The impact of exosomes derived from B-cell acute lymphoblastic leukemia as a growth factor on bone marrow mesenchymal stromal cells.

Background The incidence of various types of cancers, including leukemia, is on the rise and many challenges in both drug resistance and complications related to chemotherapy appeared. Recently, the development and application of extracellular vesicles (EV) such as exosomes in the management of cancers, especially leukemia, holds great significance. In this article, we extracted exosomes from NALM6 cells and assessed their regulatory effects on proliferation and apoptosis in mesenchymal stem cells (MSCs). Method and result We first verified the exosomes using various techniques, including flow cytometry, transient electron microscopy, dynamic light scattering (DLS), and BCA protein assay. Then MTT analysis and flowcytometry (apoptosis and cell cycle assay) besides gene expressions were employed to determine the state of MSC proliferations. The results indicated that exosome-specific pan markers like CD9, CD63, and CD81 were present. Through DLS, we found out that the mean size of the exosomes was 89.68 nm. The protein content was determined to be 956.292 µg/ml. Analysis of MTT, flow cytometry (cell cycle and apoptosis assay), and RT-qPCR showed that in the dose of 50 µg/ml the proliferation of MSCs was increased significantly (p-value < 0.05). Conclusion All these data showed that exosomes use several signaling pathways to increase the MSCs' proliferation and drug resistance, ultimately leading to high mortalities and morbidities of acute lymphoblastic leukemia.

Significance of Complement Regulatory Protein Tetraspanins in the Male Reproductive System and Fertilization.

Fertilization is a very sophisticated and unique process involving several key steps resulting in a zygote's formation. Recent research has indicated that some immune system-related cell surface molecules (CD molecules from the tetraspanin superfamily) may have a role in fertilization. Extracellular vesicles are undeniably involved in a variety of cellular functions, including reproduction. Tetraspanin proteins identified in extracellular vesicles are now used mostly as markers; mounting evidence indicates that they also participate in cell targeting, cargo selection, and extracellular vesicle formation. Their significance and potential in mammalian reproduction are currently being studied extensively. Despite the fact that the current data did not establish any theory, the crucial function of tetraspanins in the fertilization process was not ruled out, and the specific role of tetraspanins is still unknown. In this review, we bring insight into the existing knowledge regarding the expression of tetraspanins in spermatozoa and seminal fluid and their role in gamete binding and fusion.

Tetraspanin Cd9b plays a role in fertility in zebrafish.

In mice, CD9 expression on the egg is required for efficient sperm-egg fusion and no effects on ovulation or male fertility are observed in CD9 null animals. Here we show that cd9b knockout zebrafish also appear to have fertility defects. In contrast to mice, fewer eggs were laid by cd9b knockout zebrafish pairs and, of the eggs laid, a lower percentage were fertilised. These effects could not be linked to primordial germ cell numbers or migration as these were not altered in the cd9b mutants. The decrease in egg numbers could be rescued by exchanging either cd9b knockout partner, male or female, for a wildtype partner. However, the fertilisation defect was only rescued by crossing a cd9b knockout female with a wildtype male. To exclude effects of mating behaviour we analysed clutch size and fertilisation using in vitro fertilisation techniques. Number of eggs and fertilisation rates were significantly reduced in the cd9b mutants suggesting the fertility defects are not solely due to courtship behaviours. Our results indicate that CD9 plays a more complex role in fish fertility than in mammals, with effects in both males and females.

Hypoxia regulates CD9 expression and dissemination of B lymphoblasts.

Acute lymphoblastic leukemias (ALL) are the most frequent cancer in children and derive most often from B-cell precursors. Current survival rates roughly reach 90% at 10 years from diagnosis. However, 15-20% of children still relapse with a significant risk of death. Our previous work showed that the transmembrane protein CD9 plays a major role in lymphoblasts migration into sanctuary sites, especially in testis, through the activation of RAC1 signaling upon blasts stimulation with C-X-C chemokine ligand 12 (CXCL12). Here, we identified common factors shared by the bone marrow and extramedullary niches which could upregulate CD9 expression and function. We found that low oxygen levels enhance CD9 expression both at mRNA and protein levels. We further determined that Hypoxia Inducible Factor 1α (HIF1α), the master transcription factor involved in hypoxia response, binds directly CD9 promoter and induce CD9 transcription. We also showed that CD9 protein is crucial for leukemic cell adhesion and migration at low oxygen levels, possibly through its action on RAC1 signaling. Mouse xenograft experiments indicate that HIF1α signaling pathway promotes ALL cells engraftment in a CD9-dependent manner. The present work increments our understanding of CD9 implication in ALL pathogenesis.

Tetraspanin CD9 Expression Predicts Sentinel Node Status in Patients with Cutaneous Melanoma.

The tetraspanin CD9 is considered a metastasis suppressor in many cancers, however its role is highly debated. Currently, little is known about CD9 prognostic value in cutaneous melanoma. Our aim was to analyse CD9 expression in melanocytic nevi and primary cutaneous melanomas through immunohistochemistry and immunofluorescence approaches to determine its correlation with invasiveness and metastatic potential. CD9 displayed homogeneous staining in all melanocytic nevi. In contrast, it showed a complete loss of reactivity in all thin melanomas. Interestingly, CD9 was re-expressed in 46% of intermediate and thick melanomas in small tumor clusters predominantly located at sites of invasion near or inside the blood or lymphatic vessels. The most notable finding is that all CD9 stained melanomas presented sentinel node positivity. Additionally, a direct association between CD9 expression and presence of distant metastasis was reported. Finally, we confirm that CD9 expression is consistent with an early protective role against tumorigenesis, however, our data endorse in melanoma a specific function of CD9 in vascular dissemination during late tumor progression. The presence of CD9 hotspots could be essential for melanoma cell invasion in lymphatic and endothelial vessels. CD9 could be a valid prognostic factor for lymph node metastasis risk.

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. Nicotine­derived 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 CD9­integrin/CD9­transforming growth factor interaction. Hence, CD9 can play a dual role in various types of cancer.

Tetraspanin Cd9b and Cxcl12a/Cxcr4b have a synergistic effect on the control of collective cell migration.

Collective cell migration is essential for embryonic development and homeostatic processes. During zebrafish development, the posterior lateral line primordium (pLLP) navigates along the embryo flank by collective cell migration. The chemokine receptors, Cxcr4b and Cxcr7b, as well as their cognate ligand, Cxcl12a, are essential for this process. We corroborate that knockdown of the zebrafish cd9 tetraspanin orthologue, cd9b, results in mild pLL abnormalities. Through generation of CRISPR and TALEN mutants, we show that cd9a and cd9b function partially redundantly in pLLP migration, which is delayed in the cd9b single and cd9a; cd9b double mutants. This delay led to a transient reduction in neuromast numbers. Loss of both Cd9a and Cd9b sensitized embryos to reduced Cxcr4b and Cxcl12a levels. Together these results provide evidence that Cd9 modulates collective cell migration of the pLLP during zebrafish development. One interpretation of these observations is that Cd9 contributes to more effective chemokine signalling.

Multi-layered proteogenomic analysis unravels cancer metastasis directed by MMP-2 and focal adhesion kinase signaling.

The role of matrix metalloproteinase-2 (MMP-2) in tumor cell migration has been widely studied, however, the characteristics and effects of MMP-2 in clinical sample of metastatic colorectal cancer (CRC) remain poorly understood. Here, in order to unveil the perturbed proteomic signal during MMP-2 induced cancer progression, we analyzed plasma proteome of CRC patients according to disease progression, HCT116 cancer secretome upon MMP-2 knockdown, and publicly available CRC tissue proteome data. Collectively, the integrative analysis of multi-layered proteomes revealed that a protein cluster containing EMT (Epithelial-to-Mesenchymal Transition)-associated proteins such as CD9-integrin as well as MMP-2. The proteins of the cluster were regulated by MMP-2 perturbation and exhibited significantly increased expressions in tissue and plasma as disease progressed from TNM (Tumor, Node, and Metastasis) stage I to II. Furthermore, we also identified a plausible association between MMP-2 up-regulation and activation of focal adhesion kinase signaling in the proteogenomic analysis of CRC patient tissues. Based on these comparative and integrative analyses, we suggest that the high invasiveness in the metastatic CRC resulted from increased secretion of MMP-2 and CD9-integrin complex mediated by FAK signaling activation.

Light and electron-microscopic localization of CD9 and surfactant protein A and D in normal lungs of the horse.

The lung is a complex organ, and its physiology and immunology are regulated by various immune molecules and cells. Lung surfactant, a mixture of phospholipids and proteins produced by the bronchiolar and type II alveolar epithelial cells, is one such important player in lung physiology. Compared to knowledge about the biology of the surfactant in rodents and humans, only limited data are available on the surfactant in the horse. Although there are data linking levels of surfactant proteins with respiratory disease in the horse, there are no data on the cellular localization of surfactant protein A (SP-A) and surfactant protein D (SP-D). A member of the tetraspanin family of proteins, CD9 is a cell-signaling and adhesion protein and its expression has been detected in both normal and cancer cells, including those in the lung. Because there are no immunolocalization data on SP-A, SP-D, and CD9 in the normal lungs of the horse, our objective was to conduct a light and electron microscopic immunocytochemical study on normal lungs of the horse. The data showed SP-A and SP-D in bronchiolar epithelial and type II alveolar epithelial cells. These proteins were also localized in type I alveolar epithelial cells, pulmonary intravascular macrophages, and neutrophils, which is likely an outcome of endocytosis of the proteins by these cells. CD9 was present in the airway and vascular smooth muscle cells, endothelium, and blood cells, but not in the airway epithelium. These new data provide a baseline to further examine the expression and functions of SP-A, SP-D, and CD9 proteins in inflammation associated with respiratory diseases in the horse.

Le poumon est un organe complexe, et sa physiologie et son immunologie sont régulées par diverses molécules et cellules immunitaires. Le surfactant pulmonaire, un mélange de phospholipides et de protéines produits par les cellules épithéliales bronchiolaires et alvéolaires de type II, est un acteur important de la physiologie pulmonaire. Par rapport aux connaissances sur la biologie du surfactant chez les rongeurs et les humains, seules des données limitées sont disponibles sur le surfactant chez le cheval. Bien qu'il existe des données reliant les niveaux de protéines du surfactant à une maladie respiratoire chez le cheval, il n'y a pas de données sur la localisation cellulaire de la protéine de surfactant A (SP-A) et de la protéine de surfactant D (SP-D). Membre de la famille des protéines tétraspanines, CD9 est une protéine de signalisation et d'adhésion cellulaire et son expression a été détectée dans les cellules normales et cancéreuses, y compris celles du poumon. Comme il n'y a pas de données d'immunolocalisation pour SP-A, SP-D et CD9 dans les poumons normaux du cheval, notre objectif était de mener une étude immunocytochimique au microscope optique et électronique sur les poumons normaux du cheval. Les données ont montré la présence de SP-A et SP-D dans les cellules épithéliales bronchiolaires et alvéolaires de type II. Ces protéines étaient également localisées dans les cellules épithéliales alvéolaires de type I, les macrophages intravasculaires pulmonaires et les neutrophiles, ce qui est probablement le résultat de l'endocytose des protéines par ces cellules. Le CD9 était présent dans les cellules des voies respiratoires et des muscles lisses vasculaires, l'endothélium et les cellules sanguines, mais pas dans l'épithélium des voies respiratoires. Ces nouvelles données fournissent une base de référence pour examiner plus à fond l'expression et les fonctions des protéines SP-A, SP-D et CD9 dans l'inflammation associée aux maladies respiratoires chez le cheval.(Traduit par Docteur Serge Messier).

CD9 and ITGA3 are regulated during HIV-1 infection in macrophages to support viral replication.

Monocytes/macrophages are important target cells for HIV-1. Here, we investigated whether HIV-1 induces changes in the macrophage gene expression profile to support viral replication. We observed that the macrophage gene expression profiles dramatically changed upon HIV-1 infection. The majority of the HIV-1 regulated genes were also differentially expressed in M2a macrophages. The biological functions associated with the HIV-1 induced gene expression profile in macrophages were mainly related to inflammatory responses. CD9 and ITGA3 were among the top genes upregulated upon HIV-1 infection. We showed that these genes support viral replication and that downregulation of these genes decreased HIV-1 replication in macrophages. Here we showed that HIV-1 infection of macrophages induces a gene expression profile that may dampen inflammatory responses. CD9 and ITGA3 were among the top genes regulated by HIV-1 and were shown to support viral production most likely at the level of viral budding and release.

Interaction between CD9 and PI3K­p85 activates the PI3K/AKT signaling pathway in B­lineage acute lymphoblastic leukemia.

Our previous study has shown that CD9 knockdown could suppress cell proliferation, adhesion, migration and invasion, and promote apoptosis and the cytotoxicity of chemotherapeutic drugs in the B­lineage acute lymphoblastic leukemia (B­ALL) cell line SUP­B15. In this study, we further investigated the molecular mechanism underlying the effects of CD9 on leukemic cell progression and the efficacy of chemotherapeutic agents in B­ALL cells. Using the CD9­knockdown SUP­B15 cells, we demonstrated that the silencing of the CD9 gene significantly reduced the expression of phosphorylated­phosphatidylinositol­3 kinase (p­PI3K), phosphorylated­protein kinase B (p­AKT), P­glycoprotein (P­gp), multidrug resistance­associated protein 1 (MRP1), breast cancer resistance protein (BCRP), matrix metalloproteinase 2 (MMP2) and phosphorylated­focal adhesion kinase (p­FAK). In addition, glutathione S­transferase (GST) pull­down assay showed the binding between CD9 and both PI3K­p85α and PI3K­p85ß in vitro, while co­immunoprecipitation assay showed the binding between CD9 and both PI3K­p85α and PI3K­p85ß in vivo. Furthermore, the PI3K/AKT inhibitor LY294002 mirrored the effects of CD9 knockdown in SUP­B15 cells. Taken together, these findings demonstrated that CD9 activates the PI3K/AKT signaling pathway through direct interaction with PI3K­p85 in B­ALL cells. Our data provide evidence for the inhibition of the PI3K/AKT pathway as a novel therapeutic option in CD9 antigen­positive B­ALL.

Inhibition of cancer-cell migration by tetraspanin CD9-binding peptide.

A CD9-binding peptide (RSHRLRLH), screened from EWI-2, was characterized, and its effect on cellular migration and invasion was evaluated. As CD9 protein is overexpressed in cancer cells and plays an important role in cellular migration, the CD9-binding peptide preferentially inhibited the migration of cancer cells. Unlike conventional antiproliferative drugs, this CD9-binding peptide is promising as a novel precision antimigratory agent for cancer therapeutics.

Sperm-oocyte signaling: the role of IZUMO1R and CD9 in PTK2B activation and actin remodeling at the sperm binding site†.

Sperm-oocyte binding initiates an outside-in signaling event in the mouse oocyte that triggers recruitment and activation of the cytosolic protein kinase PTK2B in the cortex underlying the bound sperm. While not involved in gamete fusion, PTK2B activity promotes actin remodeling events important during sperm incorporation. However, the mechanism by which sperm-oocyte binding activates PTK2B is unknown, and the present study examined the possibility that sperm interaction with specific oocyte surface proteins plays an important role in PTK2B activation. Imaging studies revealed that as IZUMO1R and CD9 became concentrated at the sperm binding site, activated (phosphorylated) PTK2B accumulated in the cortex underlying the sperm head and in microvilli partially encircling the sperm head. In order to determine whether IZUMO1R and/or CD9 played a significant role in PTK2B recruitment and activation at the sperm binding site, the ability of oocytes null for Izumo1r or Cd9, to initiate an increase in PTK2B content and activation was tested. The results revealed that IZUMO1R played a minor role in PTK2B activation and had no effect on actin remodeling; however, CD9 played a very significant role in PTK2B activation and subsequent actin remodeling at the sperm binding site. These findings suggest the possibility that interaction of sperm surface proteins with CD9 or CD9-associated oocyte proteins triggers PTK2B activation at the sperm binding site.

Role of microRNA-335 carried by bone marrow mesenchymal stem cells-derived extracellular vesicles in bone fracture recovery.

Mesenchymal stem cells (MSCs) have the potential to reduce healing time and treat nonunion in fracture patients. In this study, bone marrow MSCs-derived extracellular vesicles (B-EVs) were firstly extracted and identified. CD9-/- and normal mice were enrolled for the establishment of fracture models and then injected with B-EVs. Osteoblast differentiation and fracture recovery were estimated. The levels of osteoblast-related genes were detected, and differentially expressed microRNAs (miRs) in B-EVs-treated normal fracture mice were screened and verified. The downstream mechanisms of miR were predicted and assessed. The loss-of functions of miR-335 in B-EV and gain-of-functions of VapB were performed in animal and cell experiments to evaluate their roles in bone fracture. Collectively, B-EVs promoted bone fracture recovery and osteoblast differentiation by releasing miR-335. miR-335 downregulation in B-EVs impaired B-EV functions in fracture recovery and osteoblast differentiation. miR-335 could target VapB, and VapB overexpression reversed the effects of B-EVs on osteoblast differentiation. B-EV treatment activated the Wnt/ß-catenin pathway in fracture mice and osteoblasts-like cells. Taken together, the study suggested that B-EVs carry miR-335 to promote bone fracture recovery via VapB and the Wnt/ß-catenin pathway. This study may offer insights into bone fracture treatment.

Two CD9 tetraspanin family members of Japanese flounder (Paralichthys olivaceus): characterization and comparative analysis of the anti-infectious immune function.

CD9 is a glycoprotein of the transmembrane 4 superfamily that is involved in various cellular processes. Studies related to the immune functions and activities of CD9 in teleost fish are limited. In this study, we characterized two CD9 homologs, PoCD9.1 and PoCD9.3, from Japanese flounder (Paralichthys olivaceus). Sequence analysis showed that PoCD9.1 and PoCD9.3 possess characteristic transmembrane 4 superfamily (TM4SF) structures. PoCD9.1 shares 70.61% sequence identity with PoCD9.3. The expression of PoCD9.1 and PoCD9.3 in the three main immune tissues was significantly induced in a time-dependent manner by extracellular and intracellular pathogen infection, which indicates that the two CD9 homologs play an important role in the response to pathogenic infection. Following infection with the extracellular pathogen Vibrio anguillarum, the expression profiles of both PoCD9.1 and PoCD9.3 were similar. After infection with the intracellular pathogen Edwardsiella piscicida, the expression levels of PoCD9.1 and PoCD9.3 were different at different stages of infection, especially in the spleen. The spleen was the most important tissue for the PoCD9.1 and PoCD9.3 responses to pathogen infection among the three examined immune tissues. Knockdown of PoCD9.1 and PoCD9.3 attenuated the ability of host cells to eliminate pathogenic bacteria, and PoCD9.1 knockdown was more lethal than PoCD9.3 knockdown for host cells with E. piscicida infection. Overexpression of PoCD9.1 and PoCD9.3 promoted host or host cell defence against E. piscicida infection. These findings suggest that PoCD9.1 and PoCD9.3 serve as immune-related factors, play an important role in the immune defence system of Japanese flounder, and display different functions in response to different pathogens at different stages of infection.

CD9 Upregulation-Decreased CCL21 Secretion in Mesenchymal Stem Cells Reduces Cancer Cell Migration.

Tetraspanin CD9 is widely expressed on various cell types, such as cancer cells and mesenchymal stem cells (MSCs), and/or cell-released exosomes. It has been reported that exosomal CD9 plays an important role in intercellular communications involved in cancer cell migration and metastasis. However, reports on the effect of the CD9 of MSCs or MSC-derived exosomes on cancer cell migration are still lacking. In this study, using a transwell migration assay, we found that both dextran-coated iron oxide nanoparticles (dex-IO NPs) and ionomycin stimulated exosomal CD9 expression in human MSCs (hMSCs); however, hMSCs could not deliver them to melanoma cells to affect cell migration. Interestingly, a reduced migration of melanoma cell line was observed when the ionomycin-incubated hMSC-conditioned media but not dex-IO NP-labeled hMSC-conditioned media were in the bottom chamber. In addition, we found that dex-IO NPs decreased cellular CD9 expression in hMSCs but ionomycin increased this. Simultaneously, we found that ionomycin suppressed the expression and secretion of the chemokine CCL21 in hMSCs. The silencing of CD9 demonstrated an inhibitory role of cellular CD9 in CCL21 expression in hMSCs, suggesting that ionomycin could upregulate cellular CD9 to decrease CCL21 expression and secretion of hMSCs, which would reduce the migration of B16F10, A549 and U87MG cancer cell lines due to chemoattraction reduction of CCL21. The present study not only highlights the important role of bone marrow-derived hMSCs' CD9-mediated CCL21 regulation in cancer bone metastasis but also suggests a new distinct pharmaceutical strategy for prevention or/and therapy of cancer metastasis.

Involvement of Cytokines and Hormones in the Development of Spermatogenesis In Vitro from Spermatogonial Cells of Cyclophosphamide-Treated Immature Mice.

Aggressive chemotherapy treatment may lead to male infertility. Prepubertal boys do not produce sperm at this age, however, they have spermatogonial stem cells in their testes. Here, we examined the effect of intraperitoneal injection of cyclophosphamide (CP) on the capacity of immature mice (IM) to develop spermatogenesis in vivo and in vitro [using methylcellulose culture system (MCS)]. Our results show a significant decrease in testicular weight, total number of testicular cells, and the number of Sertoli, peritubular, premeiotic, and meiotic/post-meiotic cells, but an increase in the percentages of damaged seminiferous tubules in CP-treated IM compared to control. The functionality of Sertoli cells was significantly affected. The addition of testosterone to isolated cells from seminiferous tubules of CP-treated IM significantly increased the percentages of premeiotic (CD9-positive cells) and meiotic/post-meiotic cells (ACROSIN-positive cells) developed in MCS compared to control. The addition of FSH did not affect developed cells in MCS compared to control, but in combination with testosterone, it significantly decreased the percentages of CD9-positive cells and ACROSIN-positive cells. The addition of IL-1 did not affect developed cells in MCS compared to control, but in combination with testosterone, it significantly increased the percentages of VASA-positive cells and BOULE-positive cells compared to IL-1 or testosterone. Addition of TNF significantly increased only CD9-positive cells in MCS compared to control, but in combination with testosterone, it significantly decreased ACROSIN-positive cells compared to testosterone. Our results show a significant impairment of spermatogenesis in the testes of CP-treated IM, and that spermatogonial cells from these mice proliferate and differentiate to meiotic/post-meiotic cells under in vitro culture conditions.

CD9, a potential leukemia stem cell marker, regulates drug resistance and leukemia development in acute myeloid leukemia.

BACKGROUND: Leukemia stem cells (LSCs) are responsible for the initiation, progression, and relapse of acute myeloid leukemia (AML). Therefore, a therapeutic strategy targeting LSCs is a potential approach to eradicate AML. In this study, we aimed to identify LSC-specific surface markers and uncover the underlying mechanism of AML LSCs. METHODS: Microarray gene expression data were used to investigate candidate AML-LSC-specific markers. CD9 expression in AML cell lines, patients with AML, and normal donors was evaluated by flow cytometry (FC). The biological characteristics of CD9-positive (CD9+) cells were analyzed by in vitro proliferation, chemotherapeutic drug resistance, migration, and in vivo xenotransplantation assays. The molecular mechanism involved in CD9+ cell function was investigated by gene expression profiling. The effects of alpha-2-macroglobulin (A2M) on CD9+ cells were analyzed with regard to proliferation, drug resistance, and migration. RESULTS: CD9, a cell surface protein, was specifically expressed on AML LSCs but barely detected on normal hematopoietic stem cells (HSCs). CD9+ cells exhibit more resistance to chemotherapy drugs and higher migration potential than do CD9-negative (CD9-) cells. More importantly, CD9+ cells possess the ability to reconstitute human AML in immunocompromised mice and promote leukemia growth, suggesting that CD9+ cells define the LSC population. Furthermore, we identified that A2M plays a crucial role in maintaining CD9+ LSC stemness. Knockdown of A2M impairs drug resistance and migration of CD9+ cells. CONCLUSION: Our findings suggest that CD9 is a new biomarker of AML LSCs and is a promising therapeutic target.

Functional Integrin Regulation Through Interactions with Tetraspanin CD9.

Integrins are adhesion receptors that mediate many intercellular and cell-extracellular matrix interactions with relevance in physiology and pathology. Unlike other cellular receptors, integrins critically require activation for ligand binding. Through interaction in cis with other molecules and the formation of tetraspanin-enriched membrane microdomains (TEMs), the tetraspanin CD9 regulates integrin activity and avidity. Here we present three techniques used to study CD9-integrin interactions and integrin activation.