Integrins as architects of cell behavior

Integrin and Its Associated Proteins as a Mediator for Mechano-Signal Transduction

Mechano-signal transduction is a process in which cells perceive extracellular mechanical signals, convert them into intracellular biochemical signals, and produce a response. Integrins are cell surface receptors that sense the extracellular mechanical cues and bind to the extracellular matrix (ECM). This binding induces integrin clustering and activation. Cytoplasmic tails of activated integrins interact and induce cytoskeleton tensions via several adaptor proteins. Integrins monitor extracellular stiffness via cytoskeleton tensions and modulate ECM stiffness via downstream signaling pathways regulating the expression of genes of ECM components. Integrin-mediated mechano-transduction is very crucial for the cell as it regulates the cell physiology both in normal and diseased conditions according to extracellular mechanical cues. It regulates cell proliferation, survival, and migration. Abnormal mechanical cues such as extreme and prolonged mechanical stress result in pathological conditions including fibrosis, cancers, skin, and autoimmune disorders. This paper aims to explore the role of integrins and their associated proteins in mechano-signal transduction. It highlights the integrins and their associated proteins as targets for therapy development. Furthermore, it also presents the challenges to the targeted drug development, which can be drug resistance and cytotoxicity. It is concluded in this paper that research on integrin-mediated mechano-signal transduction and its relationship with cell physiology and pathologies will be an important step towards the development of effective therapies.

Collagen signaling and matrix stiffness regulate multipotency in glandular epithelial stem cells in mice

Glandular epithelia, including mammary gland (MG) and prostate, are composed of luminal and basal cells. During embryonic development, glandular epithelia arise from multipotent stem cells (SCs) that are replaced after birth by unipotent basal and unipotent luminal SCs. Different conditions, such as basal cell transplantation, luminal cell ablation, and oncogene expression can reinduce adult basal SC (BaSCs) multipotency in different glandular epithelia. The mechanisms regulating the reactivation of multipotency are incompletely understood. Here, we have found that Collagen I expression is commonly upregulated in BaSCs across the different multipotent conditions. Increasing collagen concentration or stiffness of the extracellular matrix (ECM) promotes BaSC multipotency in MG and prostate organoids. Single cell RNA-seq of MG organoids in stiff conditions have uncovered the importance of β1 integrin/FAK/AP-1 axis in the regulation of BaSC multipotency. Altogether our study uncovers the key role of Collagen signaling and ECM stiffness in the regulation of multipotency in glandular epithelia.

Alpha-6 integrin deletion delays the formation of Brca1/p53-deficient basal-like breast tumors by restricting luminal progenitor cell expansion

BACKGROUND

The aberrant amplification of mammary luminal progenitors is at the origin of basal-like breast cancers associated with BRCA1 mutations. Integrins mediate cell-matrix adhesion and transmit mechanical and chemical signals that drive epithelial stem cell functions and regulate tumor progression, metastatic reactivation, and resistance to targeted therapies. Consistently, we have recently shown that laminin-binding integrins are essential for the expansion and differentiation of mammary luminal progenitors in physiological conditions. As over-expression of the laminin-binding α6 integrin (Itgα6) is associated with poor prognosis and reduced survival in breast cancer, we here investigate the role of Itgα6 in mammary tumorigenesis.

METHODS

We used Blg-Cre; Brca1F/F; Trp53F/F mice, a model that phenocopies human basal-like breast cancer with BRCA1 mutations. We generated mutant mice proficient or deficient in Itgα6 expression and followed tumor formation. Mammary tumors and pretumoral tissues were characterized by immunohistochemistry, flow cytometry, RT-qPCR, Western blotting and organoid cultures. Clonogenicity of luminal progenitors from preneoplastic glands was studied in 3D Matrigel cultures.

RESULTS

We show that Itga6 deletion favors activation of p16 cell cycle inhibitor in the preneoplastic tissue. Subsequently, the amplification of luminal progenitors, the cell of origin of Brca1-deficient tumors, is restrained in Itgα6-deficient gland. In addition, the partial EMT program operating in Brca1/p53-deficient epithelium is attenuated in the absence of Itgα6. As a consequence of these events, mammary tumor formation is delayed in Itgα6-deficient mice. After tumor formation, the lack of Itgα6 does not affect tumor growth but rather alters their differentiation, resulting in reduced expression of basal cell markers.

CONCLUSIONS

Our data indicate that Itgα6 has a pro-tumorigenic role in Blg-Cre; Brca1F/F; Trp53F/F mice developing basal-like mammary tumors. In particular, we reveal that Itgα6 is required for the luminal progenitor expansion and the aberrant partial EMT program that precedes the formation of BRCA1 deficient tumors.

Development of circadian neurovascular function and its implications

The neurovascular system forms the interface between the tissue of the central nervous system (CNS) and circulating blood. It plays a critical role in regulating movement of ions, small molecules, and cellular regulators into and out of brain tissue and in sustaining brain health. The neurovascular unit (NVU), the cells that form the structural and functional link between cells of the brain and the vasculature, maintains the blood-brain interface (BBI), controls cerebral blood flow, and surveils for injury. The neurovascular system is dynamic; it undergoes tight regulation of biochemical and cellular interactions to balance and support brain function. Development of an intrinsic circadian clock enables the NVU to anticipate rhythmic changes in brain activity and body physiology that occur over the day-night cycle. The development of circadian neurovascular function involves multiple cell types. We address the functional aspects of the circadian clock in the components of the NVU and their effects in regulating neurovascular physiology, including BBI permeability, cerebral blood flow, and inflammation. Disrupting the circadian clock impairs a number of physiological processes associated with the NVU, many of which are correlated with an increased risk of dysfunction and disease. Consequently, understanding the cell biology and physiology of the NVU is critical to diminishing consequences of impaired neurovascular function, including cerebral bleeding and neurodegeneration.

Novel hydrogels: are they poised to transform 3D cell-based assay systems in early drug discovery?

INTRODUCTION

Success in drug discovery remains unpredictable. However, more predictive and relevant disease models are becoming pivotal to demonstrating the clinical benefits of new drugs earlier in the lengthy drug discovery process. Novel hydrogel scaffolds are being developed to transform the relevance of such 3D cell-based in vitro assay systems.

AREAS COVERED

Most traditional hydrogels are still of unknown composition and suffer significant batch-to-batch variations, which lead to technical constraints. This article looks at how a new generation of novel synthetic hydrogels that are based on self-assembling peptides are poised to transform 3D cell-based assay systems by improving their relevance, reproducibility and scalability.

EXPERT OPINION

The emerging advantages of using these novel hydrogels for human 3D screening assays should enable the discovery of more cost-effective drugs, leading to improved patient benefits. Such a disruptive change could also reduce the considerable time lag from obtaining in vitro assay data to initiating clinical trials. There is now a sufficient body of data available in the literature to enable this ambition to become a reality by significantly improving the predictive validity of 3D cell-based assays in early drug discovery. Novel hydrogels are key to unlocking the full potential of these assay systems.

The dynamic kidney matrisome - is the circadian clock in control?

The circadian clock network in mammals is responsible for the temporal coordination of numerous physiological processes that are necessary for homeostasis. Peripheral tissues demonstrate circadian rhythmicity and dysfunction of core clock components has been implicated in the pathogenesis of diseases that are characterized by abnormal extracellular matrix, such as fibrosis (too much disorganized matrix) and tissue breakdown (too little matrix). Kidney disease is characterized by proteinuria, which along with the rate of filtration, displays robust circadian oscillation. Clinical observation and mouse studies suggest the presence of 24 h kidney clocks responsible for circadian oscillation in kidney function. Recent experimental evidence has also revealed that cell-matrix interactions and the biomechanical properties of extracellular matrix have key roles in regulating peripheral circadian clocks and this mechanism appears to be cell- and tissue-type specific. Thus, establishing a temporally resolved kidney matrisome may provide a useful tool for studying the two-way interactions between the extracellular matrix and the intracellular time-keeping mechanisms in this critical niche tissue. This review summarizes the latest genetic and biochemical evidence linking kidney physiology and disease to the circadian system with a particular focus on the extracellular matrix. We also review the experimental approaches and methodologies required to dissect the roles of circadian pathways in specific tissues and outline the translational aspects of circadian biology, including how circadian medicine could be used for the treatment of kidney disease.

Two Distinct Mechanisms Underlying γδ T Cell-Mediated Regulation of Collagen Type I in Lung Fibroblasts

Idiopathic pulmonary fibrosis is a chronic intractable lung disease, leading to respiratory failure and death. Although anti-fibrotic agents delay disease progression, they are not considered curative treatments, and alternative modalities have attracted attention. We examined the effect of human γδ T cells on collagen type I in lung fibroblasts. Collagen type I was markedly reduced in a γδ T cell number-dependent manner following treatment with γδ T cells expanded with tetrakis-pivaloxymethyl 2-(thiazole-2-ylamino) ethylidene-1,1-bisphosphonate (PTA) and interleukin-2. Collagen type I levels remained unchanged on addition of γδ T cells to the culture system through a trans-well culture membrane, suggesting that cell–cell contact is essential for reducing its levels in lung fibroblasts. Re-stimulating γδ T cells with (E)-4-hydroxy-3-methylbut-2-enyl diphosphate (HMBPP) reduced collagen type I levels without cell–cell contact, indicating the existence of HMBPP-induced soluble anti-fibrotic factors in γδ T cells. Adding anti-interferon-γ (IFN-γ)-neutralizing mAb restored collagen type I levels, demonstrating that human γδ T cell-derived IFN-γ reduces collagen type I levels. Conversely, interleukin-18 augmented γδ T cell-induced suppression of collagen type I. Therefore, human γδ T cells reduce collagen levels in lung fibroblasts via two distinct mechanisms; adoptive γδ T cell transfer is potentially a new therapeutic candidate.

ERK phosphorylation is dependent on cell adhesion in a subset of pediatric sarcoma cell lines

Osteosarcoma (OS) and Pax-Foxo1 fusion negative rhabdomyosarcoma (FN-RMS) are pediatric sarcomas with poor prognoses in patients with advanced disease. In both malignancies, an actin binding protein has been linked to poor prognosis. Integrin adhesion complexes (IACs) are closely coupled to actin networks and IAC-mediated signaling has been implicated in the progression of carcinomas. However, the relationship of IACs and actin cytoskeleton remodeling with cell signaling is understudied in pediatric sarcomas. Here, we tested the hypothesis that IAC dynamics affect ERK activation in OS and FN-RMS cell lines. Adhesion dependence of ERK activation differed among the OS and FN-RMS cells examined. In the OS cell lines, adhesion did not have a consistent effect on phospho-ERK (pERK). ERK phosphorylation in response to fetal calf serum or 1 ng/ml EGF was nearly as efficient in OS cell lines and one FN-RMS cell line in suspension as cells adherent to poly-l-lysine (PL) or fibronectin (FN). By contrast, adhesion to plastic, PL or FN increased ERK phosphorylation and was greater than additive with a 15 min exposure to 1 ng/ml EGF in three FN-RMS cell lines. Increases in pERK were partly dependent on FAK and PAK1/2 but independent of IAC maturation. As far as we are aware, this examination of adhesion-dependent signaling is the first in pediatric sarcomas and has led to the discovery of differences from the prevailing paradigms and differences in the degree of coupling between components in the signaling pathways among the cell lines.

SERPINA3C ameliorates adipose tissue inflammation through the Cathepsin G/Integrin/AKT pathway

OBJECTIVE

Due to the increasing prevalence of obesity and insulin resistance, there is an urgent need for better treatment of obesity and its related metabolic disorders. This study aimed to elucidate the role of SERPINA3C, an adipocyte secreted protein, in obesity and related metabolic disorders.

METHODS

Male wild type (WT) and knockout (KO) mice were fed with high-fat diet (HFD) for 16 weeks, adiposity, insulin resistance, and inflammation were assessed. AAV-mediated overexpression of SERPINA3C was injected locally in inguinal white adipose tissue (iWAT) to examine the effect of SERPINA3C. In vitro analyses were conducted in 3T3-L1 adipocytes to explore the molecular pathways underlying the function of SERPINA3C.

RESULTS

Functional exploration of the SERPINA3C knockout mice revealed that SERPINA3C deficiency led to an impaired metabolic phenotype (more severe obesity, lower metabolic rates, worse glucose intolerance and insulin insensitivity), which was associated with anabatic inflammation and apoptosis of white adipose tissues. Consistent with these results, overexpression of SERPINA3C in inguinal adipose tissue protected mice against diet-induced obesity and metabolic disorders with less inflammation and apoptosis in adipose tissue. Mechanistically, SERPINA3C inhibited Cathepsin G activity, acting as a serine protease inhibitor, which blocked Cathepsin G-mediated turnover of α5/β1 Integrin protein. Then, the preserved integrity (increase) of α5/β1 Integrin signaling activated AKT to decrease JNK phosphorylation, thereby inhibiting inflammation and promoting insulin sensitivity in adipocytes.

CONCLUSIONS/INTERPRETATION

These findings demonstrate a previously unknown SERPINA3C/Cathepsin G/Integrin/AKT pathway in regulating adipose tissue inflammation, and suggest the therapeutic potential of targeting SERPINA3C/Cathepsin G axis in adipose tissue for the treatment of obesity and metabolic diseases.

Exposure to Bacteriophages T4 and M13 Increases Integrin Gene Expression and Impairs Migration of Human PC-3 Prostate Cancer Cells

The interaction between bacteriophages and integrins has been reported in different cancer cell lines, and efforts have been undertaken to understand these interactions in tumor cells along with their possible role in gene alterations, with the aim to develop new cancer therapies. Here, we report that the non-specific interaction of T4 and M13 bacteriophages with human PC-3 cells results in differential migration and varied expression of different integrins. PC-3 tumor cells (at 70% confluence) were exposed to 1 × 10⁷ pfu/mL of either lytic T4 bacteriophage or filamentous M13 bacteriophage. After 24 h of exposure, cells were processed for a histochemical analysis, wound-healing migration assay, and gene expression profile using quantitative real-time PCR (qPCR). qPCR was performed to analyze the expression profiles of integrins ITGAV, ITGA5, ITGB1, ITGB3, and ITGB5. Our findings revealed that PC-3 cells interacted with T4 and M13 bacteriophages, with significant upregulation of ITGAV, ITGA5, ITGB3, ITGB5 genes after phage exposure. PC-3 cells also exhibited reduced migration activity when exposed to either T4 or M13 phages. These results suggest that wildtype bacteriophages interact non-specifically with PC-3 cells, thereby modulating the expression of integrin genes and affecting cell migration. Therefore, bacteriophages have future potential applications in anticancer therapies.

Bacteriophages M13 and T4 Increase the Expression of Anchorage-Dependent Survival Pathway Genes and Down Regulate Androgen Receptor Expression in LNCaP Prostate Cell Line

Wild-type or engineered bacteriophages have been reported as therapeutic agents in the treatment of several types of diseases, including cancer. They might be used either as naked phages or as carriers of antitumor molecules. Here, we evaluate the role of bacteriophages M13 and T4 in modulating the expression of genes related to cell adhesion, growth, and survival in the androgen-responsive LNCaP prostatic adenocarcinoma-derived epithelial cell line. LNCaP cells were exposed to either bacteriophage M13 or T4 at a concentration of 1 × 10⁵ pfu/mL, 1 × 10⁶ pfu/mL, and 1 × 10⁷ pfu/mL for 24, 48, and 72 h. After exposure, cells were processed for general morphology, cell viability assay, and gene expression analyses. Neither M13 nor T4 exposure altered cellular morphology, but both decreased the MTT reduction capacity of LNCaP cells at different times of treatment. In addition, genes AKT, ITGA5, ITGB1, ITGB3, ITGB5, MAPK3, and PI3K were significantly up-regulated, whilst the genes AR, HSPB1, ITGAV, and PGC1A were down-regulated. Our results show that bacteriophage M13 and T4 interact with LNCaP cells and effectively promote gene expression changes related to anchorage-dependent survival and androgen signaling. In conclusion, phage therapy may increase the response of PCa treatment with PI3K/AKT pathway inhibitors.

Transgenic overexpression of ITGB6 in intestinal epithelial cells exacerbates dextran sulfate sodium-induced colitis in mice

Integrins, as a large family of cell adhesion molecules, play a crucial role in maintaining intestinal homeostasis. In inflammatory bowel disease (IBD), homeostasis is disrupted. Integrin αvβ6, which is mainly regulated by the integrin β6 subunit gene (ITGB6), is a cell adhesion molecule that mediates cell-cell and cell-matrix interactions. However, the role of ITGB6 in the pathogenesis of IBD remains elusive. In this study, we found that ITGB6 was markedly upregulated in inflamed intestinal tissues from patients with IBD. Then, we generated an intestinal epithelial cell-specific ITGB6 transgenic mouse model. Conditional ITGB6 transgene expression exacerbated experimental colitis in mouse models of acute and chronic dextran sulphate sodium (DSS)-induced colitis. Survival analyses revealed that ITGB6 transgene expression correlated with poor prognosis in DSS-induced colitis. Furthermore, our data indicated that ITGB6 transgene expression increased macrophages infiltration, pro-inflammatory cytokines secretion, integrin ligands expression and Stat1 signalling pathway activation. Collectively, our findings revealed a previously unknown role of ITGB6 in IBD and highlighted the possibility of ITGB6 as a diagnostic marker and therapeutic target for IBD.

Evaluation of Nanotargeted 111In-Cyclic RGDfK-Liposome in a Human Melanoma Xenotransplantation Model

Nanotargeted liposomes may be modified with targeting peptide on the surface of a prepared liposome to endow specificity and elevate targeting efficiency. The aim of this study was to develop a radioactive targeted nanoparticle, the ¹¹¹In-cyclic RGDfK-liposome, and its advantage of recognizing the α_Vβ3 integrin was examined. The cyclic RGDfK modified liposomes were demonstrated the ability to bind the α_Vβ3 integrin expressed on the surface of human melanoma cell in vitro and in vivo. The effects of the cyclic RGDfK-liposome on the functioning of phagocytes was also examined, showing no considerable negative effects on the engulfment of bacteria and the generation of reactive oxygen species. Based upon these findings, the cyclic RGDfK- liposome is said to be a promising agent for tumor imaging.

A role for the alpha-8 integrin chain (itga8) in glomerular homeostasis of the kidney

Glomerulonephritis results in a dysregulation of glomerular cells and may end up in chronic alterations and subsequent loss of renal function. Therefore, understanding mechanisms, which contribute to maintain glomerular integrity, is a pivotal prerequisite for therapeutic interventions. The alpha-8 integrin chain seems to be an important player to maintain glomerular homeostasis by conferring mechanical stability and functional support for the renal capillary tuft.

Surface modification of polymeric electrospun scaffolds via a potent and high-affinity integrin α4β1 ligand improved the adhesion, spreading and survival of human chorionic villus-derived mesenchymal stem cells: a new insight for fetal tissue engineering

Cell-biomaterial interactions are primarily governed by cell adhesion, which arises from the binding of cellular integrins to the extracellular matrix (ECM). Integrins drive the assembly of focal contacts that serve as mechanotransducers and signaling nexuses for stem cells, for example integrin α4β1 plays pivotal roles in regulating mesenchymal stem cell (MSC) homing, adhesion, migration and differentiation. The strategy to control the integrin-mediated cell adhesion to bioinspired, ECM-mimicking materials is essential to regulate cell functions and tissue regeneration. Previously, using one-bead one-compound (OBOC) combinatorial technology, we discovered that LLP2A was a high-affinity peptidomimetic ligand (IC50 = 2 pM) against integrin α4β1. In this study, we identified that LLP2A had a strong binding to human early gestation chorionic villi-derived MSCs (CV-MSCs) via integrin α4β1. To improve CV-MSC seeding, expansion and delivery for regenerative applications, we constructed artificial scaffolds simulating the structure of the native ECM by immobilizing LLP2A onto the scaffold surface as cell adhesion sites. LLP2A modification significantly enhanced CV-MSC adhesion, spreading and viability on the polymeric scaffolds via regulating signaling pathways including phosphorylation of focal adhesion kinase (FAK), and AKT, NF-kB and Caspase 9. In addition, we also demonstrated that LLP2A had strong binding to MSCs of other sources, such as bone marrow-derived mesenchymal stem cells (BM-MSCs) and adipose tissue-derived mesenchymal stem cells (AT-MSCs). Therefore, LLP2A and its derivatives not only hold great promise for improving CV-MSC-mediated treatment of fetal diseases, but they can also be widely applied to functionalize various biological and medical materials, which are in need of MSC recruitment, enrichment and survival, for regenerative medicine applications.

Vinculins interaction with talin is essential for mammary epithelial differentiation

Vinculin is an essential component of cell adhesion complexes, where it regulates the strength and stability of adhesions. Whilst the role of vinculin in cell motility is well established, it remains unclear how vinculin contributes to other aspects of tissue function. Here we examine the role of vinculin in mammary epithelial cell phenotype. In these cells, correct adhesion to the extracellular matrix is essential for both the formation of polarised secretory acini and for the transcription of tissue-specific milk protein genes. We show that vinculin, through its interaction with talin, controls milk protein gene expression. However, vinculin is not required for the formation of polarised acini. This work reveals new roles for vinculin that are central to cellular differentiation, and for the ability of cells to interpret their extracellular microenvironment.

Polymicrobial interactions of Candida albicans and its role in oral carcinogenesis

The oral microbiome is composed of microorganisms residing in the oral cavity, which are critical components of health and disease. Disruption of the oral microbiome has been proven to influence the course of oral diseases, especially among immunocompromised patients. Oral microbiome is comprised of inter-kingdom microorganisms, including yeasts such as Candida albicans, bacteria, archaea and viruses. These microorganisms can interact synergistically, mutualistically and antagonistically, wherein the sum of these interactions dictates the composition of the oral microbiome. For instance, polymicrobial interactions can improve the ability of C albicans to form biofilm, which subsequently increases the colonisation of oral mucosa by the yeast. Polymicrobial interactions of C albicans with other members of the oral microbiome have been reported to enhance the malignant phenotype of oral cancer cells, such as the attachment to extracellular matrix molecules (ECM) and epithelial-mesenchymal transition (EMT). Polymicrobial interactions may also exacerbate an inflammatory response in oral epithelial cells, which may play a role in carcinogenesis. This review focuses on the role of polymicrobial interactions between C albicans and other oral microorganisms, including its role in promoting oral carcinogenesis.

Influence of the extracellular matrix on cell-intrinsic circadian clocks

Cell-autonomous circadian clocks coordinate tissue homeostasis with a 24-hourly rhythm. The molecular circadian clock machinery controls tissue- and cell type-specific sets of rhythmic genes. Disruptions of clock mechanisms are linked to an increased risk of acquiring diseases, especially those associated with aging, metabolic dysfunction and cancer. Despite rapid advances in understanding the cyclic outputs of different tissue clocks, less is known about how the clocks adapt to their local niche within tissues. We have discovered that tissue stiffness regulates circadian clocks, and that this occurs in a cell-type-dependent manner. In this Review, we summarise new work linking the extracellular matrix with differential control of circadian clocks. We discuss how the changes in tissue structure and cellular microenvironment that occur throughout life may impact on the molecular control of circadian cycles. We also consider how altered clocks may have downstream impacts on the acquisition of diseases.

Myosin 1F Regulates M1-Polarization by Stimulating Intercellular Adhesion in Macrophages

Intestinal macrophages are highly mobile cells with extraordinary plasticity and actively contribute to cytokine-mediated epithelial cell damage. The mechanisms triggering macrophage polarization into a proinflammatory phenotype are unknown. Here, we report that during inflammation macrophages enhance its intercellular adhesion properties in order to acquire a M1-phenotype. Using in vitro and in vivo models we demonstrate that intercellular adhesion is mediated by integrin-αVβ3 and relies in the presence of the unconventional class I myosin 1F (Myo1F). Intercellular adhesion mediated by αVβ3 stimulates M1-like phenotype in macrophages through hyperactivation of STAT1 and STAT3 downstream of ILK/Akt/mTOR signaling. Inhibition of integrin-αVβ3, Akt/mTOR, or lack of Myo1F attenuated the commitment of macrophages into a pro-inflammatory phenotype. In a model of colitis, Myo1F deficiency strongly reduces the secretion of proinflammatory cytokines, decreases epithelial damage, ameliorates disease activity, and enhances tissue repair. Together our findings uncover an unknown role for Myo1F as part of the machinery that regulates intercellular adhesion and polarization in macrophages.

Translating the matrix

LINKED ARTICLES

This article is part of a themed section on Translating the Matrix. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.1/issuetoc.

Disrupted circadian clocks and altered tissue mechanics in primary human breast tumours

BACKGROUND

Circadian rhythms maintain tissue homeostasis during the 24-h day-night cycle. Cell-autonomous circadian clocks play fundamental roles in cell division, DNA damage responses and metabolism. Circadian disruptions have been proposed as a contributing factor for cancer initiation and progression, although definitive evidence for altered molecular circadian clocks in cancer is still lacking. In this study, we looked at circadian clocks in breast cancer.

METHODS

We isolated primary tumours and normal tissues from the same individuals who had developed breast cancer with no metastases. We assessed circadian clocks within primary cells of the patients by lentiviral expression of circadian reporters, and the levels of clock genes in tissues by qPCR. We histologically examined collagen organisation within the normal and tumour tissue areas, and probed the stiffness of the stroma adjacent to normal and tumour epithelium using atomic force microscopy.

RESULTS

Epithelial ducts were disorganised within the tumour areas. Circadian clocks were altered in cultured tumour cells. Tumour regions were surrounded by stroma with an altered collagen organisation and increased stiffness. Levels of Bmal1 messenger RNA (mRNA) were significantly altered in the tumours in comparison to normal epithelia.

CONCLUSION

Circadian rhythms are suppressed in breast tumour epithelia in comparison to the normal epithelia in paired patient samples. This correlates with increased tissue stiffness around the tumour region. We suggest possible involvement of altered circadian clocks in the development and progression of breast cancer.

Integrin-Rac signalling for mammary epithelial stem cell self-renewal

Background

Stem cells are precursors for all mammary epithelia, including ductal and alveolar epithelia, and myoepithelial cells. In vivo mammary epithelia reside in a tissue context and interact with their milieu via receptors such as integrins. Extracellular matrix receptors coordinate important cellular signalling platforms, of which integrins are the central architects. We have previously shown that integrins are required for mammary epithelial development and function, including survival, cell cycle, and polarity, as well as for the expression of mammary-specific genes. In the present study we looked at the role of integrins in mammary epithelial stem cell self-renewal.

Methods

We used an in vitro stem cell assay with primary mouse mammary epithelial cells isolated from genetically altered mice. This involved a 3D organoid assay, providing an opportunity to distinguish the stem cell- or luminal progenitor-driven organoids as structures with solid or hollow appearances, respectively.

Results

We demonstrate that integrins are essential for the maintenance and self-renewal of mammary epithelial stem cells. Moreover integrins activate the Rac1 signalling pathway in stem cells, which leads to the stimulation of a Wnt pathway, resulting in expression of β-catenin target genes such as Axin2 and Lef1.

Conclusions

Integrin/Rac signalling has a role in specifying the activation of a canonical Wnt pathway that is required for mammary epithelial stem cell self-renewal.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1048-1) contains supplementary material, which is available to authorized users.

Tuning RGD Motif and Hyaluronan Density to Study Integrin Binding

Well-controlled surfaces with immobilized substrates enable novel approaches to investigate specific aspects of biological processes related to cell adhesion or motility. A subset of integrins, cellular transmembrane glycoproteins, recognize the evolutionarily conserved tripeptide sequence RGD, and anchor cells to their surrounding proteins as well as mediate bidirectional signaling. In this study, the main question was how co-presentation of hyaluronan (HA), an essential component of the extracellular matrix (ECM), and the RGD motif affect integrin binding. We report a method to prepare self-assembled monolayers on gold surfaces, co-presenting the cell adhesive RGD motif and small HA molecules, to investigate integrin containing proteoliposome binding. This technique enables an independent adjustment of the RGD motif and HA density while maintaining a passivating background: Layer formation and subsequent interactions with α_IIbβ₃ integrins, which are reconstituted in liposomes, was monitored by label-free quartz crystal microbalance with dissipation monitoring (QCM-D). Exceeding a critical RGD motif density of 40% results in enhanced binding of proteoliposomes. Co-presentation studies with varying HA and constant RGD motif density demonstrate that marginal amounts of HA are sufficient to prevent integrin binding. These findings are of specific importance in relation to cancer cell microenvironments, which show highly enriched HA in the surrounding ECM to reduce adhesion properties.

Control of Integrin Affinity by Confining RGD Peptides on Fluorescent Carbon Nanotubes

Integrins are transmembrane receptors that mediate cell-adhesion, signaling cascades and platelet-mediated blood clotting. Most integrins bind to the common short peptide Arg-Gly-Asp (RGD). The conformational freedom of the RGD motif determines how strong and to which integrins it binds. Here, we present a novel approach to tune binding constants by confining RGD peptide motifs via noncovalent adsorption of single-stranded DNA (ssDNA) anchors onto single-walled carbon nanotubes (SWCNTs). Semiconducting SWCNTs display fluorescence in the near-infrared (nIR) region and are versatile fluorescent building blocks for imaging and biosensing. The basic idea of this approach is that the DNA adsorbed on the SWCNT surface determines the conformational freedom of the RGD motif and affects binding affinities. The RGD motif was conjugated to different ssDNA sequences in both linear ssDNA-RGD and bridged ssDNA-RGD-ssDNA geometries. Molecular dynamics (MD) simulations show that the RGD motif in all the synthesized systems is mostly exposed to solvent and thus available for binding, but its flexibility depends on the exact geometry. The affinity for the human platelet integrin αIIbβ3 could be modulated up to 15-fold by changing the ssDNA sequence. IC50 values varied from 309 nM for (C)20-RGD/SWCNT hybrids to 29 nM for (GT)15-RGD/SWCNT hybrids. When immobilized onto surface adhesion of epithelial cells increased 6-fold for (GT)15-RGD/SWCNTs. (GT)15-RGD/SWCNTs also increased the number of adhering human platelets by a factor of 4.8. Additionally, αIIbβ3 integrins on human platelets were labeled in the nIR by incubating them with these ssDNA-peptide/SWCNT hybrids. In summary, we show that ssDNA-peptide hybrid structures noncovalently adsorb onto SWCNTs and serve as recognition units for cell surface receptors such as integrins. The DNA sequence affects the overall RGD affinity, which is a versatile and straightforward approach to tune binding affinities. In combination with the nIR fluorescence properties of SWCNTs, these new hybrid materials promise many applications in integrin targeting and bioimaging.

Group B streptococcus exploits vaginal epithelial exfoliation for ascending infection

Thirteen percent of pregnancies result in preterm birth or stillbirth, accounting for fifteen million preterm births and three and a half million deaths annually. A significant cause of these adverse pregnancy outcomes is in utero infection by vaginal microorganisms. To establish an in utero infection, vaginal microbes enter the uterus by ascending infection; however, the mechanisms by which this occurs are unknown. Using both in vitro and murine models of vaginal colonization and ascending infection, we demonstrate how a vaginal microbe, group B streptococcus (GBS), which is frequently associated with adverse pregnancy outcomes, uses vaginal exfoliation for ascending infection. GBS induces vaginal epithelial exfoliation by activation of integrin and β-catenin signaling. However, exfoliation did not diminish GBS vaginal colonization as reported for other vaginal microbes. Rather, vaginal exfoliation increased bacterial dissemination and ascending GBS infection, and abrogation of exfoliation reduced ascending infection and improved pregnancy outcomes. Thus, for some vaginal bacteria, exfoliation promotes ascending infection rather than preventing colonization. Our study provides insight into mechanisms of ascending infection by vaginal microbes.

Extracellular matrix internalization links nutrient signalling to invasive migration

Integrins are the key mediators of cell-extracellular matrix (ECM) interaction, linking the ECM to the actin cytoskeleton. Besides localizing at the cell surface, they can be internalized and transported back to the plasma membrane (recycled) or delivered to the late endosomes/lysosomes for degradation. We and others have shown that integrin can be endocytosed together with their ECM ligands. In this short review, I will highlight how extracellular protein (including ECM) endocytosis impinges on the activation of the mechanistic target of rapamycin (mTOR) pathway, a master regulator of cell metabolism and growth. This supports the intriguing hypothesis that ECM components may be considered as nutrient sources, primarily under soluble nutrient-depleted conditions.

Integral Roles for Integrins in γδ T Cell Function

Integrins are adhesion receptors on the cell surface that enable cells to respond to their environment. Most integrins are heterodimers, comprising α and β type I transmembrane glycoprotein chains with large extracellular domains and short cytoplasmic tails. Integrins deliver signals through multiprotein complexes at the cell surface, which interact with cytoskeletal and signaling proteins to influence gene expression, cell proliferation, morphology, and migration. Integrin expression on γδ T cells (γδTc) has not been systematically investigated; however, reports in the literature dating back to the early 1990s reveal an understated role for integrins in γδTc function. Over the years, integrins have been investigated on resting and/or activated peripheral blood-derived polyclonal γδTc, γδTc clones, as well as γδ T intraepithelial lymphocytes. Differences in integrin expression have been found between αβ T cells (αβTc) and γδTc, as well as between Vδ1 and Vδ2 γδTc. While most studies have focused on human γδTc, research has also been carried out in mouse and bovine models. Roles attributed to γδTc integrins include adhesion, signaling, activation, migration, tissue localization, tissue retention, cell spreading, cytokine secretion, tumor infiltration, and involvement in tumor cell killing. This review attempts to encompass all reports of integrins expressed on γδTc published prior to December 2017, highlights areas warranting further investigation, and discusses the relevance of integrin expression for γδTc function.

Not Just an Adhesion Molecule: LFA-1 Contact Tunes the T Lymphocyte Program

The α_Lβ₂ integrin LFA-1 is known to play a key role in T lymphocyte migration, which is necessary to mount a local immune response, and is also the main driver of autoimmune diseases. This migration-triggering signaling process in T cells is tightly regulated to permit an immune response that is appropriate to the local trigger, as well as to prevent deleterious tissue-damaging bystander effects. Emerging evidence shows that, in addition to prompting a diverse range of downstream signaling cascades, LFA-1 stimulation in T lymphocytes modulates gene-transcription programs, including genetic signatures of TGF-β and Notch pathways, with multifactorial biological outcomes. This review highlights recent findings and discusses molecular mechanisms by which LFA-1 signaling influence T lymphocyte differentiation into the effector subsets Th1, Th17, and induced regulatory T cells. We argue that LFA-1 contact with a cognate ligand, such as ICAM-1, independent of the immune synapse activates a late divergence in T cells' effector phenotypes, hence fine-tuning their functioning.