glycogen Synthase Kinase (GSK3β) activity by lithium chloride or Dvl gene overexpression restored β-catenin expression. We also found that increased GSK3β activity was due to decrease in Akt activity resulting from Egr-1-induced phosphatase and tensin homolog (PTEN) expression. S100A4 induced Egr-1 nuclear localization by increasing the association between Egr-1 and importin-7 and this effect was reduced in S100A4 mutants that harbored a defect in nuclear localization signals. Collectively, we verify herein that S100A4 may act as a tumor suppressor in breast cancers by down-regulating the central signaling axis for tumor cell survival.

The role of c-Src in integrin (α6β4) dependent translational control

Background

Integrin α6β4 contributes to cancer progression by stimulating transcription as well as translation of cancer related genes. Our previous study demonstrated that α6β4 stimulates translation initiation of survival factors such as VEGF by activating mTOR pathway. However, the immediate early signaling events that link α6β4 to mTOR activation needs to be defined.

Results

In the current studies, we demonstrated that c-Src is an immediate early signaling molecule that acts upstream of α6β4 dependent mTOR activation and subsequent translation of VEGF in MDA-MB-435/β4 and MDA-MB-231 cancer cells. m⁷GTP-Sepharose–binding assay revealed that Src activity is required to form eIF4F complex which is necessary for Cap-dependent translation in α6β4 expressing human cancer cells.

Conclusions

Overall, our studies suggest that integrin β4 and c-Src activation is important early signaling events to lead mTOR activation and cap-dependent translation of VEGF.

Functions of S100 proteins

The S100 protein family consists of 24 members functionally distributed into three main subgroups: those that only exert intracellular regulatory effects, those with intracellular and extracellular functions and those which mainly exert extracellular regulatory effects. S100 proteins are only expressed in vertebrates and show cell-specific expression patterns. In some instances, a particular S100 protein can be induced in pathological circumstances in a cell type that does not express it in normal physiological conditions. Within cells, S100 proteins are involved in aspects of regulation of proliferation, differentiation, apoptosis, Ca2+ homeostasis, energy metabolism, inflammation and migration/invasion through interactions with a variety of target proteins including enzymes, cytoskeletal subunits, receptors, transcription factors and nucleic acids. Some S100 proteins are secreted or released and regulate cell functions in an autocrine and paracrine manner via activation of surface receptors (e.g. the receptor for advanced glycation end-products and toll-like receptor 4), G-protein-coupled receptors, scavenger receptors, or heparan sulfate proteoglycans and N-glycans. Extracellular S100A4 and S100B also interact with epidermal growth factor and basic fibroblast growth factor, respectively, thereby enhancing the activity of the corresponding receptors. Thus, extracellular S100 proteins exert regulatory activities on monocytes/macrophages/microglia, neutrophils, lymphocytes, mast cells, articular chondrocytes, endothelial and vascular smooth muscle cells, neurons, astrocytes, Schwann cells, epithelial cells, myoblasts and cardiomyocytes, thereby participating in innate and adaptive immune responses, cell migration and chemotaxis, tissue development and repair, and leukocyte and tumor cell invasion.

The role of TG2 in regulating S100A4-mediated mammary tumour cell migration

The importance of S100A4, a Ca(2+)-binding protein, in mediating tumour cell migration, both intracellularly and extracellularly, is well documented. Tissue transglutaminase (TG2) a Ca(2+)-dependent protein crosslinking enzyme, has also been shown to enhance cell migration. Here by using the well characterised non-metastatic rat mammary R37 cells (transfected with empty vector) and highly metastatic KP1 cells (R37 cells transfected with S100A4), we demonstrate that inhibition of TG2 either by TG2 inhibitors or transfection of cells with TG2 shRNA block S100A4-accelerated cell migration in the KP1cells and in R37 cells treated with exogenous S100A4. Cell migration was also blocked by the treatment with the non-cell permeabilizing TG2 inhibitor R294, in the human breast cancer cell line MDA-MB-231 (Clone 16, which has a high level of TG2 expression). Inhibition was paralleled by a decrease in S100A4 polymer formation. In vitro co-immunoprecipitation and Far Western blotting assays and cross-linking assays showed not only the direct interaction between TG2 and S100A4, but also confirmed S100A4 as a substrate for TG2. Using specific functional blocking antibodies, a targeting peptide and a recombinant protein as a competitive treatment, we revealed the involvement of syndecan-4 and α5β1 integrin co-signalling pathways linked by activation of PKCα in this TG2 and S100A4-mediated cell migration. We propose a mechanism for TG2-regulated S100A4-related mediated cell migration, which is dependent on TG2 crosslinking.

Galectin-1 promotes lung cancer tumor metastasis by potentiating integrin α6β4 and Notch1/Jagged2 signaling pathway

Lung cancer is a major cancer, leading in both incidence and mortality in the world, and metastasis underlies the majority of lung cancer-related deaths. Galectin-1, a glycan-binding protein, has been shown to be overexpressed in lung cancer and involved in tumor-mediated immune suppression. However, the functional role of galectin-1 in lung cancer per se remains unknown. We demonstrate that ectopic expression of galectin-1 in a low-metastatic CL1-0 lung cancer cell line promotes its migration, invasion and epithelial-mesenchymal transition. Conversely, we also show that suppression of galectin-1 expression in highly invasive CL1-5 and A549 cells inhibits migration and invasion of lung cancer cell and causes a mesenchymal-epithelial transition. These effects may be transduced by increasing the expression of integrin α6β4 and Notch1/Jagged2, which in turn co-operates in the phosphorylation of AKT. The effects of galectin-1 on cancer progression are reduced when integrin β4 and Notch1 are absent. Further study has indicated that galectin-1 knockdown prevents the spread of highly metastatic Lewis lung carcinoma in vivo. Our study suggests that galectin-1 represents a crucial regulator of lung cancer metastasis. Thus, the detection and targeted treatment of galectin-1-expressing cancer serves as a new therapeutic target for lung cancer.

Pro-metastatic tumor–stroma interactions in breast cancer

The vast majority of breast cancer-related deaths are due to metastatic disease. Reciprocal and complex interactions between epithelial tumor cells and the various components of the tumor microenvironment influence tumor progression and metastases although the molecular mechanisms underlying these metastasis-promoting effects are not fully characterized. Identifying and understanding pathways of tumor–stroma cross-talk are likely to lead to the development of novel prognostic biomarkers for metastasis and strategies to prevent metastasis at its earliest stages, resulting in improved patient outcomes.

Human VRK2 (vaccinia-related kinase 2) modulates tumor cell invasion by hyperactivation of NFAT1 and expression of cyclooxygenase-2

Human VRK2 (vaccinia-related kinase 2), a kinase that emerged late in evolution, affects different signaling pathways, and some carcinomas express high levels of VRK2. Invasion by cancer cells has been associated with NFAT1 (nuclear factor of activated T cells) activation and expression of the COX-2 (cyclooxygenase 2) gene. We hypothesized that VRK proteins might play a regulatory role in NFAT1 activation in tumor cells. We demonstrate that VRK2 directly interacts and phosphorylates NFAT1 in Ser-32 within its N-terminal transactivation domain. VRK2 increases NFAT1-dependent transcription by phosphorylation, and this effect is only detected following cell phorbol 12-myristate 13-acetate and ionomycin stimulation and calcineurin activation. This NFAT1 hyperactivation by VRK2 increases COX-2 gene expression through the proximal NFAT1 binding site in the COX-2 gene promoter. Furthermore, VRK2A down-regulation by RNA interference reduces COX-2 expression at transcriptional and protein levels. Therefore, VRK2 down-regulation reduces cell invasion by tumor cells, such as MDA-MB-231 and MDA-MB-435, upon stimulation with phorbol 12-myristate 13-acetate plus ionomycin. These findings identify the first reported target and function of human VRK2 as an active kinase playing a role in regulation of cancer cell invasion through the NFAT pathway and COX-2 expression.

Palmitoylation by DHHC3 is critical for the function, expression, and stability of integrin α6β4

The laminin-binding integrin α6β4 plays key roles in both normal epithelial and endothelial cells and during tumor cell progression, metastasis, and angiogenesis. Previous cysteine mutagenesis studies have suggested that palmitoylation of α6β4 protein supports a few integrin-dependent functions and molecular associations. Here we took another approach and obtained strikingly different results. We used overexpression and RNAi knockdown in multiple cell types to identify protein acyl transferase DHHC3 as the enzyme responsible for integrin β4 and α6 palmitoylation. Ablation of DHHC3 markedly diminished integrin-dependent cellular cable formation on Matrigel, integrin signaling through Src, and β4 phosphorylation on key diagnostic amino acids (S1356 and 1424). However, unexpectedly, and in sharp contrast to prior α6β4 mutagenesis results, knockdown of DHHC3 accelerated the degradation of α6β4, likely due to an increase in endosomal exposure to cathepsin D. When proteolytic degradation was inhibited (by Pepstatin A), rescued α6β4 accumulated intracellularly, but was unable to reach the cell surface. DHHC3 ablation effects were strongly selective for α6β4. Cell-surface levels of ~10 other proteins (including α3β1) were not diminished, and the appearance of hundreds of other palmitoylated proteins was not altered. Results obtained here demonstrate a new substrate for the DHHC3 enzyme and provide novel opportunities for modulating α6β4 expression, distribution, and function.

The oncoprotein HBXIP uses two pathways to up-regulate S100A4 in promotion of growth and migration of breast cancer cells

We have reported that hepatitis B X-interacting protein (HBXIP) promotes the proliferation and migration of breast cancer cells. However, the underlying mechanism is poorly understood. In this study, we report that HBXIP works in the event through up-regulating S100A4. We observed that HBXIP expression was positively correlated to that of S100A4 in 87 clinical breast cancer tissue samples. Then, we identified that HBXIP was able to up-regulate S100A4 expression in breast cancer cells. Notably, we observed the HBXIP nuclear localization, implying that HBXIP may be associated with the promoter of S100A4. Chromatin immunoprecipitation assay (ChIP) and electrophoretic mobility shift assay (EMSA) showed that HBXIP was able to bind to the nucleotides +200~+239 region of S100A4 promoter, containing two putative recognition motif of transcription factor STAT4 and GRβ. It suggests that HBXIP is able to activate S100A4 promoter via interacting with STAT4 in breast cancer cells, leading to the up-regulation of S100A4. In addition, we identified another pathway of S100A4 up-regulation mediated by HBXIP. We found that HBXIP activated the PTEN/PI3K/AKT signaling by inducing DNA methylation of PTEN, which subsequently boosted S100A4 expression. In function, we demonstrated that HBXIP enhanced the growth or migration of breast cancer cells through S100A4 in vivo and in vitro. Collectively, we conclude that HBXIP up-regulates S100A4 through activating S100A4 promoter involving STAT4 and inducing PTEN/PI3K/AKT signaling to promote growth and migration of breast cancer cells. Our finding provides new insight into the mechanism of HBXIP in promotion of the development of breast cancer.

Cell surface glycoproteomic analysis of prostate cancer-derived PC-3 cells

Most clinically approved biomarkers of cancer are glycoproteins, and those residing on the cell surface are of particular interest in biotherapeutics. We report a method for selective labeling, affinity enrichment, and identification of cell-surface glycoproteins. PC-3 cells and primary human prostate cancer tissue were treated with peracetylated N-azidoacetylgalactosamine, resulting in metabolic labeling of cell surface glycans with the azidosugar. We used mass spectrometry to identify over 70 cell surface glycoproteins and biochemically validated CD146 and integrin beta-4, both of which are known to promote metastatic behavior. These results establish cell-surface glycoproteomics as an effective technique for discovery of cancer biomarkers.

Comparative studies of vertebrate Beta integrin genes and proteins: ancient genes in vertebrate evolution

Intregins are heterodimeric α- and β-subunit containing membrane receptor proteins which serve various cell adhesion roles in tissue repair, hemostasis, immune response, embryogenesis and metastasis. At least 18 α- (ITA or ITGA) and 8 β-integrin subunits (ITB or ITGB) are encoded on mammalian genomes. Comparative ITB amino acid sequences and protein structures and ITB gene locations were examined using data from several vertebrate genome projects. Vertebrate ITB genes usually contained 13-16 coding exons and encoded protein subunits with ~800 amino acids, whereas vertebrate ITB4 genes contained 36-39 coding exons and encoded larger proteins with ~1800 amino acids. The ITB sequences exhibited several conserved domains including signal peptide, extracellular β-integrin, β-tail domain and integrin β-cytoplasmic domains. Sequence alignments of the integrin β-cytoplasmic domains revealed highly conserved regions possibly for performing essential functions and its maintenance during vertebrate evolution. With the exception of the human ITB8 sequence, the other ITB sequences shared a predicted 19 residue α-helix for this region. Potential sites for regulating human ITB gene expression were identified which included CpG islands, transcription factor binding sites and microRNA binding sites within the 3'-UTR of human ITB genes. Phylogenetic analyses examined the relationships of vertebrate beta-integrin genes which were consistent with four major groups: 1: ITB1, ITB2, ITB7; 2: ITB3, ITB5, ITB6; 3: ITB4; and 4: ITB8 and a common evolutionary origin from an ancestral gene, prior to the appearance of fish during vertebrate evolution. The phylogenetic analyses revealed that ITB4 is the most likely primordial form of the vertebrate β integrin subunit encoding genes, that is the only β subunit expressed as a constituent of the sole integrin receptor 'α6β4' in the hemidesmosomes of unicellular organisms.

Novel effect of antihelminthic Niclosamide on S100A4-mediated metastatic progression in colon cancer

BACKGROUND

Metastasis formation in colon cancer severely reduces the survival rate in patients. S100A4, a calcium-binding protein, is implicated in promoting metastasis formation in colon cancer.

METHODS

To identify a transcription inhibitor of S100A4, high-throughput screening of 1280 pharmacologically active compounds was performed using a human colon cancer cell line expressing a S100A4 promoter-driven luciferase (LUC) reporter gene construct (HCT116-S1004p-LUC). Niclosamide, an antihelminthic agent, was identified as a potential candidate. Colon cancer cell lines (HCT116, SW620, LS174T, SW480, and DLD-1) were treated with 1 μM niclosamide to analyze the effect on S100A4 mRNA and protein expression by quantitative reverse transcription-polymerase chain reaction and immunoblot assays, and effects on cell migration, invasion, proliferation, and colony formation were also assessed in vitro. The effect of niclosamide on liver metastasis was assessed in a xenograft mouse model of human colon cancer (n = 8 mice) by in vivo imaging. The long-term effect of niclosamide on metastasis formation after discontinued treatment was quantified by scoring, and overall survival (n = 12 mice) was analyzed by Kaplan-Meier method after discontinuation of treatment. All statistical tests were two-sided.

RESULTS

Reduced S100A4 mRNA and protein expression, and inhibited cell migration, invasion, proliferation, and colony formation were observed in niclosamide-treated colon cancer cells in vitro. In vivo imaging of niclosamide-treated mice showed reduced liver metastasis compared with solvent-treated control mice (n = 4 mice per group). Compared with the control group, discontinuation of treatment for 26 days showed reduced liver metastasis formation in mice (n = 6 mice per group) (control vs discontinuous treatment, mean metastasis score = 100% vs 34.9%, mean difference = 65.1%; 95% confidence interval [CI] = 18.4% to 111.9%, P < .01) and increased overall survival (n = 6 mice per group; control vs discontinuous treatment, median survival = 24 vs 46.5 days, ratio = 0.52, 95% CI = 0.19 to 0.84, P = .001).

CONCLUSION

Niclosamide inhibits S100A4-induced metastasis formation in a mouse model of colon cancer and has therapeutic potential.

Therapeutic targeting of tumor-stroma interactions

INTRODUCTION

Cancers exist within a complex microenvironment populated by diverse cell types within a protein-rich extracellular matrix. It is becoming increasingly apparent that molecular interactions between epithelial cells and cells in the surrounding stroma promote growth, invasion and spread of the tumor itself and thus represents a crucial underlying driving force in tumorigenesis.

AREAS COVERED

This article reviews how key interactions between tumor epithelial cells and surrounding mesenchymal and immune cells can promote tumor progression and highlights molecular elements that might represent novel therapeutic targets.

EXPERT OPINION

The tumor microenvironment is increasingly being viewed as a potential therapeutic target with a number of strategies being developed to disrupt tumor-stroma interactions, in order to delay or circumvent tumor progression. Targeting elements of the tumor microenvironment, or signaling pathways in tumor cells activated as a consequence of stromal interactions, may prove a useful therapeutic strategy to prevent tumor development and progression. However, given the tumor cells' ability to circumvent various therapeutic agents when given as monotherapy, the success of these agents is likely to be seen when used in combination with existing treatments.

Mnk mediates integrin α6β4-dependent eIF4E phosphorylation and translation of VEGF mRNA

It was previously shown that integrin α6β4 contributes to translation of cancer-related mRNAs such as VEGF via initiation factor eIF4E. In this study, we found that integrin α6β4 regulates the activity of eIF4E through the Ser/Thr kinase Mnk. Although a role for Mnk in various aspects of cancer progression has been established, a link between integrin and Mnk activity has not. Here we show that Mnk1 is a downstream effector of integrin α6β4 and mediates the α6β4 signaling, important for translational control. Integrin α6β4 signals through MEK and p38 MAPK to increase phosphorylation of Mnk1 and eIF4E. Inhibition of Mnk1 activity by CGP57380 or downregulation by shRNA blocks α6β4-dependent translation of VEGF mRNA. Our studies suggest that Mnk1 could be a therapeutic target in cancers where the integrin α6β4 level is high.