Focal adhesion signaling and therapy resistance in cancer

Fibroblast activation in cancer: when seed fertilizes soil

In solid cancers, activated fibroblasts acquire the capacity to provide fertile soil for tumor progression. Specifically, cancer-associated fibroblasts (CAFs) establish a strong relationship with cancer cells. This provides advantages to both cell types: whereas cancer cells initiate and sustain CAF activation, CAFs support cancer cell growth, motility and invasion. This results in tumor progression, metastasis and chemoresistance. Numerous studies have detailed the mechanisms involved in fibroblast activation and cancer progression, some of which are reviewed in this article. Cancer cells and CAFs are "partners in crime", and their interaction is supported by inflammation. An understanding of the enemy, the cancer cell population and its "allies" should provide novel opportunities for targeted-drug development. Graphical Abstract Molecular mechanism of fibroblast activation. a Normal fibroblasts are the most common cell type in the extracellular matrix and are responsible for the synthesis of collagens and fibrilar proteins. Under normal conditions, fibroblasts maintain tissue homeostasis and contribute to proper cell communication and function. Fibroblasts can be activated by a diverse set of factors secreted from cancer or immune cells. Not only growth factors such as TGF-β, PDGF, HGF and FGF but also interleukins, metalloproteinases and reactive oxygen species can promote activation. Likewise, transcriptional factors such as NF-κB and HSF-1 play an important role, as do the gene family of metalloproteinase inhibitors, Timp and the NF-κB subunit, p62. Interestingly, fibroblasts themselves can stimulate cancer cells to support activation further. b Once activated, fibroblasts undergo a phenotype switch and become cancer-associated fibroblasts (CAFs) expressing various markers such as α-SMA, FSP1, vimentin and periostatin. c Recently, the LIF/GP130/IL6-R pathway has been identified as a signaling cascade involved in fibroblast activation. Upon LIF stimulation, JAK is phosphorylated and further activates STAT3, a transcriptional factor that is then translocated into the nucleus where it promotes the transcription of genes responsible for cell growth, differentiation, proliferation and apoptosis. Ruxolitinib can inhibit JAK and prevent STAT3 activation. Further on, the maintenance of JAK activation is supported by epigenetical changes and post-translational modifications. Once pSTAT3 is acetylated by histon acetyltransferase, p300, it leads to the loss of expression of SHP-1, which is a negative regulator of the JAK/STAT pathway. Silencing of SHP-1 steers the constitutive activation of JAK and STAT3.

Genetic analysis of radiation-specific biomarkers in sinonasal squamous cell carcinomas

The aim of this study was to investigate the differences in the gene expression profiles of radiation-sensitive (RS) and radiation-resistant (RR) sinonasal squamous cell carcinoma (SNSCC) and to identify prognostic markers for the radiation reaction of SNSCC. We first examined the differentially expressed genes (DEGs) in RS and RR SNSCC tissues by analyzing clinical samples with GeneChip Human Transcriptome Array 2.0 (HTA 2.0).To understand the functional significance of the molecular changes, we examined the DEGs with Gene Ontology (GO) and pathway analyses to identify the core genes. The expression of several core genes (CCND2, COL5A2, GADD45B, and THBS2) was confirmed with reverse transcription quantitative PCR (RT-qPCR) in a larger series of tissues. We identified 208 DEGs, of which 76 were upregulated and 132 downregulated in the RS tissues relative to the RR tissues. The DEGs were mainly involved in the regulation of cell proliferation, the NF-kappaB signaling pathway, the cell adhesion molecule signaling pathway, and the extracellular matrix-receptor interaction signaling pathway. RT-qPCR confirmed that the CCND2, COL5A2, GADD45B, and THBS2 genes were significantly differentially expressed in the RS and RR tissues, consistent with the GeneChip data. These results extend our understanding of the molecular mechanisms underlying the sensitivity of SNSCC to radiation. The DEGs are involved in the differential response to radiation therapy and the dysregulated core genes identified in this study can be used to predict radiation sensitivity in SNSCC.

The Molecular Architecture of Cell Adhesion: Dynamic Remodeling Revealed by Videonanoscopy

The plasma membrane delimits the cell, which is the basic unit of living organisms, and is also a privileged site for cell communication with the environment. Cell adhesion can occur through cell-cell and cell-matrix contacts. Adhesion proteins such as integrins and cadherins also constitute receptors for inside-out and outside-in signaling within proteolipidic platforms. Adhesion molecule targeting and stabilization relies on specific features such as preferential segregation by the sub-membrane cytoskeleton meshwork and within membrane proteolipidic microdomains. This review presents an overview of the recent insights brought by the latest developments in microscopy, to unravel the molecular remodeling occurring at cell contacts. The dynamic aspect of cell adhesion was recently highlighted by super-resolution videomicroscopy, also named videonanoscopy. By circumventing the diffraction limit of light, nanoscopy has allowed the monitoring of molecular localization and behavior at the single-molecule level, on fixed and living cells. Accessing molecular-resolution details such as quantitatively monitoring components entering and leaving cell contacts by lateral diffusion and reversible association has revealed an unexpected plasticity. Adhesion structures can be highly specialized, such as focal adhesion in motile cells, as well as immune and neuronal synapses. Spatiotemporal reorganization of adhesion molecules, receptors, and adaptors directly relates to structure/function modulation. Assembly of these supramolecular complexes is continuously balanced by dynamic events, remodeling adhesions on various timescales, notably by molecular conformation switches, lateral diffusion within the membrane and endo/exocytosis. Pathological alterations in cell adhesion are involved in cancer evolution, through cancer stem cell interaction with stromal niches, growth, extravasation, and metastasis.

Targeting of β1 integrins impairs DNA repair for radiosensitization of head and neck cancer cells

β1 Integrin-mediated cell-extracellular matrix interactions allow cancer cell survival and confer therapy resistance. It was shown that inhibition of β1 integrins sensitizes cells to radiotherapy. Here, we examined the impact of β1 integrin targeting on the repair of radiation-induced DNA double-strand breaks (DSBs). β1 Integrin inhibition was accomplished using the monoclonal antibody AIIB2 and experiments were performed in three-dimensional cell cultures and tumor xenografts of human head and neck squamous cell carcinoma (HNSCC) cell lines. AIIB2, X-ray irradiation, small interfering RNA-mediated knockdown and Olaparib treatment were performed and residual DSB number, protein and gene expression, non-homologous end joining (NHEJ) activity as well as clonogenic survival were determined. β1 Integrin targeting impaired repair of radiogenic DSB (γH2AX/53BP1, pDNA-PKcs T2609 foci) in vitro and in vivo and reduced the protein expression of Ku70, Rad50 and Nbs1. Further, we identified Ku70, Ku80 and DNA-PKcs but not poly(ADP-ribose) polymerase (PARP)-1 to reside in the β1 integrin pathway. Intriguingly, combined inhibition of β1 integrin and PARP using Olaparib was significantly more effective than either treatment alone in non-irradiated and irradiated HNSCC cells. Here, we support β1 integrins as potential cancer targets and highlight a regulatory role for β1 integrins in the repair of radiogenic DNA damage via classical NHEJ. Further, the data suggest combined targeting of β1 integrin and PARP as promising approach for radiosensitization of HNSCC.

Extracellular matrix component signaling in cancer

Cell responses to the extracellular matrix depend on specific signaling events. These are important from early development, through differentiation and tissue homeostasis, immune surveillance, and disease pathogenesis. Signaling not only regulates cell adhesion cytoskeletal organization and motility but also provides survival and proliferation cues. The major classes of cell surface receptors for matrix macromolecules are the integrins, discoidin domain receptors, and transmembrane proteoglycans such as syndecans and CD44. Cells respond not only to specific ligands, such as collagen, fibronectin, or basement membrane glycoproteins, but also in terms of matrix rigidity. This can regulate the release and subsequent biological activity of matrix-bound growth factors, for example, transforming growth factor-β. In the environment of tumors, there may be changes in cell populations and their receptor profiles as well as matrix constitution and protein cross-linking. Here we summarize roles of the three major matrix receptor types, with emphasis on how they function in tumor progression.

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.

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.

Extracellular matrix stiffness: An important regulatory factor in tumor invasion and metastasis

It has been well documented that biochemical factors of tumor microenvironment like stromal cells, immune cells, cytokines, and chemokines contribute to the regulation of tumor invasion and metastasis. However, the roles of physical factors, especially matrix rigidity or elasticity resulting from abundant matrix protein deposition and cross-linking, remain largely unexplored. Lately, with the establishment of a series of cell culturing platforms mirroring matrix stiffness, a giant leap has been witnessed in the research into mechanisms of matrix stiffness-mediated effects on tumor invasion and metastasis. This article reviews the impact of matrix stiffness on epithelial-mesenchymal transition (EMT), motility, integrin, invasion and metastasis genes, and stemness in tumors, to illustrate that matrix stiffness is also an important factor in the regulation of tumor invasion and metastasis.

Integrin α5β1 and p53 convergent pathways in the control of anti-apoptotic proteins PEA-15 and survivin in high-grade glioma

Integrin α5β1 expression is correlated with a worse prognosis in high-grade glioma. We previously unraveled a negative crosstalk between integrin α5β1 and p53 pathway, which was proposed to be part of the resistance of glioblastoma to chemotherapies. The restoration of p53 tumor-suppressor function is under intensive investigations for cancer therapy. However, p53-dependent apoptosis is not always achieved by p53-reactivating compounds such as Nutlin-3a, although full transcriptional activity of p53 could be obtained. Here we investigated whether integrin α5β1 functional inhibition or repression could sensitize glioma cells to Nutlin-3a-induced p53-dependent apoptosis. We discovered that α5β1 integrin-specific blocking antibodies or small RGD-like antagonists in association with Nutlin-3a triggered a caspase (Casp) 8/Casp 3-dependent strong apoptosis in glioma cells expressing a functional p53. We deciphered the molecular mechanisms involved and we showed the crucial role of two anti-apoptotic proteins, phosphoprotein enriched in astrocytes 15 (PEA-15) and survivin in glioma cell apoptotic outcome. PEA-15 is under α5β1 integrin/AKT (protein kinase B) control and survivin is a p53-repressed target. Moreover, interconnections between integrin and p53 pathways were revealed. Indeed PEA-15 repression by specific small-interfering RNA (siRNA)-activated p53 pathway to repress survivin and conversely survivin repression by specific siRNA decreased α5β1 integrin expression. This pro-apoptotic loop could be generalized to several glioma cell lines, whatever their p53 status, inasmuch PEA-15 and survivin protein levels were decreased. Our findings identify a novel mechanism whereby inhibition of α5β1 integrin and activation of p53 modulates two anti-apoptotic proteins crucially involved in the apoptotic answer of glioma cells. Importantly, our results suggest that high-grade glioma expressing high level of α5β1 integrin may benefit from associated therapies including integrin antagonists and repressors of survivin expression.

Alpha2beta1 integrin in cancer development and chemoresistance

Extracellular matrix, via its receptors the integrins, has emerged as a crucial factor in cancer development. The α2β1 integrin is a major collagen receptor that is widely expressed and known to promote cell migration and control tissue homeostasis. Growing evidence suggests that it can be a key pathway in cancer. Recent studies have shown that α2β1 integrin is a regulator of cancer metastasis either by promoting or inhibiting the dissemination process of cancer cells. The α2β1 integrin signaling can also enhance tumor angiogenesis. Emerging evidence supports a role for α2β1 integrin in cancer chemoresistance especially in hematological malignancies originating from the T cell lineage. In addition, α2β1 integrin has been associated with cancer stem cells. In this review, we will discuss the complex role of α2β1 integrin in these processes. Collagen is a major matrix protein of the tumor microenvironment and thus, understanding how α2β1 integrin regulates cancer pathogenesis is likely to lead to new therapeutic approaches and agents for cancer treatment.

Role of integrin-linked kinase in drug resistance of lung cancer

Objective

The objective of the present investigation was to investigate the role of integrin-linked kinase (ILK) in the gemcitabine-resistant lung cancer cell line A549 and explore the underlying mechanism.

Materials and methods

Gemcitabine-resistant A549 (A549/GemR) cell line was established by pulse-exposed to moderate concentration of gemcitabine (Gem), and the drug resistant index was measured by MTT assay. Expression of ILK in A549/GemR cell line was detected by Western blot and real-time PCR. An ILK gene-silencing cell line was constructed using lentivirus-coated ILK shRNA. MTT assay was used to detect the drug sensitivity of the A549/GemR cell line to Gem after the ILK gene silencing. Western blot was used to measure the expression of E-cadherin, fibronectin, and MRP1 (multidrug resistance-associated protein 1) after silencing the ILK gene.

Result

The drug resistance index of A549/GemR was 13.5, and the messenger RNA and protein level of ILK was increased in A549/GemR. IC₅₀ (half maximal inhibitory concentration) decreased from 14.69 to 4.13 mg/L when ILK was knocked down in A549/GemR. The expression of fibronectin and MRP1 was upregulated and E-cadherin expression was downregulated in A549/GemR, and these changes were reversed after ILK was knocked down.

Conclusion

ILK was involved in drug resistance to Gem in lung cancer, and this function may be mediated by epithelial–mesenchymal transition and the MRP1 pathway.

Bacterial genotoxins promote inside-out integrin β1 activation, formation of focal adhesion complexes and cell spreading

Integrins are membrane bound receptors that regulate several cellular processes, such as cell adhesion, migration, survival and proliferation, and may contribute to tumor initiation/progression in cells exposed to genotoxic stress. The extent of integrin activation and its role in cell survival upon intoxication with bacterial genotoxins are still poorly characterized. These toxins induce DNA strand breaks in the target cells and activate the DNA damage response (DDR), coordinated by the Ataxia Telangectasia Mutated (ATM) kinase. In the present study, we demonstrate that induction of DNA damage by two bacterial genotoxins promotes activation of integrin β1, leading to enhanced assembly of focal adhesions and cell spreading on fibronectin, but not on vitronectin. This phenotype is mediated by an ATM-dependent inside-out integrin signaling, and requires the actin cytoskeleton remodeler NET1. The toxin-mediated cell spreading and anchorage-independent survival further relies on ALIX and TSG101, two components of the endosomal sorting complex required for transport (ESCRT), known to regulate integrin intracellular trafficking. These data reveal a novel aspect of the cellular response to bacterial genotoxins, and provide new tools to understand the carcinogenic potential of these effectors in the context of chronic intoxication and infection.

The role of cytoskeleton and adhesion proteins in the resistance to photodynamic therapy. Possible therapeutic interventions

It is known that Photodynamic Therapy (PDT) induces changes in the cytoskeleton, the cell shape, and the adhesion properties of tumour cells. In addition, these targets have also been demonstrated to be involved in the development of PDT resistance. The reversal of PDT resistance by manipulating the cell adhesion process to substrata has been out of reach. Even though the existence of cell adhesion-mediated PDT resistance has not been reported so far, it cannot be ruled out. In addition to its impact on the apoptotic response to photodamage, the cytoskeleton alterations are thought to be associated with the processes of metastasis and invasion after PDT. In this review, we will address the impact of photodamage on the microfilament and microtubule cytoskeleton components and its regulators on PDT-treated cells as well as on cell adhesion. We will also summarise the impact of PDT on the surviving and resistant cells and their metastatic potential. Possible strategies aimed at taking advantage of the changes induced by PDT on actin, tubulin and cell adhesion proteins by targeting these molecules will also be discussed.