Integrins induce activation of EGF receptor: role in MAP kinase induction and adhesion-dependent cell survival

Interplay of Geometric Cues and RGD/BMP-2 Crosstalk in Directing Stem Cell Fate

Within the native microenvironment, extracellular matrix (ECM) components are thought to display a complex and heterogeneous distribution, spanning several length scales. Herein, the objective is to mimic, in vitro, the hierarchical organization of proteins and growth factors as well as their crosstalk. Photolithography technique was used to adjacently pattern geometrically defined regions of RGD and BMP-2 mimetic peptides onto glass substrates. These ECM-derived ligands are known to jointly regulate mesenchymal stem cells (MSCs) osteogenic differentiation. By manipulating the spatial distribution of dually grafted peptides, the extent of human MSCs osteogenic differentiation was significantly affected, depending on the shape of peptide micropatterns. Our data highlight the existence of a strong interplay between geometric cues and biochemical signals. Such in vitro systems provide a valuable tool to investigate mechanisms by which multiple ECM cues overlap to regulate stem cell fate, thereby contributing to the design of bioinspired biomaterials for bone tissue engineering applications.

The cancer cell adhesion resistome: mechanisms, targeting and translational approaches

Cell adhesion-mediated resistance limits the success of cancer therapies and is a great obstacle to overcome in the clinic. Since the 1990s, where it became clear that adhesion of tumor cells to the extracellular matrix is an important mediator of therapy resistance, a lot of work has been conducted to understand the fundamental underlying mechanisms and two paradigms were deduced: cell adhesion-mediated radioresistance (CAM-RR) and cell adhesion-mediated drug resistance (CAM-DR). Preclinical work has evidently demonstrated that targeting of integrins, adapter proteins and associated kinases comprising the cell adhesion resistome is a promising strategy to sensitize cancer cells to both radiotherapy and chemotherapy. Moreover, the cell adhesion resistome fundamentally contributes to adaptation mechanisms induced by radiochemotherapy as well as molecular drugs to secure a balanced homeostasis of cancer cells for survival and growth. Intriguingly, this phenomenon provides a basis for synthetic lethal targeted therapies simultaneously administered to standard radiochemotherapy. In this review, we summarize current knowledge about the cell adhesion resistome and highlight targeting strategies to override CAM-RR and CAM-DR.

EGFR and EGFRvIII Promote Angiogenesis and Cell Invasion in Glioblastoma: Combination Therapies for an Effective Treatment

Epidermal growth factor receptor (EGFR) and the mutant EGFRvIII are major focal points in current concepts of targeted cancer therapy for glioblastoma multiforme (GBM), the most malignant primary brain tumor. The receptors participate in the key processes of tumor cell invasion and tumor-related angiogenesis and their upregulation correlates with the poor prognosis of glioma patients. Glioma cell invasion and increased angiogenesis share mechanisms of the degradation of the extracellular matrix (ECM) through upregulation of ECM-degrading proteases as well as the activation of aberrant signaling pathways. This review describes the role of EGFR and EGFRvIII in those mechanisms which might offer new combined therapeutic approaches targeting EGFR or EGFRvIII together with drug treatments against proteases of the ECM or downstream signaling to increase the inhibitory effects of mono-therapies.

Regulated Entry of Hepatitis C Virus into Hepatocytes

Hepatitis C virus (HCV) is a model for the study of virus–host interaction and host cell responses to infection. Virus entry into hepatocytes is the first step in the HCV life cycle, and this process requires multiple receptors working together. The scavenger receptor class B type I (SR-BI) and claudin-1 (CLDN1), together with human cluster of differentiation (CD) 81 and occludin (OCLN), constitute the minimal set of HCV entry receptors. Nevertheless, HCV entry is a complex process involving multiple host signaling pathways that form a systematic regulatory network; this network is centrally controlled by upstream regulators epidermal growth factor receptor (EGFR) and transforming growth factor β receptor (TGFβ-R). Further feedback regulation and cell-to-cell spread of the virus contribute to the chronic maintenance of HCV infection. A comprehensive and accurate disclosure of this critical process should provide insights into the viral entry mechanism, and offer new strategies for treatment regimens and targets for HCV therapeutics.

Evidence for Integrin - Venus Kinase Receptor 1 Alliance in the Ovary of Schistosoma mansoni Females Controlling Cell Survival

In metazoan integrin signaling is an important process of mediating extracellular and intracellular communication processes. This can be achieved by cooperation of integrins with growth factor receptors (GFRs). Schistosoma mansoni is a helminth parasite inducing schistosomiasis, an infectious disease of worldwide significance for humans and animals. First studies on schistosome integrins revealed their role in reproductive processes, being involved in spermatogenesis and oogenesis. With respect to the roles of eggs for maintaining the parasite´s life cycle and for inducing the pathology of schistosomiasis, elucidating reproductive processes is of high importance. Here we studied the interaction of the integrin receptor Smβ-Int1 with the venus kinase receptor SmVKR1 in S. mansoni. To this end we cloned and characterized SmILK, SmPINCH, and SmNck2, three putative bridging molecules for their role in mediating Smβ-Int1/SmVKR1 cooperation. Phylogenetic analyses showed that these molecules form clusters that are specific for parasitic platyhelminths as it was shown for integrins before. Transcripts of all genes colocalized in the ovary. In Xenopus oocytes germinal vesicle breakdown (GVBD) was only induced if all members were simultaneously expressed. Coimmunoprecipitation results suggest that a Smβ-Int1-SmILK-SmPINCH-SmNck2-SmVKR1 complex can be formed leading to the phosphorylation and activation of SmVKR1. These results indicate that SmVKR1 can be activated in a ligand-independent manner by receptor-complex interaction. RNAi and inhibitor studies to knock-down SmILK as a representative complex member concurrently revealed effects on the extracellular matrix surrounding the ovary and oocyte localization within the ovary, oocyte survival, and egg production. By TUNEL assays, confocal laser scanning microscopy (CLSM), Caspase-3 assay, and transcript profiling of the pro-apoptotic BCL-2 family members BAK/BAX we obtained first evidence for roles of this signaling complex in mediating cell death in immature and primary oocytes. These results suggest that the Smβ-Int1/SmVKR1 signaling complex is important for differentiation and survival in oocytes of paired schistosomes.

Parasites of the genus Schistosoma cause schistosomiasis, a life-threatening infectious disease for humans and animals worldwide. Among the remarkable biological features of schistosomes is the differentiation of the female gonads which is controlled by pairing with the male and a prerequisite for egg production. Eggs, however, are not only important for the maintenance of the life-cycle; they also cause the pathological consequences of schistosomiasis. Part of the eggs gets trapped in host tissues such as liver and spleen and trigger inflammatory processes, finally leading to liver cirrhosis. Research activities of the last decade have indicated that different families of cellular and receptor-type kinases but also integrins contribute to the control of mitogenic activity and differentiation the female goands. In this context an unusual class of receptor tyrosine kinases (RTKs) has been identified, the venus kinase receptors (SmVKRs). By biochemical and molecular approaches we demonstrate that SmVKR1 activation can be achieved by cooperation with a signaling complex consisting of the beta integrin receptor Smβ-Int1 and the bridging molecules SmILK, SmPINCH, SmNck2. Besides unravelling a novel way of SmVKR1 activation, we provide evidence that this complex controls the differentiation status of oocytes by regulating cell death-associated processes.

Integrins and Cell Metabolism: An Intimate Relationship Impacting Cancer

Integrins are important regulators of cell survival, proliferation, adhesion and migration. Once activated, integrins establish a regulated link between the extracellular matrix and the cytoskeleton. Integrins have well-established functions in cancer, such as in controlling cell survival by engagement of many specific intracellular signaling pathways and in facilitating metastasis. Integrins and associated proteins are regulated by control of transcription, membrane traffic, and degradation, as well as by a number of post-translational modifications including glycosylation, allowing integrin function to be modulated to conform to various cellular needs and environmental conditions. In this review, we examine the control of integrin function by cell metabolism, and the impact of this regulation in cancer. Within this context, nutrient sufficiency or deprivation is sensed by a number of metabolic signaling pathways such as AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR) and hypoxia-inducible factor (HIF) 1, which collectively control integrin function by a number of mechanisms. Moreover, metabolic flux through specific pathways also controls integrins, such as by control of integrin glycosylation, thus impacting integrin-dependent cell adhesion and migration. Integrins also control various metabolic signals and pathways, establishing the reciprocity of this regulation. As cancer cells exhibit substantial changes in metabolism, such as a shift to aerobic glycolysis, enhanced glucose utilization and a heightened dependence on specific amino acids, the reciprocal regulation of integrins and metabolism may provide important clues for more effective treatment of various cancers.

β1 integrin signaling in asymmetric migration of keratinocytes under mechanical stretch in a co-cultured wound repair model

Background

Keratinocyte (KC) migration in re-epithelization is crucial in repairing injured skin. But the mechanisms of how mechanical stimuli regulate the migration of keratinocytes have been poorly understood.

Methods

Human immortalized keratinocyte HaCaT cells were co-cultured with skin fibroblasts on PDMS membranes and transferred to the static stretch device developed in-house for additional 6 day culture under mechanical stretch to mimic surface tension in skin. To detect the expression of proteins on different position at different time points and the effect of β1 integrin mechanotransduction on HaCaT migration, Immunofluorescence, Reverse transcription-polymerase chain reaction, Flow cytometry, Western blotting assays were applied.

Results

Mechanical receptor of β1 integrin that recognizes its ligand of collagen I was found to be strongly associated with migration of HaCaT cells since the knockdown of β1 integrin via RNA silence eliminated the key protein expression dynamically. Here the expression of vinculin was lower but that of Cdc42 was higher for the cells at outward edge than those at inward edge, respectively, supporting that the migration capability of keratinocytes is inversely correlated with the formation of focal adhesion complexes but positively related to the lamellipodia formation. This asymmetric expression feature was further confirmed by high or low expression of PI3K for outward- or inward-migrating cells. And ERK1/2 phosphorylation was up-regulated by mechanical stretch.

Conclusion

We reported here, a novel mechanotransduction signaling pathways were β1 integrin-dependent pattern of keratinocytes migration under static stretch in an in vitro co-culture model. These results provided an insight into underlying molecular mechanisms of keratinocyte migration under mechanical stimuli.

Integrins in the Spotlight of Cancer

Integrins are heterodimeric cell surface receptors that bind to different extracellular ligands depending on their composition and regulate all processes which enable multicellular life. In cancer, integrins trigger and play key roles in all the features that were once described as the Hallmarks of Cancer. In this review, we will discuss the contribution of integrins to these hallmarks, including uncontrolled and limitless proliferation, invasion of tumor cells, promotion of tumor angiogenesis and evasion of apoptosis and resistance to growth suppressors, by highlighting the latest findings. Further on, given the paramount role of integrins in cancer, we will present novel strategies for integrin inhibition that are starting to emerge, promising a hopeful future regarding cancer treatment.

Murine Polyomavirus Cell Surface Receptors Activate Distinct Signaling Pathways Required for Infection

Virus binding to the cell surface triggers an array of host responses, including activation of specific signaling pathways that facilitate steps in virus entry. Using mouse polyomavirus (MuPyV), we identified host signaling pathways activated upon virus binding to mouse embryonic fibroblasts (MEFs). Pathways activated by MuPyV included the phosphatidylinositol 3-kinase (PI3K), FAK/SRC, and mitogen-activated protein kinase (MAPK) pathways. Gangliosides and α4-integrin are required receptors for MuPyV infection. MuPyV binding to both gangliosides and the α4-integrin receptors was required for activation of the PI3K pathway; however, either receptor interaction alone was sufficient for activation of the MAPK pathway. Using small-molecule inhibitors, we confirmed that the PI3K and FAK/SRC pathways were required for MuPyV infection, while the MAPK pathway was dispensable. Mechanistically, the PI3K pathway was required for MuPyV endocytosis, while the FAK/SRC pathway enabled trafficking of MuPyV along microtubules. Thus, MuPyV interactions with specific cell surface receptors facilitate activation of signaling pathways required for virus entry and trafficking. Understanding how different viruses manipulate cell signaling pathways through interactions with host receptors could lead to the identification of new therapeutic targets for viral infection.

Virus binding to cell surface receptors initiates outside-in signaling that leads to virus endocytosis and subsequent virus trafficking. How different viruses manipulate cell signaling through interactions with host receptors remains unclear, and elucidation of the specific receptors and signaling pathways required for virus infection may lead to new therapeutic targets. In this study, we determined that gangliosides and α4-integrin mediate mouse polyomavirus (MuPyV) activation of host signaling pathways. Of these pathways, the PI3K and FAK/SRC pathways were required for MuPyV infection. Both the PI3K and FAK/SRC pathways have been implicated in human diseases, such as heart disease and cancer, and inhibitors directed against these pathways are currently being investigated as therapies. It is possible that these pathways play a role in human PyV infections and could be targeted to inhibit PyV infection in immunosuppressed patients.

Guidance of Signaling Activations by Cadherins and Integrins in Epithelial Ovarian Cancer Cells

Epithelial ovarian cancer (EOC) is the deadliest tumor among gynecological cancer in the industrialized countries. The EOC incidence and mortality have remained unchanged over the last 30 years, despite the progress in diagnosis and treatment. In order to develop novel and more effective therapeutic approaches, the molecular mechanisms involved in EOC progression have been thoroughly investigated in the last few decades. At the late stage, peritoneal metastases originate from the attachment of small clusters of cancer cells that shed from the primary site and carried by the ascites adhere to the abdominal peritoneum or omentum. This behavior suggests that cell–cell or cell–matrix adhesion mechanisms regulate EOC growth and dissemination. Complex downstream signalings, which might be influenced by functional cross-talk between adhesion molecules and co-expressed and activated signaling proteins, can affect the proliferation/survival and the migration/invasion of EOC cells. This review aimed to define the impact of the mechanisms of cell–cell, through cadherins, and cell–extracellular matrix adhesion, through integrins, on the signaling cascades induced by membrane receptors and cytoplasmic proteins known to have a role in the proliferation, migration and invasion of EOC cells. Finally, some novel approaches using peptidomimetic ligands to cadherin and integrins are summarized.

The histone H3K9 demethylase KDM3A promotes anoikis by transcriptionally activating pro-apoptotic genes BNIP3 and BNIP3L

Epithelial cells that lose attachment to the extracellular matrix undergo a specialized form of apoptosis called anoikis. Here, using large-scale RNA interference (RNAi) screening, we find that KDM3A, a histone H3 lysine 9 (H3K9) mono- and di-demethylase, plays a pivotal role in anoikis induction. In attached breast epithelial cells, KDM3A expression is maintained at low levels by integrin signaling. Following detachment, integrin signaling is decreased resulting in increased KDM3A expression. RNAi-mediated knockdown of KDM3A substantially reduces apoptosis following detachment and, conversely, ectopic expression of KDM3A induces cell death in attached cells. We find that KDM3A promotes anoikis through transcriptional activation of BNIP3 and BNIP3L, which encode pro-apoptotic proteins. Using mouse models of breast cancer metastasis we show that knockdown of Kdm3a enhances metastatic potential. Finally, we find defective KDM3A expression in human breast cancer cell lines and tumors. Collectively, our results reveal a novel transcriptional regulatory program that mediates anoikis.

DOI:http://dx.doi.org/10.7554/eLife.16844.001

Epithelial cells line the inside of blood vessels, intestines and other organs throughout the body. Any epithelial cells that become detached from their natural surroundings die by a process called anoikis (a Greek word meaning “being without a home”). This process has an important role in preventing cancer from spreading around the body because it eliminates cells that are not in their proper environment. However, some cancers that start from epithelial cells, such as breast cancer, develop resistance to anoikis. Gaining a better understanding of the cellular factors that regulate anoikis, and how resistance develops, may reveal new drug targets for the treatment of breast cancer.

Previous studies found proteins called BIM and BMF promote anoikis by inducing cell suicide. However, it is possible that other factors can also promote this process in different ways. Pedanou et al. performed a large-scale genetic screen in human breast epithelial cells and identified several new factors that promote anoikis.

Inside our cells, DNA is packaged around proteins called histones, which can influence whether a gene is switched on or off. One of the factors Pedanou et al. identified is a protein called KDM3A that can remove small chemical groups (known as methyl groups) from histones – a process that is known to switch on genes. Further experiments show that epithelial cells in their natural surroundings only produce low levels of KDM3A, but that the levels of this protein increase if these cells become detached. This promotes anoikis by activating two genes called BNIP3 and BNIP3L that induce cell suicide. However, KDM3A levels are low in human breast cancers, which suggests that these cancers become resistant to anoikis by preventing increases in KDM3A production.

Using a mouse model of breast cancer, Pedanou et al. found that switching off KDM3A in cancer cells increases their ability to move around the body. Collectively, these findings reveal a new mechanism that triggers anoikis in normal breast epithelial cells and is disabled during breast cancer development. Future challenges are to identify factors that directly regulate the production of KDM3A, and to understand how these factors are manipulated in breast cancer cells to cause anoikis resistance.

DOI:http://dx.doi.org/10.7554/eLife.16844.002

WISP-1 a novel angiogenic regulator of the CCN family promotes oral squamous cell carcinoma angiogenesis through VEGF-A expression

Oral squamous cell carcinoma (OSCC), which accounts for nearly 90% of head and neck cancers, is characterized by poor prognosis and a low survival rate. VEGF-A is the most established angiogenic factor involved in the angiogenic-regulated tumor progression. WISP-1/CCN4 is an extracellular matrix-related protein that belongs to the Cyr61, CTGF, Nov (CCN) family and regulates many biological functions, such as angiogenesis. Previous studies indicated the role of WISP-1 in tumor progression. However, the angiogenic property of WISP-1 in the cancer microenvironment has never been discussed. Here, we provide novel insights regarding the role of WISP-1 in the angiogenesis through promoting VEGF-A expression. In this study, the correlation of WISP-1 and VEGF-A was confirmed by IHC staining of specimens from patients with OSCC. In vitro results indicated that WISP-1 induced VEGF-A expression via the integrin αvβ3/FAK/c-Src pathway, which transactivates the EGFR/ERK/HIF1-α signaling pathway in OSCC. This pathway in turn induces the recruitment of endothelial progenitor cells and triggers the neovascularization in the tumor microenvironment. Our in vivo data revealed that tumor-secreted WISP-1 promoted the angiogenesis through VRGF expression and increased angiogenesis-related tumor growth. Our study offers new information that highlights WISP-1 as a potential novel therapeutic target for OSCC.

Tuning Mesenchymal Stem Cell Response onto Titanium-Niobium-Hafnium Alloy by Recombinant Fibronectin Fragments

Since metallic biomaterials used for bone replacement possess low bioactivity, the use of cell adhesive moieties is a common strategy to improve cellular response onto these surfaces. In recent years, the use of recombinant proteins has emerged as an alternative to native proteins and short peptides owing to the fact that they retain the biological potency of native proteins, while improving their stability. In the present study, we investigated the biological effect of two different recombinant fragments of fibronectin, spanning the 8-10th and 12-14th type III repeats, covalently attached to a new TiNbHf alloy using APTES silanization. The fragments were studied separately and mixed at different concentrations and compared to a linear RGD, a cyclic RGD and the full-length fibronectin protein. Cell culture studies using rat mesenchymal stem cells demonstrated that low to medium concentrations (30% and 50%) of type III 8-10th fragment mixed with type III 12-14th fragment stimulated cell spreading and proliferation compared to RGD peptides and the fragments separately. On the other hand, type III 12-14th fragment alone or mixed at low volume percentages ≤50% with type III 8-10th fragment increased alkaline phosphatase levels compared to the other molecules. These results are significant for the understanding of the role of fibronectin recombinant fragments in cell responses and thus to design bioactive coatings for biomedical applications.

Stiff substrates increase YAP-signaling-mediated matrix metalloproteinase-7 expression

Abnormally stiff substrates have been shown to trigger cancer progression. However, the detailed molecular mechanisms underlying this trigger are not clear. In this study, we cultured T84 human colorectal cancer cells on plastic dishes to create a stiff substrate or on collagen-I gel to create a soft substrate. The stiff substrate enhanced the expression of matrix metalloproteinase-7 (MMP-7), an indicator of poor prognosis. In addition, we used polyacrylamide gels (2, 67 and 126 kPa) so that the MMP-7 expression on the 126-kPa gel was higher compared with that on the 2-kPa gel. Next, we investigated whether yes-associated protein (YAP) affected the MMP-7 expression. YAP knockdown decreased MMP-7 expression. Treatment with inhibitors of epidermal growth factor receptor (EGFR) and myosin regulatory light chain (MRLC) and integrin-α2 or integrin-β1 knockdown downregulated MMP-7 expression. Finally, we demonstrated that YAP, EGFR, integrin-α2β1 and MRLC produced a positive feedback loop that enhanced MMP-7 expression. These findings suggest that stiff substrates enhanced colorectal cancer cell viability by upregulating MMP-7 expression through a positive feedback loop.

Xyloglucan from Tropaeolum majus Seeds Induces Cellular Differentiation of Human Keratinocytes by Inhibition of EGFR Phosphorylation and Decreased Activity of Transcription Factor CREB

Xyloglucan XG (molecular weight 462 kDa, 1,4-/1,4,6-(pGlc) linked backbone, side chains of 1-pXyl, 1,2-pXyl, 1-p-Gal) was isolated from the seeds of Tropaeolum majus. XG (100 μg/mL) induced terminal cellular differentiation of human keratinocytes, as demonstrated by immunofluorescence staining and Western blot using cytokeratin 10 and involucrin as marker proteins. Differentiation was also induced by XG-derived oligosaccharides (degree of polymerization 7-9). Quantitative real-time polymerase chain reaction (qPCR) revealed the induction of gene expression of typical differentiation markers (cytokeratin, filaggrin, involucrin, loricrin, transglutaminase) in a time-dependent manner. Whole human genome microarray indicated that most of upregulated genes were related to differentiation processes. Microarray findings on selected genes were subsequently confirmed by qPCR. For identification of the molecular target of xyloglucan PAGE of keratinocyte membrane preparations was performed, followed by blotting with fluorescein isothiocyanate-labeled XG. XG interacting proteins were characterized by MS. Peptide fragments of epidermal growth factor receptor (EGFR) and integrin β4 were identified. Subsequent phospho-kinase array indicated that phosphorylation of EGFR and transcription factor cAMP response element-binding protein (CREB) was decreased in the XG-treated cells. Thus, the XG-induced differentiation of keratinocytes is proposed to be mediated by the inhibition of the phosphorylation of EGFR, leading to a dimished CREB activation, which is essential for the activation of cellular differentiation.

Regulation of integrin and growth factor signaling in biomaterials for osteodifferentiation

Stem cells respond to the microenvironment (niche) they are located in. Under natural conditions, the extracellular matrix (ECM) is the essential component the in stem cell niche, in which both integrin ligands and growth factors are important regulators to directly or indirectly modulate the cell behavior. In this review, we summarize the current knowledge about the potential of integrin ligands and growth factors to induce osteogenic differentiation of stem cells, and discuss the signaling pathways that are initiated by both individual and cooperative parameters. The joint effect of integrin ligands and growth factors is highlighted as the multivalent interactions for bone therapy.

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.

How does the pathophysiological context influence delivery of bone growth factors?

"Orthobiologics" represents an important category of therapeutics for the regeneration of bone defects caused by injuries or diseases, and bone growth factors are a particularly rapidly growing sub-category. Clinical application of bone growth factors has accelerated in the last two decades with the introduction of BMPs into clinical bone repair. Optimal use of growth factor-mediated treatments heavily relies on controlled delivery, which can substantially influence the local growth factor dose, release kinetics, and biological activity. The characteristics of the surrounding environment, or "context", during delivery can dictate growth factor loading efficiency, release and biological activity. This review discusses the influence of the surrounding environment on therapeutic delivery of bone growth factors. We specifically focus on pathophysiological components, including soluble components and cells, and how they can actively influence the therapeutic delivery and perhaps efficacy of bone growth factors.

The Extracellular Matrix Regulates Granuloma Necrosis in Tuberculosis

A central tenet of tuberculosis pathogenesis is that caseous necrosis leads to extracellular matrix destruction and bacterial transmission. We reconsider the underlying mechanism of tuberculosis pathology and demonstrate that collagen destruction may be a critical initial event, causing caseous necrosis as opposed to resulting from it. In human tuberculosis granulomas, regions of extracellular matrix destruction map to areas of caseous necrosis. In mice, transgenic expression of human matrix metalloproteinase 1 causes caseous necrosis, the pathological hallmark of human tuberculosis. Collagen destruction is the principal pathological difference between humanised mice and wild-type mice with tuberculosis, whereas the release of proinflammatory cytokines does not differ, demonstrating that collagen breakdown may lead to cell death and caseation. To investigate this hypothesis, we developed a 3-dimensional cell culture model of tuberculosis granuloma formation, using bioelectrospray technology. Collagen improved survival of Mycobacterium tuberculosis-infected cells analyzed on the basis of a lactate dehydrogenase release assay, propidium iodide staining, and measurement of the total number of viable cells. Taken together, these findings suggest that collagen destruction is an initial event in tuberculosis immunopathology, leading to caseous necrosis and compromising the immune response, revealing a previously unappreciated role for the extracellular matrix in regulating the host-pathogen interaction.

Focal adhesion signaling and therapy resistance in cancer

Interlocking gene mutations, epigenetic alterations and microenvironmental features perpetuate tumor development, growth, infiltration and spread. Consequently, intrinsic and acquired therapy resistance arises and presents one of the major goals to solve in oncologic research today. Among the myriad of microenvironmental factors impacting on cancer cell resistance, cell adhesion to the extracellular matrix (ECM) has recently been identified as key determinant. Despite the differentiation between cell adhesion-mediated drug resistance (CAMDR) and cell adhesion-mediated radioresistance (CAMRR), the underlying mechanisms share great overlap in integrin and focal adhesion hub signaling and differ further downstream in the complexity of signaling networks between tumor entities. Intriguingly, cell adhesion to ECM is per se also essential for cancer cells similar to their normal counterparts. However, based on the overexpression of focal adhesion hub signaling receptors and proteins and a distinct addiction to particular integrin receptors, targeting of focal adhesion proteins has been shown to potently sensitize cancer cells to different treatment regimes including radiotherapy, chemotherapy and novel molecular therapeutics. In this review, we will give insight into the role of integrins in carcinogenesis, tumor progression and metastasis. Additionally, literature and data about the function of focal adhesion molecules including integrins, integrin-associated proteins and growth factor receptors in tumor cell resistance to radio- and chemotherapy will be elucidated and discussed.

Intestinal trefoil factor activates the PI3K/Akt signaling pathway to protect gastric mucosal epithelium from damage

Intestinal trefoil factor (ITF, also named as trefoil factor 3, TFF3) is a member of the TFF-domain peptide family, which plays an essential role in the regulation of cell survival, cell migration and maintains mucosal epithelial integrity in the gastrointestinal tract. However, the underlying mechanisms and associated molecules remain unclear. The aim of this study was to explore the protective effects of ITF on gastric mucosal epithelium injury and its possible molecular mechanisms of action. In the present study, we show that ITF was able to promote the proliferation and migration of GES-1 cells via a mechanism that involves the PI3K/Akt signaling pathway. Western blot results indicated that ITF induced a dose- and time-dependent increase in the Akt signaling pathway. ITF also plays an essential role in the restitution of GES-1 cell damage induced by lipopolysaccharide (LPS). LPS induced the apoptosis of GES-1 cells, decreased cell viability significantly (P<0.01) and led to epithelial tight junction damage, which is attenuated via ITF treatment. The protective effect of ITF on the integrity of GES-1 was abrogated by inhibition of the PI3K/Akt pathway. Taken together, our results demonstrate that ITF promotes the proliferation and migration of gastric mucosal epithelial cells and preserves gastric mucosal epithelial integrity after damage is mediated by activation of the PI3K/Akt signaling pathway. This study suggested that the PI3K/Akt pathway could act as a key intracellular pathway in the gastric mucosal epithelium that may serve as a therapeutic target to preserve epithelial integrity during injury.

Knockdown and knockout of β1-integrin in hepatocytes impairs liver regeneration through inhibition of growth factor signalling

The liver has a unique regenerative capability, which involves extensive remodelling of cell-cell and cell-matrix contacts. Here we study the role of integrins in mouse liver regeneration using Cre/loxP-mediated gene deletion or intravenous delivery of β1-integrin siRNA formulated into nanoparticles that predominantly target hepatocytes. We show that although short-term loss of β1-integrin has no obvious consequences for normal livers, partial hepatectomy leads to severe liver necrosis and reduced hepatocyte proliferation. Mechanistically, loss of β1-integrin in hepatocytes impairs ligand-induced phosphorylation of the epidermal growth factor and hepatocyte growth factor receptors, thereby attenuating downstream receptor signalling in vitro and in vivo. These results identify a crucial role and novel mechanism of action of β1-integrins in liver regeneration and demonstrate that protein depletion by nanoparticle-based delivery of specific siRNA is a powerful strategy to study gene function in the regenerating liver.

Redox circuitries driving Src regulation

SIGNIFICANCE

Here, we review recent advances with regard to the role of Src kinase in the regulation of cytoskeleton organization, cell adhesion, and motility, focusing on redox circuitries engaging this kinase for anchorage and motility, control of cell survival to anoikis, as well as metabolic deregulation, all features belonging to the new hallmarks of cancer.

RECENT ADVANCES

Several recent insights have reported that, alongside the well-known phosphorylation/dephosphorylation control, cysteine oxidation is a further mechanism of enzyme activation for both c-Src kinase and its oncogenic counterparts. Indeed, mounting evidence portrays redox regulation of Src kinase as a compulsory outcome in growth factors/cytokines signaling, integrin engagement, motility and invasiveness of tissues, receptor cross-talking at plasmamembrane, as well as during carcinogenesis and progression toward tumor malignancy or fibrotic disease. In addition, the kinase is an upstream regulator of NADPH oxidase-driven oxidants, a critical step for invadopodia formation and metastatic spread.

CRITICAL ISSUES

Not satisfactorily unraveled yet, the exact role of Src kinase in redox cancer biology needs to be implemented with studies that are aimed at clarifying (i) the exact hierarchy between oxidants sources, Src redox-dependent activation and the regulation of cell motility, and (ii) the actual susceptibility of invading cells to redox-based treatments, owing to the well-recognized ability of cancer cells to find new strategies to adapt to new environments.

FUTURE DIRECTIONS

Once these critical issues are addressed, redox circuitries involving Src kinase should potentially be used as both biomarkers and targets for personalized therapies in the fight against cancer or fibrotic diseases.

Involvement of urokinase-type plasminogen activator system in cancer: an overview

Currently, there are several studies supporting the role of urokinase-type plasminogen activator (uPA) system in cancer. The association of uPA to its receptor triggers the conversion of plasminogen into plasmin. This process is regulated by the uPA inhibitors (PAI-1 and PAI-2). Plasmin promotes degradation of basement membrane and extracellular matrix (ECM) components as well as activation of ECM latent matrix metalloproteases. Degradation and remodeling of the surrounding tissues is crucial in the early steps of tumor progression by facilitating expansion of the tumor mass, release of tumor growth factors, activation of cytokines as well as induction of tumor cell proliferation, migration, and invasion. Hence, many tumors showed a correlation between uPA system component levels and tumor aggressiveness and survival. Therefore, this review summarizes the structure of the uPA system, its contribution to cancer progression, and the clinical relevance of uPA family members in cancer diagnosis. In addition, the review evaluates the significance of uPA system in the development of cancer-targeted therapies.

α6 integrin transactivates insulin-like growth factor receptor-1 (IGF-1R) to regulate caspase-3-mediated lens epithelial cell differentiation initiation

The canonical mitochondrial death pathway was first discovered for its role in signaling apoptosis. It has since been found to have a requisite function in differentiation initiation in many cell types including the lens through low level activation of the caspase-3 protease. The ability of this pathway to function as a molecular switch in lens differentiation depends on the concurrent induction of survival molecules in the Bcl-2 and IAP families, induced downstream of an IGF-1R/NFκB coordinate survival signal, to regulate caspase-3 activity. Here we investigated whether α6 integrin signals upstream to this IGF-1R-mediated survival-linked differentiation signal. Our findings show that IGF-1R is recruited to and activated specifically in α6 integrin receptor signaling complexes in the lens equatorial region, where lens epithelial cells initiate their differentiation program. In studies with both α6 integrin knock-out mice lenses and primary lens cell cultures following α6 integrin siRNA knockdown, we show that IGF-1R activation is dependent on α6 integrin and that this transactivation requires Src kinase activity. In addition, without α6 integrin, activation and expression of NFκB was diminished, and expression of Bcl-2 and IAP family members were down-regulated, resulting in high levels of caspase-3 activation. As a result, a number of hallmarks of lens differentiation failed to be induced; including nuclear translocation of Prox1 in the differentiation initiation zone and apoptosis was promoted. We conclude that α6 integrin is an essential upstream regulator of the IGF-1R survival pathway that regulates the activity level of caspase-3 for it to signal differentiation initiation of lens epithelial cells.

Novel strategies for the treatment of chondrosarcomas: targeting integrins

Chondrosarcomas are a heterogeneous group of malignant bone tumors that are characterized by the production of cartilaginous extracellular matrix. They are the second most frequently occurring type of bone malignancy. Surgical resection remains the primary mode of treatment for chondrosarcomas, since conventional chemotherapy and radiotherapy are largely ineffective. Treatment of patients with high-grade chondrosarcomas is particularly challenging, owing to the lack of effective adjuvant therapies. Integrins are cell surface adhesion molecules that regulate a variety of cellular functions. They have been implicated in the initiation, progression, and metastasis of solid tumors. Deregulation of integrin expression and/or signaling has been identified in many chondrosarcomas. Therefore, the development of new drugs that can selectively target regulators of integrin gene expression and ligand-integrin signaling might hold great promise for the treatment of these cancers. In this review, we provide an overview of the current understanding of how growth factors, chemokines/cytokines, and other inflammation-related molecules can control the expression of specific integrins to promote cell migration. We also review the roles of specific subtypes of integrins and their signaling mechanisms, and discuss how these might be involved in tumor growth and metastasis. Finally, novel therapeutic strategies for targeting these molecules will be discussed.

Role of ion transport in control of apoptotic cell death

Cell shrinkage is a hallmark and contributes to signaling of apoptosis. Apoptotic cell shrinkage requires ion transport across the cell membrane involving K(+) channels, Cl(-) or anion channels, Na(+)/H(+) exchange, Na(+),K(+),Cl(-) cotransport, and Na(+)/K(+)ATPase. Activation of K(+) channels fosters K(+) exit with decrease of cytosolic K(+) concentration, activation of anion channels triggers exit of Cl(-), organic osmolytes, and HCO3(-). Cellular loss of K(+) and organic osmolytes as well as cytosolic acidification favor apoptosis. Ca(2+) entry through Ca(2+)-permeable cation channels may result in apoptosis by affecting mitochondrial integrity, stimulating proteinases, inducing cell shrinkage due to activation of Ca(2+)-sensitive K(+) channels, and triggering cell-membrane scrambling. Signaling involved in the modification of cell-volume regulatory ion transport during apoptosis include mitogen-activated kinases p38, JNK, ERK1/2, MEKK1, MKK4, the small G proteins Cdc42, and/or Rac and the transcription factor p53. Osmosensing involves integrin receptors, focal adhesion kinases, and tyrosine kinase receptors. Hyperosmotic shock leads to vesicular acidification followed by activation of acid sphingomyelinase, ceramide formation, release of reactive oxygen species, activation of the tyrosine kinase Yes with subsequent stimulation of CD95 trafficking to the cell membrane. Apoptosis is counteracted by mechanisms involved in regulatory volume increase (RVI), by organic osmolytes, by focal adhesion kinase, and by heat-shock proteins. Clearly, our knowledge on the interplay between cell-volume regulatory mechanisms and suicidal cell death is still far from complete and substantial additional experimental effort is needed to elucidate the role of cell-volume regulatory mechanisms in suicidal cell death.

HRas signal transduction promotes hepatitis C virus cell entry by triggering assembly of the host tetraspanin receptor complex

Hepatitis C virus (HCV) entry is dependent on coreceptor complex formation between the tetraspanin superfamily member CD81 and the tight junction protein claudin-1 (CLDN1) on the host cell membrane. The receptor tyrosine kinase EGFR acts as a cofactor for HCV entry by promoting CD81-CLDN1 complex formation via unknown mechanisms. We identify the GTPase HRas, activated downstream of EGFR signaling, as a key host signal transducer for EGFR-mediated HCV entry. Proteomic analysis revealed that HRas associates with tetraspanin CD81, CLDN1, and the previously unrecognized HCV entry cofactors integrin β1 and Ras-related protein Rap2B in hepatocyte membranes. HRas signaling is required for lateral membrane diffusion of CD81, which enables tetraspanin receptor complex assembly. HRas was also found to be relevant for entry of other viruses, including influenza. Our data demonstrate that viruses exploit HRas signaling for cellular entry by compartmentalization of entry factors and receptor trafficking.

Connective tissue growth factor is a new ligand of epidermal growth factor receptor

Chronic kidney disease is reaching epidemic proportions worldwide and there is no effective treatment. Connective tissue growth factor (CCN2) has been suggested as a risk biomarker and a potential therapeutic target for renal diseases, but its specific receptor has not been identified. Epidermal growth factor receptor (EGFR) participates in kidney damage, but whether CCN2 activates the EGFR pathway is unknown. Here, we show that CCN2 is a novel EGFR ligand. CCN2 binding to EGFR extracellular domain was demonstrated by surface plasmon resonance. CCN2 contains four distinct structural modules. The carboxyl-terminal module (CCN2(IV)) showed a clear interaction with soluble EGFR, suggesting that EGFR-binding site is located in this module. Injection of CCN2(IV) in mice increased EGFR phosphorylation in the kidney, mainly in tubular epithelial cells. EGFR kinase inhibition decreased CCN2(IV)-induced renal changes (ERK activation and inflammation). Studies in cultured tubular epithelial cells showed that CCN2(IV) binds to EGFR leading to ERK activation and proinflammatory factors overexpression. CCN2 interacts with the neurotrophin receptor TrkA, and EGFR/TrkA receptor crosstalk was found in response to CCN2(IV) stimulation. Moreover, endogenous CCN2 blockade inhibited TGF-β-induced EGFR activation. These findings indicate that CCN2 is a novel EGFR ligand that contributes to renal damage through EGFR signalling.

Anoikis molecular pathways and its role in cancer progression

Anoikis is a programmed cell death induced upon cell detachment from extracellular matrix, behaving as a critical mechanism in preventing adherent-independent cell growth and attachment to an inappropriate matrix, thus avoiding colonizing of distant organs. As anchorage-independent growth and epithelial-mesenchymal transition, two features associated with anoikis resistance, are vital steps during cancer progression and metastatic colonization, the ability of cancer cells to resist anoikis has now attracted main attention from the scientific community. Cancer cells develop anoikis resistance due to several mechanisms, including change in integrins' repertoire allowing them to grow in different niches, activation of a plethora of inside-out pro-survival signals as over-activation of receptors due to sustained autocrine loops, oncogene activation, growth factor receptor overexpression, or mutation/upregulation of key enzymes involved in integrin or growth factor receptor signaling. In addition, tumor microenvironment has also been acknowledged to contribute to anoikis resistance of bystander cancer cells, by modulating matrix stiffness, enhancing oxidative stress, producing pro-survival soluble factors, triggering epithelial-mesenchymal transition and self-renewal ability, as well as leading to metabolic deregulations of cancer cells. All these events help cancer cells to inhibit the apoptosis machinery and sustain pro-survival signals after detachment, counteracting anoikis and constituting promising targets for anti-metastatic pharmacological therapy. This article is part of a Special Section entitled: Cell Death Pathways.

BDNF protects human vascular endothelial cells from TNFα-induced apoptosis

Brain-derived neurotrophic factor (BDNF) enhances periodontal tissue regeneration. Tissue regeneration is characterized by inflammation that directs the quality of tissue repair. In this study, we investigated the anti-apoptotic effect of BDNF against the toxicity of tumor necrosis factor α (TNFα), which is known for its pro-apoptotic action in human microvascular endothelial cells (HMVECs). We demonstrate that BDNF attenuates TNFα-increased Annexin V-positive cells, lactic dehydrogenase (LDH) release, and intercellular adhesion molecule 1 (ICAM-1) mRNA and cleaved caspase-3 expression. In addition, biochemical analyses indicate that TNFα increases phosphatase and tensin homolog (PTEN) expression; however, it decreases phosphorylated PTEN. BDNF did not affect PTEN expression, but it did increase the phosphorylation of PTEN. BDNF-induced Akt phosphorylation was inhibited by TNFα. Terminal deoxynucleotidyl transferase (TdT) dUTP nick end labeling (TUNEL) assay showed that the PTEN inhibitor bpV(pic) rescues HMVECs from TNFα-induced apoptosis. In conclusion, BDNF protects HMVECs from toxicity of TNFα through the regulation of the PTEN/Akt pathway.

Expression of Lewis y antigen and integrin αv, β3 in ovarian cancer and their relationship with chemotherapeutic drug resistance

OBJECTIVE

This study investigates the expression of Lewis y antigen, integrin αv, β3 in epithelial ovarian cancer tissues. We further evaluate the relationship between their expression and chemotherapy resistance of ovarian cancer and its possible clinical significance.

METHODS

Tissues of 92 patients with ovarian cancer meeting the inclusion criteria with complete follow-up data were enrolled and divided into chemotherapy resistant group and sensitive group. The expression and relationship of Lewis y antigen and integrin αv, β3 are assessed in paraffin sections using immunohistochemistry and double-labeling immunofluorescence method. Multivariate logistic regression analysis was used to investigate the relationship between age, clinical stage, differentiation, histologic subtype, Lewis y antigen and integrin αv, β3 expression in ovarian cancer patients.

RESULTS

The expression rates of Lewis y antigen and integrin αv in the resistant group, significantly higher than the rates found in the sensitive group (p <0.05). Multivariate analysis showed that the expression of Lewis y antigen, integrin αv and ovarian cancer's clinical stage were independent, drug resistance-related risk factors. The expression levels of Lewis y antigen and integrin αv, β3 were positively correlated with each other.

CONCLUSIONS

A close correlation between Lewis y antigen, integrin αv, β3 and ovarian cancer was observed. Lewis y antigen can influence the biological behavior of a tumor cell as an important composition of integrin αv, β3 by some signal pathway. And the expression of Lewis y antigen, integrin αv and ovarian cancer's clinical stage are both independent, drug resistance-related risk factors.

The glycophorin A transmembrane sequence within integrin αvβ3 creates a non-signaling integrin with low basal affinity that is strongly adhesive under force

Integrin heterodimeric cell adhesion and signaling receptors bind ligands of the extracellular matrix and relay signals bidirectionally across cell membranes. Thereby, integrins adopt multiple conformational and functional states that control ligand binding affinity and linkage to cytosolic/cytoskeletal proteins. Here, we designed an integrin chimera encompassing the strongly dimerizing transmembrane domain (TMD) of glycophorin A (GpA) in the context of the otherwise unaltered integrin αvβ3. We hypothesized that this chimera should have a low basal affinity to soluble ligand but should be force-activatable. By cellular expression of this chimera, we found a decreased integrin affinity to a soluble peptide ligand and inhibited intracellular signaling. However, under external forces applied by an atomic force microscope or by a spinning disc device causing shear forces, the mutant caused stronger cell adhesion than the wild-type integrin. Our results demonstrate that the signaling- and migration-incapable integrin αvβ3-TMD mutant TMD-GpA shows the characteristics of a primed integrin state, which is of low basal affinity in the absence of forces, but may form strong bonds in the presence of forces. Thus, TMD-GpA may mimic a force-activatable signaling intermediate.

Chemoresistance is associated with MUC1 and Lewis y antigen expression in ovarian epithelial cancers

Objective

The aim of this study was to analyze the correlation and clinical significance between the expression of Mucin-1 (MUC1) and the Lewis y antigen with chemoresistance in ovarian epithelial cancers.

Methods

Ovarian cancer patients (n = 92) treated at our hospital from May 2005 to July 2009 were divided, according to their treatment and follow-up outcomes, into a resistant group (n = 37) or sensitive group (n = 55). The expression of MUC1 and Lewis y antigen in ovarian cancer tissues was detected using immunohistochemistry and correlated with chemoresistance.

Results

The positive rates of MUC1 and Lewis y antigen in the resistant group were both 91.89%, significantly higher than their positive rates in the sensitive group (65.45% and 69.09%, respectively, and both p < 0.05). MUC1 or Lewis y expression and the pathological stage of the tissue were independent risk factors for chemoresistance (all p < 0.05).

Conclusion

The increased expression of MUC1 and the Lewis y antigen is a significant risk factor for chemoresistance in patients with ovarian epithelial cancer.

Galectin-3- and phospho-caveolin-1-dependent outside-in integrin signaling mediates the EGF motogenic response in mammary cancer cells

Galectin-3 binding to N-glycans promotes EGF receptor signaling to integrin in mammary cancer cells. This leads to phospho-caveolin-1–, Src-, and ILK-dependent activation of RhoA, resulting in actin reorganization in circular dorsal ruffles, cell migration, and fibronectin remodeling.

In murine mammary epithelial cancer cells, galectin-3 binding to β1,6-acetylglucosaminyltransferase V (Mgat5)–modified N-glycans restricts epidermal growth factor (EGF) receptor mobility in the plasma membrane and acts synergistically with phospho-caveolin-1 to promote integrin-dependent matrix remodeling and cell migration. We show that EGF signaling to RhoA is galectin-3 and phospho-caveolin-1 dependent and promotes the formation of transient, actin-rich, circular dorsal ruffles (CDRs), cell migration, and fibronectin fibrillogenesis via Src- and integrin-linked kinase (ILK)–dependent signaling. ILK, Src, and galectin-3 also mediate EGF stimulation of caveolin-1 phosphorylation. Direct activation of integrin with Mn²⁺ induces galectin-3, ILK, and Src-dependent RhoA activation and caveolin-1 phosphorylation. This suggests that in response to EGF, galectin-3 enables outside-in integrin signaling stimulating phospho-caveolin-1–dependent RhoA activation, actin reorganization in CDRs, cell migration, and fibronectin remodeling. Similarly, caveolin-1/galectin-3–dependent EGF signaling induces motility, peripheral actin ruffling, and RhoA activation in MDA-MB-231 human breast carcinoma cells, but not HeLa cells. These studies define a galectin-3/phospho-caveolin-1/RhoA signaling module that mediates integrin signaling downstream of growth factor activation, leading to actin and matrix remodeling and tumor cell migration in metastatic cancer cells.

Tetraspanin CD63 promotes vascular endothelial growth factor receptor 2-β1 integrin complex formation, thereby regulating activation and downstream signaling in endothelial cells in vitro and in vivo

CD63 is a member of the transmembrane-4 glycoprotein superfamily (tetraspanins) implicated in the regulation of membrane protein trafficking, leukocyte recruitment, and adhesion processes. We have investigated the involvement of CD63 in endothelial cell (EC) signaling downstream of β1 integrin and VEGF. We report that silencing of CD63 in primary ECs arrested capillary sprouting and tube formation in vitro because of impaired adhesion and migration of ECs. Mechanistically, CD63 associated with both β1 integrin and the main VEGF receptor on ECs, VEGFR2. Our data suggest that CD63 serves to bridge between β1 integrin and VEGFR2 because CD63 silencing disrupted VEGFR2-β1 integrin complex formation identified using proximity ligation assays. Signaling downstream of β1 integrin and VEGFR2 was attenuated in CD63-silenced cells, although their cell surface expression levels remained unaffected. CD63 was furthermore required for efficient internalization of VEGFR2 in response to VEGF. Importantly, systemic delivery of VEGF failed to potently induce VEGFR2 phosphorylation and downstream signaling in CD63-deficient mouse lungs. Taken together, our findings demonstrate a previously unrecognized role for CD63 in coordinated integrin and receptor tyrosine kinase signaling in vitro and in vivo.

Stiff collagen matrices increase tumorigenic prolactin signaling in breast cancer cells

Clinically, circulating prolactin levels and density of the extracellular matrix (ECM) are individual risk factors for breast cancer. As tumors develop, the surrounding stroma responds with increased deposition and cross-linking of the collagen matrix (desmoplasia). In mouse models, prolactin promotes mammary carcinomas that resemble luminal breast cancers in women, and increased collagen density promotes tumor metastasis and progression. Although the contributions of the ECM to the physiologic actions of prolactin are increasingly understood, little is known about the functional relationship between the ECM and prolactin signaling in breast cancer. Here, we examined consequences of increased ECM stiffness on prolactin signals to luminal breast cancer cells in three-dimensional collagen I matrices in vitro. We showed that matrix stiffness potently regulates a switch in prolactin signals from physiologic to protumorigenic outcomes. Compliant matrices promoted physiological prolactin actions and activation of STAT5, whereas stiff matrices promoted protumorigenic outcomes, including increased matrix metalloproteinase-dependent invasion and collagen scaffold realignment. In stiff matrices, prolactin increased SRC family kinase-dependent phosphorylation of focal adhesion kinase (FAK) at tyrosine 925, FAK association with the mitogen-activated protein kinase mediator GRB2, and pERK1/2. Stiff matrices also increased co-localization of prolactin receptors and integrin-activated FAK, implicating altered spatial relationships. Together, these results demonstrate that ECM stiffness is a powerful regulator of the spectrum of prolactin signals and that stiff matrices and prolactin interact in a feed-forward loop in breast cancer progression. Our study is the first reported evidence of altered ECM-prolactin interactions in breast cancer, suggesting the potential for new therapeutic approaches.

The role of integrins in the development and homeostasis of the epidermis and skin appendages

Integrins play a critical role in the regulation of adhesion, migration, proliferation, and differentiation of cells. Because of the variety of the functions they play in the cell, they are necessary for the formation and maintenance of tissue structure integrity. The trove of data accumulated by researchers suggests that integrins participate in the morphogenesis of the epidermis and its appendages. The development of mice with tissue-specific integrin genes knockout and determination of the genetic basis for a number of skin diseases in humans showed the significance of integrins in the biology, physiology, and morphogenesis of the epidermis and hair follicles. This review discusses the data on the role of different classes of integrin receptors in the biology of epidermal cells, as well as the development of the epidermis and hair follicles.

Integrin and GPCR Crosstalk in the Regulation of ASM Contraction Signaling in Asthma

Airway hyperresponsiveness (AHR) is one of the cardinal features of asthma. Contraction of airway smooth muscle (ASM) cells that line the airway wall is thought to influence aspects of AHR, resulting in excessive narrowing or occlusion of the airway. ASM contraction is primarily controlled by agonists that bind G protein-coupled receptor (GPCR), which are expressed on ASM. Integrins also play a role in regulating ASM contraction signaling. As therapies for asthma are based on symptom relief, better understanding of the crosstalk between GPCRs and integrins holds good promise for the design of more effective therapies that target the underlying cellular and molecular mechanism that governs AHR. In this paper, we will review current knowledge about integrins and GPCRs in their regulation of ASM contraction signaling and discuss the emerging concept of crosstalk between the two and the implication of this crosstalk on the development of agents that target AHR.

Epidermal growth factor (EGF) regulates α5β1 integrin activation state in human cancer cell lines through the p90RSK-dependent phosphorylation of filamin A

BACKGROUND

Regulation of integrin activation has important implications for tumor cell invasion and metastasis.

RESULTS

EGF activates ERK/p90RSK and Rho/Rho kinase signaling in A431 and DiFi colon cancer cells, leading to phosphorylation of filamin A (FLNa) and inactivation of the α5β1 integrin receptor.

CONCLUSION

EGF promotes α5β1 inactivation through the p90RSK-dependent phosphorylation of FLNa.

SIGNIFICANCE

We have identified a novel EGF-dependent mechanism controlling the α5β1 integrin activation state. Cell adhesion, motility, and invasion are regulated by the ligand-binding activity of integrin receptors, transmembrane proteins that bind to the extracellular matrix. Integrins whose conformation allows for ligand binding and appropriate functional activity are said to be in an active state. Integrin activation and subsequent ligand binding are dynamically regulated by the association of cytoplasmic proteins with integrin intracellular domains. In this study, we evaluated the role of EGF in the regulation of the activation state of the α5β1 integrin receptor for fibronectin. The addition of EGF to either A431 squamous carcinoma cells or DiFi colon cancer cells resulted in loss of α5β1-dependent adhesion to fibronectin but no loss of integrin from the cell surface. EGF activated the EGF receptor/ERK/p90RSK and Rho/Rho kinase signaling pathways. Blocking either pathway inhibited EGF-mediated loss of adhesion, suggesting that they work in parallel to regulate integrin function. EGF treatment also resulted in phosphorylation of filamin A (FLNa), which binds and inactivates β1 integrins. EGF-mediated FLNa phosphorylation was completely blocked by an inhibitor of p90RSK and partially attenuated by an inhibitor of Rho kinase, suggesting that both pathways converge on FLNa to regulate integrin function. A431 clonal cell lines expressing non-phosphorylated dominant-negative FLNa were resistant to the inhibitory effects of EGF on integrin function, whereas clonal cell lines overexpressing wild-type FLNa were more sensitive to the inhibitory effect of EGF. These data suggest that EGF-dependent inactivation of α5β1 integrin is regulated through FLNa phosphorylation and cellular contractility.