Chinese hamster ovary cell motility to fibronectin is modulated by the second extracellular loop of CD9. Identification of a putative fibronectin binding site

miR-518f-5p decreases tetraspanin CD9 protein levels and differentially affects non-tumourigenic prostate and prostate cancer cell migration and adhesion

Tetraspanin CD9 is generally considered to be a metastasis suppressor, with decreased levels associated with progression and metastasis in many advanced stage cancers. Little is known about the cause of CD9 dysregulation in prostate cancer, however there are several miRNA-binding sites in the 3´UTR of the transcript suggesting it could be post-transcriptionally regulated. Using microarrays and luciferase assays in tumourigenic and non-tumourigenic prostate cell lines we identified miR-518f-5p as a regulator of the CD9 3'UTR gene expression, and decreased expression of endogenous CD9 in non-tumorigenic prostate RWPE1 and prostate cancer DU145 cells. This resulted in differential functional effects, in which RWPE1 cells showed increased migration and decreased adhesion to extracellular matrix substrates, whereas DU145 cells showed decreased migration and increased adhesion. Moreover, overexpression of miR-518f-5p significantly increased proliferation between 48h and 72h in normal RWPE1 cells, with no effect on tumourigenic DU145 cell proliferation. These results show that tetraspanin CD9 is regulated by miRNAs in prostate cell lines and that due to differential functional effects in non-tumourigenic versus tumourigenic prostate cells, miR-518f-5p may be an effective biomarker and/or therapeutic target for prostate cancer progression.

Modulation of paracrine signaling by CD9 positive small extracellular vesicles mediates cellular growth of androgen deprived prostate cancer

Proliferation and maintenance of both normal and prostate cancer (PCa) cells is highly regulated by steroid hormones, particularly androgens, and the extracellular environment. Herein, we identify the secretion of CD9 positive extracellular vesicles (EV) by LNCaP and DUCaP PCa cells in response to dihydrotestosterone (DHT) and use nano-LC–MS/MS to identify the proteins present in these EV. Subsequent bioinformatic and pathway analyses of the mass spectrometry data identified pathologically relevant pathways that may be altered by EV contents. Western blot and CD9 EV TR-FIA assay confirmed a specific increase in the amount of CD9 positive EV in DHT-treated LNCaP and DUCaP cells and treatment of cells with EV enriched with CD9 after DHT exposure can induce proliferation in androgen-deprived conditions. siRNA knockdown of endogenous CD9 in LNCaPs reduced cellular proliferation and expression of AR and prostate specific antigen (PSA) however knockdown of AR did not alter CD9 expression, also implicating CD9 as an upstream regulator of AR. Moreover CD9 positive EV were also found to be significantly higher in plasma from prostate cancer patients in comparison with benign prostatic hyperplasia patients. We conclude that CD9 positive EV are involved in mediating paracrine signalling and contributing toward prostate cancer progression.

Pro-MMP-9 upregulation in HT1080 cells expressing CD9 is regulated by epidermal growth factor receptor

Degradation of the surrounding extracellular matrix (ECM) by matrix metalloproteinases (MMPs) drives invasion and metastasis of cancer cells. We previously demonstrated that tetraspanin CD9 expression upregulates pro-MMP-9 expression and release and promotes cellular invasion in a human fibrosarcoma cell line (HT1080). These events were dependent upon the highly functional second extracellular loop of CD9. We report here that the epidermal growth factor receptor (EGFR) tyrosine kinase expression and activity are involved in the CD9-mediated increase in pro-MMP-9 release and cellular invasion. Pro-MMP-9 expression was significantly decreased in a dose-dependent manner using first a broad spectrum receptor tyrosine kinase inhibitor and multiple specific EGFR inhibitors in CD9-HT1080 cells. Furthermore, gefitinib treatment of CD9-HT1080 cells reduced invasion through matrigel. EGFR knockdown using short interfering RNA resulted in decreased pro-MMP-9 expression and release into the media and subsequent cellular invasion without affecting CD9 expression or localization. Conclusively, this study points to EGFR as a key mediator between CD9-mediated pro-MMP-9 release and cellular invasion of HT1080 cells.

Protein expression profile of rat type two alveolar epithelial cells during hyperoxic stress and recovery

In rodent model systems, the sequential changes in lung morphology resulting from hyperoxic injury are well characterized and are similar to changes in human acute respiratory distress syndrome. In the injured lung, alveolar type two (AT2) epithelial cells play a critical role in restoring the normal alveolar structure. Thus characterizing the changes in AT2 cells will provide insights into the mechanisms underpinning the recovery from lung injury. We applied an unbiased systems-level proteomics approach to elucidate molecular mechanisms contributing to lung repair in a rat hyperoxic lung injury model. AT2 cells were isolated from rat lungs at predetermined intervals during hyperoxic injury and recovery. Protein expression profiles were determined by using iTRAQ with tandem mass spectrometry. Of the 959 distinct proteins identified, 183 significantly changed in abundance during the injury-recovery cycle. Gene ontology enrichment analysis identified cell cycle, cell differentiation, cell metabolism, ion homeostasis, programmed cell death, ubiquitination, and cell migration to be significantly enriched by these proteins. Gene set enrichment analysis of data acquired during lung repair revealed differential expression of gene sets that control multicellular organismal development, systems development, organ development, and chemical homeostasis. More detailed analysis identified activity in two regulatory pathways, JNK and miR 374. A novel short time-series expression miner algorithm identified protein clusters with coherent changes during injury and repair. We concluded that coherent changes occur in the AT2 cell proteome in response to hyperoxic stress. These findings offer guidance regarding the specific molecular mechanisms governing repair of the injured lung.

Tetraspanin CD9 promotes the invasive phenotype of human fibrosarcoma cells via upregulation of matrix metalloproteinase-9

Tumor cell metastasis, a process which increases the morbidity and mortality of cancer patients, is highly dependent upon matrix metalloproteinase (MMP) production. Small molecule inhibitors of MMPs have proven unsuccessful at reducing tumor cell invasion in vivo. Therefore, finding an alternative approach to regulate MMP is an important endeavor. Tetraspanins, a family of cell surface organizers, play a major role in cell signaling events and have been implicated in regulating metastasis in numerous cancer cell lines. We stably expressed tetraspanin CD9 in an invasive and metastatic human fibrosarcoma cell line (CD9-HT1080) to investigate its role in regulating tumor cell invasiveness. CD9-HT1080 cells displayed a highly invasive phenotype as demonstrated by matrigel invasion assays. Statistically significant increases in MMP-9 production and activity were attributed to CD9 expression and were not due to any changes in other key tetraspanin complex members or MMP regulators. Increased invasion of CD9-HT1080 cells was reversed upon silencing of MMP-9 using a MMP-9 specific siRNA. Furthermore, we determined that the second extracellular loop of CD9 was responsible for the upregulation of MMP-9 production and subsequent cell invasion. We demonstrated for the first time that tetraspanin CD9 controls HT1080 cell invasion via upregulation of an integral member of the MMP family, MMP-9. Collectively, our studies provide mounting evidence that altered expression of CD9 may be a novel approach to regulate tumor cell progression.

The anti-CD74 humanized monoclonal antibody, milatuzumab, which targets the invariant chain of MHC II complexes, alters B-cell proliferation, migration, and adhesion molecule expression

Introduction

Targeting CD74 as the invariant chain of major histocompatibility complexes (MHC) became possible by the availability of a specific humanized monoclonal antibody, milatuzumab, which is under investigation in patients with hematological neoplasms. CD74 has been reported to regulate chemo-attractant migration of macrophages and dendritic cells, while the role of CD74 on peripheral naïve and memory B cells also expressing CD74 remains unknown. Therefore, the current study addressed the influence of milatuzumab on B-cell proliferation, chemo-attractant migration, and adhesion molecule expression.

Methods

Surface expression of CD74 on CD27^- naïve and CD27⁺ memory B cells as well as other peripheral blood mononuclear cells (PBMCs) obtained from normals, including the co-expression of CD44, CXCR4, and the adhesion molecules CD62L, β7-integrin, β1-integrin and CD9 were studied after binding of milatuzumab using multicolor flow cytometry. The influence of the antibody on B-cell proliferation and migration was analyzed in vitro in detail.

Results

In addition to monocytes, milatuzumab also specifically bound to human peripheral B cells, with a higher intensity on CD27⁺ memory versus CD27^- naïve B cells. The antibody reduced B-cell proliferation significantly but moderately, induced enhanced spontaneous and CXCL12-dependent migration together with changes in the expression of adhesion molecules, CD44, β7-integrin and CD62L, mainly of CD27^- naïve B cells. This was independent of macrophage migration-inhibitory factor as a ligand of CD74/CD44 complexes.

Conclusions

Milatuzumab leads to modestly reduced proliferation, alterations in migration, and adhesion molecule expression preferentially of CD27^- naïve B cells. It thus may be a candidate antibody for the autoimmune disease therapy by modifying B cell functions.

Tetraspanin CD9 in cell migration

Tetraspanin CD9 is associated with integrin adhesion receptors and it was reported that CD9 regulates integrin-dependent cell migration and invasion. Pro- and anti-migratory effects of CD9 have been linked to adhesion-dependent signalling pathways, including phosphorylation of FAK (focal adhesion kinase) and activation of phosphoinositide 3-kinase, p38 MAPK (mitogen-activated protein kinase) and JNK (c-Jun N-terminal kinase). In the present paper, we describe a novel mechanism whereby CD9 specifically controls localization of talin1, one of the critical regulators of integrin activation, to focal adhesions: CD9-deficiency leads to impaired localization of talin1 to focal adhesions and correlates with increased motility of breast cancer cells.

Immunohistochemical distribution of the tetraspanin CD9 in normal porcine tissues

The tetra-membrane-spanning protein, CD9 is a 24-27 kDa cell surface glycoprotein expressed in a wide variety of human cells being involved in a variety of cell processes, including signaling, adhesion, motility, fertilization and tumor cells metastasis. By means of a polyclonal antibody (N1) raised against recombinant swine CD9 protein, we studied the immunohistochemical expression of CD9 on different normal swine tissues. Immunochemistry shows that swine CD9 was distribute in a similar form than in human tissues, being present on epithelial cells of lung, liver, kidney, skin, tonsil, testis (epididymo), gut mucosa, uterus and mama. Furthermore, polyclonal antibody against swine CD9 reacts with white matter from cerebrum and cerebellum, peripheral nerves fibers and Hassal corpuscle from thymus and ovum. Platelets react strongly with our antibody, but monocytes and neutrophils react lightly. These results suggest that CD9 antigen should play a similar functional role in swine and human and therefore studies on CD9 on swine as an animal model would allow new knowledge about its role in adhesion, fertilization and tumor metastasis among other important biomedical processes.

Transmembrane interactions are needed for KAI1/CD82-mediated suppression of cancer invasion and metastasis

In transmembrane (TM) domains, tetraspanin KAI1/CD82 contains an Asn, a Gln, and a Glu polar residue. A mutation of all three polar residues largely disrupts the migration-, invasion-, and metastasis-suppressive activities of KAI1/CD82. Notably, KAI1/CD82 inhibits the formation of microprotrusions and the release of microvesicles, while the mutation disrupts these inhibitions, revealing the connections of microprotrusion and microvesicle to KAI1/CD82 function. The TM polar residues are needed for proper interactions between KAI1/CD82 and tetraspanins CD9 and CD151, which also regulate cell movement, but not for the association between KAI1/CD82 and alpha3beta1 integrin. However, KAI1/CD82 still efficiently inhibits cell migration when either CD9 or CD151 is absent. Hence, KAI1/CD82 interacts with tetraspanin and integrin by different mechanisms and is unlikely to inhibit cell migration through its associated proteins. Moreover, without significantly affecting the glycosylation, homodimerization, and global folding of KAI1/CD82, the TM interactions maintain the conformational stability of KAI1/CD82, evidenced by the facts that the mutant is more sensitive to denaturation and less associable with tetraspanins and supported by the modeling analysis. Thus, the TM interactions mediated by these polar residues determine a conformation either in or near the tightly packed TM region and this conformation and/or its change are needed for the intrinsic activity of KAI1/CD82. In contrast to immense efforts to block the signaling of cancer progression, the perturbation of TM interactions may open a new avenue to prevent cancer invasion and metastasis.

Association of tetraspanin CD9 with transmembrane TGF{alpha} confers alterations in cell-surface presentation of TGF{alpha} and cytoskeletal organization

Ligand presentation is a major determinant of receptor activation. The epidermal growth factor receptor (EGFR), a tyrosine kinase receptor, is activated by growth factors of the transforming growth factor alpha (TGFalpha) family. The tetraspanin CD9 interacts with transmembrane TGFalpha and decreases its ectodomain shedding to release soluble TGFalpha. Here we report that CD9 has a role in the maturation of transmembrane TGFalpha and its stabilization at the cell surface, and in the cell-surface distribution in polarized epithelial cells. Furthermore, coexpression of CD9 and TGFalpha confers changes in cytoskeletal organization with a decrease in actin stress fibers and focal adhesions, and changes in RhoA and Rac1 GTPase activity. These alterations are reversed by blocking EGFR signaling. Finally, we demonstrate changes in cell adhesion and migration resulting from coexpression of TGFalpha with CD9. These results provide insight into the role of CD9 in the presentation of TGFalpha in epithelial and carcinoma cells, whose physiology is driven by ligand-induced EGFR activation.

Tetraspanin CD9 regulates beta 1 integrin activation and enhances cell motility to fibronectin via a PI-3 kinase-dependent pathway

Tetraspanin CD9 regulates cell motility and other adhesive processes in a variety of tissue types. Using transfected Chinese Hamster Ovary cells as our model system, we examined the cellular pathways critical for CD9 promoted cell migration. alpha 5 beta 1 integrin was directly involved as CD9 enhanced migration was abolished by the alpha 5 beta 1 blocking antibody PB1. Furthermore, the ligand mimetic peptide RGDS, significantly upregulated the expression of a beta1 ligand induced binding site (LIBS) demonstrating for the first time that CD9 expression potentiates beta1 integrin high affinity conformation states. CD9 promoted cell motility was significantly blocked by phosphatidylinositol-3 kinase (PI-3K) inhibitors, wortmannin and LY294002, whereas inhibitors targeting protein kinase C or mitogen-activated protein kinase had no effect. PI-3K dominant/negative cDNA transfections confirmed that PI-3K was an essential component. CD9 enhanced the phosphorylation of the PI-3K substrate, Akt, in response to cell adhesion on FN. CD9 expression also upregulated p130Cas phosphorylation and total protein levels; however, p130Cas siRNA knockdown did not alter the motile phenotype. CD9 enhanced migration was also unaffected by serum deprivation suggesting that growth factors were not critical. Our studies demonstrate that CD9 upregulates beta1 LIBS, and in concert with alpha 5 beta 1, enhances cell motility to FN via a PI-3K dependent mechanism.

Identification of host proteins associated with retroviral vector particles by proteomic analysis of highly purified vector preparations

The Moloney murine leukemia virus (MMLV) belongs to the Retroviridae family of enveloped viruses, which is known to acquire minute amounts of host cellular proteins both on the surface and inside the virion. Despite the extensive use of retroviral vectors in experimental and clinical applications, the repertoire of host proteins incorporated into MMLV vector particles remains unexplored. We report here the identification of host proteins from highly purified retroviral vector preparations obtained by rate-zonal ultracentrifugation. Viral proteins were fractionated by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, in-gel tryptic digested, and subjected to liquid chromatography/tandem mass spectrometry analysis. Immunogold electron microscopy studies confirmed the presence of several host membrane proteins exposed at the vector surface. These studies led to the identification of 27 host proteins on MMLV vector particles derived from 293 HEK cells, including 5 proteins previously described as part of wild-type MMLV. Nineteen host proteins identified corresponded to intracellular proteins. A total of eight host membrane proteins were identified, including cell adhesion proteins integrin beta1 (fibronectin receptor subunit beta) and HMFG-E8, tetraspanins CD81 and CD9, and late endosomal markers CD63 and Lamp-2. Identification of membrane proteins on the retroviral surface is particularly attractive, since they can serve as anchoring sites for the insertion of tags for targeting or purification purposes. The implications of our findings for retrovirus-mediated gene therapy are discussed.

Absence of CD9 enhances adhesion-dependent morphologic differentiation, survival, and matrix metalloproteinase-2 production in small cell lung cancer cells

While adhering to extracellular matrix proteins in vitro and in vivo, small cell lung cancer (SCLC) cells frequently show morphologic differentiation and are protected from apoptosis. Integrin beta(1)-mediated protein phosphorylation is suggested to be an essential signaling event in these processes. CD9 is an almost ubiquitously expressed tetraspanin protein that suppresses tumor progression by regulating cell motility and signaling through complex formation with beta(1) integrins. We reported previously that, among tetraspanins, CD9 is selectively absent in most SCLC cells and that ectopic expression of CD9 suppresses their motility. Here, we show that the ectopic expression of CD9 suppressed neurite-like process outgrowth and promoted apoptotic death of SCLC cells that were adherent to fibronectin in serum-starved conditions. This correlated with attenuation of adhesion-dependent phosphorylation of Akt but not that of focal adhesion kinase or c-Jun NH(2)-terminal kinase. Treatment of CD9(-) parent cells with a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, inhibited process outgrowth and survival, suggesting that PI3K/Akt signaling is required for the morphologic change and cell survival. Production of matrix metalloproteinase (MMP)-2 was likewise suppressed in the CD9 transfectants and in LY294002-treated parent cells. These results suggest that the absence of CD9 in SCLC cells may contribute to postadhesive morphologic differentiation, survival, and MMP-2 production via PI3K/Akt pathway.

Tetraspanin proteins mediate cellular penetration, invasion, and fusion events and define a novel type of membrane microdomain

This review summarizes key aspects of tetraspanin proteins, with a focus on the functional relevance and structural features of these proteins and how they are organized into a novel type of membrane microdomain. Despite the size of the tetraspanin family and their abundance and wide distribution over many cell types, most have not been studied. However, from studies of prototype tetraspanins, information regarding functions, cell biology, and structural organization has begun to emerge. Genetic evidence points to critical roles for tetraspanins on oocytes during fertilization, in fungi during leaf invasion, in Drosophila embryos during neuromuscular synapse formation, during T and B lymphocyte activation, in brain function, and in retinal degeneration. From structure and mutagenesis studies, we are beginning to understand functional subregions within tetraspanins, as well as the levels of connections among tetraspanins and their many associated proteins. Tetraspanin-enriched microdomains (TEMs) are emerging as entities physically and functionally distinct from lipid rafts. These microdomains now provide a context in which to evaluate tetraspanins in the regulation of growth factor signaling and in the modulation of integrin-mediated post-cell adhesion events. Finally, the enrichment of tetraspanins within secreted vesicles called exosomes, coupled with hints that tetraspanins may regulate vesicle fusion and/or fission, suggests exciting new directions for future research.

Apoptosis protection and survival signal by the CD53 tetraspanin antigen

The CD53 antigen is a tetraspanin protein of the lymphoid-myeloid lineage, but its implication in biological effects is hardly known. Radioresistant tumor cells express very high levels of this antigen. We have studied the effect of CD53 antigen ligation on the survival response of tumor cells to serum deprivation, a well-known stimulator of cell death that may mimic the tumor environment; for this aim IR938F and Jurkat cells, a B- and T-cell lymphoma, were used. Ligation of CD53 triggers a survival response and reduces the number of cells that enter apoptosis. In CD53- stimulated cells there is a significant reduction in caspase activation, measured by caspase processing of poly ADP-ribose polymerase, as well as a reduction in the fragmentation of DNA. CD53- stimulated cells also have an increase in the level of bcl-X(L) and a reduction of bax protein, two components of the mitochondrial apoptotic pathway, changing their ratio by 24-fold in the direction of survival. This survival signal appears to be mediated by activation of the AKT, as detected by its phosphorylation in Ser473 upon CD53 ligation. The CD53 antigen interactions might contribute to cell survival in poorly vascularized regions of the tumor mass.

Identification of CD9 extracellular domains important in regulation of CHO cell adhesion to fibronectin and fibronectin pericellular matrix assembly

CD9, a 24-kDa member of the tetraspanin family, influences cellular growth and development, activation, adhesion, and motility. Our investigation focuses on the hypothesis that the CD9 second extracellular loop (EC2) is important in modulating cell adhesive events. Using a Chinese hamster ovary (CHO) cell expression system, we previously reported that CD9 expression inhibited cell adhesion to fibronectin and fibronectin matrix assembly. For the first time, a functional epitope on CD9 EC2 that regulates these processes is described. Binding of mAb7, an EC2-specific anti-CD9 monoclonal antibody, reversed the CD9 inhibitory activity on CHO cell adhesion and fibronectin matrix assembly. This reversal of cell phenotype also was observed in CHO cells expressing CD9 EC2 truncations. Furthermore, our data showed that the EC2 sequence (173)LETFTVKSCPDAIKEVFDNK(192) was largely responsible for the CD9-mediated CHO cell phenotype. Two peptides, (135)K-V(172) (peptide 5b) and (168)P-I(185) (peptide 6a), selectively blocked mAb7 binding to soluble CD9 and to CD9 on intact cells. These active peptides reversed the influence of CD9 expression on CHO cell adhesion to fibronectin. In addition, confocal microscopy revealed that CD9 colocalized with the integrin alpha(5)beta(1) and cytoskeletal F-actin in punctate clusters on the cell surface, particularly at the cell margins. Immunoprecipitation studies confirmed CD9 association with beta(1) integrin. The cellular distribution and colocalization of focal adhesion kinase and alpha-actinin with cytoskeletal actin was also influenced by CD9 expression. Thus, CD9 may exhibit its effect by modulating the composition of adhesive complexes important in facilitating cell adhesion and matrix assembly.