Toward a genetic analysis of cell-matrix adhesion

Mesodermal fibronectin controls cell shape, polarity, and mechanotransduction in the second heart field during cardiac outflow tract development

Failure in the elongation of the cardiac outflow tract (OFT) results in congenital heart disease due to the misalignment of the great arteries with the left and right ventricles. The OFT lengthens via the accretion of progenitors from the second heart field (SHF). SHF cells are exquisitely regionalized and organized into an epithelial-like layer, forming the dorsal pericardial wall (DPW). Tissue tension, cell polarity, and proliferation within the DPW are important for the addition of SHF-derived cells to the heart and OFT elongation. However, the genes controlling these processes are not completely characterized. Using conditional mutagenesis in the mouse, we show that fibronectin (FN1) synthesized by the mesoderm coordinates multiple cellular behaviors in the anterior DPW. FN1 is enriched in the anterior DPW and plays a role in OFT elongation by maintaining a balance between pro- and anti-adhesive cell-extracellular matrix (ECM) interactions and controlling DPW cell shape, polarity, cohesion, proliferation, and mechanotransduction.

A New Protein Extract Inhibitor from Hypobranchial Purple Gland of Hexaplex trunculus, a Mediterranean Mollusk, Impairs the Motility of Human Glioblastoma U87 and the HeLa Cell Line of Cervical Carcinoma Cells

The aim of this study is to evaluate the effect of hypobranchial gland protein extracts (HGPEs) of Hexaplex trunculus on the viability, cell adhesion, and migration of human U87 glioblastoma cells and the HeLa cell line obtained from epithelial cervical carcinoma cells. Analysis of the HGPE on polyacrylamide gel (12%) shows a variety of proteins whose molecular weights vary between 12 and 1OO kDa. Chromatographic analysis shows 16 peaks obtained at various retention times. Cytotoxic effect was observed after 24 hours of incubation at the concentrations 20, 40, and 60 μg/ml in a dose-dependent manner. Concentrations giving 50% inhibition (IC₅₀) are 22 μg/ml for U87 and 15 μg/ml for HeLa cells. Our results show inhibition of U87 and HeLa cancer cell adhesion at concentrations of 10 and 20 µg/ml, respectively. High-pressure liquid chromatography fractions did not show antiadhesive effect on both cancer cell lines. The presence of HGPEs completely blocked the migration of the two cancer cell lines at 10 µg/ml. This inhibition is dose-dependent. IC₅₀ is about 2.5 μg/ml for both cancer cells. The HGPE of Hexaplex trunculus may have the potential to serve as a model for future anticancer drug development with probably a synergistic activity of the proteins of this extract.

Microbe-dependent lymphatic migration of neutrophils modulates lymphocyte proliferation in lymph nodes

Neutrophil recruitment to the site of injury is an essential first step of an anti-bacterial response. However, little is known about the basis for and relevance of neutrophil migration from inflamed tissue into lymphoid organs. We established a photoconversion-based system to monitor the fate of neutrophils recruited to inflamed skin. While neutrophils are efficiently recruited to sites of both microbial and sterile lesions, subsequent re-localization to draining lymph nodes happens only when bacteria are present in the primary lesion. Skin egress of neutrophils occurs via lymphatic vessels and is dependent on CD11b and CXCR4 but not CCR7. Neutrophils are the predominant immune cell to migrate from inflamed skin into lymph nodes where they augment lymphocyte proliferation. Furthermore, inhibition of neutrophil migration from skin reduces T-cell proliferation in draining lymph nodes. Thus neutrophils mediate rapid cellular communication between the initial injury site and secondary lymphoid organs and modulate immune responsiveness.

Both sterile and microbial injuries lead to rapid neutrophil recruitment to the site of inflammation. Here the authors show that only neutrophils responding to microbial ligands leave inflamed skin and migrate to draining lymph nodes where they stimulate lymphocyte proliferation.

Redox-relevant aspects of the extracellular matrix and its cellular contacts via integrins

SIGNIFICANCE

The extracellular matrix (ECM) fulfills essential functions in multicellular organisms. It provides the mechanical scaffold and environmental cues to cells. Upon cell attachment, the ECM signals into the cells. In this process, reactive oxygen species (ROS) are physiologically used as signalizing molecules.

RECENT ADVANCES

ECM attachment influences the ROS-production of cells. In turn, ROS affect the production, assembly and turnover of the ECM during wound healing and matrix remodeling. Pathological changes of ROS levels lead to excess ECM production and increased tissue contraction in fibrotic disorders and desmoplastic tumors. Integrins are cell adhesion molecules which mediate cell adhesion and force transmission between cells and the ECM. They have been identified as a target of redox-regulation by ROS. Cysteine-based redox-modifications, together with structural data, highlighted particular regions within integrin heterodimers that may be subject to redox-dependent conformational changes along with an alteration of integrin binding activity.

CRITICAL ISSUES

In a molecular model, a long-range disulfide-bridge within the integrin β-subunit and disulfide bridges within the genu and calf-2 domains of the integrin α-subunit may control the transition between the bent/inactive and upright/active conformation of the integrin ectodomain. These thiol-based intramolecular cross-linkages occur in the stalk domain of both integrin subunits, whereas the ligand-binding integrin headpiece is apparently unaffected by redox-regulation.

FUTURE DIRECTIONS

Redox-regulation of the integrin activation state may explain the effect of ROS in physiological processes. A deeper understanding of the underlying mechanism may open new prospects for the treatment of fibrotic disorders.

Role of epithelial integrin-linked kinase in promoting intestinal inflammation: effects on CCL2, fibronectin and the T cell repertoire

Background

The role of integrin signaling in mucosal inflammation is presently unknown. Hence, we aimed to investigate the role of epithelial-derived integrin-linked kinase (ILK), a critical integrin signaling intermediary molecule, in colonic inflammation.

Methods

Conditional intestinal epithelial cell ILK knockout mice were used for assessment of acute and chronic dextran sodium sulfate (DSS) -induced colitis. Disease activity was scored using standard histological scoring, mucosal cytokines were measured using ELISA, chemokines were determined using reverse-transcription polymerase chain reaction, as well as Q-PCR, and intracellular cytokine staining performed using FACS analysis.

Results

In both acute and chronic DSS-induced colitis, compared to wild-type mice, ILK-ko mice exhibit less weight loss, and have reduced inflammatory scores. In an in vitro model system using HCT116 cells, we demonstrate that si-RNA mediated down-regulation of ILK results in a reduction in monocyte chemoattractant protein 1 (MCP1, CCL2) chemokine expression. A reduction in CCL2 levels is also observed in the tissue lysates of chronically inflamed colons from ILK-ko mice. Examination of mesenteric lymph node lymphocytes from ILK-ko mice reveals that there is a reduction in the levels of IFN gamma using intracellular staining, together with an increase in Foxp3+ T regulatory cells. Immunohistochemistry demonstrates that reduced fibronectin expression characterizes the inflammatory lesions within the colons of ILK-ko mice. Intriguingly, we demonstrate that fibronectin is directly capable of downregulating T regulatory cell development.

Conclusions

Collectively, the data indicate for the first time that ILK plays a pro-inflammatory role in intestinal inflammation, through effects on chemokine expression, the extracellular matrix and immune tolerance.

Osteoblast mineralization requires beta1 integrin/ICAP-1-dependent fibronectin deposition

ICAP-1 prevents recruitment of kindlin-2 to β1 integrin to control dynamics of fibrillar adhesion sites, fibronectin deposition, and osteoblast mineralization during bone formation.

The morphogenetic and differentiation events required for bone formation are orchestrated by diffusible and insoluble factors that are localized within the extracellular matrix. In mice, the deletion of ICAP-1, a modulator of β1 integrin activation, leads to severe defects in osteoblast proliferation, differentiation, and mineralization and to a delay in bone formation. Deposition of fibronectin and maturation of fibrillar adhesions, adhesive structures that accompany fibronectin deposition, are impaired upon ICAP-1 loss, as are type I collagen deposition and mineralization. Expression of β1 integrin with a mutated binding site for ICAP-1 recapitulates the ICAP-1–null phenotype. Follow-up experiments demonstrated that ICAP-1 negatively regulates kindlin-2 recruitment onto the β1 integrin cytoplasmic domain, whereas an excess of kindlin-2 binding has a deleterious effect on fibrillar adhesion formation. These results suggest that ICAP-1 works in concert with kindlin-2 to control the dynamics of β1 integrin–containing fibrillar adhesions and, thereby, regulates fibronectin deposition and osteoblast mineralization.

Imaging morphogenesis, in Xenopus with Quantum Dot nanocrystals

Mesoderm migration is a well studied morphogenetic movement that takes place during Xenopus gastrulation. The study of mesoderm migration and other morphogenetic movements has been primarily based on in vitro assays due to the inability to image deep tissue movements in the opaque embryo. We are the first to report the use of Near Infra Red Quantum Dots (NIR QD's) to image mesoderm migration in vivo with single cell resolution and provide quantitative in vivo data regarding migration rates. In addition we use QD's to address the function of the focal adhesion kinase (FAK) in this movement. Inhibition of FAK blocks mesoderm spreading and migration both in vitro and in vivo without affecting convergent extension highlighting the molecular differences between the two movements. These results provide new insights about the role of FAK and of focal adhesions during gastrulation and provide a new tool for the study of morphogenesis in vivo.

Cathepsin K activity-dependent regulation of osteoclast actin ring formation and bone resorption

Cathepsin K is responsible for the degradation of type I collagen in osteoclast-mediated bone resorption. Collagen fragments are known to be biologically active in a number of cell types. Here, we investigate their potential to regulate osteoclast activity. Mature murine osteoclasts were seeded on type I collagen for actin ring assays or dentine discs for resorption assays. Cells were treated with cathepsins K-, L-, or MMP-1-predigested type I collagen or soluble bone fragments for 24 h. The presence of actin rings was determined fluorescently by staining for actin. We found that the percentage of osteoclasts displaying actin rings and the area of resorbed dentine decreased significantly on addition of cathepsin K-digested type I collagen or bone fragments, but not with cathepsin L or MMP-1 digests. Counterintuitively, actin ring formation was found to decrease in the presence of the cysteine proteinase inhibitor LHVS and in cathepsin K-deficient osteoclasts. However, cathepsin L deficiency or the general MMP inhibitor GM6001 had no effect on the presence of actin rings. Predigestion of the collagen matrix with cathepsin K, but not by cathepsin L or MMP-1 resulted in an increased actin ring presence in cathepsin K-deficient osteoclasts. These studies suggest that cathepsin K interaction with type I collagen is required for 1) the release of cryptic Arg-Gly-Asp motifs during the initial attachment of osteoclasts and 2) termination of resorption via the creation of autocrine signals originating from type I collagen degradation.

The monoclonal antibody SM5-1 recognizes a fibronectin variant which is widely expressed in melanoma

Background

Previously we have generated the monoclonal antibody SM5-1 by using a subtractive immunization protocol of human melanoma. This antibody exhibits a high sensitivity for primary melanomas of 99% (248/250 tested) and for metastatic melanoma of 96% (146/151 tested) in paraffin embedded sections. This reactivity is superior to the one obtained by HMB-45, anti-MelanA or anti-Tyrosinase and is comparable to anti-S100. However, as compared to anti-S100, the antibody SM5-1 is highly specific for melanocytic lesions since 40 different neoplasms were found to be negative for SM5-1 by immunohistochemistry. The antigen recognized by SM5-1 is unknown.

Methods

In order to characterize the antigen recognized by mAb SM5-1, a cDNA library was constructed from the metastatic human melanoma cell line SMMUpos in the Uni-ZAP lambda phage and screened by mAb SM5-1. The cDNA clones identified by this approach were then sequenced and subsequently analyzed.

Results

Sequence analysis of nine independent overlapping clones (length 3100–5600 bp) represent fibronectin cDNA including the ED-A, but not the ED-B region which are produced by alternative splicing. The 89aa splicing variant of the IIICS region was found in 8/9 clones and the 120aa splicing variant in 1/9 clones, both of which are included in the CS1 region of fibronectin being involved in melanoma cell adhesion and spreading.

Conclusion

The molecule recognized by SM5-1 is a melanoma associated FN variant expressed by virtually all primary and metastatic melanomas and may play an important role in melanoma formation and progression. This antibody is therefore not only of value in immunohistochemistry, but potentially also for diagnostic imaging and immunotherapy.

Role for the α7β1 integrin in vascular development and integrity

The alpha7beta1 integrin is a laminin receptor that has been implicated in muscle disease and the development of neuromuscular and myotendinous junctions. Studies have shown the alpha7beta1 integrin is also expressed in nonskeletal muscle tissues. To identify the expression pattern of the alpha7 integrin in these tissues during embryonic development, alpha7 integrin chain knockout mice were generated by a LacZ knockin strategy. In these mice, expression from the alpha7 promoter is reported by beta-galactosidase. From embryonic day (ED) 11.5 to ED14.5, beta-galactosidase was detected in the developing central and peripheral nervous systems and vasculature. The loss of the alpha7 integrin gene resulted in partial embryonic lethality. Several alpha7 null embryos were identified with cerebrovascular hemorrhages and showed reduced vascular smooth muscle cells and cerebral vascularization. The alpha7 null mice that survived to birth exhibited vascular smooth muscle defects, including hyperplasia and hypertrophy. In addition, altered expression of alpha5 and alpha6B integrin chains was detected in the cerebral arteries of alpha7 null mice, which may contribute to the vascular phenotype. Our results demonstrate for the first time that the alpha7beta1 integrin is important for the recruitment or survival of cerebral vascular smooth muscle cells and that this integrin plays an important role in vascular development and integrity.

Tenascin-C deposition requires β3 integrin and Src

In this study we now show that deposition of the mesenchymal matrix marker, tenascin-C (TN-C), is mediated through beta3 expression and activation of Src. There was a striking upregulation of TN-C matrix organization in cell lines expressing beta3 and activated Src when compared to cell lines with neither of these attributes. When beta3 function was suppressed so was the deposition of TN-C. The same was true for function and activation of Src. When Src was inactive, the deposition of TN-C was low. We also determined that one of the downstream effectors of Src, MAPK, was also required to promote TN-C deposition. When MAPK activation was inhibited, TN-C deposition was also decreased. MMP activation is also implicated in TN-C deposition. The broad spectrum MMP inhibitor, GM6001, suppressed TN-C organization. These results indicate that beta3 integrin ligand binding and the activation of the Src/MAPK/MMP pathway modulate deposition of TN-C.

Expression of an embryonic fibronectin splicing variant in human masseter muscle

Fibronectin is an extracellular matrix protein that is a key constituent of all skeletal muscles. Its deposition increases in a number of pathological conditions, including some muscular dystrophies in which a progressive increase in lower-face height is often noted. It has been shown in other organ systems that increased deposition of fibronectin is associated with changes in the expression of differentially spliced isoforms of the molecule. This investigation documents the expression of mRNA coding for fibronectin and its splicing variants, EIIIA and EIIIB, in biopsies of masseter muscle from normal and long-face patients, using reverse transcriptase-polymerase chain reaction. Expression was compared with that occurring in anatomically and embryologically differing somatic skeletal muscle. Masseter expressed fibronectin mRNA containing the EIIIA but not the EIIIB splicing variant. Conversely, somatic skeletal muscle expressed neither the EIIIA nor EIIIB variants. There were no differences between expression of fibronectin containing the EIIIA splicing variants in masseter from normal and long faces. These results suggest that variations in fibronectin expression reflect the differing functional demands of muscles from different anatomical locations and indicate that jaw and somatic muscle belong to different allotypes.

Fibronectin and integrins in cell adhesion, signaling, and morphogenesis

Fibronectin and integrins play crucial roles in a variety of morphogenetic processes, in which they mediate cell adhesion, migration, and signal transduction. They induce hierarchical transmembrane organization of cytoskeletal and signaling molecules into multimolecular complexes of more than 30 proteins. Organization of these complexes is a synergistic process dependent on integrin aggregation and occupancy, as well as tyrosine phosphorylation. Integrins also cooperate with growth-factor receptors to enhance signaling. Fibronectin and integrins induce a variety of downstream effects, including enhanced transcription factor activity, induction of over 30 genes (> half novel), and altered expression of over 100 proteins. Fibronectin and integrins therefore trigger a hierarchy of signaling responses involved in regulating processes crucial for normal morphogenesis, including cell adhesion, migration, and specific gene expression.

Altered rate of fibronectin matrix assembly by deletion of the first type III repeats

The assembly of fibronectin (FN) into a fibrillar matrix is a complex stepwise process that involves binding to integrin receptors as well as interactions between FN molecules. To follow the progression of matrix formation and determine the stages during which specific domains function, we have developed cell lines that lack an endogenous FN matrix but will form fibrils when provided with exogenous FN. Recombinant FNs (recFN) containing deletions of either the RGD cell-binding sequence (RGD-) or the first type III repeats (FN delta III1-7) including the III1 FN binding site were generated with the baculovirus insect cell expression system. After addition to cells, recFN matrix assembly was monitored by indirect immunofluorescence and by insolubility in the detergent deoxycholate (DOC). In the absence of any native FN, FN delta III1-7 was assembled into fibrils and was converted into DOC-insoluble matrix. This process could be inhibited by the amino-terminal 70 kD fragment of FN, showing that FN delta III1-7 follows an assembly pathway similar to FN. The progression of FN delta III1-7 assembly differed from native FN in that the recFN became DOC-insoluble more quickly. In contrast, RGD- recFNs were not formed into fibrils except when added in combination with native FN. These results show that the RGD sequence is essential for the initiation step but fibrils can form independently of the III1-7 modules. The altered rate of FN delta III1-7 assembly suggests that one function of the missing repeats might be to modulate an early stage of matrix formation.