Expression and functional analysis of a novel isoform of gicerin, an immunoglobulin superfamily cell adhesion molecule

CD146, a therapeutic target involved in cell plasticity

Since its identification as a marker for advanced melanoma in the 1980s, CD146 has been found to have multiple functions in both physiological and pathological processes, including embryonic development, tissue repair and regeneration, tumor progression, fibrosis disease, and inflammations. Subsequent research has revealed that CD146 is involved in various signaling pathways as a receptor or co-receptor in these processes. This correlation between CD146 and multiple diseases has sparked interest in its potential applications in diagnosis, prognosis, and targeted therapy. To better comprehend the versatile roles of CD146, we have summarized its research history and synthesized findings from numerous reports, proposing that cell plasticity serves as the underlying mechanism through which CD146 contributes to development, regeneration, and various diseases. Targeting CD146 would consequently halt cell state shifting during the onset and progression of these related diseases. Therefore, the development of therapy targeting CD146 holds significant practical value.

Expression of placental CD146 is dysregulated by prenatal alcohol exposure and contributes in cortical vasculature development and positioning of vessel-associated oligodendrocytes

Recent data showed that prenatal alcohol exposure (PAE) impairs the "placenta-brain" axis controlling fetal brain angiogenesis in human and preclinical models. Placental growth factor (PlGF) has been identified as a proangiogenic messenger between these two organs. CD146, a partner of the VEGFR-1/2 signalosome, is involved in placental angiogenesis and exists as a soluble circulating form. The aim of the present study was to investigate whether placental CD146 may contribute to brain vascular defects described in fetal alcohol spectrum disorder. At a physiological level, quantitative reverse transcription polymerase chain reaction experiments performed in human placenta showed that CD146 is expressed in developing villi and that membrane and soluble forms of CD146 are differentially expressed from the first trimester to term. In the mouse placenta, a similar expression pattern of CD146 was found. CD146 immunoreactivity was detected in the labyrinth zone and colocalized with CD31-positive endothelial cells. Significant amounts of soluble CD146 were quantified by ELISA in fetal blood, and the levels decreased after birth. In the fetal brain, the membrane form of CD146 was the majority and colocalized with microvessels. At a pathophysiological level, PAE induced marked dysregulation of CD146 expression. The soluble form of CD146 decreased in both placenta and fetal blood, whereas it increased in the fetal brain. Similarly, the expression of several members of the CD146 signalosome, such as VEGFR2 and PSEN, was differentially impaired between the two organs by PAE. At a functional level, targeted repression of placental CD146 by in utero electroporation (IUE) of CRISPR/Cas9 lentiviral plasmids resulted in (i) a decrease in cortical vessel density, (ii) a loss of radial vascular organization, and (iii) a reduced density of oligodendrocytes. Statistical analysis showed that the more the vasculature was impaired, the more the cortical oligodendrocyte density was reduced. Altogether, these data support that placental CD146 contributes to the proangiogenic "placenta-brain" axis and that placental CD146 dysfunction contributes to the cortical oligo-vascular development. Soluble CD146 would represent a promising placental biomarker candidate representative of alcohol-induced neurovascular defects in neonates, as recently suggested by PlGF (patents WO2016207253 and WO2018100143).

Endothelial-Specific Deletion of CD146 Protects Against Experimental Glomerulonephritis in Mice

[Figure: see text].

Expression of cell adhesion molecule, Gicerin/CD146 during the formation of heart and in the cardiac hypertrophy

Gicerin/CD146 is a cell adhesion molecule which belongs to the immunoglobulin (Ig) superfamily. We have reported the existence of gicerin/CD146 in the nervous system, heart, lung and smooth muscles of blood vessels. In this study, we make a cardiac hypertrophy model rat by constricting the rat aorta (AAC, ascending aortic constriction) and examined the effect on the expression of gicerin/CD146 in the heart. We found that the expression level of gicerin/CD146 was increased by the AAC treatment. Next, stretch stimulation was applied to myocardial cell line H9c2 cells to confirm that gicerin/CD146 may participate in the cellular hypertrophy model. We also treated the cells with inhibitors of MAP pathway enzymes. In cultured myocardial cells, the expression level of gicerin/CD146 was increased by the stretch stimulation and decreased by inhibiting the MAP pathway. Based on the above findings, it is suggested that the expression of gicerin/CD146 is involved in cardiac hypertrophy, and that the MAP pathway may be involved in the expression of gicerin/CD146 RNA in the cardiomyocyte. In addition, the expression level of gicerin/CD146 RNA in neonatal rats was upregulated after birth. Therefore, it is suggested that gicerin/CD146 might participate in the increase of myocardial cell volume both in the pathway of cardiac hypertrophy and in the developmental growth of heart.

MCAM/CD146 Signaling via PLCγ1 Leads to Activation of β1-Integrins in Memory T-Cells Resulting in Increased Brain Infiltration

Multiple sclerosis is a chronic auto-inflammatory disease of the central nervous system affecting patients worldwide. Neuroinflammation in multiple sclerosis is mainly driven by peripheral immune cells which invade the central nervous system and cause neurodegenerative inflammation. To enter the target tissue, immune cells have to overcome the endothelium and transmigrate into the tissue. Numerous molecules mediate this process and, as they determine the tissue invasiveness of immune cells, display great therapeutic potential. Melanoma cell adhesion molecule (MCAM) is a membrane-anchored glycoprotein expressed by a subset of T-cells and MCAM+ T-cells have been shown to contribute to neuroinflammation in multiple sclerosis. The role of the MCAM molecule for brain invasion, however, remained largely unknown. In order to investigate the role of the MCAM molecule on T-cells, we used different in vitro and in vivo assays, including ex vivo flow chambers, biochemistry and microscopy experiments of the mouse brain. We demonstrate that MCAM directly mediates adhesion and that the engagement of MCAM induces intracellular signaling leading to β1-integrin activation on human T-cells. Furthermore, we show that MCAM engagement triggers the phosphorylation of PLCγ1 which is required for integrin activation and thus amplification of the cellular adhesive potential. To confirm the physiological relevance of our findings in vivo, we demonstrate that MCAM plays an important role in T-cell recruitment into the mouse brain. In conclusion, our data demonstrate that MCAM expressed on T-cells acts as an adhesion molecule and a signaling receptor that may trigger β1-integrin activation via PLCγ1 upon engagement.

Therapeutic and Diagnostic Antibodies to CD146: Thirty Years of Research on Its Potential for Detection and Treatment of Tumors

CD146 (MCAM, MUC18, S-Endo1) is a transmembrane glycoprotein belonging to both CAM and mucin families. It exists as different splice variants and is cleaved from the membrane by metalloproteases to generate a soluble form. CD146 is expressed by numerous cancer cells as well as being one of the numerous proteins expressed by the vascular endothelium. It has also been identified on smooth muscle cells, pericytes, and some immune cells. This protein was initially described as an actor involved in tumor growth and metastatic dissemination processes. Some recent works highlighted the role of CD146 in angiogenesis. Interestingly, this knowledge allowed the development of therapeutic and diagnostic tools specifically targeting the different CD146 variants. The first anti-CD146 antibody designed to study the function of this molecule, MUC18, was described by the Pr. J.P. Jonhson in 1987. In this review, we will discuss the 30 following years of research focused on the detection, study, and blocking of this protein in physiological and pathological processes.

CD146 (MCAM) in human cs-DLK1-/cs-CD34+ adipose stromal/progenitor cells

To precisely characterize CD146 in adipose stromal/progenitor cells (ASCs) we sorted the stromal vascular faction (SVF) of human abdominal subcutaneous white adipose tissue (sWAT) according to cell surface (cs) expression of CD146, DLK1 and CD34. This test identified three main SVF cell populations: ~50% cs-DLK1^-/cs-CD34⁺/cs-CD146^- ASCs, ~7.5% cs-DLK1⁺/cs-CD34^dim/+/cs-CD146⁺ and ~7.5% cs-DLK1⁺/cs-CD34^dim/+/cs-CD146^- cells. All cells contained intracellular CD146. Whole mount fluorescent IHC staining of small vessels detected CD146⁺ endothelial cells (CD31⁺/CD34⁺/CD146⁺) and pericytes (CD31^-/CD34^-/CD146⁺ ASCs). The cells in the outer adventitial layer showed the typical ASC morphology, were strongly CD34⁺ and contained low amounts of intracellular CD146 protein (CD31^-/CD34⁺/CD146⁺). Additionally, we detected wavy CD34^-/CD146⁺ and CD34^dim/CD146⁺ cells. CD34^dim/CD146⁺ cells were slightly more bulky than CD34^-/CD146⁺ cells. Both CD34^-/CD146⁺ and CD34^dim/CD146⁺ cells were detached from the inner pericyte layer and protruded into the outer adventitial layer. Cultured early passage ASCs contained low levels of CD146 mRNA, which was expressed in two different splicing variants, at a relatively high amount of the CD146-long form and at a relatively low amount of the CD146-short form. ASCs contained low levels of CD146 protein, which consisted predominantly long form and a small amount of short form. The CD146 protein was highly stable, and the majority of the protein was localized in the Golgi apparatus. In conclusion, the present study contributes to a better understanding of the spatial localization of CD34⁺/CD146⁺ and CD34^-/CD146⁺ cells in the adipose niche of sWAT and identifies CD146 as intracellular protein in cs-DLK1^-/cs-CD34⁺/cs-CD146^- ASCs.

Beneficial roles of melanoma cell adhesion molecule in spinal cord transection recovery in adult zebrafish

Melanoma cell adhesion molecule (MCAM) is a multifunctional protein involved in miscellaneous processes, including development and tumor angiogenesis. Here, spinal cord transection in adult zebrafish was used to investigate the effects of MCAM on spinal cord injury (SCI) and subsequent recovery. Expression of MCAM mRNA increased and co-localized with motoneurons in the spinal cord after SCI. With MCAM morpholino treatment, inhibition of MCAM retarded both axon regrowth and locomotor recovery in the spinal cord injured zebrafish. Furthermore, MCAM mRNA expression was also observed in fli1a:EGFP transgenic zebrafish, which specifically show labeled blood vessels. Inhibition of MCAM down-regulated the expression of angiogenesis-related factors, such as VEGFR-2, p-p38 and p-AKT, and the inflammatory factors TNF-α, IL-1β and IL-8. Taken together, these data suggest that MCAM may have a beneficial role in the recovery from SCI, via the promotion of neurogenesis and angiogenesis. In the context of adult zebrafish spinal cord injury, we proved that Melanoma cell adhesion molecule (MCAM) is beneficial to the recovery, possibly via mechanisms of angiogenensis and inflammation. MCAM promotes angiogenesis by adjusting VEGFR-2, p-p38 and p-AKT. MCAM affects inflammatory factors such as TNF-α, IL-1β and IL-8. Our results extend the beneficial role of MCAM in the regeneration of central nervous system.

Cell Adhesion Molecules and Ubiquitination-Functions and Significance

Cell adhesion molecules of the immunoglobulin (Ig) superfamily represent the biggest group of cell adhesion molecules. They have been analyzed since approximately 40 years ago and most of them have been shown to play a role in tumor progression and in the nervous system. All members of the Ig superfamily are intensively posttranslationally modified. However, many aspects of their cellular functions are not yet known. Since a few years ago it is known that some of the Ig superfamily members are modified by ubiquitin. Ubiquitination has classically been described as a proteasomal degradation signal but during the last years it became obvious that it can regulate many other processes including internalization of cell surface molecules and lysosomal sorting. The purpose of this review is to summarize the current knowledge about the ubiquitination of cell adhesion molecules of the Ig superfamily and to discuss its potential physiological roles in tumorigenesis and in the nervous system.

CD146, a multi-functional molecule beyond adhesion

CD146 is a cell adhesion molecule (CAM) that is primarily expressed at the intercellular junction of endothelial cells. CD146 was originally identified as a tumor marker for melanoma (MCAM) due to its existence only in melanoma but not in the corresponding normal counterpart. However CD146 is not just a CAM for the inter-cellular and cell-matrix adhesion. Recent evidence indicates that CD146 is actively involved in miscellaneous processes, such as development, signaling transduction, cell migration, mesenchymal stem cells differentiation, angiogenesis and immune response. CD146 has increasingly become an important molecule, especially identified as a novel bio-marker for angiogenesis and for cancer. Here we have reviewed the dynamic research of CD146, particularly newly identified functions and the underlying mechanisms of CD146.

Gicerin/Cd146 is involved in zebrafish cardiovascular development and tumor angiogenesis

Angiogenesis plays an important role in vertebrate development and tumor growth. In this process, gicerin, which is known as a kind of cell adhesion molecule, has recently been reported to play an important role but its in vivo function is still unclear in developing vasculature. To address this issue, we used gain-of-function and loss-of-function analyses of gicerin in zebrafish. In the gain of function experiments using enforced expression of various domains of gicerin constructs, extracellular domain induced angiogenic sprouting defects, most notably in the intersegmental vessels, whereas the cytoplasmic domain of gicerin did not affect angiogenic sprouting. Moreover, morpholino-mediated knockdown of gicerin in embryos resulted in angiogenic sprouting defects in intersegmental vessels. Mechanistically, the angiogenic function of gicerin was found to be genetically linked to VEGF signaling in the knock-down experiments using vegf-a mRNA, VEGFR inhibitor and gicerin morpholino. In addition to the physiological angiogenesis during development, gicerin morphants efficiently blocked the tumor angiogenesis in zebrafish. Thus, knock-down of gicerin might have an important implication in controlling tumor angiogenesis.

CD146 short isoform increases the proangiogenic potential of endothelial progenitor cells in vitro and in vivo

RATIONALE

CD146, a transmembrane immunoglobulin mainly expressed at the intercellular junction of endothelial cells, is involved in cell-cell cohesion, paracellular permeability, monocyte transmigration and angiogenesis. CD146 exists as 2 isoforms, short (sh) and long (lg), but which isoform is involved remains undefined.

OBJECTIVE

The recently described role of CD146 in angiogenesis prompted us to investigate which isoform was involved in this process in human late endothelial progenitors (EPCs), with the objective of increasing their proangiogenic potential.

METHODS AND RESULTS

Immunofluorescence experiments showed that, in subconfluent EPCs, shCD146 was localized in the nucleus and at the migrating edges of the membrane, whereas lgCD146 was intracellular. In confluent cells, shCD146 was redistributed at the apical membrane and lgCD146 was directed toward the junction. In contrast to lgCD146, shCD146 was overexpressed in EPCs as compared to mature endothelial cells and upregulated by vascular endothelial growth factor and SDF-1 (stromal cell-derived factor 1). Study of the properties of both isoforms in vitro provided evidence that shCD146 was involved in EPC adhesion to activated endothelium, migration, and proliferation, with a paracrine secretion of interleukin-8 or angiopoietin 2, whereas lgCD146 was implicated in stabilization of capillary-like structures in Matrigel and transendothelial permeability. In an animal model of hindlimb ischemia, transplantation of shCD146-modified EPCs selectively promoted both EPC engraftment and blood flow.

CONCLUSIONS

Altogether, these findings establish that CD146 isoforms display distinct functions in vessels regeneration. Selective improvement of therapeutic angiogenesis by shCD146 overexpression suggests a potential interest of shCD146-transduced EPCs for the treatment of peripheral ischemic disease.

Dual role of melanoma cell adhesion molecule (MCAM)/CD146 in lymphocyte endothelium interaction: MCAM/CD146 promotes rolling via microvilli induction in lymphocyte and is an endothelial adhesion receptor

The melanoma cell adhesion molecule (MCAM)/CD146 is expressed as two isoforms differing by their cytoplasmic domain (MCAM long (MCAM-l) and MCAM short (MCAM-s)). MCAM being expressed by endothelial cells and activated T cells, we analyzed its involvement in lymphocyte trafficking. The NK cell line NKL1 was transfected by MCAM isoforms and submitted to adhesion on both the endothelial cell monolayer and recombinant molecules under shear stress. MCAM-l transfection reduced rolling velocity and increased NKL1 adhesion on the endothelial cell monolayer and VCAM-1. Scanning electron microscopy revealed that MCAM-l induced microvilli formation and extension. In contrast, MCAM short or mock transfection had no effect on adhesion of NKL1 cells and microvilli formation. As shown by mutagenesis, serine 32 of the MCAM-l cytoplasmic tail, belonging to a putative protein kinase C phosphorylation site, was necessary for MCAM-l-actin cytoskeleton interaction and microvilli induction. Accordingly, chelerythrine chloride, a protein kinase C inhibitor, abolished MCAM-l-induced microvilli and rolling of MCAM-l-transfected NKL1 cells. Inhibition of adhesion under shear stress by anti-MCAM Abs suggested that both lymphoid MCAM-l and endothelial MCAM were also directly involved in lymphocyte endothelium interaction. MCAM-l-transfected NKL1 and activated CD4 T cells adhered to rMCAM under shear stress whereas anti-MCAM Ab treatment inhibited this process. Taken together, these data establish that MCAM is involved in the initial steps of lymphocyte endothelium interaction. By promoting the rolling on the inflammation marker VCAM-1 via microvilli induction and displaying adhesion receptor activity involving possible homophilic MCAM-l-MCAM-l interactions, MCAM might be involved in the recruitment of activated T cells to inflammation sites.

A dileucine motif targets MCAM-l cell adhesion molecule to the basolateral membrane in MDCK cells

Melanoma cell adhesion molecule (MCAM), an adhesion molecule belonging to the Ig superfamily, is an endothelial marker and is expressed in different epithelia. MCAM is expressed as two isoforms differing by their cytoplasmic domain: MCAM-l and MCAM-s (long and short). In order to identify the respective role of each MCAM isoform, we analyzed MCAM isoform targeting in polarized epithelial Madin-Darby canine kidney (MDCK) cells using MCAM-GFP chimeras. Confocal microscopy revealed that MCAM-s and MCAM-l were addressed to the apical and basolateral membranes, respectively. Transfection of MCAM-l mutants established that a single dileucine motif (41-42) of the cytoplasmic domain was required for MCAM-l basolateral targeting in MDCK cells. Although double labelling experiments showed that MCAM-l is not a component of adherens junctions and focal adhesions, its expression on basolateral membranes suggests that MCAM-l is involved in epithelium insuring.

BT-IgSF, a novel immunoglobulin superfamily protein, functions as a cell adhesion molecule

BT-IgSF is a newly identified cell surface glycoprotein belonging to the immunoglobulin superfamily (IgSF). We have previously shown that the expression of the BT-IgSF gene was highly restricted to brain and testis, and its transcript was detected in both neurons and glial cells. In this study, to explore its function, we generated cells overexpressing BT-IgSF proteins and analyzed their phenotypes. We found that the constitutive expression of BT-IgSF in the myeloid leukemia cell line TF-1-fms did not alter the growth rates, but caused the formation of large cell aggregates. The cell aggregates were also observed with mutant BT-IgSF lacking its cytoplasmic tail, the amino acid sequences of which were highly conserved among the BT-IgSF subgroup proteins. The neutralizing antibody to beta(1) integrin did not diminish the cell aggregate formation. These results indicate that BT-IgSF functions as a cell adhesion molecule, that its cytoplasmic tail is not essential for the function, and that beta(1) integrin is not involved in the function. We confirmed the cell adhesion function using NIH/3T3 fibroblastic cells expressing BT-IgSF in an inducible system. Flow cytometric analyses with the cells demonstrated that the cell aggregation mediated by BT-IgSF was through homophilic molecular interaction, and in a Ca(2+)/Mg(2+)-independent manner. Coupled with its restricted pattern of the expression, the cell adhesion-inducing function of BT-IgSF suggests a role of the cell surface molecule in the development/function of the central nervous system and spermatogenesis.

Molecular cloning and analysis of the mouse gicerin gene

Gicerin is a cell adhesion molecule, which has five immunoglobulin-like loop structures in an extracellular domain followed by a single transmembrane domain and a short cytoplasmic tail. We have reported that gicerin participates in neurite extension and structural organization of the nervous system, and its expression in the nervous system is high during the development and dramatically decreased after birth. To elucidate the mechanism how the expression of gicerin is regulated, we performed a genomic cloning of a mouse gicerin. A fragment of 16 kbp genomic clone contained 8 kbp gicerin gene composed of 16 exons with 6 kbp upstream region. Genomic cloning revealed that two isoforms of gicerin were generated by an alternative splicing of exon 15 results in cytoplasmic domains composed of either 63 or 21 amino acids. As for an expressional regulation of gicerin, we found that the mRNA content of gicerin in PC12 cells was regulated by cAMP. Quantitative-PCR analysis revealed that forskolin induced four-fold increase of gicerin mRNA. To characterize the involvement of its promoter region, we examined the promoter activity in PC12 cells by a luciferase-reporter assay. We found that a CRE site located at 60 bp upstream of gicerin gene was responsible for the increase of its mRNA induced by forskolin.

Gicerin/CD146 is involved in neurite extension of NGF-treated PC12 cells

Gicerin/CD146 is a cell adhesion molecule, which belongs to the immunoglobulin (Ig) superfamily. We have reported that it has a homophilic binding activity, which participates in the neurite extension from embryonic neurons. To elucidate how gicerin is involved in the neurite extension mechanism, we employed PC12 cells, which expresses gicerin/CD146. PC12 cells extend longer neurites by nerve growth factor (NGF) on gicerin substrate than on without gicerin substrate, which indicates that gicerin participates in neurite extension by NGF. We also found that the expression of gicerin in PC12 cells is induced by NGF. Over-expression of gicerin also promotes neurite extension by gicerin-gicerin homophilic interaction. These findings suggested that increase of gicerin expression by NGF promotes the gicerin-gicerin homophilic interaction resulting in the neurite extension.

Characterization of Gicerin/MUC18/CD146 in the rat nervous system

Gicerin is a cell adhesion molecule of an immunoglobulin (Ig) superfamily isolated from a chicken. It shows homophilic and heterophilic binding activities and has two isoforms. s-Gicerin which has small cytoplasmic domain and the same extracellular domain as l-gicerin shows stronger cell adhesion activity. In the chick nervous system, gicerin expression is only observed in the developmental stage when neurons extend neurites and migrate. In other tissues, gicerin participates in the tissue regeneration or oncogenesis. In this report, we identified two isoforms of rat gicerin corresponding to chicken and we concluded that gicerin is a homologue of human CD146/MUC18/MCAM. Next we generated antibody to characterize a rat gicerin in the nervous system. Gicerin is expressed in the hippocampal cells, Purkinje cells, and sensory neurons of a spinal chord of an adult rat, while expressed most abundantly in the lung. In addition to this, its expression in the hippocampus was increased by electroconvulsive shock, suggesting some role in the mature nervous system. And we also showed neurite promotion activity of gicerin from hippocampal neurons.

Induction of gicerin/CD146 in the rat carotid artery after balloon injury

Gicerin is a cell adhesion molecule belonging to the immunoglobulin superfamily. It is reported that the human homologous molecule, CD146, is expressed in the endothelial cells. Here, we found that the expression of gicerin was increased in the rat carotid arteries after balloon injury. Immunohistochemical analysis demonstrated that the expression of gicerin protein was increased in the medial smooth muscle cells prior to the formation of neointima one week after the injury and was also increased in the luminal edge of the neointima after two weeks. We employed A10 cells, a cell line derived from rat aortic smooth muscle cell, and examined the effect of growth factors on the expression of gicerin, such as IGF-1, PDGF-BB, and bFGF. We found that IGF-1, but not PDGF-BB and bFGF, significantly increases the expression of gicerin protein in A10 cells. These suggest gicerin might be involved in the arteriosclerotic neointima formation in the artery.

Expression and involvement of gicerin, a cell adhesion molecule, in the development of chick optic tectum

Gicerin is a cell adhesion molecule belonging to the immunoglobulin superfamily. It has both a homophilic binding activity and a heterophilic binding activity to neurite outgrowth factor (NOF) a molecule belonging to the laminin family. We have reported many studies on the heterophilic activity of gicerin and NOF, but the function of its homophilic binding activity in vivo had been unclear. In the retina, gicerin is expressed in retinal ganglion cells only when they extend neurites to the optic tectum. In this report we have found that gicerin is also transiently expressed in the optic tectum during this time. First, cell aggregation assays were used to show that gicerin expressed in the optic tectum displays homophilic binding activity. Then, explant cultures of embryonic day 6 chick optic tectum on gicerin-Fc chimeric protein-coated dishes and NOF-coated dishes were carried out. It was found that gicerin-gicerin homophilic interactions promoted cell migration, whereas heterophilic interactions with NOF induced neurite formation. Furthermore, when anti-gicerin antibodies were injected in order to examine the effect of gicerin protein in the formation of the tectal layer in ovo, cell migration was strongly inhibited. These data suggest that homophilic interaction of gicerin participates in the migration of neural cells during the layer formation and plays a crucial role in the organization of the optic tectum.

Gicerin, an Ig-superfamily cell adhesion molecule, promotes the invasive and metastatic activities of a mouse fibroblast cell line

Gicerin is a cell adhesion molecule in the immunoglobulin (Ig) superfamily and plays an important role during development through its adhesive properties. Gicerin has two isoforms that differ in their cytoplasmic domains; s-gicerin is the shorter and l-gicerin the longer form of the protein. Gicerin is over-expressed in some sporadic tumors as well as in developing tissues. To provide direct evidence that gicerin has the potential to participate in malignant aspects of tumor cell behavior, a gicerin cDNA was introduced into L-929 cells, an endogenous gicerin-negative mouse fibroblast and subsequently analyzed for changes in their invasive and metastatic potential by implantation into nude mice and chick embryos. Compared with parental cells, both gicerin isoform transfectants showed an enhanced cell growth and invaded deeply into surrounding tissues from implanted sites in both animal models. Furthermore, l-gicerin transfectants markedly enhanced metastasis to the lung. These findings suggest that gicerin promotes the tumor growth and invasion, and the isoform bearing the longer cytoplasmic domain may play a role in metastasis.

Involvement of gicerin in the extension of microvilli

Gicerin is a cell adhesion molecule belonging to the immunoglobulin superfamily. To study the functional differences between l- and s-gicerin, we first examined the distribution of endogenous gicerin in B16 cells and found that l-gicerin was densely localized in microvilli. To clarify the relationship between gicerin and the microvilli, we established independent stable cell lines expressing l- and s-gicerin in L cells and found that l-gicerin localized to the microvilli. Scanning electron microscopic analysis revealed that the microvilli of l-gicerin-transfected cells were longer than those of s-gicerin and control transfectants. This suggested that l-gicerin might participate in the elongation of the microvilli. When cells were double-stained with antibodies to gicerin and moesin, a microvilli-specific protein, the staining of l-gicerin corresponded to that of moesin in the elongated microvilli. Moesin was coprecipitated with glutathione S-transferase-fusion proteins of the l-gicerin cytoplasmic domain but not with the s-gicerin cytoplasmic domain. To determine the region involved in the extension of microvilli, we generated transfectants of two truncated forms of l-gicerin cytoplasmic domain, and we found that only the transfectants of the longer mutant had the longer microvilli, while the shorter mutant exhibited short microvilli. These results suggested that l-gicerin-specific amino acid residues, especially amino acids 16-39, within the cytoplasmic domain of l-gicerin might be involved in the extension of microvilli.

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

Lutheran blood group glycoprotein and its newly characterized mouse homologue specifically bind alpha5 chain-containing human laminin with high affinity

Lutheran blood group glycoproteins (Lu gps) are receptors for the extracellular matrix protein, laminin. Studies suggest that Lu gps may contribute to vaso-occlusion in sickle cell disease and it has recently been shown that sickle cells adhere to laminin isoforms containing the alpha5 chain (laminin 10/11). Laminin alpha5 is present in the subendothelium and is also a constituent of bone marrow sinusoids, suggesting a role for the Lu/laminin interaction in erythropoiesis. The objectives of the current study were to define more precisely the molecular interactions of the extracellular and intracellular regions of human Lu and to clone and characterize a mouse homologue. To this end, complementary DNA and genomic clones for the mouse homologue were sequenced and the mouse Lu gene mapped to a region on chromosome 7 with conserved synteny with human 19q13.2. Mouse and human Lu gps are highly conserved (72% identity) at the amino acid sequence level and both mouse and human Lu gps specifically bind laminin 10/11 with high affinity. Furthermore, the first 3, N-terminal, immunoglobulin superfamily domains of human Lu are critical for this interaction. The results indicated that the cytoplasmic domain of BRIC 221-labeled human Lu gp is linked with the spectrin-based skeleton, affording the speculation that this interaction may be critical for signal transduction. These results further support a role for Lu gps in sickle cell disease and indicate the utility of mouse models to explore the function of Lu gp-laminin 10/11 interaction in normal erythropoiesis and in sickle cell disease.

Cytoplasmic domain is not essential for the cell adhesion activities of gicerin, an Ig-superfamily molecule

Gicerin is a cell adhesion molecule in the immunoglobulin (Ig) superfamily and is expressed abundantly during development in the nervous system. It has homophilic cell adhesion activity and also has heterophilic binding activity with NOF (neurite outgrowth factor) and mediates neurite extension. There are two isoforms of gicerin, one with a short (s-gicerin) and the other with a longer cytoplasmic domain (l-gicerin). We have reported that s-gicerin possesses stronger activities than l-gicerin during cell aggregation, in NOF-binding, and in neurite extension. In this study, we established cell lines which expressed a mutant-gicerin whose cytoplasmic domain was deleted and we compared the above three biological activities of the mutant-gicerin with those of s- and l-gicerin. We found that the mutant-gicerin retained all these activities, but the activities were weaker than those of s-gicerin and almost the same as those of l-gicerin. We concluded that the cytoplasmic domain of gicerin is not essential for optimal adhesive activities of gicerin, but might be involved in the regulation of its activities.

Erythroid cell adhesion molecules Lutheran and LW in health and disease

The Lutheran and LW glycoproteins are blood group-active proteins found at the surface of human red cells. The Lutheran glycoprotein (Lu gp) is a member of the immunoglobulin superfamily (IgSF) that binds the extracellular matrix protein laminin, in particular, laminin isoforms containing the alpha 5 subunit. The LW glycoprotein (LW gp), also an IgSF member, has substantial sequence homology with the family of intercellular adhesion molecules (ICAMs). LW gp binds the integrin very late antigen-4 (VLA-4, alpha 4 beta 1) and alpha V-containing integrins. Studies on the expression of LW and Lu gps during erythropoiesis utilizing in vitro cultures of haemopoietic progenitor cells have shown that LW gp expression precedes that of Lu gp. These observations have led to the suggestion that LW gp on erythroblasts may interact with VLA-4 on macrophages to stabilize erythroblastic islands in normal bone marrow and that Lu gp may facilitate trafficking of more mature erythroid cells to the sinusoidal endothelium where alpha 5-containing laminins are known to be expressed. Levels of Lu gp and LW gp expression on sickle red cells are greater than on normal red cells and sickle red cells adhere to alpha 5-containing laminins. These data suggest that the Lu and LW molecules may contribute to the vaso-occlusive events associated with episodes of acute pain in sickle cell disease.

Involvement of gicerin, a cell adhesion molecule, in development and regeneration of oviduct and metastasis of oviductal adenocarcinomas of the chicken

Gicerin is a novel cell adhesion molecule in the immunoglobulin superfamily and has both homophilic adhesion and heterophilic adhesive activity to neurite outgrowth factor (NOF), an extracellular matrix protein in the laminin family. We investigated the possible involvement of gicerin in oviductal development, regeneration, and metastasis of oviductal adenocarcinomas of the chicken. In the oviductal epithelium, gicerin was expressed strongly during development, disappeared after maturation, and reappeared during regeneration. NOF was constitutively expressed in the basement membrane of the epithelium. These molecules were expressed strongly in oviductal adenocarcinomas in both primary and metastatic lesions in the mesentery. An anti-gicerin antibody inhibited the attachment of adenocarcinoma cells to the mesentery in vitro. Many cells migrated from adenocarcinoma tissues on NOF, which were inhibited by an anti-gicerin antibody. These results suggest that gicerin might play a role in oviductal development and regeneration and also in the metastasis of adenocarcinomas.

Expression of gicerin, a novel cell adhesion molecule, is upregulated in the astrocytes after hypoglossal nerve injury in rats

Gicerin is an integral membrane glycoprotein which mediates cell-cell and cell-extracellular matrix (ECM) interactions in the nervous system. We studied gicerin expression in the hypoglossal nucleus post transection using in situ hybridization and immunocytochemistry. We found that hypoglossal nerve injury resulted in a significant increase in gicerin expression. Its expression levels reached peak values in reactive astrocytes surrounding axotomized motoneurons of the ipsilateral hypoglossal nucleus 14 days after hypoglossal nerve injury. The results indicate that gicerin is up-regulated during nerve regeneration, suggesting that gicerin expressed in the reactive astrocytes might be involved in the processes of nerve regeneration.

MuSC, a novel member of the immunoglobulin superfamily, is expressed in neurons of a subset of cranial sensory ganglia in the mouse embryo

In contrast to the spinal sensory ganglia which reiterate a basic organizational and functional unit, each cranial ganglion mediates a distinct sensory modality and exhibits a characteristic pattern of peripheral and central neuronal connectivity. Molecules responsible for establishment and maintenance of the cranial ganglion-specific networks are not known. Our hamster monoclonal antibody 802C11 strongly stained neurons and their processes of the VIIIth cranial ganglion (hearing and equilibrium), but not of the Vth cranial (somatosensory) or spinal ganglia in the mouse embryo. The cellular staining pattern of positive neurons suggested that the antigen was associated with the cell membrane, and biochemical analyses of the antigen from adult mouse brain showed the antigen to be a glycosylated intrinsic membrane protein of approximately 100 kDa. The antigen was purified, and based on the partial amino acid sequences, its entire cDNA was cloned. A bacterially expressed polypeptide encoded by the cDNA was recognized by the antibody. The deduced amino acid sequence revealed that the antigen belongs to the immunoglobulin superfamily with a significant homology (73.5% identity) to chicken SC1 protein. Chicken SC1 has been shown to be a cell-cell adhesion molecule in vitro with a proposed role in neurite extension of spinal motor neurons. These results suggest that our murine SC1-related protein (MuSC) is involved in the pathfinding and/or fasciculation of specific cranial sensory nerve fibres.

Gicerin, a cell adhesion molecule, participates in the histogenesis of retina

Gicerin is a novel cell adhesion molecule that belongs to the immunoglobulin superfamily. Gicerin protein adheres to neurite outgrowth factor (NOF), an extracellular matrix protein in the laminin family, and also exhibits homophilic adhesion. Heterophilic adhesion of gicerin to NOF is thought to play an active role in neurite outgrowth of developing retinal cells in vitro. In this study, we examined the adhesion activity of gicerin during the retinal development of Japanese quail using an antibody directed against gicerin, to elucidate the biological importance of gicerin in retinal histogenesis. Immunohistochemical and Western blot analysis showed that gicerin was highly expressed in the developing retina but suppressed in the mature retina. The aggregation of neural retinal cells from 5-day embryonic quail retina was significantly inhibited when incubated with a polyclonal antibody to gicerin, suggesting that gicerin protein participates in the adhesion of neural retinal cells of the developing retina. Furthermore, histogenesis of retina both in the organ cultures and in ovo embryos was severely disrupted by incubation with a gicerin antibody. These findings provide evidence that gicerin plays an important role in retinal histogenesis.

HEMCAM, an adhesion molecule expressed by c-kit+ hemopoietic progenitors

We have characterized the adhesion molecule HEMCAM, which is expressed by hemopoietic progenitors of embryonic bone marrow. HEMCAM belongs to the immunoglobulin superfamily and consists of the V-V-C2-C2-C2 Ig domains. There are three mRNA splice variants. One has a short cytoplasmic tail; another has a long tail; while the third seems to lack transmembrane and cytoplasmic regions. Except for the NH2-terminal sequence, HEMCAM is identical to gicerin, a molecular involved in neurite outgrowth and Wilm's kidney tumor progression in the chicken and it is significantly homologous with MUC18 a molecule involved in melanoma progression and metastasis in human beings. In the bone marrow the HEMCAM+ cell population contains c-kit+ subsets. HEMCAM+ cells coexpressing the receptor tyrosine kinase c-kit give rise to T cells at a frequency of 0.17 when injected intrathymically in congenic animals. As HEMCAM+, c-kit+ cells differentiate into myeloid and erythroid CFU's the double-positive cell population seems to contain precursors for multiple lineages. HEMCAM promotes cell-cell adhesion of transfected cells. Cross-linking of murine HEMCAM leads to cell spreading of T-lymphocyte progenitors adhering to the vascular adhesion molecules, PECAM-1 and VCAM-1. Thus, HEMCAM is likely to be involved in cellular adhesion and homing processes.

Neuron-specific expression of a chicken gicerin cDNA in transient transgenic zebrafish

Gicerin, a novel cell adhesion molecule which belongs to the immunoglobulin superfamily, is expressed temporally and spatially in the developing chick brain and retina. The previous in vitro experiments using transfected cells showed that gicerin can function as a cell adhesion molecule which has both homophilic and heterophilic binding activities. For the in vivo analyses of gicerin in neural development, we tried to utilize a zebrafish system, a vertebrate suitable for studying early development. We generated transient transgenic animals by microinjecting DNA constructs into zebrafish embryos. Chicken gicerin, under control of the neurofilament gene promoter, was preferentially expressed in neuronal cells and gicerin-expressing neurons exhibited a fasciculation formation with neighboring gicerin-positive axons, which may be partly due to homophilic cell adhesion activity of gicerin. These experimental results suggest that this fast and efficient transgenic animal system is useful for studying the functional roles of neuron-specific genes during the development.