Tetraspanins and Intercellular Interactions

The Potential Role of Exosomal Proteins in Prostate Cancer

Prostate cancer is the most prevalent malignant tumor in men across developed countries. Traditional diagnostic and therapeutic methods for this tumor have become increasingly difficult to adapt to today’s medical philosophy, thus compromising early detection, diagnosis, and treatment. Prospecting for new diagnostic markers and therapeutic targets has become a hot topic in today’s research. Notably, exosomes, small vesicles characterized by a phospholipid bilayer structure released by cells that is capable of delivering different types of cargo that target specific cells to regulate biological properties, have been extensively studied. Exosomes composition, coupled with their interactions with cells make them multifaceted regulators in cancer development. Numerous studies have described the role of prostate cancer-derived exosomal proteins in diagnosis and treatment of prostate cancer. However, so far, there is no relevant literature to systematically summarize its role in tumors, which brings obstacles to the later research of related proteins. In this review, we summarize exosomal proteins derived from prostate cancer from different sources and summarize their roles in tumor development and drug resistance.

Tetraspanin CD9: A friend or foe of head and neck cancer (Review)

Head and neck cancers are diverse and complex diseases characterised by unregulated growth of tumour cells in various parts of the head and neck region, such as in the buccal mucosa, floor of the mouth, tongue, oropharynx, hypopharynx, oesophagus, nasopharynx and salivary glands. Partial or total glossectomy, radiation or chemotherapy greatly affect patient quality of life. However, even following treatment, patients may relapse. Nicotine-derived nitrosamines and alcohol are the major etiological factors underlying this deadly disease. These compounds induce DNA damage that may lead to mutation in crucial genes, such as p53 and p21, which are important to regulate cell proliferation, thus leading to cancer. CD9 is a tetraspanin, which are a group of transmembrane proteins that have a role in cell motility and adhesion. The present review aimed to explore the role of CD9 in head and neck cancer. Epidermal growth factor receptor activity and cell proliferation are regulated by the CD9-integrin/CD9-transforming growth factor interaction. Hence, CD9 can play a dual role in various types of cancer.

TSPAN1, a novel tetraspanin member highly involved in carcinogenesis and chemoresistance

The tetraspanin (TSPAN) family constitutes a poorly explored family of membrane receptors involved in various physiological processes, with relevant roles in anchoring multiple proteins, acting as scaffolding proteins, and cell signaling. Recent studies have increasingly demonstrated the involvement of TSPANs in cancer. In particular, tetraspanin 1 (also known as TSPAN1, NET-1, TM4C, C4.8 or GEF) has been implicated in cell survival, proliferation and invasion. Recently, our laboratory revealed a key role of TSPAN1 in the acquired resistance of tumor cells to conventional chemotherapy (e.g., cisplatin). In this review, we summarize and discuss the latest research on the physiological mechanisms of TSPANs in cancer and, in particular, on TSPAN1 regulating resistance to chemotherapy. A model of TSPAN1 action is proposed, and the potential of targeting TSPAN1 in anticancer therapeutic strategies is discussed.

Characteristics of TIMP1, CD63, and β1-Integrin and the Functional Impact of Their Interaction in Cancer

Tissue Inhibitor of Metalloproteases 1, also known as TIMP-1, is named for its well-established function of inhibiting the proteolytic activity of matrix metalloproteases. Given this function, many studies were carried out to verify if TIMP-1 was able to interrupt processes such as tumor cell invasion and metastasis. In contrast, many studies have shown that TIMP-1 expression is increased in several types of tumors, and this increase was correlated with a poor prognosis and lower survival in cancer patients. Later, it was shown that TIMP-1 is also able to modulate cell behavior through the induction of signaling pathways involved in cell growth, proliferation, and survival. The mechanisms involved in the regulation of the pleiotropic functions of TIMP-1 are still poorly understood. Thus, this review aimed to present literature data that show its ability to form a membrane complex with CD63 and β1-integrin, and point to N-glycosylation as a potential regulatory mechanism of the functions exerted by TIMP-1. This article reviewed the characteristics and functions performed individually by TIMP1, CD63, and β1-integrin, the roles of the TIMP-1/CD63/β1-integrin complex, both in a physiological context and in cancer, and the regulatory mechanisms involved in its assembly.

Tetraspanins, More than Markers of Extracellular Vesicles in Reproduction

The participation of extracellular vesicles in many cellular processes, including reproduction, is unquestionable. Although currently, the tetraspanin proteins found in extracellular vesicles are mostly applied as markers, increasing evidence points to their role in extracellular vesicle biogenesis, cargo selection, cell targeting, and cell uptake under both physiological and pathological conditions. In this review, we bring other insight into the involvement of tetraspanin proteins in extracellular vesicle physiology in mammalian reproduction. We provide knowledge regarding the involvement of extracellular vesicle tetraspanins in these processes in somatic cells. Furthermore, we discuss the future direction towards an understanding of their functions in the tissues and fluids of the mammalian reproductive system in gamete maturation, fertilization, and embryo development; their involvement in mutual cell contact and communication in their complexity.

CD151 promotes proliferation and migration of SK-NEP-1 cells via the GSK-3β/P21/cyclinD signaling pathway

Wilms'tumor is the most common malignant tumor with a poor clinical prognosis because of metastasis or recurrence among children worldwide. CD151, a member of transmembrane 4 superfamily, has now been confirmed to be involved in tumor progression including the proliferation, migration, invasion and metastasis of tumor cells. GSK-3β/P21/cyclinD signaling pathway plays a critical role in the cell cycle progression, regulating cellular proliferation. In this study, CD151 protein and mRNA levels were examined by western blot and RT-PCR. The proliferation of SK-NEP-1 cells was examined by CCK8 assay and the migration of SK-NEP-1 cells was detected with wound healing assay. Furthermore, p-GSK3β protein, GSK3β protein, p21protein and CyclinD protein were examined by western blot to verify whether CD151 could regulate the Wilms'tumor progression via the GSK-3β/P21/cyclinD signaling pathway. The RT-PCR and western blot results showed that CD151 protein was upregulated in Wilms'tumor cells compared with the control. The results by CCK8 assay and wound healing assay demonstrated that CD151 overexpression promoted the proliferation and migration in SK-NEP-1 cells and CD151 interference showed the opposite effects. Western blot assay revealed that CD151 activated the GSK-3β/P21/cyclinD signaling pathway and upregulated the expression of p-GSK3β protein, p21protein and CyclinD protein. It was also verified that CD151 promotes proliferation and migration of SK-NEP-1 cells through the GSK-3β/P21/cyclinD signaling pathway in this study. The specific aim of the study is to investigate and verify the role of CD151 in Wilm's tumor. Therefore, in-depth study on the molecular mechanisms will provide new strategies and methods for the treatment of Wilm's tumor.

TETRASPANINs in Plants

Tetraspanins are small transmembrane proteins that laterally associate with each other and cluster with numerous partner proteins as well as lipids. These interactions result in the formation of a distinct class of membrane domains, the tetraspanin-enriched microdomains (TEMs), which influence numerous cellular processes such as cell adhesion and fusion, intracellular membrane trafficking, signaling, morphogenesis, motility as well as interaction with pathogens and cancer development. The majority of information available about tetraspanins is based on studies using animal models or cell lines, but tetraspanins are also present in fungi and plants. Recent studies indicate that tetraspanins have important functions in plant development, reproduction and stress responses. Here we provide a brief summary of the current state of tetraspanin research in plants.

CD151 in cancer progression and metastasis: a complex scenario

Originally identified as a molecular organizer of interacting proteins into tetraspanin-enriched microdomains, the tetraspanin CD151 has now been shown to be involved in tumour progression. Increasing evidence emerging from in vitro, in vivo and clinical analyses implicates this tetraspanin in supporting growth of various types of tumours at different levels. It affects both cell autonomous behavior and communication with neighboring cells and the microenvironment. CD151 regulates post-adhesion events, that is, cell spreading, migration and invasion including subsequent intravasation and formation of metastasis. Present on both neoplastic and endothelial cells, CD151 is engaged in promotion of tumour neovascularization. The molecular mechanism of CD151 in cancer is based on its ability to organize distribution and function of interacting proteins, ie, laminin-binding integrins (α3β1, α6β1 and α6β4), receptors for growth factors (HGFR, EGFR and TGF-β1R) and matrix metalloproteinases (MMP-7, MMP-2 and MMP-9), which indicates its importance in disease development. Results of clinical analyses of CD151 expression in different types of cancer and a large number of in vivo models demonstrate its impact on tumour growth and invasion and implicate CD151 as a valuable diagnostic and prognostic marker as well as a potential target for anti-cancer therapy.

Tetraspanins CD81 and CD82 facilitate α4β1-mediated adhesion of human erythroblasts to vascular cell adhesion molecule-1

The proliferation and terminal differentiation of erythroid progenitors occurs in human bone marrow within erythroblastic islands, specialised structures consisting of a central macrophage surrounded by developing erythroid cells. Many cell-cell and cell-matrix adhesive interactions maintain and regulate the co-ordinated daily production of reticulocytes. Erythroid cells express only one integrin, α4β1, throughout differentiation, and its interactions with both macrophage Vascular Cell Adhesion Molecule-1 and with extracellular matrix fibronectin are critical for erythropoiesis. We observed that proerythroblasts expressed a broad tetraspanin phenotype, and investigated whether any tetraspanin could modulate integrin function. A specific association between α4β1 and CD81, CD82 and CD151 was demonstrated by confocal microscopy and co-immune precipitation. We observed that antibodies to CD81 and CD82 augmented adhesion of proerythroblasts to Vascular Cell Adhesion Molecule-1 but not to the fibronectin spliceoforms FnIII_12-IIICS-15 and FnIII_12–15. In contrast, different anti-CD151 antibodies augmented or inhibited adhesion of proerythroblasts to Vascular Cell Adhesion Molecule-1 and the fibronectin spliceoform FnIII_12-IIICS-15 but not to FnIII_12–15. These results strongly suggest that tetraspanins have a functional role in terminal erythropoiesis by modulating interactions of erythroblast α4β1 with both macrophages and extracellular matrix.

CD81 regulates cell migration through its association with Rac GTPase

Data presented here provide evidence for a new direct interaction of the GTPase Rac with the C-terminal cytoplasmic domain of tetraspanin CD81. Tetraspanin-enriched, microdomain-dependent compartmentalization is a novel regulatory mechanism of Rac activity turnover, which provides a novel mechanism for regulation of cell motility by tetraspanins.

CD81 is a member of the tetraspanin family that has been described to have a key role in cell migration of tumor and immune cells. To unravel the mechanisms of CD81-regulated cell migration, we performed proteomic analyses that revealed an interaction of the tetraspanin C-terminal domain with the small GTPase Rac. Direct interaction was confirmed biochemically. Moreover, microscopy cross-correlation analysis demonstrated the in situ integration of both molecules into the same molecular complex. Pull-down experiments revealed that CD81-Rac interaction was direct and independent of Rac activation status. Knockdown of CD81 resulted in enhanced protrusion rate, altered focal adhesion formation, and decreased cell migration, correlating with increased active Rac. Reexpression of wild-type CD81, but not its truncated form lacking the C-terminal cytoplasmic domain, rescued these effects. The phenotype of CD81 knockdown cells was mimicked by treatment with a soluble peptide with the C-terminal sequence of the tetraspanin. Our data show that the interaction of Rac with the C-terminal cytoplasmic domain of CD81 is a novel regulatory mechanism of the GTPase activity turnover. Furthermore, they provide a novel mechanism for tetraspanin-dependent regulation of cell motility and open new avenues for tetraspanin-targeted reagents by the use of cell-permeable peptides.

Tetraspanin CD151 stimulates adhesion-dependent activation of Ras, Rac, and Cdc42 by facilitating molecular association between β1 integrins and small GTPases

Tetraspanin CD151 associates with laminin-binding α(3)β(1)/α(6)β(1) integrins in epithelial cells and regulates adhesion-dependent signaling events. We found here that CD151 plays a role in recruiting Ras, Rac1, and Cdc42, but not Rho, to the cell membrane region, leading to the formation of α(3)β(1)/α(6)β(1) integrin-CD151-GTPases complexes. Furthermore, cell adhesion to laminin enhanced CD151 association with β(1) integrin and, thereby, increased complex formation between the β(1) family of integrins and small GTPases, Ras, Rac1, and Cdc42. Adhesion receptor complex-associated small GTPases were activated by CD151-β(1) integrin complex-stimulating adhesion events, such as α(3)β(1)/α(6)β(1) integrin-activating cell-to-laminin adhesion and homophilic CD151 interaction-generating cell-to-cell adhesion. Additionally, FAK and Src appeared to participate in this adhesion-dependent activation of small GTPases. However, engagement of laminin-binding integrins in CD151-deficient cells or CD151-specific siRNA-transfected cells did not activate these GTPases to the level of cells expressing CD151. Small GTPases activated by engagement of CD151-β(1) integrin complexes contributed to CD151-induced cell motility and MMP-9 expression in human melanoma cells. Importantly, among the four tetraspanin proteins that associate with β(1) integrin, only CD151 exhibited the ability to facilitate complex formation between the β(1) family of integrins and small GTPases and stimulate β(1) integrin-dependent activation of small GTPases. These results suggest that CD151 links α(3)β(1)/α(6)β(1) integrins to Ras, Rac1, and Cdc42 by promoting the formation of multimolecular complexes in the membrane, which leads to the up-regulation of adhesion-dependent small GTPase activation.

Hepatitis C virus induces CD81 and claudin-1 endocytosis

Hepatitis C virus (HCV) leads to progressive liver disease and hepatocellular carcinoma. Current treatments are only partially effective, and new therapies targeting viral and host pathways are required. Virus entry into a host cell provides a conserved target for therapeutic intervention. Tetraspanin CD81, scavenger receptor class B member I, and the tight-junction proteins claudin-1 and occludin have been identified as essential entry receptors. Limited information is available on the role of receptor trafficking in HCV entry. We demonstrate here that anti-CD81 antibodies inhibit HCV infection at late times after virus internalization, suggesting a role for intracellular CD81 in HCV infection. Several tetraspanins have been reported to internalize via motifs in their C-terminal cytoplasmic domains; however, CD81 lacks such motifs, leading several laboratories to suggest a limited role for CD81 endocytosis in HCV entry. We demonstrate CD81 internalization via a clathrin- and dynamin-dependent process, independent of its cytoplasmic domain, suggesting a role for associated partner proteins in regulating CD81 trafficking. Live cell imaging demonstrates CD81 and claudin-1 coendocytosis and fusion with Rab5 expressing endosomes, supporting a role for this receptor complex in HCV internalization. Receptor-specific antibodies and HCV particles increase CD81 and claudin-1 endocytosis, supporting a model wherein HCV stimulates receptor trafficking to promote particle internalization.

Probing the interaction of tetraspanin CD151 with integrin alpha 3 beta 1 using a panel of monoclonal antibodies with distinct reactivities toward the CD151-integrin alpha 3 beta 1 complex

CD151, a member of the tetraspanin family of proteins, forms a stable complex with integrin alpha 3 beta 1 and regulates integrin-mediated cell-substrate adhesion. However, the molecular basis of the stable association of CD151 with integrin alpha 3 beta 1 remains poorly understood. In the present study, we show that a panel of anti-human CD151 mAbs (monoclonal antibodies) could be divided into three groups on the basis of their abilities to co-immunoprecipitate integrin alpha 3: Group-1 mAbs were devoid of sufficient activities to co-precipitate integrin alpha 3 under both low- and high-stringency detergent conditions; Group-2 mAbs co-precipitated integrin alpha 3 under low-stringency conditions; and Group-3 mAbs exhibited strong co-precipitating activities under both conditions. Group-1 mAbs in particular exhibited increased reactivity toward integrin alpha 3 beta 1-unbound CD151, indicating that the binding sites for Group-1 mAbs are partly blocked by bound integrin alpha 3 beta 1. Epitope mapping using a series of CD151 mutants with substitutions at amino acid residues that are not conserved between human and mouse CD151 revealed that Gly(176)/Gly(177), Leu(191) and Gln(194) comprise epitopes characteristic of Group-1 mAbs. Replacement of short peptide segments, each containing one of these epitopes, with those of other tetraspanins lacking stable interactions with integrin alpha 3 beta 1 demonstrated that the segment from Cys(185) to Cys(192), including Leu(191), was involved in the stable association of CD151 with integrin alpha 3 beta 1, as was the Gln(194)-containing QRD peptide. Taken together these results indicate that two consecutive segments including two Group-1 epitopes, Leu(191) and Gln(194), comprise an interface between CD151 and integrin alpha 3 beta 1, and, along with the epitope including Gly(176)/Gly(177), are concealed by bound integrin.

The impact of cell adhesion changes on proliferation and survival during prostate cancer development and progression

In the normal prostate epithelium, androgen receptor (AR) negative basal epithelial cells adhere to the substratum, while AR expressing secretory cells lose substratum adhesion. In contrast, prostate cancer cells both express AR and adhere to a tumor basement membrane. In this review, we describe the differential expression of integrins, growth factor receptors (GFRs), and AR in normal and cancerous epithelium. In addition, we discuss how signals from integrins, GFRs, and AR are integrated to regulate the proliferation and survival of normal and malignant prostate epithelial cells. While cell adhesion is likely of great importance when considering therapeutic approaches for treatment of metastatic prostate cancer, no data on integrin expression are available from tissues of prostate cancer metastasis. However, several drug targets that are upregulated after androgen ablative therapy regulate cell adhesion and thus novel targeted therapies indirectly interfere with cell adhesion mechanisms in prostate cancer cells.

Homophilic interactions of Tetraspanin CD151 up-regulate motility and matrix metalloproteinase-9 expression of human melanoma cells through adhesion-dependent c-Jun activation signaling pathways

The tetraspanin membrane protein CD151 has been suggested to regulate cancer invasion and metastasis by initiating signaling events. The CD151-mediated signaling pathways involved in this regulation remain to be revealed. In this study, we found that stable transfection of CD151 into MelJuSo human melanoma cells lacking CD151 expression significantly increased cell motility, matrix metalloproteinase-9 (MMP-9) expression, and invasiveness. The enhancement of cell motility and MMP-9 expression by CD151 overexpression was abrogated by inhibitors and small interfering RNAs targeted to focal adhesion kinase (FAK), Src, p38 MAPK, and JNK, suggesting an essential role of these signaling components in CD151 signaling pathways. Also, CD151-induced MMP-9 expression was shown to be mediated by c-Jun binding to AP-1 sites in the MMP-9 gene promoter, indicating AP-1 activation by CD151 signaling pathways. Meanwhile, CD151 was found to be associated with alpha(3)beta(1) and alpha(6)beta(1) integrins in MelJuSo cells, and activation of associated integrins was a prerequisite for CD151-stimulated MMP-9 expression and activation of FAK, Src, p38 MAPK, JNK, and c-Jun. Furthermore, CD151 on one cell was shown to bind to neighboring cells expressing CD151, suggesting that CD151 is a homophilic interacting protein. The homophilic interactions of CD151 increased motility and MMP-9 expression of CD151-transfected MelJuSo cells, along with FAK-, Src-, p38 MAPK-, and JNK-mediated activation of c-Jun in an adhesion-dependent manner. Furthermore, C8161 melanoma cells with endogenous CD151 were also shown to respond to homophilic CD151 interactions for the induction of adhesion-dependent activation of FAK, Src, and c-Jun. These results suggest that homophilic interactions of CD151 stimulate integrin-dependent signaling to c-Jun through FAK-Src-MAPKs pathways in human melanoma cells, leading to enhanced cell motility and MMP-9 expression.

Cytoskeleton rearrangement induced by tetraspanin engagement modulates the activation of T and NK cells

The hepatitis C virus (HCV) binds to human cells through the interaction of its envelope glycoprotein E2 with the tetraspanin CD81. We have previously reported that engagement of CD81 has opposite effects on T and NK cell function, as it enhances T cell receptor-mediated T cell activation and inhibits CD16- or IL-12-mediated NK cell activation. We further investigated this dichotomy and found that another tetraspanin, CD82, induces the same opposing effects on human primary T and NK cells. Activation by other unrelated stimuli such as NKG2D- and beta-1 integrin is also reduced by CD81 ligation on NK cells. CD81 engagement by monoclonal antibody or HCV-E2 enhances zeta and Erk phosphorylation in T cells and reduces them in NK cells, reflecting the opposite functional outcomes. CD81 engagement induces dramatic morphological changes and local F-actin accumulation in both NK and T cells, indicating rearrangement of the actin cytoskeleton. Pharmacological inhibition of actin polymerization reduces T cell activation, whereas it greatly enhances NK cell activation. Importantly, treatment with actin blockers abolishes the inhibitory effect of CD81 ligation on NK cells. We propose that tetraspanin engagement leads to comparable cytoskeleton reorganization in T and NK cells, which in turn results in opposite functional outcomes.

Wound healing is defective in mice lacking tetraspanin CD151

The tetraspanin CD151 forms complexes in epithelial cell membranes with laminin-binding integrins alpha6beta4, alpha3beta1, and alpha6beta1, and modifies integrin-mediated cell migration in vitro. We demonstrate in this study that CD151 expression is upregulated in a distinct temporal and spatial pattern during wound healing, particularly in the migrating epidermal tongue at the wound edge, suggesting a role for CD151 in keratinocyte migration. We show that healing is significantly impaired in CD151-null mice, with wounds gaping wider at 7 days post-injury. The rate of re-epithelialization of the CD151-null wounds is adversely affected, with significantly less wound area being covered by migrating epidermal cells. Our studies reveal that although laminin levels are similar in wild-type and CD151-null wounds, the organization of the laminin in the basement membrane is impaired. Furthermore, upregulation of alpha6 and beta4 integrin expression is adversely affected in CD151-null mice wounds. In contrast, we find no significant effect of CD151 gene knockout on alpha3 and beta1 integrin expression in wound repair. We suggest that mice lacking the CD151 gene are defective in wound healing, primarily owing to impairment of the re-epithelialization process. This may be due to defective basement membrane formation and epithelial cell adhesion and migration.

Role of tetraspanins CD9 and CD151 in primary melanocyte motility

Tetraspanins CD9 and CD151 have been implicated in cellular motility and intercellular adhesion in several cellular types. Here, we have studied the subcellular localization and the functional role of these molecules in primary melanocytes. We found that endogenous tetraspanins preferentially clustered in areas of melanocyte homotypic intercellular contacts and at the tips of dendrites. These observations were further confirmed using time-lapse fluorescence confocal microscopy of melanocytes transfected with CD9- and CD151-GFP (green fluorescent protein) constructs, suggesting an involvement of these proteins in cellular contacts and migration. Cell adhesion and migration assays performed using blocking monoclonal antibodies against CD9 and CD151 showed no significant effect on cell-extracellular matrix adhesion, whereas the migration of melanocytes was significantly enhanced. The regulation of the migratory capacity of melanocytes by CD9 and CD151 was further confirmed knocking down the endogenous expression of these tetraspanins with small interference RNA oligonucleotides. Therefore, tetraspanin molecules are localized at motile structures in primary human melanocytes regulating the migratory capacity of these cells.

Colocalization of the tetraspanins, CO-029 and CD151, with integrins in human pancreatic adenocarcinoma: impact on cell motility

PURPOSE

Patients with pancreatic adenocarcinoma have a poor prognosis due to the extraordinary high invasive capacity of this tumor. Altered integrin and tetraspanin expression is suggested to be an important factor. We recently reported that after protein kinase C activation, colocalization of alpha6beta4 with the tetraspanin CO-029 strongly supports migration of a rat pancreatic adenocarcinoma. The finding led us to explore whether and which integrin-tetraspanin complexes influence the motility of human pancreatic tumors.

EXPERIMENTAL DESIGN

Integrin and tetraspanin expression of pancreatic and colorectal adenocarcinoma was evaluated with emphasis on colocalization and the impact of integrin-tetraspanin associations on tumor cell motility.

RESULTS

The majority of pancreatic and colorectal tumors expressed the alpha2, alpha3, alpha6, beta1, and beta4 integrins and the tetraspanins CD9, CD63, CD81, CD151, and CO-029. Expression of alpha6beta4 and CO-029 was restricted to tumor cells, whereas alpha1, alpha2, alpha3, alpha6, beta1, and CD9, CD81, CD151 were also expressed by the surrounding stroma. CD63, CD81, and beta1 expression was observed at comparably high levels in healthy pancreatic tissue. alpha3beta1 frequently colocalized and coimmunoprecipitated with CD9, CD81, and CD151, whereas alpha6beta4 colocalized and coimmunoprecipitated mostly with CD151 and CO-029. Notably, protein kinase C activation strengthened only the colocalization of CD151 and CO-029 with beta4 and was accompanied by internalization of the integrin-tetraspanin complex, decreased laminin 5 adhesion, and increased cell migration.

CONCLUSION

alpha6beta4 is selectively up-regulated in pancreatic and colorectal cancer. The association of alpha6beta4 with CD151 and CO-029 correlates with increased tumor cell motility.

Aberrant expression of tetraspanin molecules in B-cell chronic lymphoproliferative disorders and its correlation with normal B-cell maturation

Tetraspanin proteins form signaling complexes between them and with other membrane proteins and modulate cell adhesion and migration properties. The surface expression of several tetraspanin antigens (CD9, CD37, CD53, CD63, and CD81), and their interacting proteins (CD19, CD21, and HLA-DR) were analyzed during normal B-cell maturation and compared to a group of 67 B-cell neoplasias. Three patterns of tetraspanin expression were identified in normal B cells. The first corresponded to bone marrow CD10(+) B-cell precursors (BCP) which showed high expression of CD81 and CD9, low reactivity for CD53 and negativity for CD37. CD10(-) B-lymphocytes showed downregulation of CD9/CD81 and upregulation of CD53/CD37. Plasma cells showed re-expressed CD9 and downregulated CD37. Hierarchical clustering analysis of flow cytometry immunophenotypic data showed a good correlation between the tumor differentiation stage and the pattern of tetraspanin expression, with all analyzed individual samples classified into three major groups, independently of their normal or neoplastic origin. Despite this, neoplastic B-cells frequently showed aberrantly high/low expression of the different markers analyzed. Interestingly, in B-cell chronic lymphocytic leukemia, abnormal expression of CD53 and CD9 were associated with different patterns of disease infiltration, which would support the role of these molecules on modulating adhesion and migration of neoplastic B cells.

Endothelial tetraspanin microdomains regulate leukocyte firm adhesion during extravasation

Tetraspanins associate with several transmembrane proteins forming microdomains involved in intercellular adhesion and migration. Here, we show that endothelial tetraspanins relocalize to the contact site with transmigrating leukocytes and associate laterally with both intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Alteration of endothelial tetraspanin microdomains by CD9-large extracellular loop (LEL)-glutathione S-transferase (GST) peptides or CD9/CD151 siRNA oligonucleotides interfered with ICAM-1 and VCAM-1 function, preventing lymphocyte transendothelial migration and increasing lymphocyte detachment under shear flow. Heterotypic intercellular adhesion mediated by VCAM-1 or ICAM-1 was augmented when expressed exogenously in the appropriate tetraspanin environment. Therefore, tetraspanin microdomains have a crucial role in the proper adhesive function of ICAM-1 and VCAM-1 during leukocyte adhesion and transendothelial migration.

Characterization of mice lacking the tetraspanin superfamily member CD151

The tetraspanin membrane protein CD151 is a broadly expressed molecule noted for its strong molecular associations with integrins, especially alpha3beta1, alpha6beta1, alpha7beta1, and alpha6beta4. In vitro functional studies have pointed to a role for CD151 in cell-cell adhesion, cell migration, platelet aggregation, and angiogenesis. It has also been implicated in epithelial tumor progression and metastasis. Here we describe the generation and initial characterization of CD151-null mice. The mice are viable, healthy, and fertile and show normal Mendelian inheritance. They have essentially normal blood and bone marrow cell counts and grossly normal tissue morphology, including hemidesmosomes in skin, and expression of alpha3 and alpha6 integrins. However, the CD151-null mice do show phenotypes in several different tissue types. An absence of CD151 leads to a minor abnormality in hemostasis, with CD151-null mice showing longer average bleeding times, greater average blood loss, and an increased incidence of rebleeding occurrences. CD151-null keratinocytes migrate poorly in skin explant cultures. Finally, CD151-null T lymphocytes are hyperproliferative in response to in vitro mitogenic stimulation.

VLA-4 integrin concentrates at the peripheral supramolecular activation complex of the immune synapse and drives T helper 1 responses

The integrin alpha 4 beta 1 (VLA-4) not only mediates the adhesion and transendothelial migration of leukocytes, but also provides costimulatory signals that contribute to the activation of T lymphocytes. However, the behavior of alpha 4 beta 1 during the formation of the immune synapse is currently unknown. Here, we show that alpha 4 beta 1 is recruited to both human and murine antigen-dependent immune synapses, when the antigen-presenting cell is a B lymphocyte or a dendritic cell, colocalizing with LFA-1 at the peripheral supramolecular activation complex. However, when conjugates are formed in the presence of anti-alpha 4 antibodies, VLA-4 colocalizes with the CD3-zeta chain at the center of the synapse. In addition, antibody engagement of alpha 4 integrin promotes polarization toward a T helper 1 (Th1) response in human in vitro models of CD4(+) T cell differentiation and naïve T cell priming by dendritic cells. The in vivo administration of anti-alpha 4 integrin antibodies also induces an immune deviation to Th1 response that dampens a Th2-driven autoimmune nephritis in Brown Norway rats. These data reveal a regulatory role of alpha 4 integrins on T lymphocyte-antigen presenting cell cognate immune interactions.

CD151, the first member of the tetraspanin (TM4) superfamily detected on erythrocytes, is essential for the correct assembly of human basement membranes in kidney and skin

Tetraspanins are thought to facilitate the formation of multiprotein complexes at cell surfaces, but evidence illuminating the biologic importance of this role is sparse. Tetraspanin CD151 forms very stable laminin-binding complexes with integrins alpha3beta1 and alpha6beta1 in kidney and alpha3beta1 and alpha6beta4 in skin. It is encoded by a gene at the same position on chromosome 11p15.5 as the MER2 blood group gene. We show that CD151 expresses the MER2 blood group antigen and is located on erythrocytes. We examined CD151 in 3 MER2-negative patients (2 are sibs) of Indian Jewish origin with end-stage kidney disease. In addition to hereditary nephritis the sibs have sensorineural deafness, pretibial epidermolysis bullosa, and beta-thalassemia minor. The 3 patients are homozygous for a single nucleotide insertion (G383) in exon 5 of CD151, causing a frameshift and premature stop signal at codon 140. The resultant truncated protein would lack its integrin-binding domain. We conclude that CD151 is essential for the proper assembly of the glomerular and tubular basement membrane in kidney, has functional significance in the skin, is probably a component of the inner ear, and could play a role in erythropoiesis.

Fig1p facilitates Ca2+ influx and cell fusion during mating of Saccharomyces cerevisiae

During the mating process of yeast cells, two Ca2+ influx pathways become activated. The resulting elevation of cytosolic free Ca2+ activates downstream signaling factors that promote long term survival of unmated cells, but the roles of Ca2+ in conjugation have not been described. The high affinity Ca2+ influx system is composed of Cch1p and Mid1p and sensitive to feedback inhibition by calcineurin, a Ca2+/calmodulin-dependent protein phosphatase. To identify components and regulators of the low affinity Ca2+ influx system (LACS), we screened a collection of pheromone-responsive genes that when deleted lead to defects in LACS activity but not high affinity Ca2+ influx system activity. Numerous factors implicated in polarized morphogenesis and cell fusion (Fus1p, Fus2p, Rvs161p, Bni1p, Spa2p, and Pea2p) were found to be necessary for LACS activity. Each of these factors was also required for activation of the cell integrity mitogen-activated protein kinase cascade during the response to alpha-factor. Interestingly a polytopic plasma membrane protein, Fig1p, was required for LACS activity but not required for activation of Mpk1p mitogen-activated protein kinase. Mpk1p was not required for LACS activity, suggesting Mpk1p and Fig1p define two independent branches in the pheromone response pathways. Fig1p-deficient mutants exhibit defects in the cell-cell fusion step of mating, but unlike other fus1 and fus2 mutants the fusion defect of fig1 mutants can be largely suppressed by high Ca2+ conditions, which bypass the requirement for LACS. These findings suggest Fig1p is an important component or regulator of LACS and provide the first evidence for a role of Ca2+ signals in the cell fusion step of mating.

The tetraspanin CD151 functions as a negative regulator in the adhesion-dependent activation of Ras

Transmembrane proteins of the tetraspanin superfamily are associated with integrins and are thought to regulate adhesion-dependent signaling. The molecular mechanisms of this regulation remain unknown. We used rat fibroblasts to analyze the contribution of the tetraspanin CD151 in the adhesion-dependent signaling. Expression of CD151 specifically attenuated adhesion-dependent activation of Ras. Furthermore, activation of PKB/c-Akt and ERK1/2, downstream targets in the Ras signaling pathway, was also diminished in cells expressing CD151. In contrast, adhesion-dependent activation of FAK and c-Src were not affected by CD151. The attenuation of Ras signaling did not correlate with phosphorylation of Tyr925-FAK, tyrosine phosphorylation of Shc, or with assembly of the p120RasGAP-p62Dok complex. Using mutants of CD151 we established that the cytoplasmic C-terminal portion is critical for activity of CD151 toward Ras. Taken together these results identify CD151 as a negative regulator of Ras and suggest a novel mechanism of adhesion-dependent regulation of Ras activity.

Tetraspanin CD151 regulates alpha6beta1 integrin adhesion strengthening

The tetraspanin CD151 molecule associates specifically with laminin-binding integrins, including alpha6beta1. To probe strength of alpha6beta1-dependent adhesion to laminin-1, defined forces (0-1.5 nN) were applied to magnetic laminin-coated microbeads bound to NIH 3T3 cells. For NIH 3T3 cells bearing wild-type CD151, adhesion strengthening was observed, as bead detachment became more difficult over time. In contrast, mutant CD151 (with the C-terminal region replaced) showed impaired adhesion strengthening. Static cell adhesion to laminin-1, and detachment of beads coated with fibronectin or anti-alpha6 antibody were all unaffected by CD151 mutation. Hence, CD151 plays a key role in selectively strengthening alpha6beta1 integrin-mediated adhesion to laminin-1.

A functionally relevant conformational epitope on the CD9 tetraspanin depends on the association with activated beta1 integrin

Tetraspanins associate on the cell membrane with several transmembrane proteins, including members of the integrin superfamily. The tetraspanin CD9 has been implicated in cell motility, metastasis, and sperm-egg fusion. In this study we characterize the first CD9 conformation-dependent epitope (detected by monoclonal antibody (mAb) PAINS-13) whose expression depends on changes in the activation state of associated beta(1) integrins. MAb PAINS-13 precipitates CD9 under conditions that preserve the association of this tetraspanin with integrins, but not under conditions that disrupt these interactions. Induction of activation of beta(1) integrins by temperature, divalent cation Mn(2+), or mAb TS2/16 correlated with enhanced expression of the PAINS-13 epitope on a variety of cells. Through the use of different K562 myeloid leukemia transfectant cells expressing specific members of the beta(1) integrin subfamily we show that the expression of the PAINS-13 epitope depends on CD9 association with alpha(6)beta(1) integrin. The mAb PAINS-13 reactivity has been mapped to the CD9 region comprising residues 112-154 in the NH(2) half of the large extracellular loop. Also, we show that the CD9 conformation recognized by mAb PAINS-13 is functionally relevant in beta(1) integrin-mediated cellular processes including wound healing migration, tubular morphogenesis, cell adhesion and spreading and in signal transduction involving phosphatidylinositol 3-kinase activation.

A new class of tetraspanins in fungi

Tetraspanins are animal proteins involved in membrane complexes that are involved in cell adhesion, differentiation, and motility. The PLS1 gene from rice blast fungus Magnaporthe grisea encodes a protein (Pls1p) structurally related to tetraspanins that is required for pathogenicity. In Botrytis cinerea public sequences, we identified an EST homologous to PLS1. Using degenerated oligonucleotides, we amplified sequences homologous to PLS1 in fungi Colletotrichum lindemuthianum and Neurospora crassa. Analysis of N. crassa and M. grisea genome sequences revealed the presence of a single tetraspanin gene. Thus, fungi differ from animals, which contain between 20 and 37 paralogous tetraspanin genes. Fungal proteins encoded by BcPLS1, ClPLS1, and NcPLS1 display all the structural hallmarks of tetraspanins (predicted topology with four transmembrane domains, extra- and intracellular loops; conserved cysteine-based patterns in second extracellular loop). Phylogenetic analysis suggests that these genes define a new family of orthologous genes encoding fungal-specific tetraspanins.

An extracellular site on tetraspanin CD151 determines alpha 3 and alpha 6 integrin-dependent cellular morphology

The alpha 3 beta 1 integrin shows strong, stoichiometric, direct lateral association with the tetraspanin CD151. As shown here, an extracellular CD151 site (QRD(194-196)) is required for strong (i.e., Triton X-100-resistant) alpha 3 beta 1 association and for maintenance of a key CD151 epitope (defined by monoclonal antibody TS151r) that is blocked upon alpha 3 integrin association. Strong CD151 association with integrin alpha 6 beta 1 also required the QRD(194-196) site and masked the TS151r epitope. For both alpha 3 and alpha 6 integrins, strong QRD/TS151r-dependent CD151 association occurred early in biosynthesis and involved alpha subunit precursor forms. In contrast, weaker associations of CD151 with itself, integrins, or other tetraspanins (Triton X-100-sensitive but Brij 96-resistant) were independent of the QRD/TS151r site, occurred late in biosynthesis, and involved mature integrin subunits. Presence of the CD151-QRD(194-196)-->INF mutant disrupted alpha 3 and alpha 6 integrin-dependent formation of a network of cellular cables by Cos7 or NIH3T3 cells on basement membrane Matrigel and markedly altered cell spreading. These results provide definitive evidence that strong lateral CD151-integrin association is functionally important, identify CD151 as a key player during alpha 3 and alpha 6 integrin-dependent matrix remodeling and cell spreading, and support a model of CD151 as a transmembrane linker between extracellular integrin domains and intracellular cytoskeleton/signaling molecules.

Regulatory role of tetraspanin CD9 in tumor-endothelial cell interaction during transendothelial invasion of melanoma cells

Heterotypic interaction among tumor cells (TCs) and endothelial cells (ECs) may play a critical role during the vascular dissemination of neoplastic cells and during pathologic angiogenesis in tumors. To identify molecules involved in these processes, the distribution of vascular junctional proteins was first studied by immunofluorescence at sites of heterologous intercellular contact using TC-EC mosaic monolayers grown on 2-dimensional collagen. Several members of the tetraspanin superfamily, including CD9, CD81, and CD151, were found to localize at the TC-EC contact area. The localization of tetraspanins to the TC-EC heterologous contact area was also observed during the active transmigration of TCs across EC monolayers grown onto 3-dimensional collagen matrices. Dynamic studies by time-lapse immunofluorescence confocal microscopy showed an active redistribution of endothelial CD9 to points of melanoma insertion. Anti-CD9 monoclonal antibodies were found to specifically inhibit the transendothelial migration of melanoma cells; the inhibitory effect was likely caused by a strengthening of CD9-mediated heterotypic interactions of TCs to the EC monolayer. These data support a novel mechanism of tetraspanin-mediated regulation of TC transcellular migration independent of TC motility and growth during metastasis and a role for these molecules in the formation of TC-EC mosaic monolayers during tumor angiogenesis.

Complexes of tetraspanins with integrins: more than meets the eye

The transmembrane proteins of the tetraspanin superfamily are implicated in a diverse range of biological phenomena, including cell motility, metastasis, cell proliferation and differentiation. The tetraspanins are associated with adhesion receptors of the integrin family and regulate integrin-dependent cell migration. In cells attached to the extracellular matrix, the integrin-tetraspanin adhesion complexes are clustered into a distinct type of adhesion structure at the cell periphery. Various tetraspanins are associated with phosphatidylinositol 4-kinase and protein kinase C isoforms, and they may facilitate assembly of signalling complexes by tethering these enzymes to integrin heterodimers. At the plasma membrane, integrin-tetraspanin signalling complexes are partitioned into specific microdomains proximal to cholesterol-rich lipid rafts. A substantial fraction of tetraspanins colocalise with integrins in various intracellular vesicular compartments. It is proposed that tetraspanins can influence cell migration by one of the following mechanisms: (1) modulation of integrin signalling; (2) compartmentalisation of integrins on the cell surface; or (3) direction of intracellular trafficking and recycling of integrins.