β1-integrin: a potential therapeutic target in the battle against cancer recurrence

Mathematical Modeling Reveals That the Administration of EGF Can Promote the Elimination of Lymph Node Metastases by PD-1/PD-L1 Blockade

In the advanced stages of cancers like melanoma, some of the malignant cells leave the primary tumor and infiltrate the neighboring lymph nodes (LNs). The interaction between secondary cancer and the immune response in the lymph node represents a complex process that needs to be fully understood in order to develop more effective immunotherapeutic strategies. In this process, antigen-presenting cells (APCs) approach the tumor and initiate the adaptive immune response for the corresponding antigen. They stimulate the naive CD4+ and CD8+ T lymphocytes which subsequently generate a population of helper and effector cells. On one hand, immune cells can eliminate tumor cells using cell-cell contact and by secreting apoptosis inducing cytokines. They are also able to induce their dormancy. On the other hand, the tumor cells are able to escape the immune surveillance using their immunosuppressive abilities. To study the interplay between tumor progression and the immune response, we develop two new models describing the interaction between cancer and immune cells in the lymph node. The first model consists of partial differential equations (PDEs) describing the populations of the different types of cells. The second one is a hybrid discrete-continuous model integrating the mechanical and biochemical mechanisms that define the tumor-immune interplay in the lymph node. We use the continuous model to determine the conditions of the regimes of tumor-immune interaction in the lymph node. While we use the hybrid model to elucidate the mechanisms that contribute to the development of each regime at the cellular and tissue levels. We study the dynamics of tumor growth in the absence of immune cells. Then, we consider the immune response and we quantify the effects of immunosuppression and local EGF concentration on the fate of the tumor. Numerical simulations of the two models show the existence of three possible outcomes of the tumor-immune interactions in the lymph node that coincide with the main phases of the immunoediting process: tumor elimination, equilibrium, and tumor evasion. Both models predict that the administration of EGF can promote the elimination of the secondary tumor by PD-1/PD-L1 blockade.

Tunable synthetic extracellular matrices to investigate breast cancer response to biophysical and biochemical cues

The extracellular matrix (ECM) is thought to play a critical role in the progression of breast cancer. In this work, we have designed a photopolymerizable, biomimetic synthetic matrix for the controlled, 3D culture of breast cancer cells and, in combination with imaging and bioinformatics tools, utilized this system to investigate the breast cancer cell response to different matrix cues. Specifically, hydrogel-based matrices of different densities and modified with receptor-binding peptides derived from ECM proteins [fibronectin/vitronectin (RGDS), collagen (GFOGER), and laminin (IKVAV)] were synthesized to mimic key aspects of the ECM of different soft tissue sites. To assess the breast cancer cell response, the morphology and growth of breast cancer cells (MDA-MB-231 and T47D) were monitored in three dimensions over time, and differences in their transcriptome were assayed using next generation sequencing. We observed increased growth in response to GFOGER and RGDS, whether individually or in combination with IKVAV, where binding of integrin β1 was key. Importantly, in matrices with GFOGER, increased growth was observed with increasing matrix density for MDA-MB-231s. Further, transcriptomic analyses revealed increased gene expression and enrichment of biological processes associated with cell-matrix interactions, proliferation, and motility in matrices rich in GFOGER relative to IKVAV. In sum, a new approach for investigating breast cancer cell-matrix interactions was established with insights into how microenvironments rich in collagen promote breast cancer growth, a hallmark of disease progression in vivo, with opportunities for future investigations that harness the multidimensional property control afforded by this photopolymerizable system.

Chinese Herbal Medicine Wenxia Changfu Formula Reverses Cell Adhesion-Mediated Drug Resistance via the Integrin β1-PI3K-AKT Pathway in Lung Cancer

In the treatment of lung cancer, the multidrug resistance to chemotherapeutic drugs is one of the reasons of low rates for cure and treatment failure, the combination of chemotherapeutic drugs and traditional Chinese medicine can increase the sensitivity of chemotherapy and reduce its adverse effects. Our previous study has proved that Chinese herbal medicine (CHM) Wenxia Changfu Formula (WCF for short) effectively enhances chemotherapeutic efficacy in lung cancer treatment and reverses multidrug resistance in lung cancer cells in vitro. The present study aims to investigate the effect and mechanism of WCF in reversing cell adhesion-mediated drug resistance of lung cancer by using A549 three-dimensional cell culture and nude mouse model of the A549 cell line with Integrin β1 overexpression. We show that the combination of WCF with DDP can decrease proliferation of lung cancer cells by inducing cell cycle arrest and apoptosis. Moreover, we find that the combination of WCF with DDP suppresses the expression of certain molecules which regulate cell cycle and apoptosis. Mechanistically, we show that the Integrin β1, FAK, PI3K, and AKT protein expressions are suppressed by DDP and even more responses are observed when DDP and WCF are combined, showing WCF treatment enhances the effect of commonly used anticancer drugs. In line with the above findings, our results confirm that WCF reverses cell adhesion-mediated drug resistance of lung cancer via inactivating Integrin β1/PI3K/AKT and apoptosis induction.

Ganoderma immunomodulatory protein and chidamide down-regulate integrin-related signaling pathway result in migration inhibition and apoptosis induction

BACKGROUND

In terms of melanoma, recent advances have been made in target therapies and immune checkpoint inhibitors, but durable remission is rare. Ganoderma immunomodulatory proteins (GMI) induce a cytotoxic effect in cancer cells via autophagy. However, the role of GMI in melanoma is not clear.

PURPOSE

The aims of this study are to investigate the inhibiting effects of GMI combined with chidamide on survival and metastases of melanoma cells via integrin-related signaling pathway and to propose strategies for combining GMI and chidamide using animal model.

METHODS

Cell viability was measured by cell CCK-8. The activities of apoptosis- and migration-related proteins were detected on Western blot. Flow cytometry was used to analyze cell cycle distribution and sub-G1 fraction in treated melanoma cells. To evaluate the activity of combination GMI and chidamide treatment, an in vivo anti-tumor metastasis study was performed.

RESULTS

GMI combined with chidamide additively induced apoptosis. GMI inhibited the expressions of Integrin α5, αV, β1, and β3. The level of p-FAK was inhibited by GMI. Combination treatment of GMI and chidamide decreased survivin and increased cleaved caspase-7 and LC3 II/I. Integrin-αV overexpression activated p-FAK pathways in A375.S2 cells. GMI significantly inhibited cell growth and migration of A375.S2 cells on wound healing assay. In vivo, GMI combined with chidamide suppressed distal tumor metastasis.

CONCLUSION

GMI inhibits the migration and growth of melanoma cells via integrin-related signaling pathway. GMI and chidamide induces apoptosis. In vivo, GMI and chidamide additively reduce distant metastases. GMI and chidamide are potential immunotherapeutic adjuvant for metastatic melanoma.

Extracellular gamma-synuclein promotes tumor cell motility by activating β1 integrin-focal adhesion kinase signaling pathway and increasing matrix metalloproteinase-24, -2 protein secretion

Background

Increasing evidence reveals a significant correlation between gamma-synuclein (SNCG) level and tumor invasion and metastasis in various human cancers. Our previous investigation showed that SNCG could secrete into extracellular environment and promoted tumor cell motility, but the mechanism is unknown.

Methods

The membrane binding ability of SNCG was characterized by immunohistochemical staining, immunofluorescence staining and fractionation of colorectal cancer (CRC) cell membrane. Association between SNCG and β1 integrin was validated by coimmunoprecipitation and far Western blot. After inhibition of β1 integrin and focal adhesion kinase (FAK), effect of SNCG on cell motility was measured by transwell chamber assays and changes of protein levels were detected by Western blot. Association between SNCG and activated β1 integrin levels in human CRC tissues was determined by Spearman’s rank correlation analysis. Secreted proteins in conditioned medium (CM) were screened by antibody array.

Results

Extracellular SNCG bound β1 integrin on CRC cell membrane and increased levels of activated β1 integrin and FAK. Correspondingly, SNCG-enhanced cell motility was counteracted by knockdown or inhibition of β1 integrin or FAK. Further study revealed that high SNCG level indicated poor outcome and SNCG levels positively correlated with those of activated β1 integrin and phospho-FAK (Tyr³⁹⁷) in human CRC tissues. Additionally, extracellular SNCG promoted secretion of fibronectin (FN), vitronectin (VN), matrix metalloproteinase (MMP)-2, and MMP-24 from HCT116 cells. Protease activity of MMP-2 in the CM of HCT116 cells was increased by treatment with SNCG, which was abolished by inhibiting β1 integrin.

Conclusion

Our results highlight the potential role of SNCG in remodeling extracellular microenvironment and inducing β1 integrin-FAK signal pathway of CRC cells.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0783-6) contains supplementary material, which is available to authorized users.

Synergistic potentiation of the anti-metastatic effect of anti EGFR mAb by its combination with immunotherapies targeting the ganglioside NGcGM3

Several Anti-EGFR mAbs are register for the treatment of human cancer. However, their impact on patients overall survival has been limited by tumor resistance. N-Glycolyl variant of GM3 ganglioside (NGcGM3) is specifically expressed in some human tumors, and it has been associated with a poor prognosis. Several reports have documented that GM3 physically associates to EGFR inhibiting its ligand depend phosphorylation, but it also facilitates an alternative/compensatory signaling cascade mediated by Uroquinase Plasminogen Activator Receptor (uPAR) and integrin α5β1 interaction. However, the difference between NGc and N-Acetylated (NAc) variants of GM3 regarding such interactions is unknown. We hypothesized that enrichment of NGcGM3 expression in tumors relates to advantages of this ganglioside, on ensuring both EGFR and uPAR pathways optimal function. We explored the impact of combining an anti-EGFR (7A7 mAb) with anti-NGcGM3 therapies: NGcGM3/VSSP vaccine or 14F7 mAb. Both combinations synergistically increase overall survival in two models of lung metastasis: 3LL-D122 and 4T1; but combination with NGcGM3/VSSP vaccine is significantly more effective. In 3LL-D122-metastasis, of mice treated with the best combination, both EGFR and uPAR/α5β1 integrin pathways are turn off (I.e expression of uPAR/α5β1; and phosphorylation of EGFR, Stat3, Src and FAK are reduced); and tumor angiogenesis is decreased. Interestingly, combination treatment increases tumor infiltrating CD4⁺T, CD8⁺T and NK⁺-cells. Furthermore, a positive clinical outcome is reported for a cancer patient treated with an anti-EGFR mAb and anti-NGcGM3 therapy. Overall, our results support the combination of anti EGFR antibodies with therapies targeting NGcGM3 to increase their efficacy in future clinical trials.

Long-term exposure to carcinoma-associated fibroblasts makes breast cancer cells addictive to integrin β1

We studied the long-term effect of stromal factors on the development of fulvestrant-resistance (FR) and fulvestrant-induced dormancy (D). Sublines established from stroma-treated FR-cells (C-FR cells) and D-cells (C-D cells) show permanently high expression of integrin β1 as well as Bcl-3 and P-STAT3 (C-FR) or IGF1R (C-D). Yet, cells fail to withstand fulvestrant better and do not migrate or grow faster than control cells. Instead, C-D cells rely on stromal factors to perform as well as control cells. In addition, C-FR cells adapted to integrin β1 for growth in 3D cultures. These data suggest that long-term exposure to stromal factors leads to addiction rather than better performance in cellular activities. We also found that morphologically distinct breast cancer cell line subpopulations share key responses to stromal factors suggesting that intratumoral heterogeneity may play a minor role in the interaction between breast cancer and stromal cells.

RGD cadherins and α2β1 integrin in cancer metastasis: A dangerous liaison

We propose a new cadherin family classification comprising epithelial cadherins (cadherin 17 [CDH17], cadherin 16, VE-cadherin, cadherin 6 and cadherin 20) containing RGD motifs within their sequences. Expression of some RGD cadherins is associated with aggressive forms of cancer during the late stages of metastasis, and CDH17 and VE-cadherin have emerged as critical actors in cancer metastasis. After binding to α2β1 integrin, these cadherins promote integrin β1 activation, and thereby cell adhesion, invasion and proliferation, in liver and lung metastasis. Activation of α2β1 integrin provokes an affinity increase for type IV collagen, a major component of the basement membrane and a critical partner for cell anchoring in liver and other metastatic organs. Activation of α2β1 integrin by RGD motifs breaks an old paradigm of integrin classification and supports an important role of this integrin in cancer metastasis. Recently, synthetic peptides containing the RGD motif of CDH17 elicited highly specific and selective antibodies that block the ability of CDH17 RGD to activate α2β1 integrin. These monoclonal antibodies inhibit metastatic colonization in orthotopic mouse models of liver and lung metastasis for colorectal cancer and melanoma, respectively. Hopefully, blocking the cadherin RGD ligand capacity will give us control over the integrin activity in solid tumors metastasis, paving the way for development of new agents of cancer treatment.

Epidermal growth factor-mediated Rab25 pathway regulates integrin β1 trafficking in colon cancer

Background

Integrins play a critical role in carcinogenesis. Integrin β1 localization is regulated by the guanosine-5′-triphosphate hydrolase Rab25 and integrin β1 levels are elevated in the serum of colon cancer patients; thus, the present study examined the effects of epidermal growth factor (EGF) and Rab25 on integrin β1 localization in colon cancer cells.

Methods

HCT116 human colon cancer cells were treated with increasing concentrations of EGF, and cell proliferation and protein expression were monitored by MTT and western blot analyses, respectively. Cell fractionation was performed to determine integrin β1 localization in the membrane and cytosol. Integrin β1 extracellular shedding was monitored by enzyme-linked immunosorbent assays (ELISAs) with culture supernatants from stimulated cells. HCT116 cells were transfected with Rab25-specific siRNA to determine the significance of Rab25 in integrin β1 trafficking in the presence of EGF.

Results

Total integrin β1 expression increased in response to EGF and subsequently decreased at 24 h post-stimulation. A similar decrease was observed in purified membrane fractions, whereas no changes were observed in cytosolic levels. ELISAs using media from stimulated cell cultures demonstrated increased integrin β1 levels corresponding to the decrease observed in membrane fractions, suggesting that EGF induces integrin receptor shedding. EGF stimulation in Rab25-knockdown cells resulted in integrin β1 accumulation in the membrane, suggesting that Rab25 promotes integrin endocytosis.

Conclusions

Integrin β1 is shed from colon cancer cells in response to EGF stimulation in a Rab25-dependent manner. These results further the present understanding of the role of integrin β1 in colon cancer progression.

Vasodilator-stimulated phosphoprotein promotes liver metastasis of gastrointestinal cancer by activating a β1-integrin-FAK-YAP1/TAZ signaling pathway

Extracellular matrix (ECM)-induced β1-integrin-FAK signaling promotes cell attachment, survival, and migration of cancer cells in a distant organ so as to enable cancer metastasis. However, mechanisms governing activation of the β1-integrin-FAK signaling remain incompletely understood. Here, we report that vasodilator-stimulated phosphoprotein (VASP), an actin binding protein, is required for ECM–mediated β1-integrin-FAK-YAP1/TAZ signaling in gastrointestinal (GI) cancer cells and their liver metastasis. In patient-derived samples, VASP is upregulated in 53 of 63 colorectal cancers and 43 of 53 pancreatic ductal adenocarcinomas and high VASP levels correlate with liver metastasis and reduced patient survival. In a Matrigel-based 3-dimensional (3D) culture model, short hairpin RNA (shRNA)–mediated VASP knockdown in colorectal cancer cells (KM12L4, HCT116, and HT29) and pancreatic cancer cells (L3.6 and MIA PaCa-1) suppresses the growth of 3D cancer spheroids. Mechanistic studies reveal that VASP knockdown suppresses FAK phosphorylation and YAP1/TAZ protein levels, but not Akt or Erk-related pathways and that YAP1/TAZ proteins are enhanced by the β1-integrin-FAK signaling. Additionally, VASP regulates the β1-integrin-FAK-YAP1/TAZ signaling by at least two mechanisms: (1) promoting ECM-mediated β1-integrin activation and (2) regulating YAP1/TAZ dephosphorylation at downstream of RhoA to enhance the stability of YAP1/TAZ proteins. In agreement with these, preclinical studies with two experimental liver metastasis mouse models demonstrate that VASP knockdown suppresses GI cancer liver metastasis, β1-integrin activation, and YAP1/TAZ levels of metastatic cancer cells. Together, our data support VASP as a treatment target for liver metastasis of colorectal and pancreatic cancers.

A protein involved in cytoskeleton regulation and cell motility control offers a new drug target for cancer spreading to the liver. Ningling Kang Ph.D. from the Hormel Institute in Austin, Minnesota, USA, and colleagues showed that levels of this actin-binding protein, known as vasodilator-stimulated phosphoprotein (VASP), are elevated in most patients with advanced colon and pancreatic cancers and that higher VASP expression levels are linked to liver metastasis and poorer patients’ outcomes. To explore the reasons why, the researchers studied three-dimensional tumor spheroids and mouse metastasis models of these cancers, and identified the signaling pathway by which VASP promotes the survival of cancer cells in distant organs, such as the liver. What’s more, they showed that knocking down VASP of cancer cells in metastasis mouse models suppressed cancer metastatic growth in the liver, suggesting that the same might be true in patients as well.

Doxorubicin resistance in breast cancer cells is mediated by extracellular matrix proteins

Background

Cancer cell resistance to therapeutics can result from acquired or de novo-mediated factors. Here, we have utilised advanced breast cancer cell culture models to elucidate de novo doxorubicin resistance mechanisms.

Methods

The response of breast cancer cell lines (MCF-7 and MDA-MB-231) to doxorubicin was examined in an in vitro three-dimensional (3D) cell culture model. Cells were cultured with Matrigel™ enabling cellular arrangements into a 3D architecture in conjunction with cell-to-extracellular matrix (ECM) contact.

Results

Breast cancer cells cultured in a 3D ECM-based model demonstrated altered sensitivity to doxorubicin, when compared to those grown in corresponding two-dimensional (2D) monolayer culture conditions. Investigations into the factors triggering the observed doxorubicin resistance revealed that cell-to-ECM interactions played a pivotal role. This finding correlated with the up-regulation of pro-survival proteins in 3D ECM-containing cell culture conditions following exposure to doxorubicin. Inhibition of integrin signalling in combination with doxorubicin significantly reduced breast cancer cell viability. Furthermore, breast cancer cells grown in a 3D ECM-based model demonstrated a significantly reduced proliferation rate in comparison to cells cultured in 2D conditions.

Conclusion

Collectively, these novel findings reveal resistance mechanisms which may contribute to reduced doxorubicin sensitivity.

Monoclonal Antibodies Directed against Cadherin RGD Exhibit Therapeutic Activity against Melanoma and Colorectal Cancer Metastasis

Purpose: New targets are required for the control of advanced metastatic disease. We investigated the use of cadherin RGD motifs, which activate the α2β1integrin pathway, as targets for the development of therapeutic monoclonal antibodies (mAb).Experimental Design: Cadherin 17 (CDH17) fragments and peptides were prepared and used for immunization and antibody development. Antibodies were tested for inhibition of β1 integrin and cell adhesion, proliferation, and invasion assays using cell lines from different cancer types (colorectal, pancreatic, melanoma, and breast cancer). Effects of the mAbs on cell signaling were determined by Western blot analysis. Nude mice were used for survival analysis after treatment with RGD-specific mAbs and metastasis development.Results: Antibodies against full-length CDH17 failed to block the binding to α2β1 integrin. However, CDH17 RGD peptides generated highly selective RGD mAbs that blocked CDH17 and vascular-endothelial (VE)-cadherin-mediated β1 integrin activation in melanoma and breast, pancreatic, and colorectal cancer cells. Antibodies provoked a significant reduction in cell adhesion and proliferation of metastatic cancer cells. Treatment with mAbs impaired the integrin signaling pathway activation of FAK in colorectal cancer, of JNK and ERK kinases in colorectal and pancreatic cancers, and of JNK, ERK, Src, and AKT in melanoma and breast cancer. In vivo, RGD-specific mAbs increased mouse survival after inoculation of melanoma and colorectal cancer cell lines to cause lung and liver metastasis, respectively.Conclusions: Blocking the interaction between RGD cadherins and α2β1 integrin with highly selective mAbs constitutes a promising therapy against advanced metastatic disease in colon cancer, melanoma, and, potentially, other cancers. Clin Cancer Res; 24(2); 433-44. ©2017 AACRSee related commentary by Marshall, p. 253.

Drug delivery to melanoma brain metastases: Can current challenges lead to new opportunities?

Melanoma has a high propensity to metastasize to the brain, and patients with melanoma brain metastases (MBM) have an extremely poor prognosis. The recent approval of several molecularly-targeted agents (e.g., BRAF, MEK inhibitors) and biologics (anti-CTLA-4, anti-PD-1 and anti-PD-L1 antibodies) has brought new hope to patients suffering from this formerly untreatable and lethal disease. Importantly, there have been recent reports of success in some clinical studies examining the efficacy of both targeted agents and immunotherapies that show similar response rates in both brain metastases and extracranial disease. While these studies are encouraging, there remains significant room for improvement in the treatment of MBM, given the lack of durable response and the development of resistance to current therapies. Critical questions remain regarding mechanisms that lead to this lack of durable response and development of resistance, and how those mechanisms may differ in systemic sites versus brain metastases. One issue that may not be fully appreciated is that the delivery of several small molecule molecularly-targeted therapies to the brain is often restricted due to active efflux at the blood-brain barrier (BBB) interface. Inadequate local drug concentrations may be partially responsible for the development of unique patterns of resistance at metastatic sites in the brain. It is clear that there can be local, heterogeneous BBB breakdown in MBM, as exemplified by contrast-enhancement on T1-weighted MR imaging. However, it is possible that the successful treatment of MBM with small molecule targeted therapies will depend, in part, on the ability of these therapies to penetrate an intact BBB and reach the protected micro-metastases (so called "sub-clinical" disease) that escape early detection by contrast-enhanced MRI, as well as regions of tumor within MRI-detectable metastases that may have a less compromised BBB. The emergence of resistance in MBM may be related to several diverse, yet interrelated, factors including the distinct microenvironment of the brain and inadequate brain penetration of targeted therapies to specific regions of tumor. The tumor microenvironment has been ascribed to play a key role in steering the course of disease progression, by dictating changes in expression of tumor drivers and resistance-related signaling mechanisms. Therefore, a key issue to consider is how changes in drug delivery, and hence local drug concentrations within a metastatic microenvironment, will influence the development of resistance. Herein we discuss our perspective on several critical questions that focus on many aspects relevant to the treatment of melanoma brain metastases; the answers to which may lead to important advances in the treatment of this devastating disease.

RGD-Binding Integrins in Head and Neck Cancers

Alterations in integrin expression and function promote tumour growth, invasion, metastasis and neoangiogenesis. Head and neck cancers are highly vascular tumours with a tendency to metastasise. They express a wide range of integrin receptors. Expression of the αv and β1 subunits has been explored relatively extensively and linked to tumour progression and metastasis. Individual receptors αvβ3 and αvβ5 have proved popular targets for diagnostic and therapeutic agents but lesser studied receptors, such as αvβ6, αvβ8, and β1 subfamily members, also show promise. This review presents the current knowledge of integrin expression and function in squamous cell carcinoma of the head and neck (HNSCC), with a particular focus on the arginine-glycine-aspartate (RGD)-binding integrins, in order to highlight the potential of integrins as targets for personalised tumour-specific identification and therapy.

The nuclear orphan receptor NR4A1 regulates β1-integrin expression in pancreatic and colon cancer cells and can be targeted by NR4A1 antagonists

β1-Integrin is highly expressed and is a negative prognostic factor for colon and pancreatic cancer patients and the gene plays a functional role in cell migration and invasion. In this study, we demonstrate that β1-integrin expression is regulated in pancreatic and colon cancer cells by the pro-oncogenic orphan nuclear receptor 4A1 (NR4A1, Nur77, TR3) and knockdown of this receptor by RNA interference decreases β1-integrin protein and mRNA expression, α5-integrin, and also expression of β1-integrin-dependent phosphorylation of FAK (pFak). Knockdown of NR4A1 also decreased migration and fibronectin-induced adhesion in pancreatic (Panc1, L3.6 pL, and MiaPaCa2) and colon (RKO and SW480) cancer cells. 1,1-Bis(3'-indolyl)-1-(p-substituted phenyl)methane (C-DIM) compounds containing p-hydroxy (DIM-C-pPhOH) and p-carbomethoxy (DIM-C-pPhCO₂ Me) groups are NR4A1 ligands that act as antagonists for this receptor. Treatment of pancreatic and colon cancer cells with DIM-C-pPhOH or DIM-C-pPhCO₂ Me mimics the effects of NR4A1 knockdown and decreases β1-integrin expression, β1-integrin regulated genes and responses including migration and adhesion. The results demonstrate a novel method for targeting β1-integrin in colon and pancreatic cancer cells and indicate possible clinical applications for C-DIM/NR4A1 antagonists for pancreatic and colon cancer therapy.

FOXM1 transcriptionally regulates expression of integrin β1 in triple-negative breast cancer

PURPOSE

Triple-negative breast cancer (TNBC) is an aggressive type of breast cancer and associated with early metastasis, drug resistance, and poor patient survival. Fork head box M1 (FOXM1) is considered as an emerging molecular target due to its oncogenic role and high overexpression profile in 85% in TNBC. However, molecular mechanisms by which FOXM1 transcription factor mediate its oncogenic effects are not fully understood. Integrin β1 is often upregulated in invasive breast cancers and associated with poor clinical outcome and shorter overall patient survival in TNBC. However, the mechanisms regulating integrin β1 (ITGB1) gene expression have not been well elucidated.

METHODS

Normal breast epithelium (MCF10A) and TNBC cells (i.e., MDA-MB-231, BT-20 MDA-MB436) were used for the study. Small interfering RNA (siRNA)-based knockdown was used to inhibit Integrin β1 gene (mRNA) and protein expressions, which are detected by RT-PCR and Western blot, respectively. Chromatin immunoprecipitation (ChiP) and gene reporter (Luciferase) assays were used to demonstrate that FOXM1 transcription factor binds to the promoter of Integrin β1 gene and drives its expression.

RESULTS

We demonstrated that FOXM1 directly binds to the promoter of integrin β1 gene and transcriptionally regulates its expression and activity of focal adhesion kinase (FAK) in TNBC cells.

CONCLUSION

Our study suggests that FOXM1 transcription factor regulates Integrin β1 gene expression and that FOXM1/ Integrin-β1/FAK axis may play an important role in the progression of TNBC.

Mechanisms governing metastatic dormancy in breast cancer

Breast cancer is a systemic disease characterized by early dissemination of tumor cells to distant organs. In this foreign environment, tumor cells may stay in a dormant state as single cells or as micrometastases for many years before growing out into a macrometastatic lesion. As metastasis is the primary cause for breast cancer-related death, it is important to understand the mechanisms underlying the maintenance of dormancy and dormancy escape to find druggable targets to eradicate metastatic tumor cells. Metastatic dormancy is regulated by complex interactions between tumor cells and the local microenvironment. In addition, cancer-directed immunity and systemic instigation play a crucial role.

Hypoxia Selectively Enhances Integrin α5β1 Receptor Expression in Breast Cancer to Promote Metastasis

Metastasis is the leading cause of breast cancer mortality. Previous studies have implicated hypoxia-induced changes in the composition and stiffness of the extracellular matrix (ECM) in the metastatic process. Therefore, the contribution of potential ECM-binding receptors in this process was explored. Using a bioinformatics approach, the expression of all integrin receptor subunits, in two independent breast cancer patient datasets, were analyzed to determine whether integrin status correlates with a validated hypoxia-inducible gene signature. Subsequently, a large panel of breast cancer cell lines was used to validate that hypoxia induces the expression of integrins that bind to collagen (ITGA1, ITGA11, ITGB1) and fibronectin (ITGA5, ITGB1). Hypoxia-inducible factors (HIF-1 and HIF-2) are directly required for ITGA5 induction under hypoxic conditions, which leads to enhanced migration and invasion of single cells within a multicellular 3D tumor spheroid but did not affect migration in a 2D microenvironment. ITGB1 expression requires HIF-1α, but not HIF-2α, for hypoxic induction in breast cancer cells. ITGA5 (α₅ subunit) is required for metastasis to lymph nodes and lungs in breast cancer models, and high ITGA5 expression in clinical biopsies is associated with an increased risk of mortality.Implications: These results reveal that targeting ITGA5 using inhibitors that are currently under consideration in clinical trials may be beneficial for patients with hypoxic tumors. Mol Cancer Res; 15(6); 723-34. ©2017 AACR.

The translational blocking of α5 and α6 integrin subunits affects migration and invasion, and increases sensitivity to carboplatin of SKOV-3 ovarian cancer cell line

Epithelial ovarian cancer is the most lethal gynecologic malignancy. Integrins, overexpressed in cancer, are involved in various processes that favor the development of the disease. This study focused on determining the degree of involvement of α5, α6 and β3 integrin subunits in the establishment/development of epithelial ovarian cancer (EOC), such as proliferation, migration, invasion, and response to carboplatin. The translation of the α5, α6 and β3 integrins was blocked using morpholines, generating morphant cells for these proteins, which were corroborated by immunofluorescence assays. WST-1 proliferation assay showed that silencing of α5, α6, and β3 integrins does not affect the survival of morphants. Wound healing and transwell chamber assays showed that blocking α5 and α6 integrins decrease, in lesser and greater level respectively, the migratory and the invasive capacity of SKOV-3 cells. Finally, blocking α5 and α6 integrins partially sensitized the cells response to carboplatin, while blocking integrin β3 generated resistance to this drug. Statistical analyses were performed with the GraphPad Prism 5.0 software employing one way and two-way ANOVA tests; data are shown as average±SD. Results suggest that α5 and α6 integrins could become good candidates for chemotherapy targets in EOC.

hTERT promotes the invasion of gastric cancer cells by enhancing FOXO3a ubiquitination and subsequent ITGB1 upregulation

BACKGROUND AND AIMS

Human telomerase reverse transcriptase (hTERT) plays an important role in cancer invasion, but the relevant mechanism is not well known. This study aims to investigate the role and mechanism of hTERT in gastric cancer metastasis.

DESIGN

Proteomics analysis, qPCR and western blotting were used to screen for hTERT-regulated candidate molecules in gastric cancer invasion. Chromatin immunoprecipitation (ChIP) qPCR was performed to identify the binding sites of hTERT at the regulatory region of the integrin β1 (ITGB1) gene. ChIP assays were further applied to elucidate the transcription factors that bound to the regulatory region. The interactions between hTERT and the transcription factors were tested by co-immunoprecipitation (Co-IP) and glutathione S-transferase (GST) pull-down experiments. Moreover, the revealed pathway was verified in tumour-bearing nude mice and human gastric cancer tissues.

RESULTS

ITGB1 was identified as a downstream gene of hTERT, and there were two hTERT-binding regions within this gene. hTERT alleviated the binding of forkhead box O3 (FOXO3a) to FOXO3a binding element (+9972∼+9978), but it enhanced the binding of forkhead box M1 (FOXM1) to FOXM1 binding element (-1104∼-1109) in ITGB1 gene. Importantly, FOXO3a played a major role in hTERT-induced ITGB1 expression, and the hTERT/murine double minute 2 (MDM2) complex promoted the ubiquitin-mediated degradation of FOXO3a. Moreover, hTERT increased ITGB1 expression in xenograft gastric cancer, and the level of hTERT was positively correlated with that of ITGB1 in human gastric cancer tissues.

CONCLUSIONS

The hTERT/MDM2-FOXO3a-ITGB1 pathway markedly contributes to hTERT-promoted gastric cancer invasion, suggesting that this pathway might be a novel target for the prevention and treatment of gastric cancer metastasis.

From transformation to metastasis: deconstructing the extracellular matrix in breast cancer

The extracellular matrix (ECM) is a guiding force that regulates various developmental stages of the breast. In addition to providing structural support for the cells, it mediates epithelial-stromal communication and provides cues for cell survival, proliferation, and differentiation. Perturbations in ECM architecture profoundly influence breast tumor progression and metastasis. Understanding how a dysregulated ECM can facilitate malignant transformation is crucial to designing treatments to effectively target the tumor microenvironment. Here, we address the contribution of ECM mechanics to breast cancer progression, metastasis, and treatment resistance and discuss potential therapeutic strategies targeting the ECM.

Challenges in the delivery of therapies to melanoma brain metastases

Brain metastases are a major cause of morbidity and mortality in patients with advanced melanoma. Recent approval of several molecularly-targeted agents and biologics has brought hope to patients with this previously untreatable disease. However, patients with symptomatic melanoma brain metastases have often been excluded from pivotal clinical trials. This may be in part attributed to the fact that several of the approved small molecule molecularly-targeted agents are substrates for active efflux at the blood-brain barrier, limiting their effective delivery to brain metastases. We believe that successful treatment of melanoma brain metastases will depend on the ability of these agents to traverse the blood-brain barrier and reach micrometastases that are often not clinically detectable. Moreover, overcoming the emergence of a unique pattern of resistance, possibly through adequate delivery of combination targeted therapies in brain metastases will be important in achieving a durable response. These concepts, and the current challenges in the delivery of new treatments to melanoma brain metastases, are discussed in this review.

CXCL1 from tumor-associated lymphatic endothelial cells drives gastric cancer cell into lymphatic system via activating integrin β1/FAK/AKT signaling

Crosstalk between lymphatic endothelial cells (LECs) and tumor cells in the tumor microenvironment plays a crucial role in tumor metastasis. Our previous study indicated chemokine (C-X-C motif) ligand 1 (CXCL1) from LECs stimulates the metastasis of gastric cancer. However, the mechanism is still unclear. Here, we successfully isolated tumor-associated LECs (T-LECs) and normal LECs (N-LECs) from clinical samples by magnetic-activated cell sorting system (MACS) and proved that CXCL1 expression was elevated in T-LECs compared with N-LECs in situ and vitro. Besides, we demonstrated that CXCL1 secreted by T-LECs promoted the migration, invasion, and adhesion of gastric cancer cells by upregulating integrin β1, MMP2, and MMP9. Furthermore, CXCL1 induced MMP2/9 expression by activating integrin β1-FAK-AKT signaling. In the animal model, CXCL1 overexpressed in LECs increased the lymph node metastasis of gastric cancer. In conclusion, CXCL1 expression in T-LECs was upregulated, and CXCL1 secreted by T-LECs promoted the lymph node metastasis of gastric cancer through integrin β1/FAK/AKT signaling, leading to MMP2 and MMP9 expression. Therefore, CXCL1 produced in T-LECs represents a potentially promising target for treating gastric cancer.

β1 Integrin as a Prognostic and Predictive Marker in Triple-Negative Breast Cancer

Triple negative breast cancer (TNBC) displays higher risk of recurrence and distant metastasis. Due to absence of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2), TNBC lacks clinically established targeted therapies. Therefore, understanding of the mechanism underlying the aggressive behaviors of TNBC is required for the design of individualized strategies and the elongation of overall survival duration. Here, we supported a positive correlation between β1 integrin and malignant behaviors such as cell migration, invasion, and drug resistance. We found that silencing of β1 integrin inhibited cell migration, invasion, and increased the sensitivity to anti-cancer drug. In contrast, activation of β1 integrin increased cell migration, invasion, and decreased the sensitivity to anti-cancer drug. Furthermore, we found that silencing of β1 integrin abolished Focal adhesion kinese (FAK) mediated cell survival. Overexpression of FAK could restore cisplatin-induced apoptosis in β1 integrin-depleted cells. Consistent to in vitro data, β1 integrin expression was also positively correlated with FAK (p = 0.031) in clinical tissue. More importantly, β1 integrin expression was significantly correlated with patient outcome. In summary, our study indicated that β1 integrin could regulate TNBC cells migration, invasion, drug sensitivity, and be a potential prognostic biomarker in TNBC patient survival.

Expression of transmembrane protein 26 (TMEM26) in breast cancer and its association with drug response

We have previously shown that stromal cells desensitize breast cancer cells to the anti-estrogen fulvestrant and, along with it, downregulate the expression of TMEM26 (transmembrane protein 26). In an effort to study the function and regulation of TMEM26 in breast cancer cells, we found that breast cancer cells express non-glycosylated and N-glycosylated isoforms of the TMEM26 protein and demonstrate that N-glycosylation is important for its retention at the plasma membrane. Fulvestrant induced significant changes in expression and in the N-glycosylation status of TMEM26. In primary breast cancer, TMEM26 protein expression was higher in ERα (estrogen receptor α)/PR (progesterone receptor)-positive cancers. These data suggest that ERα is a major regulator of TMEM26. Significant changes in TMEM26 expression and N-glycosylation were also found, when MCF-7 and T47D cells acquired fulvestrant resistance. Furthermore, patients who received aromatase inhibitor treatment tend to have a higher risk of recurrence when tumoral TMEM26 protein expression is low. In addition, TMEM26 negatively regulates the expression of integrin β1, an important factor involved in endocrine resistance. Data obtained by spheroid formation assays confirmed that TMEM26 and integrin β1 can have opposite effects in breast cancer cells. These data are consistent with the hypothesis that, in ERα-positive breast cancer, TMEM26 may function as a tumor suppressor by impeding the acquisition of endocrine resistance. In contrast, in ERα-negative breast cancer, particularly triple-negative cancer, high TMEM26 expression was found to be associated with a higher risk of recurrence. This implies that TMEM26 has different functions in ERα-positive and -negative breast cancer.

Insulin-like growth factor binding protein-3 inhibits cell adhesion via suppression of integrin β4 expression

We previously reported that IGF binding protein-3 (IGFBP-3), a major IGF-binding protein in human serum, regulates angiogenic activities of human head and neck squamous cell carcinoma (HNSCC) cells and human umbilical vein endothelial cells (HUVECs) through IGF-dependent and IGF-independent mechanisms. However, the role of IGFBP-3 in cell adhesion is largely unknown. We demonstrate here that IGFBP-3 inhibits the adhesion of HNSCC cells and HUVECs to the extracellular matrix (ECM). IGFBP-3 reduced transcription of a variety of integrins, especially integrin β₄, and suppressed phosphorylation of focal adhesion kinase (FAK) and Src in these cells through both IGF-dependent and IGF-independent pathways. IGFBP-3 was found to suppress the transcription of c-fos and c-jun and the activity of AP1 transcription factor. The regulatory effect of IGFBP-3 on integrin β₄ transcription was attenuated by blocking c-jun and c-fos gene expression via siRNA transfection. Taken together, our data show that IGFBP-3 has IGF-dependent and -independent inhibitory effects on intracellular adhesion signaling in HNSCC and HUVECs through its ability to block c-jun and c-fos transcription and thus AP-1-mediated integrin β₄ transcription. Collectively, our data suggest that IGFPB-3 may be an effective cancer therapeutic agent by blocking integrin-mediated adhesive activity of tumor and vascular endothelial cells.

NR4A1 Antagonists Inhibit β1-Integrin-Dependent Breast Cancer Cell Migration

Overexpression of the nuclear receptor 4A1 (NR4A1) in breast cancer patients is a prognostic factor for decreased survival and increased metastasis, and this has been linked to NR4A1-dependent regulation of transforming growth factor β (TGF-β) signaling. Results of RNA interference studies demonstrate that basal migration of aggressive SKBR3 and MDA-MB-231 breast cancer cells is TGF-β independent and dependent on regulation of β1-integrin gene expression by NR4A1 which can be inhibited by the NR4A1 antagonists 1,1-bis(3'-indolyl)-1-(p-hydroxyphenyl)methane (DIM-C-pPhOH) and a related p-carboxymethylphenyl [1,1-bis(3'-indolyl)-1-(p-carboxymethylphenyl)methane (DIM-C-pPhCO2Me)] analog. The NR4A1 antagonists also inhibited TGF-β-induced migration of MDA-MB-231 cells by blocking nuclear export of NR4A1, which is an essential step in TGF-β-induced cell migration. We also observed that NR4A1 regulates expression of both β1- and β3-integrins, and unlike other β1-integrin inhibitors which induce prometastatic β3-integrin, NR4A1 antagonists inhibit expression of both β1- and β3-integrin, demonstrating a novel mechanism-based approach for targeting integrins and integrin-dependent breast cancer metastasis.

miR-17-92 plays an oncogenic role and conveys chemo-resistance to cisplatin in human prostate cancer cells

The mir-17-92 cluster consists of six mature miRNAs and is implicated in diverse human cancers by targeting mRNAs involved in distinct pathways that either promote or inhibit carcinogenesis. However, the molecular mechanism underlying the mir-17-92 cluster-mediated pro-tumorigenic or anti-tumorigenic effects has not been clearly elucidated in prostate cancer. In the present study, the role of the mir-17-92 cluster in diverse aspects of prostate cancer cells has been thoroughly investigated. Forced introduction of the mir-17-92 cluster into the androgen-independent DU145 prostate cancer cells evidently promoted cell growth due to disruption of the balance between cellular proliferation and apoptosis. Overexpression of the mir-17-92 cluster significantly improved the migration and invasion of the DU145 cells, attributed to the induction of integrin β-1. Notably, the mir-17-92 cluster conveyed chemo-resistance to cisplatin. We demonstrated that the mir-17-92 cluster suppressed the expression of inhibitor of the AKT signaling pathway and activated the AKT pathway subsequently, which played a central role in regulating cellular proliferation, apoptosis and chemo-resistance. Continuously activated ERK1/2 signaling also contributed importantly to these processes. The present study provides key evidence for crucial oncogenic role of the miR-17-92 cluster in prostate cancer cells. Further investigations are warranted to determine whether miR-17-92 cluster can be targeted for future treatment of human prostate cancer.

New mechanistic insights of integrin β1 in breast cancer bone colonization

Bone metastasis is a frequent and life-threatening complication of breast cancer. The molecular mechanisms supporting the establishment of breast cancer cells in the skeleton are still not fully understood, which may be attributed to the lack of suitable models that interrogate interactions between human breast cancer cells and the bone microenvironment. Although it is well-known that integrins mediate adhesion of malignant cells to bone extracellular matrix, their role during bone colonization remains unclear. Here, the role of β1 integrins in bone colonization was investigated using tissue-engineered humanized in vitro and in vivo bone models. In vitro, bone-metastatic breast cancer cells with suppressed integrin β1 expression showed reduced attachment, spreading, and migration within human bone matrix compared to control cells. Cell proliferation in vitro was not affected by β1 integrin knockdown, yet tumor growth in vivo within humanized bone microenvironments was significantly inhibited upon β1 integrin suppression, as revealed by quantitative in/ex vivo fluorescence imaging and histological analysis. Tumor cells invaded bone marrow spaces in the humanized bone and formed osteolytic lesions; osteoclastic bone resorption was, however, not reduced by β1 integrin knockdown. Taken together, we demonstrate that β1 integrins have a pivotal role in bone colonization using unique tissue-engineered humanized bone models.

Molecular Targeting of Integrins and Integrin-Associated Signaling Networks in Radiation Oncology

Radiation and chemotherapy are the main pillars of the current multimodal treatment concept for cancer patients. However, tumor recurrences and resistances still hamper treatment success regardless of advances in radiation beam application, particle radiotherapy, and optimized chemotherapeutics. To specifically intervene at key recurrence- and resistance-promoting molecular processes, the development of potent and specific molecular-targeted agents is demanded for an efficient, safe, and simultaneous integration into current standard of care regimens. Potential targets for such an approach are integrins conferring structural and biochemical communication between cells and their microenvironment. Integrin binding to extracellular matrix activates intracellular signaling for regulating essential cellular functions such as survival, proliferation, differentiation, adhesion, and cell motility. Tumor-associated characteristics such as invasion, metastasis, and radiochemoresistance also highly depend on integrin function. Owing to their dual functionality and their overexpression in the majority of human malignancies, integrins present ideal and accessible targets for cancer therapy. In the following chapter, the current knowledge on aspects of the tumor microenvironment, the molecular regulation of integrin-dependent radiochemoresistance and current approaches to integrin targeting are summarized.

Hydrogen peroxide regulates cell adhesion through the redox sensor RPSA

To become metastatic, a tumor cell must acquire new adhesion properties that allow migration into the surrounding connective tissue, transmigration across endothelial cells to reach the blood stream and, at the site of metastasis, adhesion to endothelial cells and transmigration to colonize a new tissue. Hydrogen peroxide (H2O2) is a redox signaling molecule produced in tumor cell microenvironment with high relevance for tumor development. However, the molecular mechanisms regulated by H2O2 in tumor cells are still poorly known. The identification of H2O2-target proteins in tumor cells and the understanding of their role in tumor cell adhesion are essential for the development of novel redox-based therapies for cancer. In this paper, we identified Ribosomal Protein SA (RPSA) as a target of H2O2 and showed that RPSA in the oxidized state accumulates in clusters that contain specific adhesion molecules. Furthermore, we showed that RPSA oxidation improves cell adhesion efficiency to laminin in vitro and promotes cell extravasation in vivo. Our results unravel a new mechanism for H2O2-dependent modulation of cell adhesion properties and identify RPSA as the H2O2 sensor in this process. This work indicates that high levels of RPSA expression might confer a selective advantage to tumor cells in an oxidative environment.

The pleiotropic role of exchange protein directly activated by cAMP 1 (EPAC1) in cancer: implications for therapeutic intervention

The pleiotropic second messenger adenosine 3',5'-cyclic monophosphate (cAMP) regulates a myriad of biological processes under both physiological and pathophysiological conditions. Exchange protein directly activated by cAMP 1 (EPAC1) mediates the intracellular functions of cAMP by acting as a guanine nucleotide exchange factor for the Ras-like Rap small GTPases. Recent studies suggest that EPAC1 plays important roles in immunomodulation, cancer cell migration/metastasis, and metabolism. These results, coupled with the successful development of EPAC-specific small molecule inhibitors, identify EPAC1 as a promising therapeutic target for cancer treatments.

β1 Integrins as Therapeutic Targets to Disrupt Hallmarks of Cancer

Integrins belong to a large family of αβ heterodimeric transmembrane proteins first recognized as adhesion molecules that bind to dedicated elements of the extracellular matrix and also to other surrounding cells. As important sensors of the cell microenvironment, they regulate numerous signaling pathways in response to structural variations of the extracellular matrix. Biochemical and biomechanical cues provided by this matrix and transmitted to cells via integrins are critically modified in tumoral settings. Integrins repertoire are subjected to expression level modifications, in tumor cells, and in surrounding cancer-associated cells, implicated in tumor initiation and progression as well. As critical players in numerous cancer hallmarks, defined by Hanahan and Weinberg (2011), integrins represent pertinent therapeutic targets. We will briefly summarize here our current knowledge about integrin implications in those different hallmarks focusing primarily on β1 integrins.

CXCL12/CXCR4 activation by cancer-associated fibroblasts promotes integrin β1 clustering and invasiveness in gastric cancer

Cancer-associated fibroblasts (CAFs) are reportedly involved in invasion and metastasis in several types of cancer, including gastric cancer (GC), through the stimulation of CXCL12/CXCR4 signaling. However, the mechanisms underlying these tumor-promoting effects are not well understood, which limits the potential to develop therapeutic targets against CAF-mediated CXCL12/CXCR4 signaling. CXCL12 expression was analyzed in resected GC tissues from 110 patients by immunohistochemistry (IHC). We established primary cultures of normal fibroblasts (NFs) and CAFs from the GC tissues and examined the functional differences between these primary fibroblasts using co-culture assays with GC cell lines. We evaluated the efficacy of a CXCR4 antagonist (AMD3100) and a FAK inhibitor (PF-573,228) on the invasive ability of GC cells. High CXCL12 expression levels were significantly associated with larger tumor size, increased tumor depth, lymphatic invasion and poor prognosis in GC. CXCL12/CXCR4 activation by CAFs mediated integrin β1 clustering at the cell surface and promoted the invasive ability of GC cells. Notably, AMD3100 was more efficient than PF-573,228 at inhibiting GC cell invasion through the suppression of integrin β1/FAK signaling. These results suggest that CXCL12 derived from CAFs promotes GC cell invasion by enhancing the clustering of integrin β1 in GC cells, resulting in GC progression. Taken together, the inhibition of CXCL12/CXCR4 signaling in GC cells may be a promising therapeutic strategy against GC cell invasion.

Loss of miR-200b promotes invasion via activating the Kindlin-2/integrin β1/AKT pathway in esophageal squamous cell carcinoma: An E-cadherin-independent mechanism

Our previous studies have shown that loss of miR-200b enhances the invasiveness of esophageal squamous cell carcinoma (ESCC) cells. However, whether the miR-200-ZEB1/2-E-cadherin regulatory cascade, a master regulator of epithelial-to-mesenchymal transition (EMT), is involved in the regulation of ESCC invasion remains elusive. Here, we show that miR-200b represses ESCC cell invasion in vivo without altering the expression of E-cadherin and vimentin, two surrogate markers of EMT. However, an inverse correlation was observed between the expression levels of miR-200b and ZEB1/2 in both ESCC cell lines (n = 7, P < 0.05) and ESCC tumor samples (n = 88, P < 0.05). Methylation of E-cadherin gene was found to block the regulation of E-cadherin by the miR-200b-ZEB1/2 axis, indicating that an E-cadherin-independent mechanism can mediate the biological function of miR-200b in ESCC. We revealed that miR-200b suppresses the integrin β1-AKT pathway via targeting Kindlin-2 to mitigate ESCC cell invasiveness. In two independent cohorts of ESCC samples (n = 20 and n = 53, respectively), Kindlin-2 expression positively correlated with the activation status of both the integrin signaling pathway and the PI3K-AKT signaling pathway (both P < 0.01). These data highlight that suppression of the Kindlin-2-integrin β1-AKT regulatory axis is an alternative mechanism underlying the tumor suppressor function of miR-200b in ESCC.

Mechanisms of Cancer Cell Dormancy--Another Hallmark of Cancer?

Disease relapse in cancer patients many years after clinical remission, often referred to as cancer dormancy, is well documented but remains an incompletely understood phenomenon on the biologic level. Recent reviews have summarized potential models that can explain this phenomenon, including angiogenic, immunologic, and cellular dormancy. We focus on mechanisms of cellular dormancy as newer biologic insights have enabled better understanding of this process. We provide a historical context, synthesize current advances in the field, and propose a mechanistic framework that treats cancer cell dormancy as a dynamic cell state conferring a fitness advantage to an evolving malignancy under stress. Cellular dormancy appears to be an active process that can be toggled through a variety of signaling mechanisms that ultimately downregulate the RAS/MAPK and PI(3)K/AKT pathways, an ability that is preserved even in cancers that constitutively depend on these pathways for their growth and survival. Just as unbridled proliferation is a key hallmark of cancer, the ability of cancer cells to become quiescent may be critical to evolving malignancies, with implications for understanding cancer initiation, progression, and treatment resistance.

Beyond RGD: virus interactions with integrins

Viruses successfully infect host cells by initially binding to the surfaces of the cells, followed by an intricate entry process. As multifunctional heterodimeric cell-surface receptor molecules, integrins have been shown to usefully serve as entry receptors for a plethora of viruses. However, the exact role(s) of integrins in viral pathogen internalization has yet to be elaborately described. Notably, several viruses harbor integrin-recognition motifs displayed on viral envelope/capsid-associated proteins. The most common of these motifs is the minimal peptide sequence for binding integrins, RGD (Arg-Gly-Asp), which is known for its role in virus infection via its ability to interact with over half of the more than 20 known integrins. Not all virus-integrin interactions are RGD-dependent, however. Non-RGD-binding integrins have also been shown to effectively promote virus entry and infection as well. Such virus-integrin binding is shown to facilitate adhesion, cytoskeleton rearrangement, integrin activation, and increased intracellular signaling. Also, we have attempted to discuss the role of carbohydrate moieties in virus interactions with receptor-like host cell surface integrins that drive the process of internalization. As much as possible, this article examines the published literature regarding the role of integrins in terms of virus infection and virus-encoded glycosylated proteins that mediate interactions with integrins, and it explores the idea of targeting these receptors as a therapeutic treatment option.

A novel tumor suppressor function of Kindlin-3 in solid cancer

Kindlin-3 (FERMT-3) is known to be central in hemostasis and thrombosis control and its deficiency disrupts platelet aggregation and causes Leukocyte Adhesion Deficiency disease. Here we report that Kindlin-3 has a tumor suppressive role in solid cancer. Our present genetic and functional data show that Kindlin-3 is downregulated in several solid tumors by a mechanism involving gene hypermethylation and deletions. In vivo experiments demonstrated that Kindlin-3 knockdown in 2 tumor cell models (breast cancer and melanoma) markedly increases metastasis formation, in accord with the in vitro increase of tumor cell malignant properties. The metastatic phenotype was supported by a mechanism involving alteration in β3-integrin activation including decreased phosphorylation, interaction with talin and the internalization of its active form leading to less cell attachment and more migration/invasion. These data uncover a novel and unexpected tumor suppressor role of Kindin-3 which can influence integrins targeted therapies development.

Genetic markers of recurrence in colorectal cancer

Colorectal cancer (CRC) worldwide belongs to one of the most frequent cancers affecting both genders. Surgery and 5-fluorouracil-based adjuvant chemotherapy are recommended for patients with high-risk stage II and stage III colon carcinoma. Mutations of genes encoding for specific proteins may have an impact on the time to recurrence. These proteins act over specific signaling pathways, are implicated in metabolic processes and regulate the cell cycle. Though many retrospective studies show strong associations between genetic mutations and the clinical outcome of patients with CRC, currently no validated biomarkers are used in clinical routine settings. Therefore, large prospective validation studies should be carried out in order to strengthen the position of genetic mutations in personalized treatment of patients with CRC.

The tumour microenvironment after radiotherapy: mechanisms of resistance and recurrence

Radiotherapy plays a central part in curing cancer. For decades, most research on improving treatment outcomes has focused on modulating radiation-induced biological effects on cancer cells. Recently, we have better understood that components within the tumour microenvironment have pivotal roles in determining treatment outcomes. In this Review, we describe vascular, stromal and immunological changes that are induced in the tumour microenvironment by irradiation and discuss how these changes may promote radioresistance and tumour recurrence. We also highlight how this knowledge is guiding the development of new treatment paradigms in which biologically targeted agents will be combined with radiotherapy.

Macrolide analog F806 suppresses esophageal squamous cell carcinoma (ESCC) by blocking β1 integrin activation

The paucity of new drugs for the treatment of esophageal squamous cell carcinoma (ESCC) limits the treatment options. This study characterized the therapeutic efficacy and action mechanism of a novel natural macrolide compound F806 in human ESCC xenograft models and cell lines. F806 inhibited growth of ESCC, most importantly, it displayed fewer undesirable side effects on normal tissues in two human ESCC xenograft models. F806 inhibited proliferation of six ESCC cells lines, with the half maximal inhibitory concentration (IC50) ranging from 9.31 to 16.43 μM. Furthermore, F806 induced apoptosis of ESCC cells, contributing to its growth-inhibitory effect. Also, F806 inhibited cell adhesion resulting in anoikis. Mechanistic studies revealed that F806 inhibited the activation of β1 integrin in part by binding to a novel site Arg610 of β1 integrin, suppressed focal adhesion formation, decreased cell adhesion to extracellular matrix and eventually triggered apoptosis. We concluded that F806 would potentially be a well-tolerated anticancer drug by targeting β1 integrin, resulting in anoikis in ESCC cells.

The ZNF304-integrin axis protects against anoikis in cancer

Ovarian cancer (OC) is a highly metastatic disease, but no effective strategies to target this process are currently available. Here, an integrative computational analysis of the Cancer Genome Atlas OC data set and experimental validation identifies a zinc finger transcription factor ZNF304 associated with OC metastasis. High tumoral ZNF304 expression is associated with poor overall survival in OC patients. Through reverse phase protein array analysis, we demonstrate that ZNF304 promotes multiple proto-oncogenic pathways important for cell survival, migration and invasion. ZNF304 transcriptionally regulates β1 integrin, which subsequently regulates Src/focal adhesion kinase and paxillin and prevents anoikis. In vivo delivery of ZNF304 siRNA by a dual assembly nanoparticle leads to sustained gene silencing for 14 days, increased anoikis and reduced tumour growth in orthotopic mouse models of OC. Taken together, ZNF304 is a transcriptional regulator of β1 integrin, promotes cancer cell survival and protects against anoikis in OC.

Role of EGFR expression levels in the regulation of integrin function by EGF

Activation of β1 integrins in dormant tumor cells has been linked to metastatic progression, suggesting that therapies designed to maintain β1 integrins in an inactive state may be useful in the prevention of metastatic disease. Our earlier studies have demonstrated that EGF regulates the activation state of the α5β1 integrin in EGFR overexpressing tumor cells through an ERK/p90RSK signaling pathway. Activation of this pathway by EGF resulted in the filamin A dependent inactivation of the α5β1 integrin receptor for fibronectin. The current study was designed to address the role of EGFR overexpression in the regulation of α5β1 integrin activation state by EGF. Lentiviral knockdown of EGFR coupled with limited dilution cloning was used to develop A431 squamous carcinoma cell lines expressing high, moderate, and low levels of EGFR. Inactivation of α5β1 integrin by EGF was shown to correlate with both the level of EGFR expression and the extent of p90RSK phosphorylation, but not with the level of ERK phosphorylation, suggesting that high levels of EGFR promote α5β1 integrin inactivation through sustained activation of p90RSK. Treatment of cells with EGFR kinase inhibitor resulted in a reactivation of the integrin which could be reversed with the phosphatase inhibitor, menadione. Taken together, these findings indicate that p90RSK may function to maintain dormancy in tumor cells expressing high levels of EGFR. © 2015 Wiley Periodicals, Inc.

Human breast cancer invasion and aggression correlates with ECM stiffening and immune cell infiltration

Tumors are stiff and data suggest that the extracellular matrix stiffening that correlates with experimental mammary malignancy drives tumor invasion and metastasis. Nevertheless, the relationship between tissue and extracellular matrix stiffness and human breast cancer progression and aggression remains unclear. We undertook a biophysical and biochemical assessment of stromal-epithelial interactions in noninvasive, invasive and normal adjacent human breast tissue and in breast cancers of increasingly aggressive subtype. Our analysis revealed that human breast cancer transformation is accompanied by an incremental increase in collagen deposition and a progressive linearization and thickening of interstitial collagen. The linearization of collagen was visualized as an overall increase in tissue birefringence and was most striking at the invasive front of the tumor where the stiffness of the stroma and cellular mechanosignaling were the highest. Amongst breast cancer subtypes we found that the stroma at the invasive region of the more aggressive Basal-like and Her2 tumor subtypes was the most heterogeneous and the stiffest when compared to the less aggressive luminal A and B subtypes. Intriguingly, we quantified the greatest number of infiltrating macrophages and the highest level of TGF beta signaling within the cells at the invasive front. We also established that stroma stiffness and the level of cellular TGF beta signaling positively correlated with each other and with the number of infiltrating tumor-activated macrophages, which was highest in the more aggressive tumor subtypes. These findings indicate that human breast cancer progression and aggression, collagen linearization and stromal stiffening are linked and implicate tissue inflammation and TGF beta.

Integrin genetic variants and stage-specific tumor recurrence in patients with stage II and III colon cancer

Integrins (ITGs) are key elements in cancer biology, regulating tumor growth, angiogenesis and lymphangiogenesis through interactions of the tumor cells with the microenvironment. Moving from the hypothesis that ITGs could have different effects in stage II and III colon cancer, we tested whether a comprehensive panel of germline single-nucleotide polymorphisms (SNPs) in ITG genes could predict stage-specific time to tumor recurrence (TTR). A total of 234 patients treated with 5-fluorouracil-based chemotherapy at the University of Southern California were included in this study. Whole-blood samples were analyzed for germline SNPs in ITG genes using PCR-restriction fragment length polymorphism or direct DNA sequencing. In the multivariable analysis, stage II colon cancer patients with at least one G allele for ITGB3 rs4642 had higher risk of recurrence (hazard ratio (HR)=4.027, 95% confidence interval (95% CI) 1.556-10.421, P=0.004). This association was also significant in the combined stage II-III cohort (HR=1.975, 95% CI 1.194-3.269, P=0.008). The predominant role of ITGB3 rs4642 in stage II diseases was confirmed using recursive partitioning, showing that ITGB3 rs4642 was the most important factor in stage II diseases. In contrast, in stage III diseases the combined analysis of ITGB1 rs2298141 and ITGA4 rs7562325 allowed to identify three distinct prognostic subgroups (P=0.009). The interaction between stage and the combined ITGB1 rs2298141 and ITGA4 rs7562325 on TTR was significant (P=0.025). This study identifies germline polymorphisms in ITG genes as independent stage-specific prognostic markers for stage II and III colon cancer. These data may help to select subgroups of patients who may benefit from ITG-targeted treatments.