β1 integrin deletion enhances progression of prostate cancer in the TRAMP mouse model

Integrating integrins with the hallmarks of cancer

Epithelial cells adhere to a specialized extracellular matrix called the basement membrane which allows them to polarize and form epithelial tissues. The extracellular matrix provides essential physical scaffolding and biochemical and biophysical cues required for tissue morphogenesis, differentiation, function, and homeostasis. Epithelial cell adhesion to the extracellular matrix (i.e., basement membrane) plays a critical role in organizing epithelial tissues, separating the epithelial cells from the stroma. Epithelial cell detachment from the basement membrane classically results in death, though detachment or invasion through the basement membrane represents a critical step in carcinogenesis. Epithelial cells bind to the extracellular matrix via specialized matrix receptors, including integrins. Integrins are transmembrane receptors that form a mechanical linkage between the extracellular matrix and the intracellular cytoskeleton and are required for anchorage-dependent cellular functions such as proliferation, migration, and invasion. The role of integrins in the development, growth, and dissemination of multiple types of carcinomas has been investigated by numerous methodologies, which has led to great complexity. To organize this vast array of information, we have utilized the "Hallmarks of Cancer" from Hanahan and Weinberg as a convenient framework to discuss the role of integrins in the pathogenesis of cancers. This review explores this biology and how its complexity has impacted the development of integrin-targeted anti-cancer therapeutics.

The Potential of Extracellular Matrix- and Integrin Adhesion Complex-Related Molecules for Prostate Cancer Biomarker Discovery

Prostate cancer is among the top five cancer types according to incidence and mortality. One of the main obstacles in prostate cancer management is the inability to foresee its course, which ranges from slow growth throughout years that requires minimum or no intervention to highly aggressive disease that spreads quickly and resists treatment. Therefore, it is not surprising that numerous studies have attempted to find biomarkers of prostate cancer occurrence, risk stratification, therapy response, and patient outcome. However, only a few prostate cancer biomarkers are used in clinics, which shows how difficult it is to find a novel biomarker. Cell adhesion to the extracellular matrix (ECM) through integrins is among the essential processes that govern its fate. Upon activation and ligation, integrins form multi-protein intracellular structures called integrin adhesion complexes (IACs). In this review article, the focus is put on the biomarker potential of the ECM- and IAC-related molecules stemming from both body fluids and prostate cancer tissue. The processes that they are involved in, such as tumor stiffening, bone turnover, and communication via exosomes, and their biomarker potential are also reviewed.

Integrins Can Act as Suppressors of Ras-Mediated Oncogenesis in the Drosophila Wing Disc Epithelium

Cancer is the second leading cause of death worldwide. Key to cancer initiation and progression is the crosstalk between cancer cells and their microenvironment. The extracellular matrix (ECM) is a major component of the tumour microenvironment and integrins, main cell-ECM adhesion receptors, are involved in every step of cancer progression. However, accumulating evidence has shown that integrins can act as tumour promoters but also as tumour suppressor factors, revealing that the biological roles of integrins in cancer are complex. This incites a better understating of integrin function in cancer progression. To achieve this goal, simple model organisms, such as Drosophila, offer great potential to unravel underlying conceptual principles. Here, we find that in the Drosophila wing disc epithelium the βPS integrins act as suppressors of tumours induced by a gain of function of the oncogenic form of Ras, RasV12. We show that βPS integrin depletion enhances the growth, delamination and invasive behaviour of RasV12 tumour cells, as well as their ability to affect the tumour microenvironment. These results strongly suggest that integrin function as tumour suppressors might be evolutionarily conserved. Drosophila can be used to understand the complex tumour modulating activities conferred by integrins, thus facilitating drug development.

Ligand-independent integrin β1 signaling supports lung adenocarcinoma development

Integrins - the principal extracellular matrix (ECM) receptors of the cell - promote cell adhesion, migration, and proliferation, which are key events for cancer growth and metastasis. To date, most integrin-targeted cancer therapeutics have disrupted integrin-ECM interactions, which are viewed as critical for integrin functions. However, such agents have failed to improve cancer patient outcomes. We show that the highly expressed integrin β1 subunit is required for lung adenocarcinoma development in a carcinogen-induced mouse model. Likewise, human lung adenocarcinoma cell lines with integrin β1 deletion failed to form colonies in soft agar and tumors in mice. Mechanistically, we demonstrate that these effects do not require integrin β1-mediated adhesion to ECM but are dependent on integrin β1 cytoplasmic tail-mediated activation of focal adhesion kinase (FAK). These studies support a critical role for integrin β1 in lung tumorigenesis that is mediated through constitutive, ECM binding-independent signaling involving the cytoplasmic tail.

Targeting Integrins for Cancer Therapy - Disappointments and Opportunities

Integrins mediate adhesive interactions between cells and their environment, including neighboring cells and extracellular matrix (ECM). These heterodimeric transmembrane receptors bind extracellular ligands with their globular head domains and connect to the cytoskeleton through multi-protein interactions at their cytoplasmic tails. Integrin containing cell–matrix adhesions are dynamic force-responsive protein complexes that allow bidirectional mechanical coupling of cells with their environment. This allows cells to sense and modulate tissue mechanics and regulates intracellular signaling impacting on cell faith, survival, proliferation, and differentiation programs. Dysregulation of these functions has been extensively reported in cancer and associated with tumor growth, invasion, angiogenesis, metastasis, and therapy resistance. This central role in multiple hallmarks of cancer and their localization on the cell surface makes integrins attractive targets for cancer therapy. However, despite a wealth of highly encouraging preclinical data, targeting integrin adhesion complexes in clinical trials has thus far failed to meet expectations. Contributing factors to therapeutic failure are 1) variable integrin expression, 2) redundancy in integrin function, 3) distinct roles of integrins at various disease stages, and 4) sequestering of therapeutics by integrin-containing tumor-derived extracellular vesicles. Despite disappointing clinical results, new promising approaches are being investigated that highlight the potential of integrins as targets or prognostic biomarkers. Improvement of therapeutic delivery at the tumor site via integrin binding ligands is emerging as another successful approach that may enhance both efficacy and safety of conventional therapeutics. In this review we provide an overview of recent encouraging preclinical findings, we discuss the apparent disagreement between preclinical and clinical results, and we consider new opportunities to exploit the potential of integrin adhesion complexes as targets for cancer therapy.

Epigenetic down-regulation of integrin α7 increases migratory potential and confers poor prognosis in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a devastating malignancy characterized by invasive growth and rapid recurrence. The identification and inhibition of molecular components leading to this migratory and invasive phenotype are thus essential. Accordingly, a genome-wide expression array analysis was performed on MPM cell lines and a set of 139 genes was identified as differentially expressed in cells with high versus low migratory activity. Reduced expression of the novel tumour suppressor integrin α7 (ITGA7) was found in highly motile cells. A significant negative correlation was observed between ITGA7 transcript levels and average displacement of cells. Forced overexpression of ITGA7 in MPM cells with low endogenous ITGA7 expression inhibited cell motility, providing direct evidence for the regulatory role of ITGA7 in MPM cell migration. MPM cells showed decreased ITGA7 expressions at both transcription and protein levels when compared to non-malignant mesothelial cells. The majority of MPM cell cultures displayed hypermethylation of the ITGA7 promoter when compared to mesothelial cultures. A statistically significant negative correlation between ITGA7 methylation and ITGA7 expression was also observed in MPM cells. While normal human pleura samples unambiguously expressed ITGA7, a varying level of expression was found in a panel of 200 human MPM samples. In multivariate analysis, ITGA7 expression was found to be an independent prognostic factor. Although there was no correlation between histological subtypes and ITGA7 expression, importantly, patients with high tumour cell ITGA7 expression had an increased median overall survival compared to the low- or no-expression groups (463 versus 278 days). In conclusion, our data suggest that ITGA7 is an epigenetically regulated tumour suppressor gene and a prognostic factor in human MPM.

A guide to mechanobiology: Where biology and physics meet

Cells actively sense and process mechanical information that is provided by the extracellular environment to make decisions about growth, motility and differentiation. It is important to understand the underlying mechanisms given that deregulation of the mechanical properties of the extracellular matrix (ECM) is implicated in various diseases, such as cancer and fibrosis. Moreover, matrix mechanics can be exploited to program stem cell differentiation for organ-on-chip and regenerative medicine applications. Mechanobiology is an emerging multidisciplinary field that encompasses cell and developmental biology, bioengineering and biophysics. Here we provide an introductory overview of the key players important to cellular mechanobiology, taking a biophysical perspective and focusing on a comparison between flat versus three dimensional substrates. This article is part of a Special Issue entitled: Mechanobiology.

Inhibitory effects of proton beam irradiation on integrin expression and signaling pathway in human colon carcinoma HT29 cells

Proton radiotherapy has been established as a highly effective modality used in the local control of tumor growth. Although proton radiotherapy is used worldwide to treat several types of cancer clinically with great success due to superior targeting and energy deposition, the detailed regulatory mechanisms underlying the functions of proton radiation are not yet well understood. Accordingly, in the present study, to assess the effects of proton beam on integrin-mediated signaling pathways, we investigated the expression of integrins related to tumor progression and integrin trafficking, and key molecules related to cell adhesion, as well as examining phosphorylation of signaling molecules involved in integrin-mediated signaling pathways. Proton beam irradiation inhibited the increase in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced integrin β1 protein expression and the gene expression of members of the integrin family, such as α5β1, α6β4, αvβ3, and αvβ6 in human colorectal adenocarcinoma HT-29 cells. Simultaneously, the gene expression of cell adhesion molecules, such as FAK and CDH1, and integrin trafficking regulators, such as RAB4, RAB11, and HAX1, was decreased by proton beam irradiation. Moreover, proton beam irradiation decreased the phosphorylation of key molecules involved in integrin signaling, such as FAK, Src, and p130Cas, as well as PKC and MAPK, which are known as promoters of cell migration, while increased the phosphorylation of AMPK and the gene expression of Rab IP4 involved in the inhibition of cell adhesion and cell spreading. Taken together, our findings suggest that proton beam irradiation can inhibit metastatic potential, including cell adhesion and migration, by modulating the gene expression of molecules involved in integrin trafficking and integrin-mediated signaling, which are necessary for tumor progression.

Integrins in development and cancer

The correct control of cell fate decisions is critical for metazoan development and tissue homeostasis. It is established that the integrin family of cell surface receptors regulate cell fate by mediating cell-cell and cell-extracellular matrix (ECM) interactions. However, our understanding of how the different family members control discrete aspects of cell biology, and how this varies between tissues and is temporally regulated, is still in its infancy. An emerging area of investigation aims to understand how integrins translate changes in tension in the surrounding microenvironment into biological responses. This is particularly pertinent due to changes in the mechanical properties of the ECM having been linked to diseases, such as cancer. In this review, we provide an overview of the roles integrins play in important developmental processes, such as proliferation, polarity, apoptosis, differentiation and maintenance of "stemness". We also discuss recent advances in integrin mechanobiology and highlight the involvement of integrins and aberrant ECM in cancer.

Discoidin domain receptor 2 signaling networks and therapy in lung cancer

Discoidin domain receptor 2 (DDR2) is an atypical receptor tyrosine kinase that binds to and is activated by collagen in the extracellular matrix. Recent exon sequencing studies have identified DDR2 to be mutated with a 3% to 4% incidence in squamous cell cancers of the lung. This article summarizes the current state of knowledge of DDR2 biology and signaling in lung squamous cell cancer. It also explores the context-dependent role of this receptor as both an oncogene and a tumor suppressor in cancer cells. Promising therapeutic opportunities based on existing and novel targeted small molecule inhibitors against DDR2 may provide new strategies for treating lung squamous cell cancer patients.

The TMEFF2 tumor suppressor modulates integrin expression, RhoA activation and migration of prostate cancer cells

Cell adhesion and migration play important roles in physiological and pathological states, including embryonic development and cancer invasion and metastasis. The type I transmembrane protein with epidermal growth factor and two follistatin motifs 2 (TMEFF2) is expressed mainly in brain and prostate and its expression is deregulated in prostate cancer. We have previously shown that TMEFF2 can function as a tumor suppressor by inhibiting cell migration and invasion of prostate cells. However, the molecular mechanisms involved in this inhibition are not clear. In this study we demonstrate that TMEFF2 affects cell adhesion and migration of prostate cancer cells and that this effect correlates with changes in integrin expression and RhoA activation. Deletion of a 13 basic-rich amino acid region in the cytoplasmic domain of TMEFF2 prevented these effects. Overexpression of TMEFF2 reduced cell attachment and migration on vitronectin and caused a concomitant decrease in RhoA activation, stress fiber formation and expression of αv, β1 and β3 integrin subunits. Conversely, TMEFF2 interference in 22Rv1 prostate cancer cells resulted in an increased integrin expression. Results obtained with a double TRAMP/TMEFF2 transgenic mouse also indicated that TMEFF2 expression reduced integrin expression in the mouse prostate. In summary, the data presented here indicate an important role of TMEFF2 in regulating cell adhesion and migration that involves integrin signaling and is mediated by its cytoplasmic domain.

Liver-specific knockout of GRP94 in mice disrupts cell adhesion, activates liver progenitor cells, and accelerates liver tumorigenesis

Liver cancer is one of the most common solid tumors, with poor prognosis and high mortality. Mutation or deletion of the tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is strongly correlated with human liver cancer. Glucose-regulated protein 94 (GRP94) is a major endoplasmic reticulum (ER) chaperone protein, but its in vivo function is still emerging. To study the role of GRP94 in maintaining liver homeostasis and tumor development, we created two liver-specific knockout mouse models with the deletion of Grp94 alone, or in combination with Pten, using the albumin-cre system. We demonstrated that while deletion of GRP94 in the liver led to hyperproliferation of liver progenitor cells, deletion of both GRP94 and PTEN accelerated development of liver tumors, including both hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC), suggestive of progenitor cell origin. Furthermore, at the premalignant stage we observed disturbance of cell adhesion proteins and minor liver injury. When GRP94 was deleted in PTEN-null livers, ERK was selectively activated.

CONCLUSION

GRP94 is a novel regulator of cell adhesion, liver homeostasis, and tumorigenesis.

β1 integrin inhibition elicits a prometastatic switch through the TGFβ-miR-200-ZEB network in E-cadherin-positive triple-negative breast cancer

Interactions with the extracellular matrix (ECM) through integrin adhesion receptors provide cancer cells with physical and chemical cues that act together with growth factors to support survival and proliferation. Antagonists that target integrins containing the β1 subunit inhibit tumor growth and sensitize cells to irradiation or cytotoxic chemotherapy in preclinical breast cancer models and are under clinical investigation. We found that the loss of β1 integrins attenuated breast tumor growth but markedly enhanced tumor cell dissemination to the lungs. When cultured in three-dimensional ECM scaffolds, antibodies that blocked β1 integrin function or knockdown of β1 switched the migratory behavior of human and mouse E-cadherin-positive triple-negative breast cancer (TNBC) cells from collective to single cell movement. This switch involved activation of the transforming growth factor-β (TGFβ) signaling network that led to a shift in the balance between miR-200 microRNAs and the transcription factor zinc finger E-box-binding homeobox 2 (ZEB2), resulting in suppressed transcription of the gene encoding E-cadherin. Reducing the abundance of a TGFβ receptor, restoring the ZEB/miR-200 balance, or increasing the abundance of E-cadherin reestablished cohesion in β1 integrin-deficient cells and reduced dissemination to the lungs without affecting growth of the primary tumor. These findings reveal that β1 integrins control a signaling network that promotes an epithelial phenotype and suppresses dissemination and indicate that targeting β1 integrins may have undesirable effects in TNBC.

β1 integrins mediate resistance to ionizing radiation in vivo by inhibiting c-Jun amino terminal kinase 1

This study was carried out to dissect the mechanism by which β1 integrins promote resistance to radiation. For this purpose, we conditionally ablated β1 integrins in the prostatic epithelium of transgenic adenocarcinoma of mouse prostate (TRAMP) mice. The ability of β1 to promote resistance to radiation was also analyzed by using an inhibitory antibody to β1 , AIIB2, in a xenograft model. The role of β1 integrins and of a β1 downstream target, c-Jun amino-terminal kinase 1 (JNK1), in regulating radiation-induced apoptosis in vivo and in vitro was studied. We show that β1 integrins promote prostate cancer (PrCa) progression and resistance to radiation in vivo. Mechanistically, β1 integrins are shown here to suppress activation of JNK1 and, consequently apoptosis, in response to irradiation. Downregulation of JNK1 is necessary to preserve the effect of β1 on resistance to radiation in vitro and in vivo. Finally, given the established crosstalk between β1 integrins and type1 insulin-like growth factor receptor (IGF-IR), we analyzed the ability of IGF-IR to modulate β1 integrin levels. We report that IGF-IR regulates the expression of β1 integrins, which in turn confer resistance to radiation in PrCa cells. In conclusion, this study demonstrates that β1 integrins mediate resistance to ionizing radiation through inhibition of JNK1 activation.

Exogenous SPARC suppresses proliferation and migration of prostate cancer by interacting with integrin β1

BACKGROUND

The matricellular protein secreted protein acidic and rich in cysteine (SPARC) plays an important role on tumor metastasis and progression in several cancers. However, the roles of SPARC in prostate cancer (PCa) remain unclear.

METHODS

To identify SPARC protein in prostate tissue, immunohistochemical analysis of SPARC was conducted using human prostate tissue microarray. To detect SPARC expression in prostate cancer (LNCaP, DU145, and PC-3) and stromal cells, RT-PCR, western blot analysis, and ELISA was conducted. To reveal the function of exogenous SPARC in PCa cells, AKT phosphorylation was confirmed by western blot analysis after coculture with stromal cells. Proliferation and migration of PCa cells were examined by addition of SPARC. The interaction between SPARC and integrin β1 was confirmed by western blot analysis after immunoprecipitation.

RESULTS

SPARC protein was expressed well in normal tissue compared with PCa tissue. ELISA showed high secreted SPARC protein in normal prostate-derived stromal cell (PrSC) compared with PCa-derived stromal cell (PCaSC) and PCa. PCa cells cocultured with PrSC showed reduced AKT phosphorylation more than with PCaSC. PCa cells cocultured with PrSC whose SPARC was knocked-down restored AKT phosphorylation. Moreover, PCa cells treated with SPARC led to reduced AKT phosphorylation. Immunoprecipitation with SPARC revealed interaction of SPARC and integrin β1 in PCa cells. Inhibited proliferation and migration of PCa cells by SPARC was restored by integrin β1 neutralizing antibody.

CONCLUSIONS

Reduced SPARC secretion from stromal cells might affect PCa progression mediating through limiting AKT phosphorylation after interaction with integrin β1.

Integrin Signaling as a Cancer Drug Target

Integrins are transmembrane receptors that mediate cell adhesion to neighboring cells and to the extracellular matrix. Here, the various modes in which integrin-mediated adhesion regulates intracellular signaling pathways impinging on cell survival, proliferation, and differentiation are considered. Subsequently, evidence that integrins also control crucial signaling cascades in cancer cells is discussed. Lastly, the important role of integrin signaling in tumor cells as well as in stromal cells that support cancer growth, metastasis, and therapy resistance indicates that integrin signaling may be an attractive target for (combined) cancer therapy strategies. Current approaches to target integrins in this context are reviewed.

Integrin signaling in control of tumor growth and progression

Interactions with the extracellular matrix (ECM) provide cells with physical and chemical cues that act in concert with growth factors to support survival and proliferation. Transmembrane receptors of the integrin family mediate ECM attachment and play important roles in sensing and responding to ECM properties. Integrin signaling involves large integrin-associated intracellular protein complexes that act as anchors for the cytoskeleton and as signaling hotspots where enzymes and substrates are concentrated. Moreover, many different growth factor signaling cascades are amplified when cells are attached to the ECM. Integrins are involved in many pathologies; here we focus on their roles in cancer. Although "anchorage-independence" is a hallmark of cancer cells, genetic studies clearly show that integrins and associated proteins provide essential support for early tumor development and growth. Integrins also provide support during later stages of tumor progression but in some scenarios they appear to have suppressive activity, which is currently not understood.