Regulation of cell migration in atherosclerosis

Mind bomb 2 promotes cell migration and epithelial structure by regulating adhesion complexes and the actin cytoskeleton

Cell migration is essential in animal development and co-opted during metastasis and inflammatory diseases. Some cells migrate collectively, which requires them to balance epithelial characteristics such as stable cell-cell adhesions with features of motility like rapid turnover of adhesions and dynamic cytoskeletal structures. How this is regulated is not entirely clear but important to understand. While investigating Drosophila oogenesis, we found that the putative E3 ubiquitin ligase, Mind bomb 2 (Mib2), is required to promote epithelial stability and the collective cell migration of border cells. Through biochemical analysis, we identified components of Mib2 complexes, which include E-cadherin and α- and β-catenins, as well as actin regulators. We also found that three Mib2 interacting proteins, RhoGAP19D, Supervillin, and Myosin heavy chain-like, affect border cell migration. mib2 mutant main body follicle cells have drastically reduced E-cadherin-based adhesion complexes and diminished actin filaments. We conclude that Mib2 acts to stabilize E-cadherin-based adhesion complexes and promote a robust actin cytoskeletal network, which is important for maintenance of epithelial integrity. The interaction with cadherin adhesion complexes and other cytoskeletal regulators contribute to its role in collective cell migration. Since Mib2 is well conserved, it may have similar functional significance in other organisms.

Two RECK Splice Variants (Long and Short) Are Differentially Expressed in Patients with Stable and Unstable Coronary Artery Disease: A Pilot Study

Primary prevention is crucial for coronary heart disease (CAD) and the identification of new reliable biomarkers might help risk stratification or predict adverse coronary events. Alternative splicing (AS) is a less investigated genetic factors implicated in CAD etiology. We performed an RNA-seq study on PBMCs from CAD patients and control subjects (CTR) and observed 113 differentially regulated AS events (24 up and 89 downregulated) in 86 genes. The RECK (Reversion-inducing-cysteine-rich protein with Kazal motifs) gene was further analyzed in a larger case study (24 CTR subjects, 72 CAD and 32 AMI patients) for its Splicing-Index FC (FC = −2.64; p = 0.0217), the AS event involving an exon (exon 18), and its role in vascular inflammation and remodeling. We observed a significant downregulation of Long RECK splice variant (containing exon 18) in PBMCs of AMI compared to CTR subjects (FC = −3.3; p < 0.005). Interestingly, the Short RECK splice variant (lacking exon 18) was under-expressed in AMI compared to both CTR (FC = −4.5; p < 0.0001) and CAD patients (FC = −4.2; p < 0.0001). A ROC curve, constructed combining Long and Short RECK expression data, shows an AUC = 0.81 (p < 0.001) to distinguish AMI from stable CAD patients. A significant negative correlation between Long RECK and triglycerides in CTR group and a positive correlation in the AMI group was found. The combined evaluation of Long and Short RECK expression levels is a potential genomic biomarker for the discrimination of AMI from CAD patients. Our results underline the relevance of deeper studies on the expression of these two splice variants to elucidate their functional role in CAD development and progression.

GAGA Regulates Border Cell Migration in Drosophila

Collective cell migration is a complex process that happens during normal development of many multicellular organisms, as well as during oncological transformations. In Drosophila oogenesis, a small set of follicle cells originally located at the anterior tip of each egg chamber become motile and migrate as a cluster through nurse cells toward the oocyte. These specialized cells are referred to as border cells (BCs) and provide a simple and convenient model system to study collective cell migration. The process is known to be complexly regulated at different levels and the product of the slow border cells (slbo) gene, the C/EBP transcription factor, is one of the key elements in this process. However, little is known about the regulation of slbo expression. On the other hand, the ubiquitously expressed transcription factor GAGA, which is encoded by the Trithorax-like (Trl) gene was previously demonstrated to be important for Drosophila oogenesis. Here, we found that Trl mutations cause substantial defects in BC migration. Partially, these defects are explained by the reduced level of slbo expression in BCs. Additionally, a strong genetic interaction between Trl and slbo mutants, along with the presence of putative GAGA binding sites within the slbo promoter and enhancer, suggests the direct regulation of this gene by GAGA. This idea is supported by the reduction in the slbo-Gal4-driven GFP expression within BC clusters in Trl mutant background. However, the inability of slbo overexpression to compensate defects in BC migration caused by Trl mutations suggests that there are other GAGA target genes contributing to this process. Taken together, the results define GAGA as another important regulator of BC migration in Drosophila oogenesis.

Identification of Novel Regulators of the JAK/STAT Signaling Pathway that Control Border Cell Migration in the Drosophila Ovary

The Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signaling pathway is an essential regulator of cell migration both in mammals and fruit flies. Cell migration is required for normal embryonic development and immune response but can also lead to detrimental outcomes, such as tumor metastasis. A cluster of cells termed “border cells” in the Drosophila ovary provides an excellent example of a collective cell migration, in which two different cell types coordinate their movements. Border cells arise within the follicular epithelium and are required to invade the neighboring cells and migrate to the oocyte to contribute to a fertilizable egg. Multiple components of the STAT signaling pathway are required during border cell specification and migration; however, the functions and identities of other potential regulators of the pathway during these processes are not yet known. To find new components of the pathway that govern cell invasiveness, we knocked down 48 predicted STAT modulators using RNAi expression in follicle cells, and assayed defective cell movement. We have shown that seven of these regulators are involved in either border cell specification or migration. Examination of the epistatic relationship between candidate genes and Stat92E reveals that the products of two genes, Protein tyrosine phosphatase 61F (Ptp61F) and brahma (brm), interact with Stat92E during both border cell specification and migration.

[Association between IGF system and PAPP-A in coronary atherosclerosis]

Atherosclerosis is a condition that involves multiple pathophysiological mechanisms and whose knowledge has not been fully elucidated. Often, scientific advances on the atherogenic pathophysiology generate that molecules not previously considered in the scene of this disease, were attributed actions on the onset or progression of it. A representative example is the study of a new mechanism involved in the atherogenic process, consisting of the association between the insulin-like growth factor (IGF) system and pregnancy-associated plasma protein-A (PAPP-A). Insulin-like growth factor system is a family of peptides that include 3 peptide hormones, 4 transmembrane receptors and 6 binding proteins. Insulin-like growth factor-1 (IGF-1) is the main ligand of the IGF system involved in coronary atherosclerosis. IGF-1 exerts its effects via activation of the IGF-1R receptor on vascular smooth muscle cells or macrophages. In vascular smooth muscle cells promotes migration and prevents apoptosis which increases plaque stability while in macrophages reduces reverse cholesterol transport leading to the formation of foam cells. Regulation of IGF-1 endothelial bioavailability is carried out by IGFBP proteases, mainly by PAPP-A. In this review, we address the mechanisms between IGF system and PAPP-A in atherosclerosis with emphasis on molecular effects on vascular smooth muscle cells and macrophages.

Autologous vein graft stenosis inhibited by orphan nuclear receptor Nur77-targeted siRNA

Neointimal hyperplasia plays an important role in autologous vein graft stenosis, and orphan receptor TR3/nur77 (Nur77) might play an essential role, but the mechanisms are still unclear. Here, we investigated the function of Nur77 in autologous vein graft stenosis. Rat vascular smooth muscle cell A7r5 was used for evaluating the function of Nur77 and screen siRNAs. Meanwhile, rat vein graft models were constructed for investigating the stenosis inhibition effects of Nur77-targeted siRNAs. The mRNA and protein levels of Nur77 were highly expressed in A7r5 cell, and could be significantly inhibited by the pre-designed siRNAs; the proliferation of A7r5 cell was also inhibited by the siRNAs. Furthermore, the intimal thickening in rat vein graft models was inhibited when knocking down the expression of Nur77 by siRNA. The results suggest that Nur77-targeted siRNA can inhibit autologous vein graft stenosis, Nur77 may play an important role in autologous vein graft stenosis, and Nur77 targeted siRNAs may be a therapy method for anti-stenosis of autologous vein graft.

Channel-independent influence of connexin 43 on cell migration

In this review we focus on the role of connexins, especially of Cx43, as modulators of migration - a fundamental process in embryogenesis and in physiologic functions of the adult organism. This impact of connexins is partly mediated by their function as intercellular channels but an increasing number of studies support the view that at least part of the effects are truly independent of the channel function. The channel-independent function comprises extrinsic guidance of migrating cells due to connexin mediated cell adhesion as well as intracellular processes. Cx43 has been shown to exert effects on migration by interfering with receptor signalling, cytoskeletal remodelling and tubulin dynamics. These effects are mainly dependent on the presence of the carboxyl tail of Cx43. The molecular basis of this channel-independent connexin function is still not yet fully understood but early results open an exciting view towards new functions of connexins in the cell. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Tissue-specific renin-angiotensin system in pulmonary lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM), a multisystem disease found in middle-aged women, is characterized by cystic lung destruction and abdominal tumors (e.g., angiomyolipomas, lymphangioleimyomas), resulting from proliferation of abnormal-appearing, smooth muscle-like cells (LAM cells). The LAM cells, in combination with other cells, form nodular structures within the lung interstitium and in the walls of the cysts. LAM cells contain mutations in the tuberous sclerosis complex TSC1 and/or TSC2 genes, which lead to dysregulation of the mammalian target of rapamycin, affecting cell growth and proliferation. Proliferation and migration of vascular smooth muscle cells and production of angiogenic factors are regulated, in part, by angiotensin II. To determine whether a LAM-specific renin-angiotensin system might play a role in the pathogenesis of LAM, we investigated the expression of genes and gene products of this system in LAM nodules. mRNA for angiotensinogen was present in RNA isolated by laser-captured microdissection from LAM nodules. Angiotensin I-converting enzyme and chymase-producing mast cells were present within the LAM nodules. We detected renin in LAM cells, as determined by the presence of mRNA and immunohistochemistry. Angiotensin II type 1 and type II receptors were identified in LAM cells by immunohistochemistry and immunoblotting of microdissected LAM nodules. Angiotensin II is localized in cells containing alpha-smooth muscle actin (LAM cells). A LAM-specific renin-angiotensin system appears to function within the LAM nodule as an autocrine system that could promote LAM cell proliferation and migration, and could represent a pharmacologic target.

Methods for the detection of paxillin post-translational modifications and interacting proteins by mass spectrometry

Methods for the simultaneous identification of interacting proteins and post-translational modifications of the focal adhesion adapter protein, paxillin, are presented. The strategy includes (1) lower-level, transient transfection of FLAG-GFP-Paxillin into HEK293 cells, (2) incubation of cells with phosphatase inhibitors prior to lysis, (3) purification of paxillin by anti-FLAG immunoprecipitation, (4) analysis of peptides generated from on-beads digestion using LTQ-FT or LTQ-ETD mass spectrometry, and (5) enrichment of phosphopeptide methyl esters with IMAC. Using the above strategies, we identify 29 phosphorylation sites (19 novel and 10 previously reported) and a novel glycosylation site on Ser 74. Furthermore, with this method, we simultaneously detect 10 co-purifying proteins which are present in focal adhesion complexes. Extension of these methods to other substrates should facilitate generation of global phosphorylation maps and protein-protein interactions for any protein of interest.

Transcription Factor SOX18 Is Expressed in Human Coronary Atherosclerotic Lesions and Regulates DNA Synthesis and Vascular Cell Growth

OBJECTIVE

SOX18, a member of the SOX gene family (SRY-like 3-hydroxy-3-methylglutaryl box gene), is a transcription factor expressed in the development of blood vessels during embryogenesis. We analyzed SOX18 expression in human coronary atherosclerotic lesions and investigated its potential function in vascular cells.

METHODS AND RESULTS

In advanced human coronary atherosclerotic lesions, SOX18 immunostaining was localized in endothelial cells (on the luminal surface, in vasa vasorum, and in intimal neovessels) and in vascular smooth muscle cells (VSMCs) scattered in the intima, colocalizing with proliferating cell nuclear antigen. In cell cultures, SOX18 was mainly localized in subconfluent and denuded areas. Significant SOX18 mRNA levels (by Northern blot analysis and reverse transcription-polymerase chain reaction) were detected in cell cultures from human umbilical vein endothelial cells and human VSMCs. Antisense SOX18 inhibited DNA synthesis ([3H]thymidine incorporation) and vascular cell growth. Antisense SOX18 also significantly reduced VSMC regrowth after injury in an in vitro model of wound repair.

CONCLUSIONS

Our results indicate that SOX18 is involved in vascular cell growth and suggest that this transcription factor may play a role in atherosclerosis.

Directional persistence of EGF-induced cell migration is associated with stabilization of lamellipodial protrusions

Migrating cells can sustain a relatively constant direction of lamellipodial protrusion and locomotion over timescales ranging from minutes to hours. However, individual waves of lamellipodial extension occur over much shorter characteristic times. Little understanding exists regarding how cells might integrate biophysical processes across these disparate timescales to control the directional persistence of locomotion. We address this issue by examining the effects of epidermal growth factor (EGF) stimulation on long-timescale directional persistence and short-timescale lamellipodial dynamics of EGF receptor-transfected Chinese hamster ovary cells migrating on fibronectin-coated substrata. Addition of EGF increased persistence, with the magnitude of increase correlating with fibronectin coating concentration. Kymographic analysis of EGF-stimulated lamellipodial dynamics revealed that the temporal stability of lamellipodial protrusions similarly increased with fibronectin concentration. A soluble RGD peptide competitor reduced both the persistence of long-timescale cell paths and the stability of short-timescale membrane protrusions, indicating that cell-substratum adhesion concomitantly influences lamellipodial dynamics and directional persistence. These results reveal the importance of adhesion strength in regulating the directional motility of cells and suggest that the short-timescale kinetics of adhesion complex formation may play a key role in modulating directional persistence over much longer timescales.

On How Insulin May Influence Ageing and Become Atherogenic throughout the Insulin-Like Growth Factor-1 Receptor Pathway: In vitro Studies with Human Vascular Smooth Muscle Cells

BACKGROUND

It is known that growth factors play a role in ageing and atherogenesis, and insulin develops mitogenic activity in vitro.

OBJECTIVES

This study focuses on the pathway by which insulin induces proliferation and mobility in vascular smooth muscle cells (SMCs) compared with that of insulin-like growth factor-1 (IGF-1), because they are two basic phenomena for atherogenesis that could also help to understand the role of insulin in the ageing process.

METHODS

Bromodeoxyuridine DNA incorporation, chemotaxis and the appearance of membrane ruffles were measured in cultured SMCs after incubation with insulin or IGF-1 in the presence of insulin or IGF-1 receptor-blocking antibodies.

RESULTS

Insulin-induced SMC proliferation through the IGF-1 receptors; indeed, the blockade of insulin receptors does not inhibit the mitogenic influence of insulin. On the contrary, insulin-induced cell migration was inhibited by blocking the insulin receptor but not the IGF-1 receptor. Nevertheless, in less differentiated SMCs from non-confluent cultures, the migratory response was significantly higher and insulin lost its receptor specificity. It was stimulated through receptors both for insulin and IGF-1. In these cases the IGF-1 action was similar. Insulin-induced F-actin rearrangements took place through both types of receptors, but IGF-1 was a little more specific through its own receptors.

CONCLUSION

The pathway activated by insulin to induce SMC proliferation is not different from that of IGF-1, whereas the unspecific mechanism inducing mobility in growing cells seems to be related to a higher sensitivity response. Cells with the highest mitotic activity have the highest mobility in which stimulation of receptor specificity is lost for either insulin or IGF-1. Extrapolating these results to in vivo, insulin could become relevant for inducing stabilization and also side effects in ageing.

Macrophage level is not affected by monocyte chemotactic protein-1 in invasive ductal breast carcinoma

PURPOSE AND METHOD

Monocyte chemotactic protein-1 (MCP-1) is a chemokine involved in the macrophage infiltration of tumor tissue. Tumor-associated macrophages (TAMs) are a population of mononuclear phagocytic cells that can have a complex function in tumor biology. The aim of this study was to determine the possible correlation between parenchymal MCP-1 expression and TAM level by immunohistochemical analysis of 97 invasive ductal breast carcinomas, not otherwise specified (NOS), and to investigate their relation with tumor size, histological grade, mitotic activity index (MAI) and lymph node status. Secondly, the MCP-1 mRNA was determined by reverse transcriptase-polymerase chain reaction (RT-PCR) in eight samples of normal breast tissue and 27 samples of invasive breast carcinomas and compared with TAMs.

RESULTS

MCP-1 immunoreactivity was present in tumor cells (17/97), but also in TAMs, fibroblasts and endothelial cells. The statistical analysis did not show a significant correlation between MCP-1 expression in tumoral epithelium and tumor size, histological grade, MAI, lymph node status or TAMs. The results of RT-PCR showed that, in all cases of breast carcinomas (27/27) and the majority of normal breast tissues (7/8), the number of detected MCP-1 cDNA copies was above the detection limit. However, carcinomas showed higher levels of MCP-1 mRNA than normal breast tissue. Nevertheless, the statistical analysis did not find a significant correlation between MCP-1 expression and macrophage infiltrations.

CONCLUSION

These results indicate that MCP-1 is probably not the only and/or crucial factor involved in macrophage attraction to tumor locus in breast carcinoma.

Proliferative aspects of airway smooth muscle

Increased airway smooth muscle (ASM) mass is perhaps the most important component of the airway wall remodeling process in asthma. Known mediators of ASM proliferation in cell culture models fall into 2 categories: those that activate receptors with intrinsic receptor tyrosine kinase activity and those that have their effects through receptors linked to heterotrimeric guanosine triphosphate-binding proteins. The major candidate signaling pathways activated by ASM mitogens are those dependent on extracellular signal-regulated kinase and phosphoinositide 3'-kinase. Increases in ASM mass may also involve ASM migration, and in culture, the key signaling mechanisms have been identified as the p38 mitogen-activated protein kinase and the p21-activated kinase 1 pathways. New evidence from an in vivo rat model indicates that primed CD4(+) T cells are sufficient to trigger ASM and epithelial remodeling after allergen challenge. Hyperplasia has been observed in an equine model of asthma and may account for the increase in ASM mass. Reduction in the rate of apoptosis may also play a role. beta(2)-Adrenergic receptor agonists and glucocorticoids have antiproliferative activity against a broad spectrum of mitogens, although it has become apparent that mitogens are differentially sensitive. Culture of ASM on collagen type I has been shown to enhance proliferative activity and prevent the inhibitory effect of glucocorticoids, whereas beta(2)-agonists are minimally affected. There is no evidence that long-acting beta(2)-agonists are more effective than short-acting agonists, but persistent stimulation of the beta(2)-adrenergic receptor probably helps suppress growth responses. The maximum response of fluticasone propionate against thrombin-induced proliferation is increased when it is combined with salmeterol.

Chemokine receptor–8 (CCR8) mediates human vascular smooth muscle cell chemotaxis and metalloproteinase-2 secretion

The response of the arterial vascular wall to injury is characterized by vascular smooth muscle cell (VSMC) migration, a process requiring metalloproteinase production. This migration is induced by cytokines, however the agonists involved are not fully defined. The CC chemokine receptor 8 (CCR8) is expressed on monocytes and T lymphocytes and is the sole receptor for the human CC chemokine 1 (CCL1, I-309) and for the viral chemokine, vCCL1 (viral macrophage inflammatory protein 1 [vMIP-1]). We have reported that CCR8 is expressed on human umbilical vein endothelial cells (HUVECs) and mediates chemotaxis induced by CCL1. The conditioned medium from incubation mixtures of lipoprotein(a) (Lp(a)) and HUVECs (LCM) contained CCL1 and stimulated both monocyte and HUVEC chemotaxis, providing novel mechanisms for the atherogenicity of Lp(a). We now report that CCL1, vCCL1, and LCM stimulate chemotaxis of human VSMCs that is blocked by murine monoclonal antibody against CCR8 and by the G-protein inhibitor pertussis toxin. The effect of anti-CCR8 was specific, as this antibody failed to effect the chemotaxis of VSMCs in response to CCL3 or by platelet-derived growth factor BB (PDGF-BB). VSMCs contained CCR8 mRNA and CCR8 antigen coprecipitated with VSMC membranes. Antibodies against metalloproteinase-2 (MMP-2) inhibited the CCL1-induced chemotaxis of VSMCs, whereas anti–MMP-9 was less effective. CCL1 induced VSMC pro–MMP-2 mRNA and protein secretion. Poxvirus MC148 inhibited the increase in MMP-2 induced by CCL1, documenting that CCR8 was the receptor responsible. In mouse femoral arteries, CCR8 and TCA3 antigen colocalized with VSMCs and were up-regulated after injury. The induction of CCR8 and CCL1/TCA3 under conditions associated with VSMC proliferation and migration raises the possibility that CCR8 may play an important role in vessel wall pathology.

Age-Dependent Decline of In Vitro Migration (Basal and Stimulated by IGF-1 or Insulin) of Human Vascular Smooth Muscle Cells

Since biological aging causes a decrease in functions such as cell proliferation, we have studied the possible effect of age on the migration capacity of human vascular smooth muscle cells (SMCs). To this aim, the migration activity of cultured SMCs from arteries of male human donors ranging in age from 43-77 years was determined in a Boyden chamber, under basal conditions and after insulin-like growth factor-1 (IGF-1) or insulin stimulation. Migration activity decreased with donor age (r2 = 87%, 85%, and 78%, respectively). IGF-1 and insulin significantly reduced the age-dependent relationship observed in basal conditions, so that, comparing young with old, both IGF-1 and insulin stimulated SMC migration similarly, although the effect of age remained in absolute terms. In this article, we conclude that the age-dependent decline of migration activity--similar to what has already been shown for SMC proliferation--may be part of the biological ageing phenotype, which is not overcome by hormone stimulation.