Signal co-operation between integrins and other receptor systems

Integrin receptors play a role in the internalin B-dependent entry of Listeria monocytogenes into host cells

Listeria monocytogenes enters non-phagocytic cells by binding its surface proteins inlA (internalin) and inlB to the host's E-cadherin and Met, respectively. The two internalins play either separate or cooperative roles in the colonization of infected tissues. Here, we studied bacterial uptake into HeLa cells using an L. monocytogenes mutant strain (DeltainlA) carrying a deletion in the gene coding for inlA. The DeltainlA mutant strain showed the capability to invade HeLa cells. The monoclonal anti-beta(3)- and anti-beta(1)-integrin subunit antibodies prevented bacterial uptake into the cells, while the anti-beta(2)- and anti-beta(4)-integrin subunit antibodies failed to affect L. monocytogenes entry into HeLa cells. Three structurally distinct disintegrins (kistrin, echistatin and flavoridin) also inhibited bacterial uptake, showing different potencies correlated to their selective affinity for the beta(3)- and beta(1)-integrin subunits. In addition to inducing Met phosphorylation, infection of cells by the L. monocytogenes DeltainlA mutant strain promoted the tyrosine phosphorylation of the focal adhesion-associated proteins FAK and paxillin. Our findings provide the first evidence that beta(3)- and beta(1)-integrin receptors play a role in the inlB-dependent internalization of L. monocytogenes into host cells.

Transforming growth factor-{beta}1 induces Smad3-dependent {beta}1 integrin gene expression in epithelial-to-mesenchymal transition during chronic tubulointerstitial fibrosis

Transforming growth factor-β1 (TGF-β1)-induced epithelial-to-mesenchymal transition (EMT) contributes to the pathophysiological development of kidney fibrosis. Although it was reported that TGF-β1 enhances β(1) integrin levels in NMuMG cells, the detailed molecular mechanisms underlying TGF-β1-induced β(1) integrin gene expression and the role of β(1) integrin during EMT in the renal system are still unclear. In this study, we examined the role of β(1) integrin in TGF-β1-induced EMT both in vitro and in vivo. TGF-β1-induced augmentation of β(1) integrin expression was required for EMT in several epithelial cell lines, and knockdown of Smad3 inhibited TGF-β1-induced augmentation of β(1) integrin. TGF-β1 triggered β(1) integrin gene promoter activity as assessed by luciferase activity assay. Both knockdown of Smad3 and mutation of the Smad-binding element to block binding to the β(1) integrin promoter markedly reduced TGF-β1-induced β(1) integrin promoter activity. Chromatin immunoprecipitation assay showed that TGF-β1 enhanced Smad3 binding to the β(1) integrin promoter. Furthermore, induction of unilateral ureteral obstruction triggered increases of β(1) integrin in both renal epithelial and interstitial cells. In human kidney with chronic tubulointerstitial fibrosis, we also found a concomitant increase of β(1) integrin and α-smooth muscle actin in tubule epithelia. Blockade of β(1) integrin signaling dampened the progression of fibrosis. Taken together, β(1) integrin mediates EMT and subsequent tubulointerstitutial fibrosis, suggesting that inhibition of β(1) integrin is a possible therapeutic target for prevention of renal fibrosis.

Celastrol acts as a potent antimetastatic agent targeting beta1 integrin and inhibiting cell-extracellular matrix adhesion, in part via the p38 mitogen-activated protein kinase pathway

Malignant tumors remain a significant health threat, with death often occurring as a result of metastasis. Cell adhesion is a crucial step in the metastatic cascade of tumor cells, and interruption of this step is considered to be a logical strategy for prevention and treatment of tumor metastasis. Celastrol [3-hydroxy-24-nor-2-oxo-1(10),3,5,7-friedelatetraen-29-oic acid], a quinone methide triterpene from the medicinal plant Tripterygium wilfordii, possesses antitumor activities, whereas the underlying mechanism(s) remains elusive. Here, we found that celastrol inhibited cell-extracellular matrix (ECM) adhesion of human lung cancer 95-D and mouse melanoma B16F10 cells. This inhibition was achieved through suppressing beta1 integrin ligand affinity and focal adhesion formation, accompanied by the reduced phosphorylation of focal adhesion kinase (FAK). In understanding the underlying mechanisms, we found that celastrol activated p38 mitogen-activated protein kinase (MAPK) by phosphorylation before the decrement of phosphorylated FAK and that this action was independent of the presence of fibronectin. Using 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580), a specific inhibitor of p38 MAPK, the effects of celastrol on beta1 integrin function, cell-ECM adhesion, and phosphorylation of FAK were partially attenuated. In addition, focal adhesion-dependent cell migration and invasion were both inhibited by treatment with celastrol. Finally, the antimetastatic activity of celastrol was examined in vivo using the B16F10-green fluorescent protein-injected C57BL/6 mouse model, as indicated by decreased pulmonary metastases in celastrol-administrated mice. Taken together, these data demonstrate for the first time that celastrol exerts potent antimetastatic activity both in vitro and in vivo, and they provide new evidence for the critical roles of p38 MAPK in the regulation of integrin function and cell adhesion.

Differentiation of pre-osteoblast cells on poly(ethylene terephthalate) grafted with RGD and/or BMPs mimetic peptides

The bone morphogenetic proteins (BMPs) are cytokines of the transforming growth factor beta family. Some BMPs such as BMP-2, BMP-7 and BMP-9 play a major role in the bone and cartilage formation. The BMP peptides corresponding to residues 73-92, 89-117, and 68-87 of BMP-2, BMP-7 and BMP-9 respectively as well as adhesion peptides (GRGDSPC) were grafted onto polyethylene terephthatalate (PET) surfaces. We evaluated the state of differentiation of pre-osteoblastic cells. The behavior of these cells on various functionalized surfaces highlighted the activity of the mimetic peptides immobilized on surfaces. The induced cells (observed in the case of surfaces grafted with BMP-2, 7 or 9 mimetic peptides and GRGDSPC peptides) were characterized on several levels. First of all, we focused on the evaluation of the osteoblastic markers such as the transcriptional factor Runx2, which is a critical regulator of osteoblastic differentiation. Secondly, the results obtained showed that these induced cells take a different morphology compared to the cells in a state of proliferation or in a state of extracellular matrix production. Induced cells were characterized by an increased thickness compared to non-induced cells. Thus, our studies prove a direct correlation between cell morphology and state of induction. Thereafter, we focused on characterizing the extracellular matrix formed by the cells on various surfaces. The extracellular matrix thickness was more significant in the case of surfaces grafted with mimetic peptides of the BMP-2, 7 or 9 and GRGDSPC peptides which once again proves their activity when immobilized on material surface. These results demonstrate that GRGDSPC and BMPs peptides, grafted to PET surface, act to enhance osteogenic differentiation and mineralization of pre-osteoblastic cells. These findings are potentially useful in developing engineered biomaterials for bone regeneration.

A small fibronectin-mimicking protein from bacteria induces cell spreading and focal adhesion formation

Fibronectin, a 250-kDa eukaryotic extracellular matrix protein containing an RGD motif plays crucial roles in cell-cell communication, development, tissue homeostasis, and disease development. The highly complex fibrillar fibronectin meshwork orchestrates the functions of other extracellular matrix proteins, promoting cell adhesion, migration, and intracellular signaling. Here, we demonstrate that CagL, a 26-kDa protein of the gastric pathogen and type I carcinogen Helicobacter pylori, mimics fibronectin in various cellular functions. Like fibronectin, CagL contains a RGD motif and is located on the surface of the bacterial type IV secretion pili as previously shown. CagL binds to the integrin receptor alpha(5)beta(1) and mediates the injection of virulence factors into host target cells. We show that purified CagL alone can directly trigger intracellular signaling pathways upon contact with mammalian cells and can complement the spreading defect of fibronectin(-/-) knock-out cells in vitro. During interaction with various human and mouse cell lines, CagL mimics fibronectin in triggering cell spreading, focal adhesion formation, and activation of several tyrosine kinases in an RGD-dependent manner. Among the activated factors are the nonreceptor tyrosine kinases focal adhesion kinase and Src but also the epidermal growth factor receptor and epidermal growth factor receptor family member Her3/ErbB3. Interestingly, fibronectin activates a similar range of tyrosine kinases but not Her3/ErbB3. These findings suggest that the bacterial protein CagL not only exhibits functional mimicry with fibronectin but is also capable of activating fibronectin-independent signaling events. We thus postulate that CagL may contribute directly to H. pylori pathogenesis by promoting aberrant signaling cross-talk within host cells.

Dissecting the transcriptional networks underlying breast cancer: NR4A1 reduces the migration of normal and breast cancer cell lines

Introduction

Breast cancer currently accounts for more than one-quarter of all female cancers and, despite the great progress in treatment observed in the past few years, the need for identification of new gene targets that can be used for diagnosis, prognosis and therapy is evident. A previous study identified the transcription factor NR4A1 as a gene upregulated in primary breast cancer compared with normal tissue by microarray analysis and sequencing technologies. The purpose of the study was to identify the role of NR4A1 in normal mammary epithelial and breast cancer cell biology.

Methods

NR4A1 expression in breast tumours was assessed by semiquantitative and real-time PCR using RNA from normal and tumour samples or breast cancer cell lines. Immunohistochemistry on tissue microarrays was performed to check NR4A1 protein expression in breast tumours. MCF-10A and 226L normal mammary epithelial cells as well as the tumour lines PMC42, ZR-75-1 and MDA-MB-231 were transduced with full-length NR4A1, and the ability of NR4A1-overexpressing cells to migrate was tested using scratch wound or transwell migration assays. Proliferation was measured using the MTT and BrdU assays, while apoptosis was determined by the Annexin V assay. The ability of the cells to adhere to extracellular matrix was tested by adhesion assays and integrin cell surface expression was measured by flow cytometry. Activation of the FAK as well as ERK1/2 and PI3K pathways was checked by western blotting.

Results

Breast tissue microarray analysis showed NR4A1 expression in primary tumours, which was reduced in higher grade and metastatic tumours. Ectopic expression of NR4A1 in MCF-10A, 226L, PMC42 and ZR-75-1 cells led to reduced ability of the cells to migrate, while no differences were observed in their proliferation and apoptotic index. NR4A1 expression altered the ability of the MCF-10A cells to adhere to the extracellular matrix and affected cell surface expression of integrins.

Conclusions

NR4A1 acts as an antimigratory factor in two normal mammary epithelial and two breast cancer cell lines tested. It is therefore possible that NR4A1 acts as an antimigratory factor in breast tumours, and further studies should be conducted to understand the mechanisms involved.

Role of a disintegrin and metalloprotease 10 in Staphylococcus aureus alpha-hemolysin-mediated cellular injury

Staphylococcus aureus alpha-hemolysin (Hla), a potent cytotoxin, plays an important role in the pathogenesis of staphylococcal diseases, including those caused by methicillin-resistant epidemic strains. Hla is secreted as a water-soluble monomer that undergoes a series of conformational changes to generate a heptameric, beta-barrel structure in host membranes. Structural maturation of Hla depends on its interaction with a previously unknown proteinaceous receptor in the context of the cell membrane. It is reported here that a disintegrin and metalloprotease 10 (ADAM10) interacts with Hla and is required to initiate the sequence of events whereby the toxin is transformed into a cytolytic pore. Hla binding to the eukaryotic cell requires ADAM10 expression. Further, ADAM10 is required for Hla-mediated cytotoxicity, most notably when the toxin is present at low concentrations. These data thus implicate ADAM10 as the probable high-affinity toxin receptor. Upon Hla binding, ADAM10 relocalizes to caveolin 1-enriched lipid rafts that serve as a platform for the clustering of signaling molecules. It is demonstrated that the Hla-ADAM10 complex initiates intracellular signaling events that culminate in the disruption of focal adhesions.

Syndecan- and integrin-binding peptides synergistically accelerate cell adhesion

Integrins and syndecans mediate cell adhesion to extracellular matrix and their synergistic cooperation is implicated in cell adhesion processes. We previously identified two active peptides, AG73 and EF1, from the laminin alpha1 chain LG4 module, that promote cell attachment through syndecan- and alpha2beta1 integrin-binding, respectively. Here, we examined time-dependent cell attachment on the mixed peptides AG73/EF1. The AG73/EF1 promoted stronger and more rapid cell attachment, spreading, FAK phosphorylation that reached a maximum at 20 min than that on AG73 (40 min) or EF1 (90 min) supplied singly. Thus, the syndecan- and alpha2beta1 integrin-binding peptides synergistically affect cells and accelerate cell adhesion.

Free edges in epithelial cell sheets stimulate epidermal growth factor receptor signaling

Epithelia tend to migrate when edges are present, for instance, after wounding or during development. Using a new tissue culture model, we found that the existence of free edges is in itself a signal that causes activation of the epidermal growth factor and cell motility.

The ability of epithelia to migrate and cover wounds is essential to maintaining their functions as physical barriers. Wounding induces many cues that may affect the transition to motility, including the immediate mechanical perturbation, release of material from broken cells, new interactions with adjacent extracellular matrix, and breakdown of physical separation of ligands from their receptors. Depending on the exact nature of wounds, some cues may be present only transiently or insignificantly. In many epithelia, activation of the epidermal growth factor receptor (EGFR) is a central event in induction of motility, and we find that its continuous activation is required for progression of healing of wounds in sheets of corneal epithelial cells. Here, we examine the hypothesis that edges, which are universally and continuously present in wounds, are a cue. Using a novel culture model we find that their presence is sufficient to cause activation of the EGFR and increased motility of cells in the absence of other cues. Edges that are bordered by agarose do not induce activation of the EGFR, indicating that activation is not due to loss of any specific type of cell–cell interaction but rather due to loss of physical constraints.

Controlled spatial and conformational display of immobilised bone morphogenetic protein-2 and osteopontin signalling motifs regulates osteoblast adhesion and differentiation in vitro

Background

The interfacial molecular mechanisms that regulate mammalian cell growth and differentiation have important implications for biotechnology (production of cells and cell products) and medicine (tissue engineering, prosthetic implants, cancer and developmental biology). We demonstrate here that engineered protein motifs can be robustly displayed to mammalian cells in vitro in a highly controlled manner using a soluble protein scaffold designed to self assemble on a gold surface.

Results

A protein was engineered to contain a C-terminal cysteine that would allow chemisorption to gold, followed by 12 amino acids that form a water soluble coil that could switch to a hydrophobic helix in the presence of alkane thiols. Bioactive motifs from either bone morphogenetic protein-2 or osteopontin were added to this scaffold protein and when assembled on a gold surface assessed for their ability to influence cell function. Data demonstrate that osteoblast adhesion and short-term responsiveness to bone morphogenetic protein-2 is dependent on the surface density of a cell adhesive motif derived from osteopontin. Furthermore an immobilised cell interaction motif from bone morphogenetic protein supported bone formation in vitro over 28 days (in the complete absence of other osteogenic supplements). In addition, two-dimensional patterning of this ligand using a soft lithography approach resulted in the spatial control of osteogenesis.

Conclusion

These data describe an approach that allows the influence of immobilised protein ligands on cell behaviour to be dissected at the molecular level. This approach presents a durable surface that allows both short (hours or days) and long term (weeks) effects on cell activity to be assessed. This widely applicable approach can provide mechanistic insight into the contribution of immobilised ligands in the control of cell activity.

Selection in spatial stochastic models of cancer: migration as a key modulator of fitness

Background

We study the selection dynamics in a heterogeneous spatial colony of cells. We use two spatial generalizations of the Moran process, which include cell divisions, death and migration. In the first model, migration is included explicitly as movement to a proximal location. In the second, migration is implicit, through the varied ability of cell types to place their offspring a distance away, in response to another cell's death.

Results

In both models, we find that migration has a direct positive impact on the ability of a single mutant cell to invade a pre-existing colony. Thus, a decrease in the growth potential can be compensated by an increase in cell migration. We further find that the neutral ridges (the set of all types with the invasion probability equal to that of the host cells) remain invariant under the increase of system size (for large system sizes), thus making the invasion probability a universal characteristic of the cells selection status. We find that repeated instances of large scale cell-death, such as might arise during therapeutic intervention or host response, strongly select for the migratory phenotype.

Conclusions

These models can help explain the many examples in the biological literature, where genes involved in cell's migratory and invasive machinery are also associated with increased cellular fitness, even though there is no known direct effect of these genes on the cellular reproduction. The models can also help to explain how chemotherapy may provide a selection mechanism for highly invasive phenotypes.

Reviewers

This article was reviewed by Marek Kimmel and Glenn Webb.

GPR56 plays varying roles in endogenous cancer progression

GPR56, a non-classical adhesion receptor, was previously reported to suppress tumor growth and metastasis in xenograft models using human melanoma cell lines. To understand whether GPR56 plays similar roles in the development of endogenous tumors, we analyzed cancer progression in Gpr56 (-/-) mice using a variety of transgenic cancer models. Our results showed that GPR56 suppressed prostate cancer progression in the TRAMP model on a mixed genetic background, similar to its roles in progression of melanoma xenografts. However, its roles in other cancer types appeared to be complex. It had marginal effects on tumor onset of mammary tumors in the MMTV-PyMT model, but had no effects on subsequent tumor progression in either the MMTV-PyMT mice or the melanoma model, Ink4a/Arf (-/-) tyr-Hras. These results indicate diverse roles of GPR56 in cancer progression and provide the first genetic evidence for the involvement of an adhesion GPCR in endogenous cancer development.

Synergistic effects of tethered growth factors and adhesion ligands on DNA synthesis and function of primary hepatocytes cultured on soft synthetic hydrogels

The composition, presentation, and spatial orientation of extracellular matrix molecules and growth factors are key regulators of cell behavior. Here, we used self-assembling peptide nanofiber gels as a modular scaffold to investigate how fibronectin-derived adhesion ligands and different modes of epidermal growth factor (EGF) presentation synergistically regulate multiple facets of primary rat hepatocyte behavior in the context of a soft gel. In the presence of soluble EGF, inclusion of dimeric RGD and the heparin binding domain from fibronectin (HB) increased hepatocyte aggregation, spreading, and metabolic function compared to unmodified gels or gels modified with a single motif, but unlike rigid substrates, gels failed to induce DNA synthesis. Tethered EGF dramatically stimulated cell aggregation and spreading under all adhesive ligand conditions and also preserved metabolic function. Surprisingly, tethered EGF elicited DNA synthesis on gels with RGD and HB. Phenotypic differences between soluble and tethered EGF stimulation of cells on peptide gels are correlated with differences in expression and phosphorylation the EGF receptor and its heterodimerization partner ErbB2, and activation of the downstream signaling node ERK1/2. These modular matrices reveal new facets of hepatocellular biology in culture and may be more broadly useful in culture of other soft tissues.

Cell migration-the role of integrin glycosylation

BACKGROUND

Cell migration is an essential process in organ homeostasis, in inflammation, and also in metastasis, the main cause of death from cancer. The extracellular matrix (ECM) serves as the molecular scaffold for cell adhesion and migration; in the first phase of migration, adhesion of cells to the ECM is critical. Engagement of integrin receptors with ECM ligands gives rise to the formation of complex multiprotein structures which link the ECM to the cytoplasmic actin skeleton. Both ECM proteins and the adhesion receptors are glycoproteins, and it is well accepted that N-glycans modulate their conformation and activity, thereby affecting cell-ECM interactions. Likely targets for glycosylation are the integrins, whose ability to form functional dimers depends upon the presence of N-linked oligosaccharides. Cell migratory behavior may depend on the level of expression of adhesion proteins, and their N-glycosylation that affect receptor-ligand binding.

SCOPE OF REVIEW

The mechanism underlying the effect of integrin glycosylation on migration is still unknown, but results gained from integrins with artificial or mutated N-glycosylation sites provide evidence that integrin function can be regulated by changes in glycosylation.

GENERAL SIGNIFICANCE

A better understanding of the molecular mechanism of cell migration processes could lead to novel diagnostic and therapeutic approaches and applications. For this, the proteins and oligosaccharides involved in these events need to be characterized.

Neuropilin-1 antagonism in human carcinoma cells inhibits migration and enhances chemosensitivity

BACKGROUND

Neuropilin-1 (NRP1) is a non-tyrosine kinase receptor for vascular endothelial growth factor (VEGF) recently implicated in tumour functions.

METHODS

In this study we used a specific antagonist of VEGF binding to the NRP1 b1 domain, EG3287, to investigate the functional roles of NRP1 in human carcinoma cell lines, non-small-cell lung A549, kidney ACHN, and prostate DU145 cells expressing NRP1, and the underlying mechanisms involved.

RESULTS

EG3287 potently displaced the specific binding of VEGF to NRP1 in carcinoma cell lines and significantly inhibited the migration of A549 and ACHN cells. Neuropilin-1 downregulation by siRNA also decreased cell migration. EG3287 reduced the adhesion of A549 and ACHN cells to extracellular matrix (ECM), and enhanced the anti-adhesive effects of a beta1-integrin function-blocking antibody. EG3287 increased the cytotoxic effects of the chemotherapeutic agents 5-FU, paclitaxel, or cisplatin on A549 and DU145 cells, through inhibition of integrin-dependent cell interaction with the ECM.

CONCLUSIONS

These findings indicate that NRP1 is important for tumour cell migration and adhesion, and that NRP1 antagonism enhances chemosensitivity, at least in part, by interfering with integrin-dependent survival pathways. A major implication of this study is that therapeutic strategies targeting NRP1 in tumour cells may be particularly useful in combination with other drugs for combating tumour survival, growth, and metastatic spread independently of an antiangiogenic effect of blocking NRP1.

Interleukin-1 Receptor-Associated Kinase-1 (IRAK-1) functionally associates with PKCepsilon and VASP in the regulation of macrophage migration

Macrophage migration is mediated by complex cellular signaling processes and cytoskeleton re-arrangement. In particular, recent advances indicate that the innate immunity signaling process plays a key role in the regulation of macrophage migration. In this report, we have provided evidence demonstrating the involvement of a key innate immunity signaling kinase, Interleukin-1 Receptor-Associated Kinase-1 (IRAK-1) as a critical modulator of macrophage migration. Macrophage migration induced by phorbol 12-myristate 13-acetate (PMA) is significantly attenuated in IRAK-1(-/-) macrophages as compared to wild type macrophages. Mechanistically, we demonstrated that IRAK-1 works downstream of PKCepsilon and upstream of VASP, a member of Ena/VASP family proteins. IRAK-1 forms a close complex with PKCepsilon as well as VASP, and participates in PMA-induced phosphorylation of VASP. Notably, IRAK-1 contains a novel EVH1 domain binding motif (L(167)WPPPP) within its N-terminus, which is responsible for its interaction with VASP. The mutant IRAK-1 (L167A/W168A) fails to associate with VASP. Our findings provide a novel facet regarding the molecular signaling process regulating macrophage migration.

An abundance of ubiquitously expressed genes revealed by tissue transcriptome sequence data

The parts of the genome transcribed by a cell or tissue reflect the biological processes and functions it carries out. We characterized the features of mammalian tissue transcriptomes at the gene level through analysis of RNA deep sequencing (RNA-Seq) data across human and mouse tissues and cell lines. We observed that roughly 8,000 protein-coding genes were ubiquitously expressed, contributing to around 75% of all mRNAs by message copy number in most tissues. These mRNAs encoded proteins that were often intracellular, and tended to be involved in metabolism, transcription, RNA processing or translation. In contrast, genes for secreted or plasma membrane proteins were generally expressed in only a subset of tissues. The distribution of expression levels was broad but fairly continuous: no support was found for the concept of distinct expression classes of genes. Expression estimates that included reads mapping to coding exons only correlated better with qRT-PCR data than estimates which also included 3′ untranslated regions (UTRs). Muscle and liver had the least complex transcriptomes, in that they expressed predominantly ubiquitous genes and a large fraction of the transcripts came from a few highly expressed genes, whereas brain, kidney and testis expressed more complex transcriptomes with the vast majority of genes expressed and relatively small contributions from the most expressed genes. mRNAs expressed in brain had unusually long 3′UTRs, and mean 3′UTR length was higher for genes involved in development, morphogenesis and signal transduction, suggesting added complexity of UTR-based regulation for these genes. Our results support a model in which variable exterior components feed into a large, densely connected core composed of ubiquitously expressed intracellular proteins.

A variety of genes are active within the nuclei of our cells. Some are needed for the day-to-day maintenance of cell functions, while others have roles that are more specific to certain tissues or particular cell types; for example, only the pancreas produces insulin. As a result, every tissue has its own profile of gene activity. Since active genes produce RNA, tissue differences in gene activity can be probed by characterizing the RNA they contain. Essentially the entire set of RNAs or ‘transcriptome’ has been sequenced from various tissues, and we used these data to compare the degree of specialization of different tissues and to investigate the set of ‘core’ genes active in every tissue. A central observation was that there are an abundance of such core genes, and that these genes account for the majority of the transcriptome in each tissue. These findings will aid in the understanding of what makes tissues, and cell types, different from each other and what each requires to function.

Advanced glycation end products in extracellular matrix proteins contribute to the failure of sensory nerve regeneration in diabetes

OBJECTIVE

The goal of this study was to characterize glycation adducts formed in both in vivo extracellular matrix (ECM) proteins of endoneurium from streptozotocin (STZ)-induced diabetic rats and in vitro by glycation of laminin and fibronectin with methylglyoxal and glucose. We also investigated the impact of advanced glycation end product (AGE) residue content of ECM on neurite outgrowth from sensory neurons.

RESEARCH DESIGN AND METHODS

Glycation, oxidation, and nitration adducts of ECM proteins extracted from the endoneurium of control and STZ-induced diabetic rat sciatic nerve (3-24 weeks post-STZ) and of laminin and fibronectin that had been glycated using glucose or methylglyoxal were examined by liquid chromatography with tandem mass spectrometry. Methylglyoxal-glycated or unmodified ECM proteins were used as substrata for dissociated rat sensory neurons as in vitro models of regeneration.

RESULTS

STZ-induced diabetes produced a significant increase in early glycation N(epsilon)-fructosyl-lysine and AGE residue contents of endoneurial ECM. Glycation of laminin and fibronectin by methylglyoxal and glucose increased glycation adduct residue contents with methylglyoxal-derived hydroimidazolone and N(epsilon)-fructosyl-lysine, respectively, of greatest quantitative importance. Glycation of laminin caused a significant decrease in both neurotrophin-stimulated and preconditioned sensory neurite outgrowth. This decrease was prevented by aminoguanidine. Glycation of fibronectin also decreased preconditioned neurite outgrowth, which was prevented by aminoguanidine and nerve growth factor.

CONCLUSIONS

Early glycation and AGE residue content of endoneurial ECM proteins increase markedly in STZ-induced diabetes. Glycation of laminin and fibronectin causes a reduction in neurotrophin-stimulated neurite outgrowth and preconditioned neurite outgrowth. This may provide a mechanism for the failure of collateral sprouting and axonal regeneration in diabetic neuropathy.

Integrin signal masks growth-promotion activity of HB-EGF in monolayer cell cultures

The extracellular environment and tissue architecture contribute to proper cell function and growth control. Cells growing in monolayers on standard polystyrene tissue culture plates differ in their shape, growth rate and response to external stimuli, compared with cells growing in vivo. Here, we showed that the EGFR (epidermal growth factor receptor) ligand heparin-binding EGF-like growth factor (HB-EGF) strongly stimulated cell growth in nude mice, but not in cells cultured in vitro. We explored the effects of HB-EGF on cell growth under various cell culture conditions and found that growth promotion by HB-EGF was needed in three-dimensional (3D) or two-dimensional (2D) culture systems in which cell-matrix adhesion was reduced. Under such conditions, cell growth was extremely suppressed in the absence of HB-EGF, but markedly potentiated in the presence of HB-EGF. When the integrin signal was reduced using antibodies or knockout of either integrin β1 or focal adhesion kinase (FAK), cells showed HB-EGF-dependent growth. We also showed that EGF, transforming growth factor-α (TGFα) or ligands of other receptor tyrosine kinases (RTKs) stimulated cell growth in 3D culture, but not in tissue culture plates. These results indicate that the integrin signal was sufficient to support cell growth in 2D tissue culture plates without addition of the growth factor, whereas stimulation by growth factors was clearly demonstrated in culture systems in which integrin signals were attenuated.

Sensing invasion: cell surface receptors driving spreading of glioblastoma

Glioblastoma multiforme (GBM) is the most common malignant brain tumour in adults. One main source of its high malignancy is the invasion of isolated tumour cells into the surrounding parenchyma, which makes surgical resection an insufficient therapy in nearly all cases. The invasion is triggered by several cell surface receptors including receptor tyrosine kinases (RTKs), G protein-coupled receptors (GPCRs), TGF-beta receptor, integrins, immunoglobulins, tumour necrosis factor (TNF) family, cytokine receptors, and protein tyrosine phosphatase receptors. The cross-talk between cell-surface receptors and the redundancy of downstream effectors make analysis of invasive signals even more complex. Therapies involving inhibition of single receptors do not give promising outcomes and a thorough knowledge of invasive signals of common and exclusive signalling components is required for design of best combinatory treatment schemes to fight the disease.

Long-term virus-induced alterations of CYP3A-mediated drug metabolism: a look at the virology, immunology and molecular biology of a multi-faceted problem

Virus infections are on the rise. Although the first description of CYP expression during virus infection was recorded 50 years ago, mechanistic studies of this phenomenon only began to appear in the last decade due to breakthroughs in molecular biology, genomic and transgenic technology. This review describes the relationship(s) among CYP-mediated drug metabolism, virus infection and the immune response and evaluates in vitro and in vivo models for mechanistic studies. The first studies that assessed CYP expression during infection focused on inflammatory mediators and the innate immune response at early time points. Recent studies assessing virus infection and its effect on hepatic CYP expression noted more long-term effects. An obvious approach toward understanding how viruses affect hepatic CYP3A expression and function would be to assess key regulators of CYP during infection. Improvements in techniques to identify post-translational modifications of CYP and systems that focus on virus-receptor interactions which allow subtraction and addition of immunological and regulatory elements that drive CYP will demonstrate that long-term changes in drug metabolism start from the time the virus enters the circulation, are reinforced by virus binding to cellular targets and further solidified by changes in cellular processes long after the virus is cleared.

Mapping the ligand-binding pocket of integrin alpha5beta1 using a gain-of-function approach

Integrin alpha5beta1 is a key receptor for the extracellular matrix protein fibronectin. Antagonists of human integrin alpha5beta1 have therapeutic potential as anti-angiogenic agents in cancer and diseases of the eye. However, the structure of the integrin is unsolved and the atomic basis of fibronectin and antagonist binding by integrin alpha5beta1 is poorly understood. In the present study, we demonstrate that zebrafish alpha5beta1 integrins do not interact with human fibronectin or the human alpha5beta1 antagonists JSM6427 and cyclic peptide CRRETAWAC. Zebrafish alpha5beta1 integrins do bind zebrafish fibronectin-1, and mutagenesis of residues on the upper surface and side of the zebrafish alpha5 subunit beta-propeller domain shows that these residues are important for the recognition of the Arg-Gly-Asp (RGD) motif and the synergy sequence [Pro-His-Ser-Arg-Asn (PHSRN)] in fibronectin. Using a gain-of-function analysis involving swapping regions of the zebrafish integrin alpha5 subunit with the corresponding regions of human alpha5 we show that blades 1-4 of the beta-propeller are required for human fibronectin recognition, suggesting that fibronectin binding involves a broad interface on the side and upper face of the beta-propeller domain. We find that the loop connecting blades 2 and 3 of the beta-propeller, the D3-A3 loop, contains residues critical for antagonist recognition, with a minor role played by residues in neighbouring loops. A new homology model of human integrin alpha5beta1 supports an important function for D3-A3 loop residues Trp157 and Ala158 in the binding of antagonists. These results will aid the development of reagents that block integrin alpha5beta1 functions in vivo.

SPARC: a matricellular regulator of tumorigenesis

Although many clinical studies have found a correlation of SPARC expression with malignant progression and patient survival, the mechanisms for SPARC function in tumorigenesis and metastasis remain elusive. The activity of SPARC is context- and cell-type-dependent, which is highlighted by the fact that SPARC has shown seemingly contradictory effects on tumor progression in both clinical correlative studies and in animal models. The capacity of SPARC to dictate tumorigenic phenotype has been attributed to its effects on the bioavailability and signaling of integrins and growth factors/chemokines. These molecular pathways contribute to many physiological events affecting malignant progression, including extracellular matrix remodeling, angiogenesis, immune modulation and metastasis. Given that SPARC is credited with such varied activities, this review presents a comprehensive account of the divergent effects of SPARC in human cancers and mouse models, as well as a description of the potential mechanisms by which SPARC mediates these effects. We aim to provide insight into how a matricellular protein such as SPARC might generate paradoxical, yet relevant, tumor outcomes in order to unify an apparently incongruent collection of scientific literature.

Interplay between cell adhesion and growth factor receptors: from the plasma membrane to the endosomes

The emergence of multicellular animals could only take place once evolution had produced molecular mechanisms for cell adhesion and communication. Today, all metazoans express integrin-type adhesion receptors and receptors for growth factors. Integrins recognize extracellular matrix proteins and respective receptors on other cells and, following ligand binding, can activate the same cellular signaling pathways that are regulated by growth factor receptors. Recent reports have indicated that the two receptor systems also collaborate in many other ways. Here, we review the present information concerning the role of integrins as assisting growth factor receptors and the interplay between the receptors in cell signaling and in the orchestration of receptor recycling.

Integrins and cell-fate determination

All cellular processes are determined by adhesive interactions between cells and their local microenvironment. Integrins, which constitute one class of cell-adhesion receptor, are multifunctional proteins that link cells to the extracellular matrix and organise integrin adhesion complexes at the cell periphery. Integrin-based adhesions provide anchor points for assembling and organising the cytoskeleton and cell shape, and for orchestrating migration. Integrins also control the fate and function of cells by influencing their proliferation, apoptosis and differentiation. Moreover, new literature demonstrates that integrins control the cell-division axis at mitosis. This extends the influence of integrins over cell-fate decisions, as daughter cells are frequently located in new microenvironments that determine their behaviour following cell division. In this Commentary, I describe how integrins influence cell-fate determination, placing particular emphasis on their role in influencing the direction of cell division and the orientation of the mitotic spindle.