Deletion of tetraspanin CD9 diminishes lymphangiogenesis in vivo and in vitro

Elucidating hippocampal proteome dynamics in moderate hepatic encephalopathy rats: insights from high-resolution mass spectrometry

Hepatic encephalopathy (HE) is a debilitating neurological disorder associated with liver failure and characterized by impaired brain function. Decade-long studies have led to significant advances in our understanding of HE; however, effective therapeutic management of HE is lacking, and HE continues to be a significant cause of morbidity and mortality in patients, underscoring the need for continued research into its pathophysiology and treatment. Accordingly, the present study provides a comprehensive overview aimed at elucidating the molecular underpinnings of HE and identifying potential therapeutic targets. A moderate-grade HE model was induced in rats using thioacetamide, which simulates the liver damage observed in patients, and its impact on cognitive function, neuronal arborization, and cellular morphology was also evaluated. We employed label-free LC-MS/MS proteomics to quantitatively profile hippocampal proteins to explore the molecular mechanism of HE pathogenesis; 2175 proteins were identified, 47 of which exhibited significant alterations in moderate-grade HE. The expression of several significantly upregulated proteins, such as FAK1, CD9 and Tspan2, was further validated at the transcript and protein levels, confirming the mass spectrometry results. These proteins have not been previously reported in HE. Utilizing Metascape, a tool for gene annotation and analysis, we further studied the biological pathways integral to brain function, including gliogenesis, the role of erythrocytes in maintaining blood-brain barrier integrity, the modulation of chemical synaptic transmission, astrocyte differentiation, the regulation of organ growth, the response to cAMP, myelination, and synaptic function, which were disrupted during HE. The STRING database further elucidated the protein‒protein interaction patterns among the differentially expressed proteins. This study provides novel insights into the molecular mechanisms driving HE and paves the way for identifying novel therapeutic targets for improved disease management.

Immunophenotypic portrait of leukemia-associated-phenotype markers in B acute lymphoblastic leukemia

BACKGROUND

Multiparametric flow cytometry (MFC) is an essential diagnostic tool in B acute lymphoblastic leukemia (B ALL) to determine the B-lineage affiliation of the blast population and to define their complete immunophenotypic profile. Most MFC strategies used in routine laboratories include leukemia-associated phenotype (LAP) markers, whose expression profiles can be difficult to interpret. The aim of our study was to reach a better understanding of 7 LAP markers' landscape in B ALL: CD9, CD21, CD66c, CD58, CD81, CD123, and NG2.

METHODS

Using a 10-color MFC approach, we evaluated the level of expression of 7 LAP markers including CD9, CD21, CD66c, CD58, CD81, CD123, and NG2, at the surface of normal peripheral blood leukocytes (n = 10 healthy donors), of normal precursor B regenerative cells (n = 40 uninvolved bone marrow samples) and of lymphoblasts (n = 100 peripheral blood samples or bone marrow samples from B ALL patients at diagnosis). The expression profile of B lymphoblasts was analyzed according the presence or absence of recurrent cytogenetic aberrations. The prognostic value of the 7 LAP markers was examined using Maxstat R algorithm.

RESULTS

In order to help the interpretation of the MFC data in routine laboratories, we first determined internal positive and negative populations among normal leukocytes for each of the seven evaluated LAP markers. Second, their profile of expression was evaluated in normal B cell differentiation in comparison with B lymphoblasts to establish a synopsis of their expression in normal hematogones. We then evaluated the frequency of expression of these LAP markers at the surface of B lymphoblasts at diagnosis of B ALL. CD9 was expressed in 60% of the cases, CD21 in only 3% of the cases, CD58 in 96% of the cases, CD66c in 45% of the cases, CD81 in 97% of the cases, CD123 in 72% of the cases, and NG2 in only 2% of the cases. We confirmed the interest of the CD81/CD58 MFI expression ratio as a way to discriminate hematogones from lymphoblasts. We observed a significant lower expression of CD9 and of CD81 at the surface of B lymphoblasts with a t(9;22)(BCR-ABL) in comparison with B lymphoblasts without any recurrent cytogenetic alteration (p = 0.0317 and p = 0.0011, respectively) and with B lymphoblasts harboring other cytogenetic recurrent abnormalities (p = 0.0032 and p < 0.0001, respectively). B lymphoblasts with t(1;19) at diagnosis significantly overexpressed CD81 when compared with B lymphoblasts with other recurrent cytogenetic abnormalities or without any recurrent alteration (p = 0.0001). An overexpression of CD58 was also observed in the cases harboring this abnormal cytogenetic event, when compared with B lymphoblasts with other recurrent cytogenetic abnormalities (p = 0.030), or without any recurrent alteration (p = 0.0002). In addition, a high expression of CD123, of CD58 and of CD81 was associated with a favorable prognosis in our cohort of pediatric and young adult B ALL patients. We finally built a risk score based on the expression of these 3 LAP markers, this scoring approach being able to split these patients into a high-risk group (17%) and a better outcome group (83%, p < 0.0001).

CONCLUSION

The complexity of the phenotypic signature of lymphoblasts at diagnosis of B ALL is illustrated by the variability in the expression of LAP antigens. Knowledge of the expression levels of these markers in normal leukocytes and during normal B differentiation is crucial for an optimal interpretation of diagnostic cytometry results and serves as a basis for the biological follow-up of B ALL.

Tetraspanins set the stage for bone marrow microenvironment-induced chemoprotection in hematologic malignancies

Despite recent advances in the treatment of hematologic malignancies, relapse still remains a consistent issue. One of the primary contributors to relapse is the bone marrow microenvironment providing a sanctuary to malignant cells. These cells interact with bone marrow components such as osteoblasts and stromal cells, extracellular matrix proteins, and soluble factors. These interactions, mediated by the cell surface proteins like cellular adhesion molecules (CAMs), induce intracellular signaling that leads to the development of bone marrow microenvironment-induced chemoprotection (BMC). Although extensive study has gone into these CAMs, including the development of targeted therapies, very little focus in hematologic malignancies has been put on a family of cell surface proteins that are just as important for mediating bone marrow interactions: the transmembrane 4 superfamily (tetraspanins; TSPANs). TSPANs are known to be important mediators of microenvironmental interactions and metastasis based on numerous studies in solid tumors. Recently, evidence of their possible role in hematologic malignancies, specifically in the regulation of cellular adhesion, bone marrow homing, intracellular signaling, and stem cell dynamics in malignant hematologic cells has come to light. Many of these effects are facilitated by associations with CAMs and other receptors on the cell surface in TSPAN-enriched microdomains. This could suggest that TSPANs play an important role in mediating BMC in hematologic malignancies and could be used as therapeutic targets. In this review, we discuss TSPAN structure and function in hematologic cells, their interactions with different cell surface and signaling proteins, and possible ways to target/inhibit their effects.

Prognostic value and multifaceted roles of tetraspanin CD9 in cancer

CD9 is a crucial regulator of cell adhesion in the immune system and plays important physiological roles in hematopoiesis, blood coagulation or viral and bacterial infections. It is involved in the transendothelial migration of leukocytes which might also be hijacked by cancer cells during their invasion and metastasis. CD9 is found at the cell surface and the membrane of exosomes affecting cancer progression and therapy resistance. High expression of CD9 is mostly associated with good patients outcome, with a few exceptions. Discordant findings have been reported for breast, ovarian, melanoma, pancreatic and esophageal cancer, which might be related to using different antibodies or inherent cancer heterogeneity. According to in vitro and in vivo studies, tetraspanin CD9 is not clearly associated with either tumor suppression or promotion. Further mechanistic experiments will elucidate the role of CD9 in particular cancer types and specific conditions.

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.

The Effect of Terpenoid Natural Chinese Medicine Molecular Compound on Lung Cancer Treatment

Among all malignant tumors in the whole universe, the incidence and mortality of lung cancer disease rank first. Especially in the past few years, the occurrence of lung cancer in the urban population has continued to increase, which seriously threatens the lives and health of people. Among the many treatments for lung cancer, chemotherapy is the best one, but traditional chemotherapy has low specificity and drug resistance. To address the above issue, this study reviews the five biological pathways that common terpenoid compounds in medicinal plants interfere with the occurrence and development of lung cancer: cell proliferation, cell apoptosis, cell autophagy, cell invasion, metastasis, and immune mechanism regulation. In addition, the mechanism of the terpenoid natural traditional Chinese medicine monomer compound combined with Western medicine in the multipathway antilung cancer is summarized.

TNF-α Carried by Plasma Extracellular Vesicles Predicts Knee Osteoarthritis Progression

Objectives

To identify plasma extracellular vesicles (EVs) associated with radiographic knee osteoarthritis (OA) progression.

Methods

EVs of small (SEV), medium (MEV) and large (LEV) sizes from plasma of OA participants (n=30) and healthy controls (HCs, n=22) were profiled for surface markers and cytokine cargo by high-resolution flow cytometry. The concentrations of cytokines within (endo-) and outside (exo-) EVs were quantified by multiplex ELISA. EV associations with knee radiographic OA (rOA) progression were assessed by multivariable linear regression (adjusted for baseline clinical variables of age, gender, BMI and OA severity) and receiver operating characteristic (ROC) curve analysis.

Results

Based on integrated mean fluorescence intensity (iMFI), baseline plasma MEVs carrying CD56 (corresponding to natural killer cells) predicted rOA progression with highest area under the ROC curve (AUC) 0.714 among surface markers. Baseline iMFI of TNF-α in LEVs, MEVs and SEVs, and the total endo-EV TNF-α concentration, predicted rOA progression with AUCs 0.688, 0.821, 0.821, 0.665, respectively. In contrast, baseline plasma exo-EV TNF-α (the concentration in the same unit of plasma after EV depletion) did not predict rOA progression (AUC 0.478). Baseline endo-EV IFN-γ and exo-EV IL-6 concentrations were also associated with rOA progression, but had low discriminant capacity (AUCs 0.558 and 0.518, respectively).

Conclusions

Plasma EVs carry pro-inflammatory cargo that predict risk of knee rOA progression. These findings suggest that EV-associated TNF-α may be pathogenic in OA. The sequestration of pathogenic TNF-α within EVs may provide an explanation for the lack of success of systemic TNF-α inhibitors in OA trials to date.

Extracellular Vesicles as Biological Indicators and Potential Sources of Autologous Therapeutics in Osteoarthritis

Along with cytokines, extracellular vesicles (EVs) released by immune cells in the joint contribute to osteoarthritis (OA) pathogenesis. By high-resolution flow cytometry, we characterized 18 surface markers and 4 proinflammatory cytokines carried by EVs of various sizes in plasma and synovial fluid (SF) from individuals with knee OA, with a primary focus on immune cells that play a major role in OA pathogenesis. By multiplex immunoassay, we also measured concentrations of cytokines within (endo) and outside (exo) EVs. EVs carrying HLA-DR, -DP and -DQ were the most enriched subpopulations in SF relative to plasma (25–50-fold higher depending on size), suggesting a major contribution to the SF EV pool from infiltrating immune cells in OA joints. In contrast, the CD34⁺ medium and small EVs, reflecting hematopoietic stem cells, progenitor cells, and endothelial cells, were the most significantly enriched subpopulations in plasma relative to SF (7.3- and 7.7-fold higher). Ratios of EVs derived from neutrophils and lymphocytes were highly correlated between SF and plasma, indicating that plasma EVs could reflect OA severity and serve as systemic biomarkers of OA joint pathogenesis. Select subsets of plasma EVs might also provide next generation autologous biological products for intra-articular therapy of OA joints.

Expression of CD9 on porcine lymphocytes and its relation to T cell differentiation and cytokine production

In this work, we report on two novel monoclonal antibodies, specific for porcine CD9. CD9 is a tetraspanin that is expressed on a wide variety of cells. We phenotyped porcine immune cell subsets and found that CD9 was expressed on all monocytes as well as a subset of B cells. CD9 was variably expressed on T cells, with CD4 T cells containing the highest frequency of CD9⁺ cells. CD9 expression positively correlated with the frequency of central memory CD4 T cells in ex vivo PBMC. Therefore, we proceeded to explore CD9 as a marker of T cell function. Here we observed that CD9 was expressed on the vast majority of long-lived influenza A virus-specific effector cells that retained the capacity for cytokine production in response to in vitro recall antigen. Therefore, the new antibodies enable the detection of a cell surface molecule with functional relevance to T cells. Considering the importance of CD9 in membrane remodelling across many cell types, they will also benefit the wider field of swine biomedical research.

Role of lymphatic endothelial cells in the tumor microenvironment-a narrative review of recent advances

Background

As lymphatic vessel is a major route for solid tumor metastasis, they are considered an essential part of tumor drainage conduits. Apart from forming the walls of lymphatic vessels, lymphatic endothelial cells (LECs) have been found to play multiple other roles in the tumor microenvironment, calling for a more in-depth review. We hope that this review may help researchers gain a detailed understanding of this fast-developing field and shed some light upon future research.

Methods

To achieve an informative review of recent advance, we carefully searched the Medline database for English literature that are openly published from the January 1995 to December 2020 and covered the topic of LEC or lymphangiogenesis in tumor progression and therapies. Two different authors independently examined the literature abstracts to exclude possible unqualified ones, and 310 papers with full texts were finally retrieved.

Results

In this paper, we discussed the structural and molecular basis of tumor-associated LECs, together with their roles in tumor metastasis and drug therapy. We then focused on their impacts on tumor cells, tumor stroma, and anti-tumor immunity, and the molecular and cellular mechanisms involved. Special emphasis on lung cancer and possible therapeutic targets based on LECs were also discussed.

Conclusions

LECs can play a much more complex role than simply forming conduits for tumor cell dissemination. Therapies targeting tumor-associated lymphatics for lung cancer and other tumors are promising, but more research is needed to clarify the mechanisms involved.

CD9, a tetraspanin target for cancer therapy?

In the present minireview, we intend to provide a brief history of the field of CD9 involvement in oncogenesis and in the metastatic process of cancer, considering its potential value as a tumor-associated antigenic target. Over the years, CD9 has been identified as a favorable prognostic marker or predictor of metastatic potential depending on the cancer type. To understand its implications in cancer beside its use as an antigenic biomarker, it is essential to know its physiological functions, including its molecular partners in a given cell system. Moreover, the discovery that CD9 is one of the most specific and broadly expressed markers of extracellular membrane vesicles, nanometer-sized entities that are released into extracellular space and various physiological body fluids and play a role in intercellular communication under physiological and pathological conditions, notably the establishment of cancer metastases, has added a new dimension to our knowledge of CD9 function in cancer. Here, we will discuss these issues as well as the possible cancer therapeutic implications of CD9, their limitations, and pitfalls.

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/β-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/β-catenin pathway. This study may offer insights into bone fracture treatment.

Integrative Analysis Reveals Common and Unique Roles of Tetraspanins in Fibrosis and Emphysema

While both chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) are multifactorial disorders characterized by distinct clinical and pathological features, their commonalities and differences have not been fully elucidated. We sought to investigate the preventive roles of tetraspanins Cd151 and Cd9 -that are involved in diverse cellular processes in lung pathophysiology- in pulmonary fibrosis and emphysema, respectively, and to obtain a deeper understanding of their underlying molecular mechanisms toward facilitating improved therapeutic outcomes. Using an integrative approach, we examined the transcriptomic changes in the lungs of Cd151- and Cd9-deficient mice using functional-enrichment-analysis, pathway-perturbation-analysis and protein-protein-interaction (PPI) network analysis. Circadian-rhythm, extracellular-matrix (ECM), cell-adhesion and inflammatory responses and associated factors were prominently influenced by Cd151-deletion. Conversely, cellular-junctions, focal-adhesion, vascular-remodeling, and TNF-signaling were deeply impacted by Cd9-deletion. We also highlighted a “common core” of factors and signaling cascades that underlie the functions of both Cd151 and Cd9 in lung pathology. Circadian dysregulation following Cd151-deletion seemingly facilitated progressive fibrotic lung phenotype. Conversely, TGF-β signaling attenuation and TNF-signaling activation emerged as potentially novel functionaries of Cd9-deletion-induced emphysema. Our findings offer promising avenues for developing novel therapeutic treatments for pulmonary fibrosis and emphysema.

Tetraspanins: useful multifunction proteins for the possible design and development of small-molecule therapeutic tools

Tetraspanins constitute a well-conserved superfamily of four-span small membrane proteins (TM4SF), with >30 members in humans, with important roles in numerous mechanisms of cell biology. Moreover, tetraspanins associate with either specific partner proteins or another tetraspanin, generating a network of interactions involved in cell and membrane compartmentalization and having a role in cellular development, proliferation, activation, motility, and membrane fusions. Therefore, tetraspanins are considered regulators of cellular signaling and are often depicted as 'molecular facilitators'. In view of these many physiological functions, it is likely that these molecules are important actors in pathological processes. In this review, we present the main characteristics of this superfamily, providing a more detailed description of some significant representatives and discuss their relevance as potential targets for the design and development of small-molecule therapeutics in different pathologies.

Tetraspanin CD9 affects HPV16 infection by modulating ADAM17 activity and the ERK signalling pathway

Human papillomaviruses (HPV) are causative agents of various tumours such as cervical cancer. HPV binding to the cell surface of keratinocytes leads to virus endocytosis at tetraspanin enriched microdomains. Complex interactions of the capsid proteins with host proteins as well as ADAM17-dependent ERK1/2 signal transduction enable the entry platform assembly of the oncogenic HPV type 16. Here, we studied the importance of tetraspanin CD9, also known as TSPAN29, in HPV16 infection of different epithelial cells. We found that both overexpression and loss of the tetraspanin decreased infection rates in cells with low endogenous CD9 levels, while reduction of CD9 expression in keratinocytes that exhibit high-CD9 protein amounts, led to an increase of infection. Therefore, we concluded that low-CD9 supports infection. Moreover, we found that changes in CD9 amounts affect the shedding of the ADAM17 substrate transforming growth factor alpha (TGFα) and the downstream phosphorylation of ERK. These effects correlate with those on infection rates suggesting that a specific CD9 optimum promotes ADAM17 activity, ERK signalling and virus infection. Together, our findings implicate that CD9 regulates HPV16 infection through the modulation of ADAM17 sheddase activity.

Cd9 Protects Photoreceptors from Injury and Potentiates Edn2 Expression

Purpose

Cd9 is a tetraspanin membrane protein that plays various roles in tissue development and disease pathogenesis, especially in cancer, but the expression patterns and function of Cd9 in retinal development and disease are not well understood. We asked its roles during retinal photoreceptor degeneration by using CD9-knockout mice.

Methods

Cd9 knockout mice and rd1 mice were used to examine roles of Cd9 for progression of photoreceptor degeneration. Reverse transcription-polymerase chain reaction and immunohistochemistry were mainly used as analytical methods.

Results

Cd9 transcripts were only weakly expressed in retina at embryonic day 14, but its expression level subsequently increased and peaked at around postnatal day 12. In 6-week-old female mice derived retina, mRNA expression decreased slightly but was maintained at a significant level. Published RNA-sequencing data and immunohistochemistry indicated that Cd9 was expressed abundantly in Müller glia and weakly in other retinal neurons. Notably, when photoreceptors were damaged, Cd9 expression was increased in rod photoreceptors and decreased in Müller glia. Cd9 knockout mice retinas developed normally; however, once the retina suffered damage, degeneration of photoreceptors was more severe in Cd9 knockout retinas than control retinas. Induction of Edn2, which is known to protect against photoreceptor damage, was severely hampered. In addition, induction of Socs3, which is downstream of gp130 (Il6st), was weaker in Cd9 knockout retinas.

Conclusions

Taken together, these findings indicate that, although Cd9 was dispensable for normal gross morphological development, it protected rod photoreceptors and enhanced Edn2 expression, possibly through modulation of gp130 signaling.

Migrasome and Tetraspanins in Vascular Homeostasis: Concept, Present, and Future

Cell migration plays a critical role in vascular homeostasis. Under noxious stimuli, endothelial cells (ECs) migration always contributes to vascular repair, while enhanced migration of vascular smooth muscle cells (VSMCs) will lead to pathological vascular remodeling. Moreover, vascular activities are involved in communication between ECs and VSMCs, between ECs and immune cells, et al. Recently, Ma et al. (2015) discovered a novel migration-dependent organelle “migrasome,” which mediated release of cytoplasmic contents, and this process was defined as “migracytosis.” The formation of migrasome is precisely regulated by tetraspanins (TSPANs), cholesterol and integrins. Migrasomes can be taken up by neighboring cells, and migrasomes are distributed in many kinds of cells and tissues, such as in blood vessel, human serum, and in ischemic brain of human and mouse. In addition, the migrasome elements TSPANs are wildly expressed in cardiovascular system. Therefore, TSPANs, migrasomes and migracytosis might play essential roles in regulating vascular homeostasis. In this review, we will discuss the discoveries of migration-dependent migrasome and migracytosis, migrasome formation, the basic differences between migrasomes and exosomes, the distributions and functions of migrasome, the functions of migrasome elements TSPANs in vascular biology, and discuss the possible roles of migrasomes and migracytosis in vascular homeostasis.

Tetraspanin CD53 Promotes Lymphocyte Recirculation by Stabilizing L-Selectin Surface Expression

Tetraspanins regulate key processes in immune cells; however, the function of the leukocyte-restricted tetraspanin CD53 is unknown. Here we show that CD53 is essential for lymphocyte recirculation. Lymph nodes of Cd53-/- mice were smaller than those of wild-type mice due to a marked reduction in B cells and a 50% decrease in T cells. This reduced cellularity reflected an inability of Cd53-/- B and T cells to efficiently home to lymph nodes, due to the near absence of L-selectin from Cd53-/- B cells and reduced stability of L-selectin on Cd53-/- T cells. Further analyses, including on human lymphocytes, showed that CD53 stabilizes L-selectin surface expression and may restrain L-selectin shedding via both ADAM17-dependent and ADAM17-independent mechanisms. The disruption in lymphocyte recirculation in Cd53-/- mice led to impaired immune responses dependent on antigen delivery to lymph nodes. Together these findings demonstrate an essential role for CD53 in lymphocyte trafficking and immunity.

Thrombopoietin Metabolically Primes Hematopoietic Stem Cells to Megakaryocyte-Lineage Differentiation

During acute myelosuppression or thrombocytopenia, bone marrow (BM) hematopoietic cells respond rapidly to replenish peripheral blood platelets. While the cytokine thrombopoietin (Thpo) both regulates platelet production and maintains HSC potential, whether Thpo controls megakaryocyte (Mk)-lineage differentiation of HSCs is unclear. Here, we show that Thpo rapidly upregulates mitochondrial activity in HSCs, an activity accompanied by differentiation to an Mk lineage. Moreover, in unperturbed hematopoiesis, HSCs with high mitochondrial activity exhibit Mk-lineage differentiation in vitro and myeloid lineage-biased reconstitution in vivo. Furthermore, Thpo skewed HSCs to express the tetraspanin CD9, a pattern correlated with mitochondrial activity. Mitochondria-active HSCs are resistant to apoptosis and oxidative stress upon Thpo stimulation. Thpo-regulated mitochondrial activity associated with mitochondrial translocation of STAT3 phosphorylated at serine 727. Overall, we report an important role for Thpo in regulating rapid Mk-lineage commitment. Thpo-dependent changes in mitochondrial metabolism prime HSCs to undergo direct differentiation to an Mk lineage.

Tspan8 and Tspan8/CD151 knockout mice unravel the contribution of tumor and host exosomes to tumor progression

BACKGROUND

The tetraspanins Tspan8 and CD151 promote metastasis, exosomes (Exo) being suggested to be important in the crosstalk between tumor and host. The contribution of Tspan8 and CD151 to host versus tumor-derived exosome (TEX) activities being not defined, we approached the questions using 3-methylcholanthrene-induced (MCA) tumors from wt, Tspan8ko, CD151ko and Tspan8/CD151 (db)ko mice, implanted into tetraspanin-competent and deficient hosts.

METHODS

Tumor growth and dissemination, hematopoiesis and angiogenesis were surveyed in wild type (wt), Tspan8ko, CD151ko and dbko mice bearing tetraspanin-competent and -deficient MCA tumors. In vitro studies using tumor cells, bone marrow cells (BMC) and endothelial cells (EC) elaborated the mechanism of serum (s)Exo- and TEX-induced target modulation.

RESULTS

Tumors grew in autochthonous and syngeneic hosts differing in Tspan8- and/or CD151-competence. However, Tspan8ko- and/or CD151ko-tumor cell dissemination and settlement in metastatic organs was significantly reduced in the autochthonous host, and less severely in the wt-host. Impaired wt-MCA tumor dissemination in the ko-host confirmed a contribution of host- and tumor-Tspan8/-CD151 to tumor cell dissemination, delivery of sExo and TEX being severely impaired by a Tspan8ko/CD151ko. Coculturing tumor cells, BMC and EC with sExo and TEX revealed minor defects in epithelial mesenchymal transition and apoptosis resistance of ko tumors. Strongly reduced migratory and invasive capacity of Tspan8ko/CD151ko-MCA relies on distorted associations with integrins and CAM and missing Tspan8/CD151-promoted recruitment of proteases. The defects, differing between Tspan8ko- and CD151ko-MCA, were rescued by wt-TEX and, less efficiently Tspan8ko- and CD151ko-TEX. Minor defects in hematopoietic progenitor maturation were based on the missing association of hematopoietic growth factors /- receptors with CD151 and, less pronounced, Tspan8. Rescue of impaired angiogenesis in ko mice by wt-sExo and promotion of angiogenesis by TEX depended on the association of Tspan8 and CD151 with GPCR and RTK in EC and tumor cells.

CONCLUSIONS

Tspan8-/CD151-TEX play central roles in tumor progression. Tspan8-/CD151-sExo and TEX contribute by stimulating angiogenesis. Tspan8 and CD151 fulfill these tasks by associating with function-relevant proteins, the additive impact of Tspan8 and CD151 relying on differences in preferred associations. The distinct Tspan8 and CD151 contributions suggest a blockade of TEX-Tspan8 and -CD151 promising for therapeutic intervention.

Vascular endothelial growth factor-C promotes human mesenchymal stem cell migration via an ERK-and FAK-dependent mechanism

Vascular endothelial cell growth factor-C (VEGF-C) is a member of the VEGF family and plays a role in various biological activities. VEGF-C enhances proliferation and migration of lymphatic endothelial cells and vascular endothelial cells through VEGF receptor 2 (VEGFR2) and/or receptor 3 (VEGFR3), and thereby induces lymphangiogenesis or angiogenesis. However, it remains unclear whether VEGF-C promotes the migration of mesenchymal stem cells (MSCs). Here, we investigated the effects of VEGF-C on the migration of MSCs and evaluated the underlying molecular mechanisms. VEGF-C treatment significantly induced the migration of MSCs, which is accompanied by the promotion of actin cytoskeletal reorganization and focal adhesion assembly. VEGF-C treatment enhanced the phosphorylation of VEGFR2 and VEGFR3 proteins in MSCs, and pretreatment with VEGFR2 and VEGFR3 kinase inhibitors effectively suppressed the VEGF-C-induced MSC migration. In addition, VEGF-C treatment promoted phosphorylation of ERK and FAK proteins in MSCs, and inhibition of VEGFR2 and VEGFR3 signaling pathways abolished the VEGF-C-induced activation of ERK and FAK proteins. Furthermore, treatment with ERK and FAK inhibitors suppressed VEGF-C-induced actin cytoskeletal reorganization and focal adhesion assembly, and then significantly inhibited MSCs migration. These results suggest that VEGF-C-induced MSC migration is mediated via VEGFR2 and VEGFR3, and follows the activation of the ERK and FAK signaling pathway. Thus, VEGF-C may be valuable in tissue regeneration and repair in MSC-based therapy.

Systematic biology analysis on photosynthetic carbon metabolism of maize leaf following sudden heat shock under elevated CO2

Plants would experience more complex environments, such as sudden heat shock (SHS) stress combined with elevated CO₂ in the future, and might adapt to this stressful condition by optimizing photosynthetic carbon metabolism (PCM). It is interesting to understand whether this acclimation process would be altered in different genotypes of maize under elevated CO₂, and which metabolites represent key indicators reflecting the photosynthetic rates (P_N) following SHS. Although B76 had greater reduction in P_N during SHS treatment, our results indicated that P_N in genotype B76, displayed faster recovery after SHS treatment under elevated CO₂ than in genotype B106. Furthermore, we employed a stepwise feature extraction approach by partial linear regression model. Our findings demonstrated that 9 key metabolites over the total (35 metabolites) can largely explain the variance of P_N during recovery from SHS across two maize genotypes and two CO₂ grown conditions. Of these key metabolites, malate, valine, isoleucine, glucose and starch are positively correlated with recovery pattern of P_N. Malate metabolites responses to SHS were further discussed by incorporating with the activities and gene expression of three C₄ photosynthesis-related key enzymes. We highlighted the importance of malate metabolism during photosynthesis recovery from short-term SHS, and data integration analysis to better comprehend the regulatory framework of PCM in response to abiotic stress.

Double deletion of tetraspanins CD9 and CD81 in mice leads to a syndrome resembling accelerated aging

Chronic obstructive pulmonary disease (COPD) has been recently characterized as a disease of accelerated lung aging, but the mechanism remains unclear. Tetraspanins have emerged as key players in malignancy and inflammatory diseases. Here, we found that CD9/CD81 double knockout (DKO) mice with a COPD-like phenotype progressively developed a syndrome resembling human aging, including cataracts, hair loss, and atrophy of various organs, including thymus, muscle, and testis, resulting in shorter survival than wild-type (WT) mice. Consistent with this, DNA microarray analysis of DKO mouse lungs revealed differential expression of genes involved in cell death, inflammation, and the sirtuin-1 (SIRT1) pathway. Accordingly, expression of SIRT1 was reduced in DKO mouse lungs. Importantly, siRNA knockdown of CD9 and CD81 in lung epithelial cells additively decreased SIRT1 and Foxo3a expression, but reciprocally upregulated the expression of p21 and p53, leading to reduced cell proliferation and elevated apoptosis. Furthermore, deletion of these tetraspanins increased the expression of pro-inflammatory genes and IL-8. Hence, CD9 and CD81 might coordinately prevent senescence and inflammation, partly by maintaining SIRT1 expression. Altogether, CD9/CD81 DKO mice represent a novel model for both COPD and accelerated senescence.

Leaf Photosynthetic Parameters Related to Biomass Accumulation in a Global Rice Diversity Survey

Mining natural variations is a major approach to identify new options to improve crop light use efficiency. So far, successes in identifying photosynthetic parameters positively related to crop biomass accumulation through this approach are scarce, possibly due to the earlier emphasis on properties related to leaf instead of canopy photosynthetic efficiency. This study aims to uncover rice (Oryza sativa) natural variations to identify leaf physiological parameters that are highly correlated with biomass accumulation, a surrogate of canopy photosynthesis. To do this, we systematically investigated 14 photosynthetic parameters and four morphological traits in a rice population, which consists of 204 U.S. Department of Agriculture-curated minicore accessions collected globally and 11 elite Chinese rice cultivars in both Beijing and Shanghai. To identify key components responsible for the variance of biomass accumulation, we applied a stepwise feature-selection approach based on linear regression models. Although there are large variations in photosynthetic parameters measured in different environments, we observed that photosynthetic rate under low light (Alow) was highly related to biomass accumulation and also exhibited high genomic inheritability in both environments, suggesting its great potential to be used as a target for future rice breeding programs. Large variations in Alow among modern rice cultivars further suggest the great potential of using this parameter in contemporary rice breeding for the improvement of biomass and, hence, yield potential.

Exosomal tetraspanins mediate cancer metastasis by altering host microenvironment

The metastases of malignant tumors develop through a cascade of events. The establishment of a pre-metastatic micro-environment is initiated by communication between tumors and host. Exosomes come into focus as the most potent intercellular communicators playing a pivotal role in this process. Cancer cells release exosomes into the extracellular environment prior to metastasis. Tetraspanin is a type of 4 times transmembrane proteins. It may be involved in cell motility, adhesion, morphogenesis, as well as cell and vesicular membrane fusion. The exosomal tetraspanin network is a molecular scaffold connecting various proteins for signaling transduction. The complex of tetraspanin-integrin determines the recruiting cancer exosomes to pre-metastatic sites. Tetraspanin is a key element for the target cell selection of exosomes uptake that may lead to the reprogramming of target cells. Reprogrammed target cells assist pre-metastatic niche formation. Previous reviews have described the biogenesis, secretion and intercellular interaction of exosomes in various tumors. However, there is a lack of reviews on the topic of exosomal tetraspanin in the context of cancer. In this review, we will describe the main characteristics of exosomal tetraspanin in cancer cells. We will also discuss how the cancer exosomal tetraspanin alters extracellular environment and regulates cancer metastasis.

Tetraspanins Function as Regulators of Cellular Signaling

Tetraspanins are molecular scaffolds that distribute proteins into highly organized microdomains consisting of adhesion, signaling, and adaptor proteins. Many reports have identified interactions between tetraspanins and signaling molecules, finding unique downstream cellular consequences. In this review, we will explore these interactions as well as the specific cellular responses to signal activation, focusing on tetraspanin regulation of adhesion-mediated (integrins/FAK), receptor-mediated (EGFR, TNF-α, c-Met, c-Kit), and intracellular signaling (PKC, PI4K, β-catenin). Additionally, we will summarize our current understanding for how tetraspanin post-translational modifications (palmitoylation, N-linked glycosylation, and ubiquitination) can regulate signal propagation. Many of the studies outlined in this review suggest that tetraspanins offer a potential therapeutic target to modulate aberrant signal transduction pathways that directly impact a host of cellular behaviors and disease states.

Mesenchymal Stem Cell-Derived Exosomes Promote Fracture Healing in a Mouse Model

: Paracrine signaling by bone-marrow-derived mesenchymal stem cells (MSCs) plays a major role in tissue repair. Although the production of regulatory cytokines by MSC transplantation is a critical modulator of tissue regeneration, we focused on exosomes, which are extracellular vesicles that contain proteins and nucleic acids, as a novel additional modulator of cell-to-cell communication and tissue regeneration. To address this, we used radiologic imaging, histological examination, and immunohistochemical analysis to evaluate the role of exosomes isolated from MSC-conditioned medium (CM) in the healing process in a femur fracture model of CD9^-/- mice, a strain that is known to produce reduced levels of exosomes. We found that the bone union rate in CD9^-/- mice was significantly lower than wild-type mice because of the retardation of callus formation. The retardation of fracture healing in CD9^-/- mice was rescued by the injection of exosomes, but this was not the case after the injection of exosomes-free conditioned medium (CM-Exo). The levels of the bone repair-related cytokines, monocyte chemotactic protein-1 (MCP-1), MCP-3, and stromal cell-derived factor-1 in exosomes were low compared with levels in CM and CM-Exo, suggesting that bone repair may be in part mediated by other exosome components, such as microRNAs. These results suggest that exosomes in CM facilitate the acceleration of fracture healing, and we conclude that exosomes are a novel factor of MSC paracrine signaling with an important role in the tissue repair process.

SIGNIFICANCE

This work focuses on exosomes, which are extracellular vesicles, as a novel additional modulator of cell-to-cell communication. This study evaluated the role of exosomes isolated from mesenchymal stem cell (MSC)-conditioned medium (MSC-CM) in the fracture-healing process of CD9^-/- mice, a strain that is known to produce reduced levels of exosomes. Retardation of fracture healing in CD9^-/- mice was rescued by the injection of MSC exosomes, but this was not the case after the injection of exosome-free CM. This study finds that MSC exosomes are a novel factor of MSC paracrine signaling, with an important role in the tissue repair process.

Preventive Role of Tetraspanin CD9 in Systemic Inflammation of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is frequently associated with extrapulmonary complications, including cardiovascular disease, diabetes, and osteoporosis. Persistent, low-grade, systemic inflammation underlies these comorbid disorders. Tetraspanins, which have a characteristic structure spanning the membrane four times, facilitate lateral organization of molecular complexes and thereby form tetraspanin-enriched microdomains that are distinct from lipid rafts. Recent basic research has suggested a preventive role of tetraspanin CD9 in COPD. CD9-enriched microdomains negatively regulate LPS-induced receptor formation by preventing CD14 from accumulating into the rafts, and decreased CD9 in macrophages enhances inflammation in mice. Mice doubly deficient in CD9 and a related tetraspanin, CD81, show pulmonary emphysema, weight loss, and osteopenia, a phenotype akin to human COPD. A therapeutic approach to up-regulating CD9 in macrophages might improve the clinical course of patients with COPD with comorbidities.

Exosomes as therapeutics: The implications of molecular composition and exosomal heterogeneity

Harnessing exosomes as therapeutic drug delivery vehicles requires a better understanding of exosomal composition and their mode of action. A full appreciation of all the exosomal components (proteins, lipids, and RNA content) will be important for the design of effective exosome-based or exosome-mimicking drug carriers. In this review we describe the presence of rarely studied, non-coding RNAs that exist in high numbers in exosomes. We discuss the implications of the molecular composition and heterogeneity of exosomes on their biological and therapeutic effects. Finally, we highlight outstanding questions with regard to RNA loading into exosomes, analytical methods to sort exosomes and their sub-populations, and the effects of exosomal proteins and lipids on recipient cells. Investigations into these facets of exosome biology will further advance the field, could lead to the clinical translation of exosome-based therapeutics, and aid in the reverse-engineering of synthetic exosomes. Although synthetic exosomes are still an underexplored area, they could offer researchers a way to manufacture exosomes with highly defined structure, composition, and function.

Function and Dynamics of Tetraspanins during Antigen Recognition and Immunological Synapse Formation

Tetraspanin-enriched microdomains (TEMs) are specialized membrane platforms driven by protein–protein interactions that integrate membrane receptors and adhesion molecules. Tetraspanins participate in antigen recognition and presentation by antigen-­presenting cells (APCs) through the organization of pattern-recognition receptors (PRRs) and their downstream-induced signaling, as well as the regulation of MHC-II–peptide trafficking. T lymphocyte activation is triggered upon specific recognition of antigens present on the APC surface during immunological synapse (IS) formation. This dynamic process is characterized by a defined spatial organization involving the compartmentalization of receptors and adhesion molecules in specialized membrane domains that are connected to the underlying cytoskeleton and signaling molecules. Tetraspanins contribute to the spatial organization and maturation of the IS by controlling receptor clustering and local accumulation of adhesion receptors and integrins, their downstream signaling, and linkage to the actin cytoskeleton. This review offers a perspective on the important role of TEMs in the regulation of antigen recognition and presentation and in the dynamics of IS architectural organization.

Autoantibodies to tetraspanins (CD9, CD81 and CD82) in demyelinating diseases

Tetraspanin family proteins, CD9, CD81 and CD82 are expressed in the oligodendrocytes and Schwann cells. We investigated autoantibodies to tetraspanin proteins in patients with demyelinating diseases. Sera were collected from 119 multiple sclerosis patients, 19 neuromyelitis optica, 42 acute inflammatory demyelinating polyneuropathy, 23 chronic inflammatory demyelinating polyneuropathy and 13 acute motor axonal neuropathy as well as 55 healthy controls. Few multiple sclerosis and acute inflammatory demyelinating polyneuropathy patients had autoantibodies that were weakly reactive to CD9 or CD81 but the significance is unclear. It is unlikely that these autoantibodies are pathogenic or serve as potential biomarkers in demyelinating diseases.

Tetraspanins in cell migration

Tetraspanins are a superfamily of small transmembrane proteins that are expressed in almost all eukaryotic cells. Through interacting with one another and with other membrane and intracellular proteins, tetraspanins regulate a wide range of proteins such as integrins, cell surface receptors, and signaling molecules, and thereby engage in diverse cellular processes ranging from cell adhesion and migration to proliferation and differentiation. In particular, tetraspanins modulate the function of proteins involved in all determining factors of cell migration including cell-cell adhesion, cell-ECM adhesion, cytoskeletal protrusion/contraction, and proteolytic ECM remodeling. We herein provide a brief overview of collective in vitro and in vivo studies of tetraspanins to illustrate their regulatory functions in the migration and trafficking of cancer cells, vascular endothelial cells, skin cells (keratinocytes and fibroblasts), and leukocytes. We also discuss the involvement of tetraspanins in various pathologic and remedial processes that rely on cell migration and their potential value as targets for therapeutic intervention.

New insights into the role of podoplanin in epithelial-mesenchymal transition

Podoplanin is a small mucin-like transmembrane protein expressed in several adult tissues and with an important role during embryogenesis. It is needed for the proper development of kidneys and lungs as well as accurate formation of the lymphatic vascular system. In addition, it is involved in the physiology of the immune system. A wide variety of tumors express podoplanin, both in the malignant cells and in the stroma. Although there are exceptions, the presence of podoplanin results in poor prognosis. The main consequence of forced podoplanin expression in established and tumor-derived cell lines is an increase in cell migration and, eventually, the triggering of an epithelial-mesenchymal transition, whereby cells acquire a fibroblastoid phenotype and increased motility. We will examine the current status of the role of podoplanin in the induction of epithelial-mesenchymal transition as well as the different interactions that lead to this program.

Overexpression of CD9 correlates with tumor stage and lymph node metastasis in esophageal squamous cell carcinoma

OBJECTIVE

Esophageal squamous cell carcinoma (ESCC) is one of the leading causes of cancer deaths worldwide. CD9 has been reported to play a critical role in cell motility, growth and metastasis of multiple cancers. The present study investigated the clinicopathological features of CD9, and its biological characteristics in ESCC.

METHODS

Fifteen normal esophageal tissue specimens, fifty-three ESCC adjacent tissues and one hundred and four ESCC tissues were included in this study. Using immunohistochemistry (IHC), the expression levels of CD9 were evaluated among different samples. And its clinicopathological parameters and its prognostic factors were analyzed. Western blotting was used to measure CD9 expression and colony formation was performed to determine the effect of CD9 on cell growth in ESCC TE-1 cells.

RESULTS

Compared with normal esophageal tissues and tumor adjacent tissues, CD9 expression level is significantly higher in ESCC tissues. CD9 expression correlated with tumor stage (P=0.022) and lymph node metastasis (P=0.019) in ESCC patients. Furthermore, the small interfering RNA-mediated silencing of CD9 expression in TE-1 cells resulted in increased proliferation as evidenced by increased colony number and colony size.

CONCLUSION

CD9 expression is upregulated in ESCC tissues and its expression is correlated with tumor stage and lymph node metastasis in ESCC patients. CD9 suppresses the proliferation of TE-1 cells. CD9 may present a potential in tumor progression in ESCC.

Identification of CD34+ and CD34- leukemia-initiating cells in MLL-rearranged human acute lymphoblastic leukemia

Translocation of the mixed-lineage leukemia (MLL) gene with AF4, AF9, or ENL results in acute leukemia with both lymphoid and myeloid involvement. We characterized leukemia-initiating cells (LICs) in primary infant MLL-rearranged leukemia using a xenotransplantation model. In MLL-AF4 patients, CD34(+)CD38(+)CD19(+) and CD34(-)CD19(+) cells initiated leukemia, and in MLL-AF9 patients, CD34(-)CD19(+) cells were LICs. In MLL-ENL patients, either CD34(+) or CD34(-) cells were LICs, depending on the pattern of CD34 expression. In contrast, in patients with these MLL translocations, CD34(+)CD38(-)CD19(-)CD33(-) cells were enriched for normal hematopoietic stem cells (HSCs) with in vivo long-term multilineage hematopoietic repopulation capacity. Although LICs developed leukemic cells with clonal immunoglobulin heavy-chain (IGH) rearrangement in vivo, CD34(+)CD38(-)CD19(-)CD33(-) cells repopulated recipient bone marrow and spleen with B cells, showing broad polyclonal IGH rearrangement and recipient thymus with CD4(+) single positive (SP), CD8(+) SP, and CD4(+)CD8(+) double-positive (DP) T cells. Global gene expression profiling revealed that CD9, CD32, and CD24 were over-represented in MLL-AF4, MLL-AF9, and MLL-ENL LICs compared with normal HSCs. In patient samples, these molecules were expressed in CD34(+)CD38(+) and CD34(-) LICs but not in CD34(+)CD38(-)CD19(-)CD33(-) HSCs. Identification of LICs and LIC-specific molecules in primary human MLL-rearranged acute lymphoblastic leukemia may lead to improved therapeutic strategies for MLL-rearranged leukemia.

Sentinel lymph node metastases in cancer: causes, detection and their role in disease progression

Malignant tumors of ectodermal or endodermal origin may metastasize to the sentinel lymph node, the first lymph node encountered by tumor cells that enter lymphatics in the organ of origin. This pathway is enabled by the anatomy of the disease and the causes of metastasis are the result of complex interactions that include mechanical forces within the tumor and host tissues, and molecular factors initiated by tumor cell proliferation, elaboration of cytokines and changes in the tumor microenvironment. Mechanical stresses may influence complex biochemical, genetic and other molecular events and enhance the likelihood of metastasis. This paper summarizes our understanding of interacting molecular, anatomical and mechanical processes which facilitate metastasis to SLNs. Our understanding of these interacting events is based on a combination of clinical and basic science research, in vitro and in vivo, including studies in lymphatic embryology, anatomy, micro-anatomy, pathology, physiology, molecular biology and mechanobiology. The presence of metastatic tumor in the SLN is now more accurately identifiable and, based upon prospective clinical trials, paradigm-changing SLN biopsy has become the standard of clinical practice in breast cancer and melanoma.

Tetraspanins at a glance

Tetraspanins are a family of proteins with four transmembrane domains that play a role in many aspects of cell biology and physiology; they are also used by several pathogens for infection and regulate cancer progression. Many tetraspanins associate specifically and directly with a limited number of proteins, and also with other tetraspanins, thereby generating a hierarchical network of interactions. Through these interactions, tetraspanins are believed to have a role in cell and membrane compartmentalization. In this Cell Science at a Glance article and the accompanying poster, we describe the basic principles underlying tetraspanin-based assemblies and highlight examples of how tetraspanins regulate the trafficking and function of their partner proteins that are required for the normal development and function of several organs, including, in humans, the eye, the kidney and the immune system.

Tetraspanins CD9 and CD151 at the immune synapse support T-cell integrin signaling

Understanding how the immune response is activated and amplified requires detailed knowledge of the stages in the formation of the immunological synapse (IS) between T lymphocytes and antigen-presenting cells (APCs). We show that tetraspanins CD9 and CD151 congregate at the T-cell side of the IS. Silencing of CD9 or CD151 blunts the IL-2 secretion and expression of the activation marker CD69 by APC-conjugated T lymphocytes, but does not affect the accumulation of CD3 or actin to the IS, or the translocation of the microtubule-organizing center toward the T-B contact area. CD9 or CD151 silencing diminishes the relocalization of α4β1 integrin to the IS and reduces the accumulation of high-affinity β1 integrins at the cell-cell contact. These changes are accompanied by diminished phosphorylation of the integrin downstream targets FAK and ERK1/2. Our results suggest that CD9 and CD151 support integrin-mediated signaling at the IS.

Lymphangiogenesis and lymphatic vessel remodelling in cancer

The generation of new lymphatic vessels through lymphangiogenesis and the remodelling of existing lymphatics are thought to be important steps in cancer metastasis. The past decade has been exciting in terms of research into the molecular and cellular biology of lymphatic vessels in cancer, and it has been shown that the molecular control of tumour lymphangiogenesis has similarities to that of tumour angiogenesis. Nevertheless, there are significant mechanistic differences between these biological processes. We are now developing a greater understanding of the specific roles of distinct lymphatic vessel subtypes in cancer, and this provides opportunities to improve diagnostic and therapeutic approaches that aim to restrict the progression of cancer.

Role of motility-related protein-1 in promoting the development of several types of cancer (Review)

Motility-related protein-1 (CD9), a type of cell surface glycoprotein comprising a four-pass transmembrane domain that forms multimeric complexes with other cell surface proteins, belongs to the tetraspanins family. From previous studies, we know that CD9 is considered to function primarily as a progression and metastasis suppressor in a variety of cancers, including breast, non-small cell lung colon and myeloma. However, an expanding body of literature has shown the contradictory outcome that tetraspanin CD9 is also vital in promoting cancer progression in several types of cancer. This review summarizes the recent studies on CD9 and concludes that it does not always act as a progression and metastasis suppressor. Conversely, in specific cases, CD9 may promote tumor progression through the following three aspects: Facilitating tumor cell transmigration, increasing tumor cell motility and hastening the growth of some cancers. In addition, CD9 appears to be an important marker of cancer stem cells in certain types of tumor.

Tetraspanin proteins promote multiple cancer stages

An abundance of evidence shows supporting roles for tetraspanin proteins in human cancer. Many studies show that the expression of tetraspanins correlates with tumour stage, tumour type and patient outcome. In addition, perturbations of tetraspanins in tumour cell lines can considerably affect cell growth, morphology, invasion, tumour engraftment and metastasis. This Review emphasizes new studies that have used de novo mouse cancer models to show that select tetraspanin proteins have key roles in tumour initiation, promotion and metastasis. This Review also emphasizes how tetraspanin proteins can sometimes participate in tumour angiogenesis. These recent data build an increasingly strong case for tetraspanins as therapeutic targets.

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.