Monocytic cells synthesize, adhere to, and migrate on laminin-8 (alpha 4 beta 1 gamma 1)

Metabolic reservoir cycles in cancer

Cancer cells possess various biological processes to ensure survival and proliferation even under unfavorable conditions such as hypoxia, nutrient deprivation, and oxidative stress. One of the defining hallmarks of cancer cells is their ability to reprogram their metabolism to suit their needs. Building on over a decade of research in the field of cancer metabolism, numerous unique metabolic capabilities are still being discovered in the present day. One recent discovery in the field of cancer metabolism that was hitherto unexpected is the ability of cancer cells to store vital metabolites in forms that can be readily converted to glucose and glutamine for later use. We called these forms "metabolic reservoirs." While many studies have been conducted on storage molecules such as glycogen, triglyceride, and phosphocreatine (PCr), few have explored the concept of "metabolic reservoirs" for cancer as a whole. In this review, we will provide an overview of this concept, the previously known reservoirs including glycogen, triglyceride, and PCr, and the new discoveries made including the newly discovered reservoirs such as N-acetyl-aspartyl-glutamate (NAAG), lactate, and γ- aminobutyric acid (GABA). We will also discuss whether disrupting these reservoir cycles may be a new avenue for cancer treatment.

The extracellular matrix of hematopoietic stem cell niches

•

Comprehensive overview of different classes of ECM molecules in the HSC niche.

•

Overview of current knowledge on role of biophysics of the HSC niche.

•

Description of approaches to create artificial stem cell niches for several application.

•

Importance of considering ECM in drug development and testing.

Hematopoietic stem cells (HSCs) are the life-long source of all types of blood cells. Their function is controlled by their direct microenvironment, the HSC niche in the bone marrow. Although the importance of the extracellular matrix (ECM) in the niche by orchestrating niche architecture and cellular function is widely acknowledged, it is still underexplored. In this review, we provide a comprehensive overview of the ECM in HSC niches. For this purpose, we first briefly outline HSC niche biology and then review the role of the different classes of ECM molecules in the niche one by one and how they are perceived by cells. Matrix remodeling and the emerging importance of biophysics in HSC niche function are discussed. Finally, the application of the current knowledge of ECM in the niche in form of artificial HSC niches for HSC expansion or targeted differentiation as well as drug testing is reviewed.

Endothelial Basement Membrane Laminins as an Environmental Cue in Monocyte Differentiation to Macrophages

Monocyte differentiation to macrophages is triggered by migration across the endothelial barrier, which is constituted by both endothelial cells and their underlying basement membrane. We address here the role of the endothelial basement membrane laminins (laminins 411 and 511) in this monocyte to macrophage switch. Chimeric mice carrying CX3CR1-GFP bone marrow were employed to track CCL2-induced monocyte extravasation in a cremaster muscle model using intravital microscopy, revealing faster extravasation in mice lacking endothelial laminin 511 (Tek-cre::Lama5^−/−) and slower extravasation in mice lacking laminin 411 (Lama4^−/−). CX3CR1-GFP^low extravasating monocytes were found to have a higher motility at laminin 511 low sites and to preferentially exit vessels at these sites. However, in vitro experiments reveal that this is not due to effects of laminin 511 on monocyte migration mode nor on the tightness of the endothelial barrier. Rather, using an intestinal macrophage replenishment model and in vitro differentiation studies, we demonstrate that laminin 511, together with the attached endothelium, promote monocyte differentiation to macrophages. Macrophage differentiation is associated with a change in integrin profile, permitting differentiating macrophages to distinguish between laminin 511 high and low areas and to preferentially migrate across laminin 511 low sites. These studies highlight the endothelial basement membrane as a critical site for monocyte differentiation to macrophages, which may be relevant to the differentiation of other cells at vascular niches.

CD146, from a melanoma cell adhesion molecule to a signaling receptor

CD146 was originally identified as a melanoma cell adhesion molecule (MCAM) and highly expressed in many tumors and endothelial cells. However, the evidence that CD146 acts as an adhesion molecule to mediate a homophilic adhesion through the direct interactions between CD146 and itself is still lacking. Recent evidence revealed that CD146 is not merely an adhesion molecule, but also a cellular surface receptor of miscellaneous ligands, including some growth factors and extracellular matrixes. Through the bidirectional interactions with its ligands, CD146 is actively involved in numerous physiological and pathological processes of cells. Overexpression of CD146 can be observed in most of malignancies and is implicated in nearly every step of the development and progression of cancers, especially vascular and lymphatic metastasis. Thus, immunotherapy against CD146 would provide a promising strategy to inhibit metastasis, which accounts for the majority of cancer-associated deaths. Therefore, to deepen the understanding of CD146, we review the reports describing the newly identified ligands of CD146 and discuss the implications of these findings in establishing novel strategies for cancer therapy.

Malignant Transformation and Associated Biomarkers of Ovarian Endometriosis: A Narrative Review

This review focuses on pathogenesis of endometriosis, its possible biomarkers and role in endometriosis-associated ovarian cancer. We analyzed various databases to obtain new insights, theories, and biomarkers associated with endometriosis. There are several theories of endometriosis development and biomarker changes including atypical forms. A number of studies have attempted to establish specific, reliable biomarkers to help diagnose endometriosis and endometriosis-associated diseases on the basis of different pathogenetic pathways. Nevertheless, despite intensive research extending even to the molecular level, the origin, natural history, malignant transformation, and laboratory management of endometriosis and related diseases are not yet clearly defined. Therefore, early laboratory diagnoses of endometriosis, its atypical form, and endometriosis-associated ovarian tumors are important problems that require further study in the context of advanced therapeutic strategies to provide maximal health benefits to patients.

The Tumor Microenvironment: Focus on Extracellular Matrix

The extracellular matrix (ECM) regulates the development and maintains tissue homeostasis. The ECM is composed of a complex network of molecules presenting distinct biochemical properties to regulate cell growth, survival, motility, and differentiation. Among their components, proteoglycans (PGs) are considered one of the main components of ECM. Its composition, biomechanics, and anisotropy are exquisitely tuned to reflect the physiological state of the tissue. The loss of ECM's homeostasis is seen as one of the hallmarks of cancer and, typically, defines transitional events in tumor progression and metastasis. In this chapter, we discuss the types of proteoglycans and their roles in cancer. It has been observed that the amount of some ECM components is increased, while others are decreased, depending on the type of tumor. However, both conditions corroborate with tumor progression and malignancy. Therefore, ECM components have an increasingly important role in carcinogenesis and this leads us to believe that their understanding may be a key in the discovery of new anti-tumor therapies. In this book, the main ECM components will be discussed in more detail in each chapter.

Potential role of Lu/BCAM in HIV-related atherosclerosis

Atheromatous lesions are formed by macrophages and low-density lipoprotein cholesterol invading the vascular intima. Here we show that increasing cholesterol levels are associated with peripheral monocyte depletion and this imbalance is aggravated by carriage of Lu/BCAM leukocyte adhesion molecules. This is true only in HIV infection and probably explains the risk of atherosclerosis observed in HIV-positive patients.

Regulation of the Immune System by Laminins

Laminins are trimeric proteins that are major components of the basement membranes that separate endothelia and epithelia from the underlying tissue. Sixteen laminin isoforms have been described, each with distinct tissue expression patterns and functions. While laminins have a critical structural role, recent evidence also indicates that they also impact the migration and functions of immune cells. Laminins are differentially expressed upon immunity or tolerance and orientate the immune response. This review will summarize the structure of laminins, the modulation of their expression, and their interactions with the immune system. Finally, the role of the laminins in autoimmune diseases and transplantation will be discussed.

Laminins 411 and 421 differentially promote tumor cell migration via α6β1 integrin and MCAM (CD146)

α4-laminins, such as laminins 411 and 421, are mesenchymal laminins expressed by blood and lymphatic vessels and some tumor cells. Laminin-411 promotes migration of leukocytes and endothelial cells, but the effect of this laminin and laminin-421 on tumor cells is poorly understood. In the present study, we demonstrate that laminin-411 and, to a greater extent, laminin-421 significantly promote migration of tumor cells originated from melanomas, gliomas and different carcinomas via α6β1 integrin. In solid-phase binding assays, both laminins similarly bound α6β1 integrin but only laminin-421, among several laminin isoforms, readily bound MCAM (CD146), a cell-surface adhesion molecule strongly associated with tumor progression. Accordingly, a function-blocking mAb to MCAM inhibited tumor cell migration on laminin-421 but not on laminins 411 or 521. In tumor tissues, melanoma cells co-expressed MCAM, laminin α4, β1, β2 and γ1 chains, and integrin α6 and β1 chains. The present data highlight the novel role of α4-laminins in tumor cell migration and identify laminin-421 as a primary ligand for MCAM and a putative mediator of tumor invasion and metastasis.

Molecular aspects of development and regulation of endometriosis

Endometriosis is a common and painful condition affecting women of reproductive age. While the underlying pathophysiology is still largely unknown, much advancement has been made in understanding the progression of the disease. In recent years, a great deal of research has focused on non-invasive diagnostic tools, such as biomarkers, as well as identification of potential therapeutic targets. In this article, we will review the etiology and cellular mechanisms associated with endometriosis as well as the current diagnostic tools and therapies. We will then discuss the more recent genomic and proteomic studies and how these data may guide development of novel diagnostics and therapeutics. The current diagnostic tools are invasive and current therapies primarily treat the symptoms of endometriosis. Optimally, the advancement of "-omic" data will facilitate the development of non-invasive diagnostic biomarkers as well as therapeutics that target the pathophysiology of the disease and halt, or even reverse, progression. However, the amount of data generated by these types of studies is vast and bioinformatics analysis, such as we present here, will be critical to identification of appropriate targets for further study.

Role of CX3CR1 receptor in monocyte/macrophage driven neovascularization

Monocyte/Macrophages are implicated in initiation of angiogenesis, tissue/organ perfusion and atherosclerosis biology. We recently showed that chemokine receptor CX₃CR1 is an essential regulator of monocyte/macrophage derived smooth muscle cell differentiation in the vessel wall after injury. Here we hypothesised the contribution of CX₃CR1- CX₃CL1 interaction to in vivo neovascularization and studied the functional consequences of genetic and pharmacologic targeting of CX₃CR1 in formation, maturation and maintenance of microvascular integrity. Cells functionally deficient in CX₃CR1 lacked matrix tunnelling and tubulation capacity in a 3D Matrigel assay. These morphogenic and cytokinetic responses were driven by CX₃CL1-CX₃CR1 interaction and totally abrogated by a Rho antagonist. To evaluate the role of CX₃CR1 system in vivo, Matrigel plugs were implanted in competent CX₃CR1^+/gfp and functionally deficient CX₃CR1^gfp/gfp mice. Leaky microvessels (MV) were formed in the Matrigel implanted in CX₃CR1^gfp/gfp but not in CX₃CR1^+/gfp mice. In experimental plaque neovascularization immature MV phenotype was observed in CX₃CR1^gfp/gfp mice, lacking CX₃CR1 positive smooth muscle-like cells, extracellular collagen and basement membrane (BM) laminin compared to competent CX₃CR1^+/gfp mice. This was associated with increased extravasation of platelets into the intima of CX₃CR1^gfp/gfp but not functionally competent CX₃CR1 mice. Pharmacologic targeting using CX₃CR1 receptor antagonist in wild type mice resulted in formation of plaque MV with poor BM coverage and a leaky phenotype. Our data indicate a hitherto unrecognised role for functional CX₃CR1 in Matrigel and experimental plaque neovascularization in vivo, which may buttress MV collectively in favour of a more stable non-leaky phenotype.

NHE-1 and β1 integrin dependent monocyte adhesion and migration after glucose, insulin or PPARγ stimulation

In the present study the effect of high glucose concentrations, insulin, PPARγ activators (rosiglitazone) and NHE-1 inhibitors (cariporide) in atherosclerosis-related functions of human monocytes was investigated. Monocyte adhesion to laminin-1, collagen type IV and endothelial cells, as well as monocyte migration through the same substrates were studied. Incubation of the monocyte suspension with high glucose concentrations, insulin and rosiglitazone induced all the studied atherosclerosis-related functions of the monocytes. In all these functions the addition of cariporide counteracted the activity of glucose, insulin and rosiglitazone. The use of antigen for β1 integrin also counteracted the activity of the above in monocyte adhesion in all three substrates. The data of the present study suggests that PPARγ activation in monocytes induces atherosclerosis, and that NHE-1 and β1 integrin play an important role in the beginning of atherosclerosis.

An adhesion protein of Salmonella enterica serovar Typhi is required for pathogenesis and potential target for vaccine development

More than half of all Salmonella enterica serovar Typhi genes still remain unannotated. Although pathogenesis of S. Typhi is incompletely understood, treatment of typhoid fever is complicated by the emergence of drug resistance. Effectiveness of the currently available vaccines is also limited. In search of novel virulence proteins, we have identified several putative adhesins of S. Typhi through computational approaches. Our experiment shows that a 27-kDa outer membrane protein (T2544) plays a major role in bacterial adhesion to the host through high-affinity binding to laminin. Its role in bacterial pathogenesis is underscored by reduced systemic invasion and a 10-fold higher LD(50) of the mutant bacteria in mice. T2544 is strongly immunogenic as revealed by the detection of sustained high titers of serum IgG and intestinal secretory IgA in the immunized mice. In vitro, T2544 antiserum enhanced uptake and clearance of Salmonella by macrophages and augmented complement-mediated lysis, indicating a contribution of T2544-specific antibodies to the killing process. This correlates well with the observed protection of mice immunized with recombinant T2544 or passively immunized with T2544 antiserum against subsequent bacterial challenge, suggesting that T2544-specific antibodies are involved in protection. The present study describes an adhesion protein of S. Typhi that contributes to bacterial pathogenesis. Protective antibodies in mice, rapid seroconversion of naturally infected individuals with increasing titers of anti-T2544 IgG from acute to convalescent sera suggesting antibody response in humans, and wide distribution and conservation of the cell-surface adhesin in the clinical isolates of different Salmonella serovars make T2544 a potential vaccine candidate.

Oxidized laminin-1 induces increased monocyte attachment and expression of ICAM-1 in endothelial cells

Atherosclerosis has been associated with increased oxidative stress and monocyte recruitment by endothelial cells. Sub-endothelial basement membrane proteins, such as laminins that play a central role in cell adhesion, are exposed to reactive oxygen species. In the present study monocyte attachment on human umbilical cord vein endothelial cells (HUVEC) that were preattached to oxidized or native laminin, was investigated. Intracellular cell adhesion molecule-1 (ICAM-1) expression by HUVEC was estimated by an enzyme-linked immunosorbent assay. HUVEC attachment to oxidized or native laminin-1 was examined using the Hemacolor kit. Anti-alphaL, anti-alphaM, anti-alpha2 and anti-beta2 integrin subunit antibodies were used in order to further investigate the above phenomena. HUVEC that were preattached to oxidized laminin expressed higher levels of ICAM-1 and monocytes attached at a higher degree to these cells as compared to HUVEC that were preattached to native laminin. Incubation of monocytes with monoclonal antibodies against the alphaM and beta2 integrin subunits equalized the above mentioned differences. Moreover, HUVEC attached to oxidized laminin at a higher degree as compared to native laminin. This difference was equalized after incubation with the antibody against the alpha2 integrin subunit. These results indicate a modified interaction between HUVEC and the basement membranes in cases where laminin is oxidatively modified. This modified interaction results in increased ICAM-1 expression by endothelial cells and consequently increased monocyte recruitment capacity.

Monocyte attachment to laminin in diabetes mellitus: The role of ATP

Monocyte-extracellular matrix interactions have been implicated in atherosclerosis pathophysiology. Laminin, the main basement membrane protein contains cell binding domains that can be cryptic, presented only after protein modification. In the present study we evaluated monocyte attachment to laminin-1 in the presence of ATP. Monocytes were derived from either healthy volunteers or patients with diabetes mellitus type II. For the estimation of monocyte attachment to laminin the myeloperoxidase assay was used. Monocytes derived from diabetic patients, showed an increased ability to attach to laminin (p = 0.0055). The presence of ATP increased the attachment of control monocytes to laminin (p = 0.0022). On the contrary, the presence of ATP did not affect the attachment of monocytes derived from diabetic patients to laminin. Our results indicate a modified interaction between monocytes and laminin-1 in diabetes mellitus.

Alpha4 chain laminins are widely expressed in renal cell carcinomas and have a de-adhesive function

Laminin (Lm) alpha4 chain, a constituent of Lm-411 and Lm-421, is mainly localized to mesenchyme-derived tissues, and is suggested to have a role in formation and function of endothelium, transmigration of inflammatory cells through endothelium, and invasion of certain tumors. In this study, we evaluated the distribution of alpha4 chain Lms in 33 conventional (clear cell) renal cell carcinomas (RCCs) (31 primary tumors, two metastases), two papillary RCCs, and two oncocytomas by immunohistochemistry. In all tumors, immunoreactivity for Lm alpha4 chain was found in vasculature and stroma. Basement membranes were detected around tumor cell islets in 34/37 tumors. They showed immunoreactivity for Lm alpha4 chain in 28/34 cases. Northern blotting, inhibition of protein secretion with monensin, and immunoprecipitation combined with Western blotting showed that Caki-2, ACHN, and Caki-1 renal carcinoma cell lines produce alpha4 chain Lms. In cell adhesion assay, recombinant human Lm-411 did not promote adhesion of renal carcinoma cells but inhibited adhesion to fibronectin (Fn). In cell migration assay, the cells migrated more on Lm-411 than on Fn. The results suggest that alpha4 chain Lms have a de-adhesive function and could thus play a role in detachment, migration and invasion of renal carcinoma cells in vivo.

Enhanced laminin carbonylation by monocytes in diabetes mellitus

OBJECTIVES

Monocyte-extracellular matrix interactions have been implicated in atherosclerosis pathophysiology. In the present study we evaluated the oxidation of laminin by monocytes derived from either diabetic patients or healthy volunteers. Moreover, reactive oxygen species production was measured. Monocyte attachment and migration through oxidized and non-oxidized laminin were also studied.

DESIGN AND METHODS

Laminin oxidation was tested by a sensitive ELISA assay in isolated monocytes. ROS production was measured with fluorescent indicators. 35S-methionine was used for evaluating monocyte attachment. Monocyte migration through laminin was examined on transwells.

RESULTS

Monocytes derived from patients with diabetes mellitus showed an increased ability to carbonylate and attach to laminin. Diabetic monocytes produced increased levels of ROS as compared to controls. Our results showed the involvement of the alpha2 integrin subunit in monocyte attachment to both native and oxidized laminin in control and diabetic monocytes.

CONCLUSIONS

The results indicate a modified interaction between monocytes and laminin in diabetes.

Laminin isoforms in development and disease

The members of the laminin family of heterotrimers are major constituents of all basement membranes, sheet-like extracellular structures, present in almost all organs. The laminins bind to cell surface receptors and thereby tightly connect the basement membrane to the adjacent cell layer. This provides for the specific basement membrane functions to stabilize cellular structures, to serve as effective physical barriers, and furthermore, to govern cell fate by inducing intracellular signalling cascades. Many different types of diseases involve basement membranes and laminins. Metastasizing solid tumors must pass through basement membranes to reach the vascular system, and various microbes and viruses enter the cells through direct interaction with laminins. Furthermore, whereas mutations in one specific laminin chain lead to a muscular disorder, mutations of other laminin chains cause skin blistering and kidney defects, respectively. This review summarizes recent progress concerning the molecular mechanisms of laminins in development and disease. The current knowledge may lead to clinical treatment of lamininopathies and may include stem-cell approaches as well as gene therapy.

Laminins containing the beta2 chain modulate the precise organization of CNS synapses

Synapses are formed and stabilized by concerted interactions of pre-, intra-, and post-synaptic components; however, the precise nature of the intrasynaptic components in the CNS remains obscure. Potential intrasynaptic components include extracellular matrix molecules such as laminins; here, we isolate beta2-containing laminins, including perhaps laminins 13 (alpha3beta2gamma3) and 14 (alpha4beta2gamma3), from CNS synaptosomes suggesting a role for these molecules in synaptic organization. Indeed, hippocampal synapses that form in vivo in the absence of these laminins are malformed at the ultrastructural level and this malformation is replicated in synapses formed in vitro, where laminins are provided largely by the post-synaptic neuron. This recapitulation of the in vivo function of laminins in vitro suggests that the malformations are a direct consequence of the removal of laminins from the synapse. Together, these results support a role for neuronal laminins in the structural integrity of central synapses.

Extensive extracellular matrix depositions in active multiple sclerosis lesions

In the central nervous system, basement membrane (BM) constituents are predominantly associated with the vasculature. However, under inflammatory conditions, the expression of BM components may alter. Here, we investigated the distribution of several BM components, including laminin, collagen type IV and heparan sulfate proteoglycans in various multiple sclerosis (MS) lesions. We observed irregular and discontinuous BMs in active lesions. Throughout active MS lesions, we found dense networks of BM proteins, which were surprisingly not associated with the cerebrovasculature. These striking parenchymal networks were not observed in chronic inactive MS lesions and brains of non-neurological controls. In addition, we studied the distribution of transforming growth factor-beta1 (TGF-beta1), since it is known as a major modulator of ECM production. Leukocytes, in particular CD68-positive macrophages, expressed high levels of TGF-beta1 and were located in close proximity to parenchymal BM deposits in the MS lesions. We postulate that these BM networks may play a role in the further recruitment of inflammatory cells and form a barrier for axonal regeneration.

Rat glomerular mesangial cells require laminin-9 to migrate in response to insulin-like growth factor binding protein-5

Temporal and spatial differences in extracellular matrix play critical roles in cell proliferation, differentiation and migration. Different migratory stimuli use different substrates and receptors to achieve cell migration. To understand the mechanism of insulin-like growth factor binding protein-5 (IGFBP-5)-induced migration in mesangial cells, the roles of integrins and substrates were examined. IGFBP-5 induced an increase in mRNA expression for laminin (LN) chains lama4, lamb2, and lamc1, suggesting that LN-9 might be required for migration. Antibodies to the LNalpha(4) and LNbeta(2) chains, but not LNbeta(1), blocked IGFBP-5-induced migration. Anti-sense morpholino oligonucleotide inhibition of expression of LNalpha(4) substantially reduced expression of LN-8/9 (alpha(4)beta(1)gamma(1)/alpha(4)beta(2)gamma(1), 411/421) and prevented IGFBP-5-induced migration. Anti-sense inhibition of lamb2 reduced expression of LN-9. Absence of LN-9 prevented IGFBP-5-induced migration, which was not preserved by continued expression of LN-8. The requirement for LN-9 was further supported by studies of T98G cells, which express predominantly LN-8. IGFBP-5 had little effect on migration in these cells, but increased migration when T98G cells were plated on LN-8/9. IGFBP-5-mediated mesangial cell migration was inhibited by antibodies that block attachment to alpha(6)beta(1)-integrins but was unaffected by antibodies and disintegrins that block binding to other integrins. Furthermore, in cells with anti-sense inhibited expression of LN-9, integrin alpha(6)beta(1) was no longer detected on the cell surface. These studies suggest the specificity of mechanisms of migration induced by specific stimuli and for the first time demonstrate a unique function for LN-9 in mediating IGFBP-5-induced migration.

Contribution of alpha6 integrins to hematopoietic stem and progenitor cell homing to bone marrow and collaboration with alpha4 integrins

The laminin receptor integrin alpha6 chain is ubiquitously expressed in human and mouse hematopoietic stem and progenitor cells. We have studied its role for homing of stem and progenitor cells to mouse hematopoietic tissues in vivo. A function-blocking anti-integrin alpha6 antibody significantly reduced progenitor cell homing to bone marrow (BM) of lethally irradiated mice, with a corresponding retention of progenitors in blood. Remarkably, the anti-integrin alpha6 antibody profoundly inhibited BM homing of long-term multilineage engrafting stem cells, studied by competitive repopulation assay and analysis of donor-derived lymphocytes and myeloid cells in blood 16 weeks after transplantation. A similar profound inhibition of long-term stem cell homing was obtained by using a function-blocking antibody against alpha4 integrin, studied in parallel. Furthermore, the anti-integrin alpha6 and alpha4 antibodies synergistically inhibited homing of short-term repopulating stem cells. Intravenous injection of anti-integrin alpha6 antibodies, in contrast to antibodies against alpha4 integrin, did not mobilize progenitors or enhance cytokine-induced mobilization by G-CSF. Our results provide the first evidence for a distinct functional role of integrin alpha6 receptor during hematopoietic stem and progenitor cell homing and collaboration of alpha6 integrin with alpha4 integrin receptors during homing of short-term stem cells.

Relaxin stimulates leukocyte adhesion and migration through a relaxin receptor LGR7-dependent mechanism

Leukocytes are critical effectors of inflammation and tumor biology. Chemokine-like factors produced by such inflammatory sites are key mediators of tumor growth that activate leukocytic recruitment and tumor infiltration and suppress immune surveillance. Here we report that the endocrine peptide hormone, relaxin, is a regulator of leukocyte biology with properties important in recruitment to sites of inflammation. This study uses the human monocytic cell line THP-1 and normal human peripheral blood mononuclear cells to define a novel role for relaxin in regulation of leukocyte adhesion and migration. Our studies indicate that relaxin promotes adenylate cyclase activation, substrate adhesion, and migratory capacity of mononuclear leukocytes through a relaxin receptor LGR7-dependent mechanism. Relaxin-stimulated cAMP accumulation was observed to occur primarily in non-adherent cells. Relaxin stimulation results in increased substrate adhesion and increased migratory activity of leukocytes. In addition, relaxin-stimulated substrate adhesion resulted in enhanced chemotaxis to monocyte chemoattractant protein-1. These responses in THP-1 and peripheral blood mononuclear cells are relaxin dose-dependent and proportional to cAMP accumulation. We further demonstrate that LGR7 is critical for mediating these biological responses by use of RNA interference lentiviral short hairpin constructs. In summary, we provide evidence that relaxin is a novel leukocyte stimulatory agent with properties affecting adhesion and chemomigration.

Basement membrane proteins in multiple sclerosis-associated inflammatory cuffs: potential role in influx and transport of leukocytes

Perivascular accumulation of macrophages and lymphocytes is a prominent feature of multiple sclerosis (MS) pathology. To enter the brain parenchyma, immune cells need to migrate across the blood-brain barrier through a number of well-defined processes. So far, little attention has been given to the role of the basement membrane (BM) in leukocyte recruitment into the central nervous system (CNS). Here, we characterized the molecular composition of the vascular and astroglial BMs in chronic active and active MS lesions with large perivascular infiltrates using antibodies directed against several extracellular matrix (ECM) proteins. A differential expression of specific laminin chains in vascular and astroglial BMs was observed. Interestingly, we found fiber-like depositions of ECM within inflammatory cuffs. These structures were immunopositive for several laminin isoforms, fibronectin, collagen IV, and heparan sulfate proteoglycans. Strikingly, we observed myelin-laden macrophages in the Virchow-Robin space. Because BM molecules are in close contact with these cells, we postulate that BM proteins within inflammatory cuffs may serve as a conduit network and therefore facilitate the transport of myelin-containing phagocytes out of the CNS toward peripheral lymph nodes.

Downregulation of laminin alpha4 chain expression inhibits glioma invasion in vitro and in vivo

The laminin family is a structural constituent of the extracellular matrix that plays an essential role in promoting the motility of infiltrative tumor cells. We investigated the role of laminin alpha4 chain, a subset of laminin-8, -9 and -14, in the motile and invasive activities of human glioma cells. All malignant glioma cell lines examined expressed more mRNA for the laminin alpha4 and beta1 chains than for the beta2 chain, indicating that these cells predominantly express the laminin-8 isoform. Introducing an antisense oligonucleotide for laminin alpha4 chain (AS-Ln-alpha4) into the glioma cells resulted in downregulation of laminin alpha4 expression. AS-Ln-alpha4 also significantly suppressed glioma cell adhesion and migration. Furthermore, invasiveness was significantly reduced in cells transfected with AS-Ln-alpha4 compared to those transfected with the sense oligonucleotide (S-Ln-alpha4). Indeed, when glioma spheroids were implanted into rat brain slices, AS-Ln-alpha4-transfected cells failed to invade surrounding normal brain tissues. In addition, intracerebral injection of glioma cells transfected with AS-Ln-alpha4 into nude mice resulted in the formation of a noninvasive tumor, whereas injection of cells transfected with S-Ln-alpha4 resulted in diffuse invasion of brain tissue. These results suggest that mainly laminin-8 is essential for the invasive activity of human glioma cells; thus, a novel therapeutic strategy could target this molecule to treat patients with malignant glioma.

Expression and function of laminins in the embryonic and mature vasculature

Endothelial cells of the blood and lymphatic vasculature are polarized cells with luminal surfaces specialized to interact with inflammatory cells upon the appropriate stimulation; they contain specialized transcellular transport systems, and their basal surfaces are attached to an extracellular basement membrane. In adult tissues the basement membrane forms a continuous sleeve around the endothelial tubes, and the interaction of endothelial cells with basement membrane components plays an important role in the maintenance of vessel wall integrity. During development, the basement membrane of endothelium provides distinct spatial and molecular information that influences endothelial cell proliferation, migration, and differentiation/maturation. Microvascular endothelium matures into phenotypically distinct types: continuous, fenestrated, and discontinuous, which also differ in their permeability properties. Development of these morphological and physiological differences is thought to be controlled by both soluble factors in the organ or tissue environment and by cell-cell and cell-matrix interactions. Basement membranes of endothelium, like those of other tissues, are composed of laminins, type IV collagens, heparan sulfate proteoglycans, and nidogens. However, isoforms of all four classes of molecules exist, which combine to form structurally and functionally distinct basement membranes. The endothelial cell basement membranes have been shown to be unique with respect to their laminin isoform composition. Laminins are a family of glycoprotein heterotrimers composed of an alpha, beta, and gamma chain. To date, 5alpha, 4beta, and 3gamma laminin chains have been identified that can combine to form 15 different isoforms. The laminin alpha-chains are considered to be the functionally important portion of the heterotrimers, as they exhibit tissue-specific distribution patterns and contain the major cell interaction sites. Vascular endothelium expresses only two laminin isoforms, and their expression varies depending on the developmental stage, vessel type, and the activation state of the endothelium. Laminin 8 (composed of laminin alpha4, beta1, and gamma1 chains) is expressed by all endothelial cells regardless of their stage of development, and its expression is strongly upregulated by cytokines and growth factors that play a role in inflammatory events. Laminin 10 (composed of laminin alpha5, beta1, and gamma1 chains) is detectable primarily in endothelial cell basement membranes of capillaries and venules commencing 3-4 wk after birth. In contrast to laminin 8, endothelial cell expression of laminin 10 is upregulated only by strong proinflammatory signals and, in addition, angiostatic agents such as progesterone. Other extracellular matrix molecules, such as BM40 (also known as SPARC/osteonectin), thrombospondins 1 and 2, fibronectin, nidogens 1 and 2, and collagen types VIII, XV, and XVIII, are also differentially expressed by endothelium, varying with the endothelium type and/or pathophysiological state. The data argue for a dynamic endothelial cell extracellular matrix that presents different molecular information depending on the type of endothelium and/or physiological situation. This review outlines the unique structural and functional features of vascular basement membranes, with focus on the endothelium and the laminin family of glycoproteins.

Transmigration through venular walls: a key regulator of leukocyte phenotype and function

Leukocyte transmigration is a key event in host defense. As well as delivering leukocytes to sites of inflammation, this response also has an important role in immunity by regulating the responsiveness and behavior of leukocytes in the extravascular tissue. Recent evidence suggests that these events are associated with phenotypic and functional changes in migrating leukocytes mediated by signaling and transcriptional events triggered by the molecular interactions involved in leukocyte transendothelial cell migration. Transfer of membrane proteins from endothelial cells to migrating leukocytes and interaction of leukocytes with components of the perivascular basement membrane might also contribute to this effect. This Review will discuss the characteristics, potential mechanisms and the relevance of transmigration-induced change in leukocyte phenotype and responsiveness both within physiological and pathological scenarios.

Laminin-1 is phosphorylated by ecto-protein kinases of monocytes

Monocytes encounter basement membranes and interact with laminins while crossing the vascular barrier. It is known that these cells possess ecto-protein kinase activity on their surface. Several proteins of the extracellular matrix can be phosphorylated by ectokinases. Therefore, it has been hypothesized that monocyte ectokinases could phosphorylate laminins and influence their biological properties. In order to test the above hypothesis, we used intact human monocytes and adenosine triphosphate labeled with radioactive phosphate at the third phosphate ([gamma-32P]-ATP) to phosphorylate laminin-1. Autoradiography after sodium dodecyl sulphate polyacrylamyde gel electrophoresis (SDS-PAGE) electrophoresis indicated phosphorylation of laminin-1 on the beta and/or gamma chains. After phosphorylation, phosphoserine could be detected on Western blots by a specific monoclonal antibody. Phosphorylation was not detected when monocytes were pre-treated with trypsin and was inhibited by a specific ecto-protein kinase inhibitor (K252b). Laminin phosphorylation was also inhibited by heparin, a known inhibitor of casein kinase II and by pretreatment of monocytes by a monoclonal anti-casein kinase II antibody. Heparin binding, cell attachment and proliferation, and monocyte migration were enhanced on the phosphorylated laminin-1 as compared to the non-phosphorylated controls. These data indicate that laminin-1 can be phosphorylated by monocyte casein kinase II type ectokinase. This phosphorylation influences important functions of laminin and therefore could provide an additional means for the interaction of monocytes with basement membranes.

Blockade of α6integrin inhibits IL-1β- but not TNF-α-induced neutrophil transmigration in vivo

In vitro and in vivo evidence supports a functional role for the integrin alpha6beta1 in neutrophil migration through the perivascular basement membrane, a response that in vivo appears to be associated with platelet/endothelial cell adhesion molecule-1 (PECAM-1)-mediated up-regulation of alpha6beta1 on the cell surface of transmigrating leukocytes. As the involvement of PECAM-1 in leukocyte migration is cytokine-specific, the aim of the present study was to investigate whether alpha6beta1 exhibited a similar profile of stimulus specificity in this context. The cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) were used to elicit neutrophil migration in two murine models of inflammation, migration through cremasteric venules, as observed by intravital microscopy, and migration into the peritoneal cavity. The role of alpha6beta1 was investigated using an alpha6 integrin-blocking monoclonal antibody GoH3. In both models, GoH3 significantly inhibited neutrophil transmigration induced by IL-1beta but not TNF-alpha. This cytokine-specific role of alpha6 integrin was associated with enhanced cell-surface expression of alpha6beta1 on transmigrated neutrophils (as compared with blood cells) in response to IL-1beta but not TNF-alpha. Using lipopolysaccharide as an inflammatory stimulus in the cremaster muscle model, the study also provides evidence for the involvement of alpha6 integrin in leukocyte transmigration as mediated by endogenously generated IL-1beta. Collectively, the findings demonstrate that alpha6beta1 blockade inhibits neutrophil migration induced by exogenous and endogenous IL-1beta but not TNF-alpha, observations that are associated with increased expression of the integrin on transmigrated leukocytes.

An endothelial laminin isoform, laminin 8 (α4β1γ1), is secreted by blood neutrophils, promotes neutrophil migration and extravasation, and protects neutrophils from apoptosis

During extravasation, neutrophils migrate through the perivascular basement membrane (BM), a specialized extracellular matrix rich in laminins. Laminins 8 (LN-8) (α4β1γ1) and 10 (LN-10) (α5β1γ1) are major components of the endothelial BM, but expression, recognition, and use of these laminin isoforms by neutrophils are poorly understood. In the present study, we provide evidence, using a panel of novel monoclonal antibodies against human laminin α4 (LNα4) chain, that neutrophils contain and secrete LN-8, and that this endogenous laminin contributes to chemoattractant-induced, αMβ2-integrin–dependent neutrophil migration through albumin-coated filters. Phorbol ester–stimulated neutrophils adhered to recombinant human (rh) LN-8, rhLN-10, and mouse LN-1 (mLN-1) (α1β1γ1) via αMβ2-integrin, and these laminin isoforms strongly promoted chemoattractant-induced neutrophil migration via the same integrin. However, only rhLN-8 enhanced the spontaneous migration. In addition, recruitment of neutrophils into the peritoneum following an inflammatory stimulus was impaired in LNα4-deficient mice. rhLN-8 also protected isolated neutrophils from spontaneous apoptosis. This study is the first to identify a specific laminin isoform in neutrophils and provides evidence for the role of LN-8 in the adhesion, migration, extravasation, and survival of these cells.

Differential expression of basement membrane components in lymphatic tissues

Peripheral lymphoid tissues act as important organs of immunological defense. Characteristic of their architecture is the rich reticular fiber meshwork composed of various extracellular matrix (ECM) molecules with which the stationary non-lymphatic cells stay in intimate contact and form channels through which the lymphatic cells travel. Here we studied the distribution of various laminin (Ln) chains and different types of collagens in human spleen, lymph node, and tonsil to clarify their chain-specific distribution. The most widely distributed proteins in all these organs were Ln chains alpha5, beta1, gamma1 and collagen types IV and XVIII, which were present in practically all compartments. Conversely, Ln alpha1, alpha2, alpha4, and type VII collagen showed a more restricted expression pattern. A unique feature was that Ln alpha3-, beta3-, and gamma2-chains, which normally are not localized to the vascular wall in non-lymphatic tissues, were present also in capillary basement membranes (BMs) of the follicular structures of lymph node and tonsil and in Ln alpha1-chain and type VII collagen also in the splenic white pulp. We also found that collagen XVII was exclusively present in the ring fibers of the spleen. The results indicate that BMs of lymphatic tissues contain a variety of macromolecules that probably contribute strongly to immunological events. In addition, capillaries of the lymphoid tissue exhibit a specified BM composition resembling that in epithelial BMs of non-lymphoid tissues.

Rac regulates integrin-mediated endothelial cell adhesion and migration on laminin-8

Blood vessel formation requires endothelial cell interactions with the extracellular matrix through cell surface receptors, and signaling events that control endothelial cell adhesion, migration, and lumen formation. Laminin-8 (alpha4beta1gamma1) is present in all basement membranes of blood vessels in fetal and adult tissues, but despite its importance in vessel formation, its role in endothelial cell adhesion and migration remains undefined. We examined adhesion and migration of HMEC-1 human microvascular endothelial cells on laminin-8 with an emphasis on the integrin-mediated signaling events, as compared with those on laminin-10/11 and fibronectin. We found that laminin-8 was less potent in HMEC-1 cell adhesion than laminin-1, laminin-10/11, and fibronectin, and mediated cell adhesion through alpha6beta1 integrin. Despite its weak cell-adhesive activity, laminin-8 was as potent as laminin-10/11 in promoting cell migration. Cells adhering to laminin-8 displayed streaks of thin actin filaments and formed lamellipodia at the leading edge of the cells, as observed with cells adhering to laminin-10/11, while cells on fibronectin showed thick actin stress fibers and large focal adhesions. Pull-down assays of GTP-loaded Rho, Rac, and Cdc42 demonstrated that Rac, but not Rho or Cdc42, was preferentially activated on laminin-8 and laminin-10/11, when compared with fibronectin. Furthermore, a dominant-negative mutant of Rac suppressed cell spreading, lamellipodial formation, and migration on laminin-8, but not on fibronectin. These results, taken together, indicate that Rac is activated during endothelial cell adhesion to laminin-8, and is pivotal for alpha6beta1 integrin-mediated cell spreading and migration on laminin-8.

Laminin-8/9 is synthesized by rat glomerular mesangial cells and is required for PDGF-induced mesangial cell migration

BACKGROUND

Laminin (LM), the major glycoprotein component of basement membranes is expressed as multiple isoforms in a developmentally regulated and tissue-specific manner. LM alpha4 has a limited tissue distribution and is highly expressed in the developing glomerulus. In the present study, we investigate the in vivo and in vitro expression and function of LM alpha4 in the glomerulus.

METHODS

LM alpha4 expression was examined by Northern blot, reverse transcription polymerase chain reaction (RT-PCR), Western blot, and immunofluorescence microscopy. Mesangial cells (MC) were plated on purified LM-1, LM-2, and LM-8/9. Immunofluorescence microscopy was performed to examine the cellular phenotypes induced by LM-1 and LM-8/9. A modified Boyden chamber method was used to assess laminin participation in platelet-derived growth factor (PDGF)-stimulated migration.

RESULTS

mRNA for LMalpha4 is expressed in cultured rat MC, and isolated rat and mouse glomeruli, but not in cultured rat glomerular epithelial cells or glomerular endothelial cells. Using antibodies specific for LM alpha4, a 240 kD band was detected in MC extract and a slightly smaller band was identified in extracted rat glomeruli. Purified LM-8/9 had MC adhesive activity comparable to LM-1 and LM-2. MC attached to LM-8/9 exhibited a unique phenotype. In contrast to LM-1, attachment of MC to LM-8/9 produced a highly arborized cell morphology with significantly reduced formation of focal contacts or stress fibers. LM alpha4 is utilized by MC during PDGF-stimulated migration.

CONCLUSION

LM alpha4 is synthesized by MC and persists in the mature glomerulus. LM-8/9 stimulates a unique cellular morphology, and they are utilized in PDGF-induced migration. These factors suggest that LM alpha4 plays an important role in MC differentiation and in the maintenance of MC phenotype.

Preferential locomotion of leukemic cells towards laminin isoforms 8 and 10

To identify the laminin isoforms of the basement membranes that could be implicated in the extravasation process of neoplastic lymphocytes, a number of purified laminins and one native renal laminin complex were comparatively investigated for their ability to promote migration of neoplastic lymphocytes in vitro. The identity/composition of a human placental laminin complex was asserted by combining immunochemical assays, sequence determination of tryptic peptides, and ultrastructural analysis to be composed predominantly of laminin-10 in which the coiled-coil C-terminal regions and the G globular domain of the alpha5 chain were preserved intact despite the enzymatic treatment used for its isolation. Lymphoma and leukemic cell lines failed to migrate towards laminin-4, -9, -11, moved poorly in response to laminin-1, -2/4, -5 and the renal laminin complex, but markedly locomoted towards the subendothelial laminin-8 and -10. The motility-promoting interaction with these latter laminins was interchangeably mediated by the alpha3beta1 and alpha6beta1 integrins. Lymphocyte locomotion on laminins assayed in the presence of cytokines was either reduced or enhanced suggesting that local cytokine milieu could further influence motility response.

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.

Laminin chains in rat and human peripheral nerve: distribution and regulation during development and after axonal injury

During nerve growth, axons are dependent upon contact with matrix components, such as laminins, for elongation, guidance, and trophic support. Semiquantitative in situ hybridization histochemistry and immunohistochemistry (IHC) were used to identify laminin chains in normal peripheral nerves, during postnatal development, after sciatic nerve transection (SNT), and after sciatic nerve crush (SNC). Laminin alpha2, alpha4, beta1, beta2, and gamma1 chain mRNAs were all expressed at high levels in newborn rat sciatic nerves with declining levels during later developmental stages. At the adult stage, no laminin chain mRNA was detectable. Of interest, the mRNA levels for alpha4 chain declined faster than those for alpha2. After SNT, laminin alpha2, alpha4, beta1, and gamma1 mRNA levels were up-regulated at the site of the injury, with the most profound reaction in the proximal nerve stump. Laminin alpha2 and alpha4 chains differed in that the mRNA levels of alpha4 were up-regulated earlier and declined quicker, whereas alpha2 had a later onset, with high levels remaining even after 6 weeks. After SNC, there was an initial up-regulation of the same laminin chain mRNAs as after SNT in the nerve, however, less intense, and at 6 weeks after SNC, all laminin mRNA levels studied had returned to normal. IHC of adult human normal and transected peripheral nerves stained positive for laminin alpha2, alpha4, beta1, and gamma1 chains in close relation to neurofilament labeled axons. Laminin alpha3, alpha4, alpha5, beta1, beta2, and gamma1 chains were found in blood vessel-like structures and alpha3, alpha4, alpha5, beta2, and gamma1 in the perineurium. These results and a previously published description of integrin regulation in spinal motoneurons suggest that both laminin-2 (alpha2beta1gamma1) and laminin-8 (alpha4beta1gamma1) are important for the postnatal nerve development and axonal regeneration after injury and that laminin-8 may have important functions especially early postnatally and early after adult nerve lesion.

Laminin gamma2 chain as a stromal cell marker of the human bone marrow microenvironment

Laminins are large heterotrimeric molecules consisting of alpha, beta and gamma chains. At present, five alpha chains, three beta chains and three gamma chains have been characterized. Laminin-5 (alpha3beta3gamma2) is the only isoform known to date which contains a gamma2 chain. In human bone marrow, non-haematopoietic stromal cells expressed the laminin gamma2 chain, whereas bone marrow mononuclear cells did not. Co-localization of the gamma2 chain was detected with the laminin alpha4 and alpha5 chains, and co-immunoprecipitation studies revealed a new isoform consisting of alpha5, beta2 and gamma2 chains. The laminin gamma2 chain was also co-localized with alpha-sm-actin in bone marrow, but it was not expressed in endothelial cells or megakaryocytes, indicating that the gamma2 chain is exclusively expressed in vivo in bone marrow stromal cells. The laminin gamma2 chain containing isoform LN-5 was shown to be an adhesive substrate for a small subpopulation of bone marrow mononuclear cells and also for peripheral blood platelets. Taken together, these results indicate that (I) laminin isoforms containing the gamma2 chain can act as adhesive substrates for human haematopoietic cells, and (II) the laminin gamma2 chain can be used as a specific marker molecule for human bone-marrow-derived stromal cells.

Localization of laminin alpha4-chain in developing and adult human tissues

Recent studies suggest important functions for laminin-8 (Ln-8; alpha4beta1gamma1) in vascular and blood cell biology, but its distribution in human tissues has remained elusive. We have raised a monoclonal antibody (MAb) FC10, and by enzyme-linked immunoassay (EIA) and Western blotting techniques we show that it recognizes the human Ln alpha4-chain. Immunoreactivity for the Ln alpha4-chain was localized in tissues of mesodermal origin, such as basement membranes (BMs) of endothelia, adipocytes, and skeletal, smooth, and cardiac muscle cells. In addition, the Ln alpha4-chain was found in regions of some epithelial BMs, including epidermis, salivary glands, pancreas, esophageal and gastric glands, intestinal crypts, and some renal medullary tubules. Developmental differences in the distribution of Ln alpha4-chain were detected in skeletal muscle, walls of vessels, and intestinal crypts. Ln alpha4- and Ln alpha2-chains co-localized in BMs of fetal skeletal muscle cells and in some epithelial BMs, e.g., in gastric glands and acini of pancreas. Cultured human pulmonary artery endothelial (HPAE) cells produced Ln alpha4-chain as M(r) 180,000 and 200,000 doublet and rapidly deposited it to the growth substratum. In cell-free extracellular matrices of human kidney and lung, Ln alpha4-chain was found as M(r) 180,000 protein.

Laminin isoforms in tumor invasion, angiogenesis and metastasis

Laminins are a growing family of alphabetagamma heterotrimeric proteins, commonly found in basement membranes (BMs). These large molecules promote cell adhesion and migration via integrins and other cell-surface receptors. Over 12 laminin isoforms are presently known. The various isoforms have a cell- and tissue-specific expression and are differentially recognized by integrins. Expression of laminin isoforms in tumors usually reflects expression in their normal counterparts. However, during tumor invasion, loss of the BM barrier occurs and a discontinuous pattern of laminin staining is observed. In carcinomas, tumor cells at the invading front strongly express intracellularly the gamma2 chain, a component of laminin-5. Remodeling of the vascular BM is observed during angiogenesis, and penetration of several BMs occurs during tumor dissemination and metastasis. Thus, disregulated cell-laminin interactions are major traits of malignant disorders.

Cell adhesion and migration properties of beta 2-integrin negative polymorphonuclear granulocytes on defined extracellular matrix molecules. Relevance for leukocyte extravasation

Regulated adhesion of leukocytes to the extracellular matrix is essential for transmigration of blood vessels and subsequent migration into the stroma of inflamed tissues. Although beta(2)-integrins play an indisputable role in adhesion of polymorphonuclear granulocytes (PMN) to endothelium, we show here that beta(1)- and beta(3)-integrins but not beta(2)-integrin are essential for the adhesion to and migration on extracellular matrix molecules of the endothelial cell basement membrane and subjacent interstitial matrix. Mouse wild type and beta(2)-integrin null PMN and the progranulocytic cell line 32DC13 were employed in in vitro adhesion and migration assays using extracellular matrix molecules expressed at sites of extravasation in vivo, in particular the endothelial cell laminins 8 and 10. Wild type and beta(2)-integrin null PMN showed the same pattern of ECM binding, indicating that beta(2)-integrins do not mediate specific adhesion of PMN to the extracellular matrix molecules tested; binding was observed to the interstitial matrix molecules, fibronectin and vitronectin, via integrins alpha(5)beta(1) and alpha(v)beta(3), respectively; to laminin 10 via alpha(6)beta(1); but not to laminins 1, 2, and 8, collagen type I and IV, perlecan, or tenascin-C. PMN binding to laminins 1, 2, and 8 could not be induced despite surface expression of functionally active integrin alpha(6)beta(1), a major laminin receptor, demonstrating that expression of alpha(6)beta(1) alone is insufficient for ligand binding and suggesting the involvement of accessory factors. Nevertheless, laminins 1, 8, and 10 supported PMN migration, indicating that differential cellular signaling via laminins is independent of the extent of adhesion. The data demonstrate that adhesive and nonadhesive interactions with components of the endothelial cell basement membrane and subjacent interstitium play decisive roles in controlling PMN movement into sites of inflammation and illustrate that beta(2)-integrins are not essential for such interactions.

Endothelial cell laminin isoforms, laminins 8 and 10, play decisive roles in T cell recruitment across the blood-brain barrier in experimental autoimmune encephalomyelitis

An active involvement of blood-brain barrier endothelial cell basement membranes in development of inflammatory lesions in the central nervous system (CNS) has not been considered to date. Here we investigated the molecular composition and possible function of the extracellular matrix encountered by extravasating T lymphocytes during experimental autoimmune encephalomyelitis (EAE). Endothelial basement membranes contained laminin 8 (alpha4beta1gamma1) and/or 10 (alpha5beta1gamma1) and their expression was influenced by proinflammatory cytokines or angiostatic agents. T cells emigrating into the CNS during EAE encountered two biochemically distinct basement membranes, the endothelial (containing laminins 8 and 10) and the parenchymal (containing laminins 1 and 2) basement membranes. However, inflammatory cuffs occurred exclusively around endothelial basement membranes containing laminin 8, whereas in the presence of laminin 10 no infiltration was detectable. In vitro assays using encephalitogenic T cell lines revealed adhesion to laminins 8 and 10, whereas binding to laminins 1 and 2 could not be induced. Downregulation of integrin alpha6 on cerebral endothelium at sites of T cell infiltration, plus a high turnover of laminin 8 at these sites, suggested two possible roles for laminin 8 in the endothelial basement membrane: one at the level of the endothelial cells resulting in reduced adhesion and, thereby, increased penetrability of the monolayer; and secondly at the level of the T cells providing direct signals to the transmigrating cells.

Laminin-8 (alpha4beta1gamma1) is synthesized by lymphoid cells, promotes lymphocyte migration and costimulates T cell proliferation

Laminins are a growing family of large heterotrimeric proteins with cell adhesive and signalling functions. They are major components of basement membranes and are found in many organs, including the vasculature and other compartments of bone marrow, thymus, lymph nodes and spleen. However, expression, recognition and use of laminin isoforms by lymphoid cells are poorly understood. In the present study, lymphoid T cells (Jurkat) were found to synthesize laminin alpha4, beta1 and gamma1 mRNAs and polypeptides and to assemble the chains into laminin-8. Lymphoblastoid B (NAD-20) cells, lymphoid NK (NKL) cells and blood lymphocytes also contained laminin-8 and, after cell permeabilization, practically all blood lymphocytes reacted with mAbs to laminin beta1 and gamma1 chains. Following stimulation, blood lymphocytes secreted laminin-8, and this laminin isoform, but not laminin-10/11(alpha5beta1gamma1/alpha5beta2gamma1), promoted chemokine-induced migration of the cells. In an activation-dependent manner, purified blood CD4 T cells adhered to immobilized laminin-8 and laminin-10/11 by using alpha6beta1 integrin, but minimally to laminin-1 (alpha1beta1gamma1). Accordingly, laminin-8 and laminin-10/11, but not laminin-1, strongly costimulated proliferation of the T cells via the same integrin. Thus, lymphoid cells are able to synthesize and secrete complete laminin molecules. In addition, synthesis of laminin-8 and recognition of laminin-8 and -10/11 by lymphocytes indicate relevance of these laminin isoforms in lymphocyte physiology.