Involvement of gicerin in the extension of microvilli

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.

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, 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.

mTOR is required for asymmetric division through small GTPases in mouse oocytes

Mammalian target of rapamycin (mTOR) is central to the control of cell proliferation, growth, and survival in mammalian cells. Prolonged treatment with rapamycin inhibits mTOR complex 2 (mTORC2) activity, and both the mTORC1-mediated S6K1 and 4E-BP1/eIF4E pathways are essential for TORC2-mediated RhoA, Cdc42, and Rac1 expression during cell motility and F-actin reorganization. The functions of mTOR in the mouse oocyte remain unclear, however. The present study shows that rapamycin affects mTOR expression and cytoskeleton reorganization during meiotic maturation of mouse oocytes. mTOR mRNA was expressed in germinal vesicles (GV) until metaphase I (MI), and increased during metaphase II (MII). Immunostaining showed that mTOR localized around the spindle and in the cytoplasm of oocytes. Treatment of oocytes with rapamycin decreased mTOR at the RNA and protein level, and altered asymmetric division. Formation of the actin cap and the cortical granule-free domain were also disrupted after rapamycin treatment, indicating the failure of spindle migration. Injection of an anti-mTOR antibody yielded results consistent with those obtained for rapamycin treatment, further confirming the involvement of mTOR in oocyte polarity. Furthermore, rapamycin treatment reduced the mRNA expression of small GTPases (RhoA, Cdc42, and Rac1), which are crucial regulatory factors for cytoskeleton reorganization. Taken together, these results suggest that rapamycin inhibits spindle migration and asymmetric division during mouse oocyte maturation via mTOR-mediated small GTPase signaling pathways.

Formation of microvilli and phosphorylation of ERM family proteins by CD43, a potent inhibitor for cell adhesion: cell detachment is a potential cue for ERM phosphorylation and organization of cell morphology

CD43/sialophorin/leukosialin, a common leukocyte antigen, is known as an inhibitor for cell adhesion. The ectodomain of CD43 is considered as a molecular barrier for cell adhesion, while the cytoplasmic domain has a binding site for Ezrin/Radixin/Moesin (ERM). We found expression of CD43 induced cell rounding, inhibition of cell re-attachment, augmentation of microvilli, and phosphorylation of ERM in HEK293T cells. Mutant studies revealed the ectodomain of CD43, but not the intracellular domain, essential and sufficient for all these phenomena. We also found that forced cell detachment by itself induced phosphorylation of ERM in HEK293T cells. Taken together, these findings indicate that inhibition of cell adhesion by the ectodomain of CD43 induces phosphorylation of ERM, microvilli formation, and eventual cell rounding. Furthermore, our study suggests a novel possibility that cell detachment itself induces activation of ERM and modification of cell shape.

Towards understanding the mode of action of the multifaceted cell adhesion receptor CD146

CD146, also known as melanoma cell adhesion molecule or MCAM, is a key cell adhesion protein in vascular endothelial cell activity and angiogenesis. CD146 promotes tumor progression of many cancers including melanoma and prostate. Strikingly, its expression is frequently lost in breast carcinoma cells, and it may act as a suppressor of breast cancer progression. While upstream mechanisms regulating CD146 are well documented, our understanding of the downstream molecular events underlying its mode of action remains to be elucidated. This review aims to focus on the progress in understanding the signaling mechanisms and the functional relevance of CD146, a multifaceted molecule, in cancer with particular emphasis on its role in inhibiting breast cancer progression.

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.

Oocyte CD9 is enriched on the microvillar membrane and required for normal microvillar shape and distribution

Microvilli are found on the surface of many cell types, including the mammalian oocyte, where they are thought to act in initial contact of sperm and oocyte plasma membranes. CD9 is currently the only oocyte protein known to be required for sperm-oocyte fusion. We found CD9 is localized to the oocyte microvillar membrane using transmission electron microscopy (TEM). Scanning electron microscopy (SEM) showed that CD9 null oocytes, which are unable to fuse with sperm, have an altered length, thickness and density of their microvilli. One aspect of this change in morphology was quantified using TEM by measuring the radius of curvature at the microvillar tips. A small radius of curvature is thought to promote fusibility and the radius of curvature of microvillar tips on CD9 wild-type oocytes was found to be half that of the CD9 null oocytes. We found that oocyte CD9 co-immunoprecipitates with two Ig superfamily cis partners, EWI-2 and EWI-F, which could have a role in linking CD9 to the oocyte microvillar actin core. We also examined latrunculin B-treated oocytes, which are known to have reduced fusion ability, and found altered microvillar morphology by SEM and TEM. Our data suggest that microvilli may participate in sperm-oocyte fusion. Microvilli could act as a platform to concentrate adhesion/fusion proteins and/or provide a membrane protrusion with a low radius of curvature. They may also have a dynamic interaction with the sperm that serves to capture the sperm cell and bring it into close contact with the oocyte plasma membrane.

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.

Hyaluronan synthesis induces microvillus-like cell surface protrusions

Hyaluronan synthases (HASs) are plasma membrane enzymes that simultaneously elongate, bind, and extrude the growing hyaluronan chain directly into extracellular space. In cells transfected with green fluorescent protein (GFP)-tagged Has3, the dorsal surface was decorated by up to 150 slender, 3-20-microm-long microvillus-type plasma membrane protrusions, which also contained filamentous actin, the hyaluronan receptor CD44, and lipid raft microdomains. Enzymatic activity of HAS was required for the growth of the microvilli, which were not present in cells transfected with other GFP proteins or inactive GFP-Has3 mutants or in cells incubated with exogenous soluble hyaluronan. The microvilli induced by HAS3 were gradually withered by introduction of an inhibitor of hyaluronan synthesis and rapidly retracted by hyaluronidase digestion, whereas they were not affected by competition with hyaluronan oligosaccharides and disruption of the CD44 gene, suggesting independence of hyaluronan receptors. The data bring out the novel concept that the glycocalyx created by dense arrays of hyaluronan chains, tethered to HAS during biosynthesis, can induce and maintain prominent microvilli.

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.

Reticulon3 expression in rat optic and olfactory systems

Reticulon3 (RTN3), which belongs to a reticulon family, is first isolated from the retina, but little is known about its function. We investigated the distribution of RTN3 in rat retina and olfactory bulb by immunohistochemistry. In the retina, Müller cells highly expressed RTN3. The expression level of RTN3 in the optic nerve was high in the embryo, but low in the adult. In the olfactory system, RTN3 was highly expressed in the olfactory nerve both in developmental and adult stages. Further, RTN3 was co-localized with synaptophysin in tubulovesicular structures in the developing axon of cultured cortical neurons. These results suggest that RTN3 may play an important role in the developing axons and also in some glial cells such as Müller cells.

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.

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.