Evidence that distinct states of the integrin alpha6beta1 interact with laminin and an ADAM

Regulation of integrin α6A by lactogenic hormones in rat pancreatic β-cells: Implications for the physiological adaptation to pregnancy

AIM

During pregnancy, the maternal β-cell mass is increased in order to adapt to the physiological changes in insulin demand. Lactogenic hormones stimulate rodent β-cell attachment and proliferation in vitro. The aim of this study was to identify adhesion molecules involved in expansion of the β-cell mass during pregnancy in the rat.

METHODS

Quantitative RT-PCR was used to evaluate the expression of several integrins and laminins in isolated neonatal rat islets in response to growth hormone (GH) and prolactin (PRL) treatment. Double-immunofluorescence staining of rat pancreas was used to localize the expression of integrin α6β1. β-cell proliferation was evaluated by incorporation of bromodeoxyuridine (BrdU). The role of STAT5 phosphorylation was tested by addition of STAT5 mutants.

RESULTS

We found that the mRNA level of integrin-α6A, was upregulated 2.5-fold by PRL or GH. During pregnancy, a biphasic 3.4-4.5-fold increase of integrin-α6A and B mRNA levels was detected. A disintegrin peptide (DP) reduced the hormone-stimulated mitotic activity in neonatal rat β-cells from 2.9 ± 0.4-fold to 1.3 ± 0.3-fold. The hormone-induced expression of α6β1 integrin was shown to be mediated via STAT5 as a dominant negative (DN) mutant prevented and a constitutive active (CA) mutant augmented the hGH-stimulated expression. The DP was found to inhibit hGH-induced transactivation of the PRL receptor promoter 1A and reduce the hGH-induced phosphorylation of STAT5.

CONCLUSION

These results show that integrin-α6 in β-cells is upregulated by lactogenic hormones and is required but not sufficient for the expansion of the β-cell mass in pregnancy in the rat, which may have implications for the understanding and treatment of gestational diabetes mellitus.

Proteolytic fragments of fibronectin function as matrikines driving the chemotactic affinity of prostate cancer cells to human bone marrow mesenchymal stromal cells via the α5β1 integrin

The haematopoietic niche is contributed to by bone marrow-resident mesenchymal stromal cells (BM-MSCs) and subverted by prostate cancer cells. To study mechanisms by which BM-MSCs and prostate cancer cells may interact, we assessed the migration, invasion, adhesion and proliferation of bone-derived prostate cancer cells (PC-3) in co-culture with pluripotent human BM-MSCs. We observed a strong adhesive, migratory and invasive phenotype of PC-3 cells with BM- MSC-co-culture and set out to isolate and characterize the bioactive principle. Initial studies indicated that chemotaxis was secondary to a protein residing in the >100kDa fraction. Size-exclusion chromatography (SEC) recovered peak activity in a high-molecular weight fraction containing thrombospondin-1 (TSP1). While TSP1 immunodepletion decreased activity, put-back with purified TSP1 did not reproduce bioactivity. Further purification of the TSP1-containing high-molecular weight fraction of the BM-MSC secretome with heparin-affinity chromatography recovered bioactivity with highly restricted bands on polyacrylamide gel electrophoresis, determined by mass spectroscopy to be proteolytic fragments of fibronectin (FN). Put-back experiments with full-length FN permitted adhesion but failed to induce migration. Monospecific antibodies to FN blocked adhesion. Proteolytic cleavage of FN generated FN fragments which now induced migration. Neutralizing monoclonal antibodies to FN receptors α5 and β1 integrins, and α5 knockdown specifically blocked migration and adhesion.

CONCLUSION

Fibronectin fragments (FNFr) function as matrikines driving the chemotactic affinity of prostate cancer cells via the α5β1 integrin. Taken together with the high-frequency of α5β1 expression in disseminated prostate cancer cells in bone marrow aspirates from patients, the FNFr/FN-α5β1 interaction warrants further study as a therapeutic target.

3D matrix microenvironment for targeted differentiation of embryonic stem cells into neural and glial lineages

The onset of neurodegenerative disorders is characterized by the progressive dysfunction and loss of subpopulations of specialized cells within specific regions of the central nervous system (CNS). Since CNS has a limited ability for self-repair and regeneration under such conditions, clinical transplantation of stem cells has been explored as an alternative. Although embryonic stem cells (ESCs) offer a promising therapeutic platform to treat a variety of neurodegenerative disorders, the niche microenvironment, which could regulate their differentiation into specialized lineages on demand, needs to be optimized for successful clinical transplantation. Here, we evaluated the synergistic role of matrix microenvironment (type, architecture, composition, stiffness) and signaling molecules (type, dosage) on murine ESC differentiation into specific neural and glial lineages. ESCs were cultured as embryoid bodies on either 2D substrates or within 3D scaffolds, in the presence or absence of retinoic acid (RA) and sonic hedgehog (Shh). Results showed that ESCs maintained their stemness even after 4 days in the absence of exogenous signaling molecules, as evidenced by Oct-4 staining. RA at 1 μM dosage was deemed optimal for neural differentiation and neurite outgrowth on collagen-1 coated substrates. Significant neural differentiation with robust neurite outgrowth and branching was evident only on collagen-1 coated 2D substrates and within 3D matrigel scaffolds, in the presence of 1 μM RA. Blocking α6 or β1 integrin subunits on differentiating cells inhibited matrigel-induced effects on neural differentiation and neurite outgrowth. Hydrogel concentration strongly regulated formation of neural and astrocyte lineages in 1 μM RA additive cultures. When RA and Shh were provided, either alone or together, 3D collagen-1 scaffolds enhanced significant motor neuron formation, while 3D matrigel stimulated dopaminergic neuron differentiation. These results suggest a synergistic role of microenvironmental cues for ESC differentiation and maturation, with potential applications in cell transplantation therapy.

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

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

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

Human salivary gland stem cells: isolation, propagation, and characterization

Stem cells are of outstanding interest for a variety of applications in regenerative medicine. The identification and characterization of novel tissue sources in order to reduce donor site morbidity and to provide specific cells in clinically applicable numbers have led to the detection of stem cells in almost all adult tissues. Salivary glands are of specific interest to our lab, as these tissues are easily accessible for the head and neck surgeon with low donor site morbidity. On the other hand, they possess an endocrine and exocrine function and thus play a very specific role in the human body. Stem cell identity however can only be demonstrated using a combination of different methods in vitro, as there is not a single marker or feature allowing for definite identification of such cells. In this chapter, we provide a comprehensive summary of our experimental methods for the isolation and characterization of human salivary gland stem cells in vitro.

Molecular and protein characterization of two species of the latrunculin-producing sponge Negombata from the Red Sea

Red Sea sponges offer a potential for production of novel drugs and prototypes. The genus Negombata is a type of sponges abundant in the Red Sea. This sponge produces latrunculins that have well documented antitumor activity in addition to antimicrobial and antiviral effects. The identification of Negombata species is based on morphology and microscopical examination of megascleres of spicules. However, these criteria have proven to be unreliable for identification. Therefore, this study was established to test the accuracy of the spicules based taxonomy against molecular and protein profiles for the two species of Negombata: N. magnifica and N. corticata. About 700 bp of cytochrome c oxidase I gene was sequenced from the tissues of the two Negombata species. Additionally total proteins were extracted from Negombata samples collected from different locations during different seasons and separated by denaturing polyacrylamide gel electrophoresis. Characteristic different protein profiles were obtained for both species. The data obtained from cytochrome c oxidase I gene sequencing and protein profiles can reliably differentiate between different species of Negombata in the Red Sea.

ADAM-17: the enzyme that does it all

This review focuses on the role of ADAM-17 in disease. Since its debut as the tumor necrosis factor converting enzyme (TACE), ADAM-17 has been reported to be an indispensible regulator of almost every cellular event from proliferation to migration. The central role of ADAM-17 in cell regulation is rooted in its diverse array of substrates: cytokines, growth factors, and their receptors as well as adhesion molecules are activated or inactivated by their cleavage with ADAM-17. It is therefore not surprising that ADAM-17 is implicated in numerous human diseases including cancer, heart disease, diabetes, rheumatoid arthritis, kidney fibrosis, Alzheimer's disease, and is a promising target for future treatments. The specific role of ADAM-17 in the pathophysiology of these diseases is very complex and depends on the cellular context. To exploit the therapeutic potential of ADAM-17, it is important to understand how its activity is regulated and how specific organs and cells can be targeted to inactivate or activate the enzyme.

Basement membrane in pancreatic islet function

Clinical treatment of diabetic patients by islet transplantation faces various complications. At present, in vitro expansion of islets occurs at the cost of their essential features, which are insulin production and release. However, the recent discovery of blood vessel/beta-cell interactions as an important aspect of insulin transcription, secretion, and proliferation might point us to ways of how this problem could be overcome. The correct function of beta-cells depends on the presence of a basement membrane, a specialized extracellular matrix located around the blood vessel wall in mouse and human pancreatic islets. In this chapter, we summarize how the vascular basement membrane influences insulin transcription, insulin secretion, and beta-cell proliferation. In addition, a brief overview about basement membrane components and their interactions with cell surface receptors is given.

Cell-extracellular matrix interactions regulate neural differentiation of human embryonic stem cells

Background

Interactions of cells with the extracellular matrix (ECM) are critical for the establishment and maintenance of stem cell self-renewal and differentiation. However, the ECM is a complex mixture of matrix molecules; little is known about the role of ECM components in human embryonic stem cell (hESC) differentiation into neural progenitors and neurons.

Results

A reproducible protocol was used to generate highly homogenous neural progenitors or a mixed population of neural progenitors and neurons from hESCs. This defined adherent culture system allowed us to examine the effect of ECM molecules on neural differentiation of hESCs. hESC-derived differentiating embryoid bodies were plated on Poly-D-Lysine (PDL), PDL/fibronectin, PDL/laminin, type I collagen and Matrigel, and cultured in neural differentiation medium. We found that the five substrates instructed neural progenitors followed by neuronal differentiation to differing degrees. Glia did not appear until 4 weeks later. Neural progenitor and neuronal generation and neurite outgrowth were significantly greater on laminin and laminin-rich Matrigel substrates than on other 3 substrates. Laminin stimulated hESC-derived neural progenitor expansion and neurite outgrowth in a dose-dependent manner. The laminin-induced neural progenitor expansion was partially blocked by the antibody against integrin α6 or β1 subunit.

Conclusion

We defined laminin as a key ECM molecule to enhance neural progenitor generation, expansion and differentiation into neurons from hESCs. The cell-laminin interactions involve α6β1 integrin receptors implicating a possible role of laminin/α6β1 integrin signaling in directed neural differentiation of hESCs. Since laminin acts in concert with other ECM molecules in vivo, evaluating cellular responses to the composition of the ECM is essential to clarify further the role of cell-matrix interactions in neural derivation of hESCs.

Distinct roles of integrins alpha6 and alpha4 in homing of fetal liver hematopoietic stem and progenitor cells

Homing of hematopoietic stem cells (HSCs) into the bone marrow (BM) is a prerequisite for establishment of hematopoiesis during development and following transplantation. However, the molecular interactions that control homing of HSCs, in particular, of fetal HSCs, are not well understood. Herein, we studied the role of the alpha6 and alpha4 integrin receptors for homing and engraftment of fetal liver (FL) HSCs and hematopoietic progenitor cells (HPCs) to adult BM by using integrin alpha6 gene-deleted mice and function-blocking antibodies. Both integrins were ubiquitously expressed in FL Lin(-)Sca-1(+)Kit(+) (LSK) cells. Deletion of integrin alpha6 receptor or inhibition by a function-blocking antibody inhibited FL LSK cell adhesion to its extracellular ligands, laminins-411 and -511 in vitro, and significantly reduced homing of HPCs to BM. In contrast, the anti-integrin alpha6 antibody did not inhibit BM homing of HSCs. In agreement with this, integrin alpha6 gene-deleted FL HSCs did not display any homing or engraftment defect compared with wild-type littermates. In contrast, inhibition of integrin alpha4 receptor by a function-blocking antibody virtually abrogated homing of both FL HSCs and HPCs to BM, indicating distinct functions for integrin alpha6 and alpha4 receptors during homing of fetal HSCs and HPCs.

The ADAMs family: coordinators of nervous system development, plasticity and repair

A disintegrin and metalloprotease (ADAM) transmembrane proteins have metalloprotease, integrin-binding, intracellular signaling and cell adhesion activities. In contrast to other metalloproteases, ADAMs are particularly important for cleavage-dependent activation of proteins such as Notch, amyloid precursor protein (APP) and transforming growth factor alpha (TGFalpha), and can bind integrins. Not surprisingly, ADAMs have been shown or suggested to play important roles in the development of the nervous system, where they regulate proliferation, migration, differentiation and survival of various cells, as well as axonal growth and myelination. On the eleventh anniversary of the naming of this family of proteins, the relatively unknown ADAMs are emerging as potential therapeutic targets for neural repair. For example, over-expression of ADAM10, one of the alpha-secretases for APP, can prevent amyloid formation and hippocampal defects in an Alzheimer mouse model. Another example of this potential neural repair role is the finding that ADAM21 is uniquely associated with neurogenesis and growing axons of the adult brain. This comprehensive review will discuss the growing literature about the roles of ADAMs in the developing and adult nervous system, and their potential roles in neurological disorders. Most excitingly, the expanding understanding of their normal roles suggests that they can be manipulated to promote neural repair in the degenerating and injured adult nervous system.

Quantitative determination of latrunculins A and B in the Red Sea sponge Negombata magnifica by high performance liquid chromatography

An accurate, reproducible and sensitive method for the quantitative determination of latrunculins A and B in the organic extract of the Red Sea sponge Negombata magnifica was developed and validated. Latrunculin A and B concentrations were determined by RP-C18-HPLC and a mobile phase consisting of acetonitrile and water (60:40, v/v). The flow rate utilized was 1 mL min(-1) and the detector was set at 235 nm. The HPLC analysis of several N. magnifica samples collected from different locations in the Red Sea revealed that Ras Mohamed had the highest concentrations of latrunculin A, while Safaga had the highest levels of latrunculin B. Also, a comparison between latrunculin concentrations in the summer and winter revealed that the yield of latrunculins were generally higher in the winter.

Expression and relationship of male reproductive ADAMs in mouse

A number of a disintegrin and metalloprotease (ADAM) family members are expressed in mammalian male reproductive organs such as testis and epididymis. These reproductive ADAMs are divided phylogenically into three major groups: ADAMs 1, 4, 6, 20, 21, 24, 25, 26, 29, 30, and 34 (the first group); ADAMs 2, 3, 5, 27, and 32 (the second group); and ADAMs 7 and 28 (the third group). Previous mouse knockout studies indicate that ADAM1, ADAM2, and ADAM3 have intricate expressional relationships, playing critical roles in fertilization. In the present study, we analyzed processing, biochemical characteristics, localization, and expressional relationship of the previously-unexplored, second-group ADAMs (ADAM5, ADAM27, and ADAM32). We found that all of the three ADAMs are made as precursors in the testis and processed during epididymal maturation, and that ADAM5 and ADAM32, but not ADAM27, are located on the sperm surface. Using sperm from Adam2(-/-) and Adam3(-/-) mice, we found that, among the three ADAMs, the level of ADAM5 is modestly and severely reduced in Adam3 and Adam2 knockout sperm, respectively. Further, we analyzed ADAM7, an epididymis-derived sperm surface ADAM from the separate phylogenetic group, in the knockout sperm. We found that the level of ADAM7 is also significantly reduced in both Adam2 and Adam3-null sperm. Taken together, our results suggest a novel expressional relationship of ADAM5 and ADAM7 with ADAM2 and ADAM3, which play critical roles in fertilization.

Cyclic FEE peptide increases human gamete fusion and potentiates its RGD-induced inhibition

BACKGROUND

Alpha6beta1 integrin has been proposed to act as a sperm receptor on the mouse oocyte by interacting with spermatozoon fertilin beta. We investigated, in humans, whether oocyte integrins could act similarly in gamete fusion, using a cyclic peptide containing the putative disintegrin-binding domain of human fertilin beta [cyclic FEE (cFEE)] and RGD peptide.

METHODS

Zona-free eggs were inseminated in the absence or presence of peptides. To maintain the membrane protein pattern, the zona pellucida was removed by microdissection. Immunofluorescence and confocal microscopy were used to detect integrin subunits on the oocyte.

RESULTS

Unexpectedly, cFEE alone increased human gamete fusion by 94% instead of inhibiting fertilization. Furthermore, cFEE together with RGD potentiated the RGD-induced inhibition of fertilization in a dose-dependent manner. The data suggested the hypothesis of integrin cross-talk, further supported by the co-localization of alpha6beta1 and alphavbeta3 integrins, the putative receptors of cFEE and RGD peptides, respectively.

CONCLUSIONS

RGD-sensitive and -insensitive integrins may be associated in a multimolecular complex working as a sperm receptor on the human oocyte membrane. Supplementation of human IVF culture medium with cFEE peptide might improve fertilization rates in ART.

Cell migration: mechanisms of rear detachment and the formation of migration tracks

Cell migration is central to many biological and pathological processes, including embryogenesis, tissue repair and regeneration as well as cancer and the inflammatory response. In general, cell migration can be usefully conceptualized as a cyclic process. The initial response of a cell to a migration-promoting agent is to polarize and extend protrusions in the direction of migration. These protrusions can be large, broad lamellipodia or spike-like filopodia, are usually driven by actin polymerization, and are stabilized by adhering to the extracellular matrix (ECM) via transmembrane receptors of the integrin family linked to the actin cytoskeleton. These adhesions serve as traction sites for migration as the cell moves forward over them, and they must be disassembled at the cell rear, allowing it to detach. The mechanisms of rear detachment and the regulatory processes involved are not well understood. The disassembly of adhesions that is required for detachment depends on a coordinated interaction of actin and actin-binding proteins, signaling molecules and effector enzymes including proteases, kinases and phosphatases. Originally, the biochemically regulated processes leading to rear detachment of migrating cells were thought not to be necessarily accompanied by any loss of cell material. However, it has been shown that during rear detachment long tubular extensions, the retracting fibers, are formed and that "membrane ripping" occurs at the cell rear. By this process, a major fraction of integrin-containing cellular material is left behind forming characteristic migration tracks that exactly mark the way a cell has taken.

Integrin-growth factor interactions as regulators of oligodendroglial development and function

Central nervous system (CNS) development requires mechanisms for the regulation of cell number. Although growth factors are essential determinants of the proliferation and apoptosis that determine final numbers, the long-range nature of signals from diffusible growth factors makes them insufficient for the provision of the precise and localized signals required. Integration of integrin and growth factor receptor signaling in controlling cell behavior has been an important theme of research over the past several years. The focus of this review is on the mechanisms by which integrin-growth factor interactions regulate the development of oligodendrocytes and provide a mechanism for controlling, both in space and in time, oligodendrocyte numbers in the developing CNS.

ADAM23 is a cell-surface glycoprotein expressed by central nervous system neurons

Several members of the ADAM (a disintegrin and metalloprotease) family of proteins have been implicated in biological processes ranging from fertilization to myoblast fusion and neural cell fate determination. These proteins have so far been studied mostly in terms of their protease activity, but a considerable amount of evidence suggests that many ADAMs are also important as receptors for cell-surface integrins. We have shown that, for one such member of the family, ADAM23, mRNA transcripts are expressed in neuronal cells throughout the rat brain, at all stages of postnatal development, and that particularly high transcript concentrations are found in the hippocampus and cerebellum. Using an antibody that we raised against the rat ADAM23 disintegrin domain, we found that ADAM23 is present at detectable levels only in nervous system tissue. Our analysis of ADAM23 expression in cultured cerebellar granule cells (CGCs) furthermore suggested that this protein is synthesized as a glycosylated precursor of about 100 kD whose maturation depends on cleavage by furin or a related enzyme. We have also shown ADAM23 to be expressed primarily as a cell-surface protein that appears to be localized to sites of intercellular contact. Taken together, these data are consistent with a model wherein ADAM23 serves to mediate cell-cell interactions within the mammalian CNS.

Skeletal phenotype of growing transgenic mice that express a function-perturbing form of beta1 integrin in osteoblasts

Skeletal modeling entails the deposition of large amounts of extracellular matrix (ECM) to form structures tailored to withstand increasing mechanical loads during rapid growth. Specific ECM molecules bind to integrin receptors on the cell surface, thereby triggering a cascade of signaling events that affect critical cell functions. To evaluate the role of integrins during skeletal growth, transgenic mice were engineered to express a function-perturbing fragment of beta1 integrin consisting of the transmembrane domain and cytoplasmic tail under the control of the osteocalcin promoter (TG mice). Thus, transgene expression was targeted to mature cells of the osteoblast lineage, and herein we show that cultured cells resembling osteocytes from 90-day-old TG mice display impaired adhesion to collagen I, a ligand for beta1 integrin. To determine the influence of beta1 integrin on bones that are responsible for providing structural support during periods of rapid growth, we examined the phenotype of the appendicular skeleton in TG mice compared to wild type (WT) mice. According to radiographs, bones from mice of both genotypes between 14 and 90 days of age appeared similar in gross structure and density, although proximal tibiae from 35-90 days old TG mice were less curved than those of WT mice (72-92% TG/WT). Although there were only mild and transient differences in absolute bone mass and strength, once normalized to body mass, the tibial dry mass (79.1% TG/WT females), ash mass (78.5% TG/WT females), and femoral strength in torsion (71.6% TG/WT females) were reduced in TG mice compared to WT mice at 90 days of age. Similar effects of genotype on bone mass and curvature were observed in 1-year-old retired breeders, indicating that these phenotypic differences between TG and WT mice were stable well into adulthood. Effects of genotype on histomorphometric indices of cancellous bone turnover were minimal and evident only transiently during growth, but when present they demonstrated differences in osteoblast rather than osteoclast parameters. Together, these results suggest that integrin signals generated during growth enhance the acquisition of a skeletal mass, structure, and strength to withstand the mechanical loads generated by weight-bearing.

Fertilin beta peptidic liposomes inhibit fertilization by steric blockage

Liposomes presenting fertilinbeta peptides are inhibitors of mouse in vitro fertilization. We undertook a study of the relationship between IC(50) and mole fraction of fertilinbeta in the liposome, and the size dependence of inhibition of fertilization to understand the mechanism of their inhibition. Our results indicate that a small number of multivalent contacts are required for efficient attachment of inhibitor to receptor on the target membrane, and that, as designed, the liposomes target the egg membrane but not the sperm membrane. The size dependence of the liposome inhibition demonstrates that the liposomes physically block access of the sperm to the egg membrane thereby preventing sperm binding to all egg receptors not just the fertilinbeta receptor.

Overexpression of ADAM9 in non-small cell lung cancer correlates with brain metastasis

The "a disintegrin and metalloprotease" (ADAM) family contributes to regulation of the cell-cell and cell-matrix interactions that are critical determinants of malignancy. To determine the relationship between metastasis and ADAM proteins, we compared the mRNA levels of ADAM9, -10, -12, -15, and -17 in sublines of an EBC-1 lung cancer cell line that were highly metastatic to either brain or bone. ADAM9 mRNA levels were significantly higher in highly brain-metastatic sublines than in the parent or highly bone-metastatic sublines. To elucidate the role of ADAM9 in brain metastasis, we stably transfected A549 and EBC-1 cells with a full-length ADAM9 expression vector. Compared with mock-transfectants, ADAM9 overexpression resulted in increased invasive capacity in response to nerve growth factor, increased adhesion to brain tissue, and increased expression of integrin alpha 3 and beta 1 subunits. Administration of the anti-beta 1 monoclonal antibody attenuated this increase in invasive and adhesive activity. Intravenous administration of ADAM9-overexpressing A549 cells to mice resulted in micrometastatic foci in the brain and multiple metastatic colonies in the lungs. In contrast, administration of parent and mock-transfected A549 cells to mice resulted in lung tumors without brain metastasis. These results suggest that ADAM9 overexpression enhances cell adhesion and invasion of non-small cell lung cancer cells via modulation of other adhesion molecules and changes in sensitivity to growth factors, thereby promoting metastatic capacity to the brain.

Extracellular matrix: recent advances on its role in junction dynamics in the seminiferous epithelium during spermatogenesis

Spermatogenesis takes place in the seminiferous epithelium of the mammalian testis in which one type A1 spermatogonium (diploid, 2n) gives rise to 256 spermatids (haploid, 1n). To accomplish this, developing germ cells, such as preleptotene and leptotene spermatocytes, residing in the basal compartment of the seminiferous epithelium must traverse the blood-testis barrier (BTB) entering into the adluminal compartment for further development into round, elongating, and elongate spermatids. Recent studies have shown that the basement membrane in the testis (a modified form of extracellular matrix, ECM) is important to the event of germ cell movement across the BTB because proteins in the ECM were shown to regulate BTB dynamics via the interactions between collagens, proteases, and protease inhibitors, possibly under the regulation of cytokines. While these findings are intriguing, they are not entirely unexpected. For one, the basement membrane in the testis is intimately associated with the BTB, which represents the basolateral region of Sertoli cells. Also, Sertoli cell tight junctions (TJs) that constitute the BTB are present side-by-side with cell-cell actin-based adherens junctions (AJ, such as basal ectoplasmic specialization [ES]) and intermediate filament-based desmosome-like junctions. As such, the relative morphological layout between TJs, AJs, and desmosome-like junctions in the seminiferous epithelium is in sharp contrast to other epithelia where TJs are located at the apical portion of an epithelium or endothelium, furthest away from ECM, to be followed by AJs and desmosomes, which in turn constitute the junctional complex. For another, anchoring junctions between a cell epithelium and ECM found in multiple tissues, also known as focal contacts (or focal adhesion complex, FAC, an actin-based cell-matrix anchoring junction type), are the most efficient junction type that permits rapid junction restructuring to accommodate cell movement. It is therefore physiologically plausible, and perhaps essential, that the testis is using some components of the focal contacts to regulate rapid restructuring of AJs between Sertoli and germ cells when germ cells traverse the seminiferous epithelium. Indeed, recent findings have shown that the apical ES, a testis-specific AJ type in the seminiferous epithelium, is equipped with proteins of FAC to regulate its restructuring. In this review, we provide a timely update on this exciting yet rapidly developing field regarding how the homeostasis of basement membrane in the tunica propria regulates BTB dynamics and spermatogenesis in the testis, as well as a critical review on the molecular architecture and the regulation of ES in the seminiferous epithelium.

Recognition of the N-terminal modules of thrombospondin-1 and thrombospondin-2 by alpha6beta1 integrin

In addition to its recognition by alpha3beta1 and alpha4beta1 integrins, the N-terminal pentraxin module of thrombospondin-1 is a ligand for alpha6beta1 integrin. alpha6beta1 integrin mediates adhesion of human microvascular endothelial and HT-1080 fibrosarcoma cells to immobilized thrombospondin-1 and recombinant N-terminal regions of thrombospondin-1 and thrombospondin-2. alpha6beta1 also mediates chemotaxis of microvascular cells to thrombospondin-1 and thrombospondin-2. Using synthetic peptides, LALERKDHSG was identified as an alpha6beta1-binding sequence in thrombospondin-1. This peptide inhibited alpha6beta1-dependent cell adhesion to thrombospondin-1, thrombospondin-2, and the E8 fragment of murine laminin-1. The Glu residue in this peptide was required for activity, and the corresponding residue (Glu90) in the N-terminal module of thrombospondin-1 was required for its recognition by alpha6beta1, but not by alpha4beta1. alpha6beta1 was also expressed in human umbilical vein endothelial cells; but in these cells, only certain agonists could activate the integrin to recognize thrombospondins. Selective activation of alpha6beta1 integrin in microvascular endothelial cells by the anti-beta1 antibody TS2/16 therefore accounts for their adhesion responses to thrombospondins and explains the distinct functions of alpha4beta1 and alpha6beta1 integrins as thrombospondin receptors in microvascular and large vessel endothelial cells.

ADAM12 induces actin cytoskeleton and extracellular matrix reorganization during early adipocyte differentiation by regulating beta1 integrin function

Changes in cell shape are a morphological hallmark of differentiation. In this study we report that the expression of ADAM12, a disintegrin and metalloprotease, dramatically affects cell morphology in preadipocytes, changing them from a flattened, fibroblastic appearance to a more rounded shape. We showed that the highest levels of ADAM12 mRNA were detected in preadipocytes at the critical stage when preadipocytes become permissive for adipogenic differentiation. Furthermore, as assessed by immunostaining, ADAM12 was transiently expressed at the cell surface concomitant with the reduced activity of beta1 integrin. Co-immunoprecipitation studies indicated the formation of ADAM12/beta1 integrin complexes in these preadipocytes. Overexpression of ADAM12 at the cell surface of 3T3-L1 preadipocytes achieved by transient transfection or retroviral transduction led to the disappearance of the extensive network of actin stress fibers that are characteristic of these cells, and its reorganization into a cortical network located beneath the cell membrane. The cells became more rounded, exhibited fewer vinculin-positive focal adhesions, and adhered less efficiently to fibronectin in attachment assays. Moreover, ADAM12-expressing cells were more prone to apoptosis, which could be prevented by treating the cells with beta1-activating antibodies. A reduced and re-organized fibronectin-rich extracellular matrix accompanied these changes. In addition, beta1 integrin was more readily extracted with Triton X-100 from cells overexpressing ADAM12 than from control cells. Collectively, these results show that surface expression of ADAM12 impairs the function of beta1 integrins and, consequently, alters the organization of the actin cytoskeleton and extracellular matrix. These events may be necessary for early adipocyte differentiation.

Integrin shedding as a mechanism of cellular adaptation during cardiac growth

Integrin-mediated cell-extracellular matrix (ECM) interactions are essential for multiple cellular processes; however, little is known regarding integrin turnover during these events. Recent studies have demonstrated shedding of cell surface molecules and suggested this as a potential mechanism for integrin turnover. Confocal microscopy of mouse hearts under different physiological conditions demonstrated the presence of beta(1)-integrin-immunoreactive material in the interstitium. Culture media from neonatal rat cardiac myocytes and fibroblasts contained a 55-kDa fragment of beta(1)-integrin. Attachment to ECM components, response to phorbol 12-myristate 13-acetate stimulation, and matrix metalloproteinase inhibition assays demonstrated that fibroblasts responded differently to the fragment compared with myocytes. The beta(1)-integrin fragment stimulated myocyte attachment to collagen and the fragment itself bound a variety of ECM proteins. These studies indicate that as myocytes and fibroblasts change size and shape, cellular contacts with the ECM are altered, resulting in the liberation of a beta(1)-integrin fragment from the cell surface. Integrin shedding may represent a novel mechanism of rapidly modifying cell-ECM contacts during various cellular processes.

None of the integrins known to be present on the mouse egg or to be ADAM receptors are essential for sperm-egg binding and fusion

Antibody inhibition and alpha6beta1 ligand binding experiments indicate that the egg integrin alpha6beta1 functions as a receptor for sperm during gamete fusion; yet, eggs null for the alpha6 integrin exhibit normal fertilization. Alternative integrins may be involved in sperm-egg binding and fusion and could compensate for the absence of alpha6beta1. Various beta1 integrins and alphav integrins are present on mouse eggs. Some of these integrins are also reported to be receptors for ADAMs, which are expressed on sperm. Using alpha3 integrin null eggs, we found that the alpha3beta1 integrin was not essential for sperm-egg binding and fusion. Oocyte-specific, beta1 integrin conditional knockout mice allowed us to obtain mature eggs lacking all beta1 integrins. We found that the beta1 integrin null eggs were fully functional in fertilization both in vivo and in vitro. Furthermore, neither anti-mouse beta3 integrin function-blocking monoclonal antibody (mAb) nor alphav integrin function-blocking mAb inhibited sperm binding to or fusion with beta1 integrin null eggs. Thus, function of beta3 or alphav integrins does not seem to be involved in compensating for the absence of beta1 integrins. These results indicate that none of the integrins known to be present on mouse eggs or to be ADAM receptors are essential for sperm-egg binding/fusion, and thus, egg integrins may not play the role in gamete fusion previously attributed to them.

Laminin isoform-specific promotion of adhesion and migration of human bone marrow progenitor cells

Laminins are alphabetagamma heterotrimeric extracellular proteins that regulate cellular functions by adhesion to integrin and nonintegrin receptors. Laminins containing alpha4 and alpha5 chains are expressed in bone marrow, but their interactions with hematopoietic progenitors are unknown. We studied human bone marrow cell adhesion to laminin-10/11 (alpha5beta1gamma1/alpha5beta2gamma1), laminin-8 (alpha4beta1gamma1), laminin-1 (alpha1beta1gamma1), and fibronectin. About 35% to 40% of CD34(+) and CD34(+)CD38(-) stem and progenitor cells adhered to laminin-10/11, and 45% to 50% adhered to fibronectin, whereas they adhered less to laminin-8 and laminin-1. Adhesion of CD34(+)CD38(-) cells to laminin-10/11 was maximal without integrin activation, whereas adhesion to other proteins was dependent on protein kinase C activation by 12-tetradecanoyl phorbol-13-acetate (TPA). Fluorescence-activated cell-sorting (FACS) analysis showed expression of integrin alpha6 chain on most CD34(+) and CD34(+)CD38(-) cells. Integrin alpha6 and beta1 chains were involved in binding of both cell fractions to laminin-10/11 and laminin-8. Laminin-10/11 was highly adhesive to lineage-committed myelomonocytic and erythroid progenitor cells and most lymphoid and myeloid cell lines studied, whereas laminin-8 was less adhesive. In functional assays, both laminin-8 and laminin-10/11 facilitated stromal-derived factor-1alpha (SDF-1alpha)-stimulated transmigration of CD34(+) cells, by an integrin alpha6 receptor-mediated mechanism. In conclusion, we demonstrate laminin isoform-specific adhesive interactions with human bone marrow stem, progenitor, and more differentiated cells. The cell-adhesive laminins affected migration of hematopoietic progenitors, suggesting a physiologic role for laminins during hematopoiesis.

Developmental regulation and neuronal expression of the cellular disintegrin ADAM11 gene in mouse nervous system

ADAM11 is the prototype member of the predominantly CNS-associated clade of the ADAM metalloprotease-disintegrins that has been implicated in neural adhesion and axon guidance. The present study describes the spatiotemporal expression pattern of the ADAM11 gene in adult and developing mouse, and identifies the cells expressing the gene. In the adult CNS, ADAM11 mRNA was present throughout the forebrain, including different cortical fields and diencephalic nuclei. In brainstem, low to moderate expression was detected in certain midbrain nuclei, while several pontine and medullary nuclei showed a very strong signal. High expression was observed in the cerebellar cortex and spinal cord. In addition, ADAM11 was expressed in ganglia of the peripheral nervous system (PNS), retinae, testes, liver, and at lower levels in epidermal and mucosal epithelia, kidney, and salivary gland. The expression was localized to neurons in all examined CNS and PNS subfields. During pre- and perinatal development, ADAM11 was differentially expressed both in the developing PNS and CNS, as well as in heart, kidney, eyes, and brown fat. The present results suggest a widespread involvement of ADAM11 in neuron-neuron or neuron-glial cell interactions during development as well as in the adult nervous system. They provide novel complementary information to recently accumulated data on CNS integrin gene expression and offer useful clues for further studies of the neural functions of ADAMs and integrins.

Proprotein convertases in tumor progression and malignancy: novel targets in cancer therapy

The mammalian subtilisin/kexin-like proprotein convertase (PC) family has been implicated in the activation of a wide spectrum of proteins. These proteins are usually synthesized as inactive precursors before their conversion to fully mature bioactive forms. A large majority of these active proteins such as matrix metalloproteases, growth factors, and adhesion molecules are crucial in the processes of cellular transformation, acquisition of the tumorigenic phenotype, and metastases formation. Inhibition of PCs significantly affects the malignant phenotype of various tumor cells. In addition to direct tumor cell proliferation and migration blockade, PC inhibitors can also be used to target tumor angiogenesis. In this Review article we discuss a number of recent findings on the clinical relevance of PCs in cancer patients, their implication in the regulation of multiple cellular functions that impact on the invasive/metastatic potential of cancer cells. Thus, PC inhibitors may constitute new promising agents for the treatment of multiple tumors and/or in adjuvant therapy to prevent recurrence.

Expression of fertilin and CD9 in bovine trophoblast and endometrium during implantation

The superficial placentation of cattle involves the development of fetal binucleate cells that arise from the chorion and migrate between adjacent cell tight junctions to fuse with maternal epithelium. Thus, the temporal and spatial patterns of expression of the cell migration, adhesion, and fusion molecules fertilin and CD9 were investigated in bovine trophoblast and endometrium. Bovine fertilin alpha and fertilin beta messenger RNA sequences were amplified by reverse transcriptase-polymerase chain reaction in testis (positive control), peri-implantation (Days 18, 19, and 21), and postimplantation (Days 35-40) trophoblast RNA, but not in caruncular endometrium (Day 40). Northern blot analysis indicated that the transcript hybridizing to fertilin alpha in trophoblast RNA was approximately 4.0 kilobases (kb), whereas in testis, 2 transcripts of approximately 3.3 and 3.8 kb were indicated. The transcript hybridizing to the fertilin beta probe was also larger in trophoblast than in testis ( approximately 3.8 vs. 2.4 kb, respectively). In situ hybridization revealed that fertilin beta mRNA was expressed by trophoblast cells, including binucleate cells. Immunohistochemical study of CD9, a member of the transmembrane-4-superfamily which is thought to be involved in sperm-egg fusion, showed that CD9 was present on the apical surface of uterine epithelium and in a subpopulation of binucleate cells of the trophoblast. Immunoprecipitation followed by Western blot analysis showed association between CD9 and integrin alpha3 in endometrium. The results support the hypothesis that fertilin and CD9 are involved in bovine binucleate cell migration and fusion.

Inhibitory effects of salmosin, a disintegrin, on posterior capsular opacification in vitro and in vivo

The proliferation, migration and transdifferentiation of the remaining lens epithelial cells (LECs) after cataract surgery are a major cause of posterior capsular opacification (PCO). It has previously been reported that salmosin, a novel disintegrin, significantly inhibits solid tumor growth in mice by perturbation of tumor-specific angiogenesis via blocking alpha v beta 3 integrin expressed on vascular endothelial cells. In this study, the inhibitory function of salmosin in PCO was investigated and was found that salmosin inhibits the attachment of bovine LECs and rabbit lens cells (N/N1003A) to extracellular matrix-coated plates. The anti-adhesive activity of salmosin was approximately 1000 times higher than that of synthetic Arg-Gly-Asp peptide. In addition, the cell proliferation and migration of bovine LECs and N/N1003A were strongly inhibited by salmosin, whereas the proliferation of corneal endothelial cells was less affected. LEC migration and proliferation were also decreased by salmosin treatment in rabbit eyes without any toxic effect in the cornea, iris and retina. In this study, salmosin was shown to specifically inhibit LEC migration and proliferation in an animal model. Therefore, the authors suggest that further investigation may show salmosin to be a good candidate for inhibiting PCO development.

Molecular cloning and expression analysis of a novel member of the Disintegrin and Metalloprotease-Domain (ADAM) family

We cloned and characterized the cDNA and the expression pattern of a novel member of the murine 'Disintegrin and Metalloprotease-Domain Family' (ADAM). The predicted protein sequence reveals highest homology to the testase-subgroup, composed of ADAM 24, ADAM 25 and ADAM 26 and is therefore called testase 4. Reverse transcription-polymerase chain reaction showed a strong expression of testase 4 in the adult testis, but not in any other organ or embryonic stage tested. Careful characterization by in situ hybridization confirmed specific expression of testase 4 in maturing sperm cells of 6-week-old mice, whereas no specific hybridization pattern was detectable in testes of 2.5-week-old mice. These data indicate a correlation between testase 4 expression and spermatogenesis and/or fertilization.

Analysis of the roles of RGD-binding integrins, alpha(4)/alpha(9) integrins, alpha(6) integrins, and CD9 in the interaction of the fertilin beta (ADAM2) disintegrin domain with the mouse egg membrane

Fertilin beta (also known as ADAM2), a mammalian sperm protein that mediates gamete cell adhesion during fertilization, is a member of the ADAM protein family whose members have disintegrin domains with homology to integrin ligands found in snake venoms. Fertilin beta utilizes an ECD sequence within its disintegrin domain to interact with the egg plasma membrane; the Asp is especially critical. Based on what is known about different integrin subfamilies and their ligands, we sought to characterize fertilin beta binding sites on mouse eggs, focusing on integrin subfamilies that recognize short peptide sequences that include an Asp residue: the alpha(5)/alpha(8)/alpha(v)/alpha(IIb) or RGD-binding subfamily (alpha(5)beta(1), alpha(8)beta(1), alpha(V)beta(1), alpha(V)beta(3), alpha(V)beta(5), alpha(V)beta(6), alpha(V)beta(8), and alpha(IIb)beta(3)) and the alpha(4)/alpha(9) subfamily (alpha(4)beta(1), alpha(9)beta(1), and alpha(4)beta(7)). We tested peptide sequences known to perturb interactions mediated by these integrins in two different assays for fertilin beta binding. Peptides with the sequence MLDG, which perturb alpha(4)/alpha(9) integrin-mediated interactions, significantly inhibit fertilin beta binding to eggs, which suggests a role for a member of this integrin subfamily as a fertilin beta receptor. RGD peptides, which perturb alpha(5)/alpha(8)/alpha(v)/alpha(IIb) integrin-mediated interactions, have partial inhibitory activity. The anti-alpha(6) antibody GoH3 has little or no inhibitory activity. An antibody to the integrin-associated tetraspanin protein CD9 inhibits the binding of a multivalent presentation of fertilin beta (immobilized on beads) but not soluble fertilin beta, which we speculate has implications for the role of CD9 in the strengthening of fertilin beta-mediated cell adhesion but not in initial ligand binding.

The lymphocyte metalloprotease MDC-L (ADAM 28) is a ligand for the integrin alpha4beta1

The interaction of lymphocytes with other cells is critical for normal immune surveillance and response. MDC-L (ADAM 28), a member of the ADAM (a disintegrin and metalloprotease) protein family, is expressed on the surface of human lymphocytes. ADAMs possess a disintegrin-like domain similar in sequence to small non-enzymatic snake venom peptides that act as integrin antagonists. We report here that the disintegrin domain of MDC-L is recognized by the leukocyte integrin alpha(4)beta(1). Recombinant Fc fusion proteins possessing the disintegrin domain of MDC-L supported adhesion of the T-lymphoma cell line, Jurkat, in a concentration- and divalent cation-dependent manner. Adhesion of Jurkat cells to the disintegrin domain of MDC-L was inhibited by an anti-MDC-L monoclonal antibody (mAb), Dis1-1. The epitope for mAb Dis1-1 was localized within 59 residues of the disintegrin domain. Recombinant expression of this 59-residue fragment of the disintegrin domain also supported cell adhesion. Adhesion of Jurkat cells to the MDC-L disintegrin domain was specifically inhibited by anti-alpha(4) and anti-beta(1) function-blocking mAbs. Furthermore, adhesion of various cell lines to MDC-L correlated with expression of the integrin alpha(4)-subunit. Transfected K562 cells expressing alpha(4)beta(1) adhered to the disintegrin domain in contrast to non-transfected K562 cells. We further investigated the binding of recombinant MDC-L disintegrin domain (rDis-Fc) in solution. The rDis-Fc was found to bind to Jurkat cells in solution in a concentration-dependent and saturable manner. Both adhesion and solution binding of rDis-Fc was inhibited by the alpha(4)beta(1) ligand mimetic CS-1 peptide. Additionally, recognition of the MDC-L disintegrin domain required "activation" of lymphocyte beta(1) integrins. The interaction of MDC-L with alpha(4)beta(1) may potentially regulate metalloprotease function by targeting or sequestering the active protease on the cell surface. These results suggest a potential role for the lymphocyte ADAM, MDC-L, in the interaction of lymphocytes with alpha(4)beta(1)-expressing leukocytes.

Oolemmal proteomics

Fertilization is defined as a series of gametic interactions in which capacitated sperm must first penetrate the egg vestments and then bind to and fuse with the egg plasma membrane (oolemma). The molecular basis of sperm-egg binding and fusion has yet to be elucidated due, in part, to how little is known about the array of proteins residing on the oolemma. Proteomics is an emerging area of research that directly evaluates protein expression by resolving, identifying, quantitating, and characterizing proteins utilizing a variety of techniques including high resolution two-dimensional polyacrylamide gel electrophoresis (2D PAGE), tandem mass spectrometry, and computer analysis. Our research group has utilized 2D PAGE to begin building a mouse oocyte proteomic database, with over 500 silver-stained proteins being resolved and digitized to date. Cell-surface labeling with biotin has identified a subset of 80 putative egg surface proteins. Amino acid microsequences from over 30 of the surface-labeled proteins has been obtained by tandem mass spectrometry. Sequences from eight of these proteins do not match any sequences from protein and DNA databanks, indicating that these proteins are novel. Our major current research goal is to clone, characterize, and express the novel proteins that are shown to be ovary-specific and investigate their functional roles in sperm-egg interaction.

Trophoblast-specific expression and function of the integrin alpha 7 subunit in the peri-implantation mouse embryo

For implantation and placentation to occur, mouse embryo trophoblast cells must penetrate the uterine stroma to make contact with maternal blood vessels. A major component of the uterine epithelial basement membrane and underlying stromal matrix with which they interact is the extracellular matrix protein laminin. We have identified integrin alpha 7 beta 1 as a major receptor for trophoblast-laminin interactions during implantation and yolk sac placenta formation. It is first expressed by trophectoderm cells of the late blastocyst and by all trophectoderm descendants in the early postimplantation embryo through E8.5, then disappears except in cells at the interface between the allantois and the ectoplacental plate. Integrin alpha 7 expression is a general characteristic of the early differentiation stages of rodent trophoblast, given that two different cultured trophoblast cell lines also express this integrin. Trophoblast cells interact with at least three different laminin isoforms (laminins 1, 2/4, and 10/11) in the blastocyst and in the uterus at the time of implantation. Outgrowth assays using function-blocking antibodies show that alpha 7 beta 1 is the major trophoblast receptor for laminin 1 and a functional receptor for laminins 2/4 and 10/11. When trophoblast cells are cultured on substrates of these three laminins, they attach and spread on all three, but show decreased proliferation on laminin 1. These results show that the alpha 7 beta 1 integrin is expressed by trophoblast cells and acts as receptor for several isoforms of laminin during implantation. These interactions are not only important for trophoblast adhesion and spreading but may also play a role in regulating trophectoderm proliferation and differentiation.

Analysis of fertilin alpha (ADAM1)-mediated sperm-egg cell adhesion during fertilization and identification of an adhesion-mediating sequence in the disintegrin-like domain

Fertilin alpha (also known as ADAM1) is a member of the ADAM (A disintegrin and A metalloprotease domain) family of proteins. In this study, we examine the mechanism of mouse fertilin alpha's in adhesion of sperm to the egg plasma membrane during fertilization. We find that recombinant forms of fertilin alpha corresponding to either the disintegrin-like domain or the cysteine-rich domain and the EGF-like repeat can perturb sperm-egg binding, suggesting that both of these domains can participate in fertilin alpha-mediated adhesion events. In further examination of the fertilin alpha disintegrin-like domain, we find that a subdomain of disintegrin-like domain with the sequence DLEECDCG outside the putative disintegrin loop but with homology to the fertilin beta disintegrin loop can inhibit the binding of both sperm and recombinant fertilin alpha to eggs, suggesting that this is an adhesion-mediating motif of the fertilin alpha disintegrin-like domain. This sequence also inhibits the binding of recombinant fertilin beta to eggs and thus is the first peptide sequence found to block two different sperm ligands. Finally, a monoclonal antibody to the tetraspanin protein CD9, KMC.8, inhibited the binding of recombinant fertilin alpha to eggs in one type of binding assay, suggesting that, under certain conditions, fertilin alpha may interact with a KMC.8-sensitive binding site on the egg plasma membrane.

Fertilin beta and other ADAMs as integrin ligands: insights into cell adhesion and fertilization

One of the most important cell-cell interactions is that of the sperm with the egg. This interaction, which begins with cell adhesion and culminates with membrane fusion, is mediated by multiple molecules on the gametes. One of the best-characterized of these molecules is fertilin beta, a ligand on mammalian sperm and one of the first ADAMs (A Disintegrin and A Metalloprotease domain) to be identified. Fertilin beta (also known as ADAM2) participates in sperm-egg membrane binding, and it has long been hypothesized that this function is achieved through the interaction of the disintegrin domain of fertilin beta with an integrin on the egg surface. There are now approximately 30 members of the ADAM family and, to date, five different ADAMs (fertilin beta, ADAM9, ADAM12, ADAM15, ADAM23) have been described to interact with integrins (specifically alpha(6)beta(1), alpha(v)beta(3), alpha(9)beta(1), alpha(v)beta(5), and/or alpha(5)beta(1)). This field will be discussed with respect to what is known about specific ADAMs and the integrins with which they interact, and what the implications are for sperm-egg interactions and for integrin function. These data will also be discussed in the context of recent knockout studies, which show that eggs lacking the alpha(6) integrin subunit can be fertilized, and eggs lacking the integrin-associated tetraspanin protein CD9 fail to fertilize. Key issues in cell adhesion that pertain to gametes and fertilization will also be highlighted.

The Alzheimer amyloid precursor protein (APP) and FE65, an APP-binding protein, regulate cell movement

FE65 binds to the Alzheimer amyloid precursor protein (APP), but the function of this interaction has not been identified. Here, we report that APP and FE65 are involved in regulation of cell movement. APP and FE65 colocalize with actin and Mena, an Abl-associated signaling protein thought to regulate actin dynamics, in lamellipodia. APP and FE65 specifically concentrate with beta 1-integrin in dynamic adhesion sites known as focal complexes, but not in more static adhesion sites known as focal adhesions. Overexpression of APP accelerates cell migration in an MDCK cell wound--healing assay. Coexpression of APP and FE65 dramatically enhances the effect of APP on cell movement, probably by regulating the amount of APP at the cell surface. These data are consistent with a role for FE65 and APP, possibly in a Mena-containing macromolecular complex, in regulation of actin-based motility.

N-cadherin is involved in axon-oligodendrocyte contact and myelination

We have analyzed the influence of the calcium-dependent cell adhesion molecule, N-cadherin, on events leading to CNS myelination. Interactions between axons and oligodendrocyte progenitor (OP) cells and the CG4 OP cell line were examined by video-microscopy. OPs cocultured with dorsal root ganglia explants migrated around the culture and formed numerous contacts with axons. The duration of these contacts depended on the morphology of the OP, with OPs containing four or more processes forming long-lasting contacts and OPs with three or fewer processes forming short-termed contacts. Treatment with N-cadherin function blocking peptides approximately halved the duration of contacts made by cells with four or more processes but contact times for cells with three or less processes were unaffected. The L7 cadherin-blocking antibody and calcium withdrawal had similar effects. Contacts with axons regenerating from explants of adult retina, which do not have N-cadherin on their surface was examined. The contact duration of OPs to adult retina axons was short and similar in length to those formed between OPs and dorsal root ganglion axons in the presence of cadherin blocking reagents. Oligodendrocyte myelination was examined in organotypic rat cerebellar slice cultures, taken before myelination at postnatal day 10 and then allowed to myelinate in vitro over 7 days. When incubated with an N-cadherin function-blocking peptide, myelination of Purkinje cell axons was reduced to about half of control levels, while control peptides were without effect. Cadherin-blockade did not prevent maturation of OPs, since oligodendrocytes showing myelin basic protein immunostaining were still found in these cultures. However, many of the cell processes did not colocalize with calbindin-positive axons. From these data we conclude that N-cadherin is important for the initial contact between a myelinating oligodendrocyte and axons and significantly contributes to the success of myelination.

HEMCAM/CD146 downregulates cell surface expression of (β)1 integrins

HEMCAM/gicerin, an immunoglobulin superfamily protein, is involved in homophilic and heterophilic adhesion. It interacts with NOF (neurite outgrowth factor), a molecule of the laminin family. Alternative splicing leads to mRNAs coding for HEMCAM with a short (HEMCAM-s) or a long cytoplasmic tail (HEMCAM-l). To investigate the cellular function of these two variants, we stably transfected murine fibroblasts with either form of HEMCAM. Expression of each isoform of this protein in L cells delayed proliferation and modified their adhesion properties to purified extracellular matrix proteins. Expression of either HEMCAM-s or HEMCAM-l inhibited integrin-dependent adhesion and spreading of fibroblasts to laminin 1, showing that this phenomenon did not depend on the cytoplasmic region. By contrast, L-cell adhesion and spreading to fibronectin depended on the HEMCAM isoform expressed. Flow cytometry and immunoprecipitation studies revealed that the expression of HEMCAM downregulated expression of the laminin-binding integrins (α)3 (β)1, (α)6 (β)1 and (α)7 (β)1, and fibronectin receptor (α)5 (β)1 from the cell surface. Semi-quantitative PCR and northern blot experiments showed that the expression of (α)6 (β)1 integrin modified by HEMCAM occurred at a translation or maturation level. Thus, our data demonstrate that HEMCAM regulates fibroblast adhesion by controlling (β)1 integrin expression. http://www.biologists.com/JCS/movies/jcs1886.html

Testase 1 (ADAM 24) a plasma membrane-anchored sperm protease implicated in sperm function during epididymal maturation or fertilization

Plasma membrane-anchored proteases have key roles in cell signaling, migration and refashioning the cell surface and its surroundings. We report the first example of a plasma membrane-anchored protease on mature sperm, testase 1 (ADAM 24). Unlike other studied sperm ADAMs (fertilin (α) and (β), cyritestin) whose metalloprotease domains are removed during sperm development, we found testase 1 retains an active metalloprotease domain, suggesting it acts as a protease on mature sperm. Testase 1 is a glycoprotein (molecular mass 88 kDa), localized to the equatorial region of the plasma membrane of cauda epididymal sperm. Typically, proteolytic removal of the pro-domain is an initial activation step for ADAM proteases. The pro-domain of the testase 1 precursor (108 kDa) is proteolytically removed as sperm transit the caput epididymis to produce processed (mature) testase 1 (88 kDa). Testase 1 is unique among all studied ADAMs in that its proteolytic processing occurs on the sperm plasma membrane instead of at an intracellular site (the Golgi). Using GST-fusion proteins and a synthetic testase 1 C-terminal peptide, we found that the cytoplasmic tail of testase 1 could be phosphorylated in vitro by protein kinase C (PKC). Thus testase 1 apparently has a cytoplasmic PKC phosphorylation site(s). Protein kinase C is known to stimulate other ADAMs' protease activity. Because events of the acrosome reaction include PKC activation, we speculate that testase 1 protease function could be important in sperm penetration of the zona pellucida after sperm PKC is activated during the acrosome reaction.

Sequence-specific interaction between the disintegrin domain of mouse ADAM 3 and murine eggs: role of beta1 integrin-associated proteins CD9, CD81, and CD98

ADAM 3 is a sperm surface glycoprotein that has been implicated in sperm-egg adhesion. Because little is known about the adhesive activity of ADAMs, we investigated the interaction of ADAM 3 disintegrin domains, made in bacteria and in insect cells, with murine eggs. Both recombinant proteins inhibited sperm-egg binding and fusion with potencies similar to that which we recently reported for the ADAM 2 disintegrin domain. Alanine scanning mutagenesis revealed a critical importance for the glutamine at position 7 of the disintegrin loop. Fluorescent beads coated with the ADAM 3 disintegrin domain bound to the egg surface. Bead binding was inhibited by an authentic, but not by a scrambled, peptide analog of the disintegrin loop. Bead binding was also inhibited by the function-blocking anti-alpha6 monoclonal antibody (mAb) GoH3, but not by a nonfunction blocking anti-alpha6 mAb, or by mAbs against either the alphav or beta3 integrin subunits. We also present evidence that in addition to the tetraspanin CD9, two other beta1-integrin-associated proteins, the tetraspanin CD81 as well as the single pass transmembrane protein CD98 are expressed on murine eggs. Antibodies to CD9 and CD98 inhibited in vitro fertilization and binding of the ADAM 3 disintegrin domain. Our findings are discussed in terms of the involvement of multiple sperm ADAMs and multiple egg beta1 integrin-associated proteins in sperm-egg binding and fusion. We propose that an egg surface "tetraspan web" facilitates fertilization and that it may do so by fostering ADAM-integrin interactions.

Phosphorylation of a conserved integrin alpha 3 QPSXXE motif regulates signaling, motility, and cytoskeletal engagement

Integrin alpha 3A cytoplasmic tail phosphorylation was mapped to amino acid S1042, as determined by mass spectrometry, and confirmed by mutagenesis. This residue occurs within a "QPSXXE" motif conserved in multiple alpha chains (alpha 3A, alpha 6A, alpha 7A), from multiple species. Phosphorylation of alpha 3A and alpha 6A did not appear to be directly mediated by protein kinase C (PKC) alpha, beta, gamma, delta, epsilon, zeta, or mu, or by any of several other known serine kinases, although PKC has an indirect role in promoting phosphorylation. A S1042A mutation did not affect alpha 3-Chinese hamster ovary (CHO) cell adhesion to laminin-5, but did alter 1) alpha 3-dependent tyrosine phosphorylation of focal adhesion kinase and paxillin (in the presence or absence of phorbol 12-myristate 13 acetate stimulation), and p130(CAS) (in the absence of phorbol 12-myristate 13 acetate stimulation), 2) the shape of cells spread on laminin-5, and 3) alpha 3-dependent random CHO cell migration on laminin-5. In addition, S1042A mutation altered the PKC-dependent, ligand-dependent subcellular distribution of alpha 3 and F-actin in CHO cells. Together, the results demonstrate clearly that alpha 3A phosphorylation is functionally relevant. In addition, the results strongly suggest that alpha 3 phosphorylation may regulate alpha 3 integrin interaction with the cytoskeleton.

MDC-9 (ADAM-9/Meltrin gamma) functions as an adhesion molecule by binding the alpha(v)beta(5) integrin

MDC-9 is a widely expressed member of the metalloproteinase/disintegrin/cysteine-rich protein family. The disintegrin domain of MDC-9 lacks an RGD motif but has recently been reported to bind the alpha(6)beta(1) integrin; however, it is unclear whether MDC-9 can bind other integrins. In the present study myeloma cells, but not lymphoblastoid cells, were shown to bind to immobilised, recombinantly expressed MDC-9 disintegrin domain (A9dis). Binding was divalent cation-dependent, being supported by Mn(2+) and Ca(2+). Adhesion of myeloma cells to A9dis was completely inhibited by an antibody to the alpha(v)beta(5) integrin but not by antibodies to other subunits. RGD-containing peptides had no effect on binding, suggesting that MDC-9 interacts with alpha(v)beta(5) in an RGD-independent manner. Flow cytometric analyses demonstrated that myeloma cells, but not lymphoblastoid cells, expressed alpha(v)beta(5) on the cell membrane. These data indicated that the disintegrin domain of MDC-9 can function as an adhesion molecule by interacting with an alpha(v)beta(5) integrin.