Characterization of the novel human transmembrane protein 9 (TMEM9) that localizes to lysosomes and late endosomes

TMEM9 promotes lung adenocarcinoma progression via activating the MEK/ERK/STAT3 pathway to induce VEGF expression

Abnormal Transmembrane protein 9 (TMEM9) expression has been identified in various human tumors. However, the prognostic potential and mechanistic role of TMEM9 in lung adenocarcinoma (LUAD) remain unclear. Here, we first found a significant upregulation of TMEM9 in LUAD tissues, and TMEM9 expression was positively correlated with microvessel density (MVD), T stage, and clinical stage. Survival analysis demonstrated TMEM9 was an independent indicator of poor prognosis in LUAD patients. In addition, downregulation of TMEM9 suppressed tumor growth and metastasis in vitro and in vivo models, and reduced HUVEC proliferation, migration, and tube formation in a cancer cell/HUVEC coculture model. Furthermore, TMEM9 upregulated VEGF expression, and VEGF-neutralizing antibodies reversed HUVEC angiogenesis and cancer cell migration ability caused by overexpression of TMEM9. In contrast, recombinant VEGF (rVEGF) abolished the inhibitory effect of TMEM9-knockdown LUAD cells on HUVEC angiogenesis and tumor cell migration. Moreover, we showed that TMEM9 upregulated VEGF expression by activating the mitogen-activated protein kinase/extracellular signal-regulated kinase/STAT3 (MEK/ERK/STAT3) pathway. Together, our study provides mechanistic insights into the role of TMEM9 in LUAD and highlights the potential of targeting the TMEM9/MEK/ERK/STAT3/VEGF pathway as a novel therapy for preventing LUAD progression.

Identification of biomarker candidates for exfoliative glaucoma from autoimmunity profiling

BACKGROUND

Exfoliative glaucoma (XFG) is a subtype of open-angle glaucoma characterized by distinctive extracellular fibrils and a yet unknown pathogenesis potentially involving immune-related factors. The aim of this exploratory study was to identify biomarkers for XFG using data from autoimmunity profiling performed on blood samples from a Scandinavian cohort of patients.

METHODS

Autoantibody screening was analyzed against 258 different protein fragments in blood samples taken from 30 patients diagnosed with XFG and 30 healthy donors. The 258 protein fragments were selected based on a preliminary study performed on 3072 randomly selected antigens and antigens associated with the eye. The "limma" package was used to perform moderated t-tests on the proteomic data to identify differentially expressed reactivity between the groups.

RESULTS

Multiple associated genes were highlighted as possible biomarker candidates including FUT2, CDH5, and the LOX family genes. Using seven variables, our binary logistic regression model was able to classify the cases from the controls with an AUC of 0.85, and our reduced model using only one variable corresponding to the FUT2 gene provided an AUC of 0.75, based on LOOCV. Furthermore, over-representation gene analysis was performed to identify pathways that were associated with antigens differentially bound to self-antibodies. This highlighted the enrichment of pathways related to collagen fibril formation and the regulatory molecules mir-3176 and mir-876-5p.

CONCLUSIONS

This study suggests several potential biomarkers that may be useful in developing further models of the pathology of XFG. In particular, CDH5, FUT2, and the LOX family seem to have a relationship which merits additional exploration.

The transmembrane proteins (TMEM) and their role in cell proliferation, migration, invasion, and epithelial-mesenchymal transition in cancer

Transmembrane proteins (TMEM) are located in the different biological membranes of the cell and have at least one passage through these cellular compartments. TMEM proteins carry out a wide variety of functions necessary to maintain cell homeostasis TMEM165 participates in glycosylation protein, TMEM88 in the development of cardiomyocytes, TMEM45A in epidermal keratinization, and TMEM74 regulating autophagy. However, for many TMEM proteins, their physiological function remains unknown. The role of these proteins is being recently investigated in cancer since transcriptomic and proteomic studies have revealed that exits differential expression of TMEM proteins in different neoplasms concerning cancer-free tissues. Among the cellular processes in which TMEM proteins have been involved in cancer are the promotion or suppression of cell proliferation, epithelial-mesenchymal transition, invasion, migration, intravasation/extravasation, metastasis, modulation of the immune response, and response to antineoplastic drugs. Inclusive data suggests that the participation of TMEM proteins in these cellular events could be carried out through involvement in different cell signaling pathways. However, the exact mechanisms not clear. This review shows a description of the involvement of TMEM proteins that promote or decrease cell proliferation, migration, and invasion in cancer cells, describes those TMEM proteins for which both a tumor suppressor and a tumor promoter role have been identified, depending on the type of cancer in which the protein is expressed. As well as some TMEM proteins involved in chemoresistance. A better characterization of these proteins is required to improve the understanding of the tumors in which their expression and function are altered; in addition to improving the understanding of the role of these proteins in cancer will show those TMEM proteins be potential candidates as biomarkers of response to chemotherapy or prognostic biomarkers or as potential therapeutic targets in cancer.

TMEM9-v-ATPase Activates Wnt/β-Catenin Signaling Via APC Lysosomal Degradation for Liver Regeneration and Tumorigenesis

BACKGROUND AND AIMS

How Wnt signaling is orchestrated in liver regeneration and tumorigenesis remains elusive. Recently, we identified transmembrane protein 9 (TMEM9) as a Wnt signaling amplifier.

APPROACH AND RESULTS

TMEM9 facilitates v-ATPase assembly for vesicular acidification and lysosomal protein degradation. TMEM9 is highly expressed in regenerating liver and hepatocellular carcinoma (HCC) cells. TMEM9 expression is enriched in the hepatocytes around the central vein and acutely induced by injury. In mice, Tmem9 knockout impairs hepatic regeneration with aberrantly increased adenomatosis polyposis coli (Apc) and reduced Wnt signaling. Mechanistically, TMEM9 down-regulates APC through lysosomal protein degradation through v-ATPase. In HCC, TMEM9 is overexpressed and necessary to maintain β-catenin hyperactivation. TMEM9-up-regulated APC binds to and inhibits nuclear translocation of β-catenin, independent of HCC-associated β-catenin mutations. Pharmacological blockade of TMEM9-v-ATPase or lysosomal degradation suppresses Wnt/β-catenin through APC stabilization and β-catenin cytosolic retention.

CONCLUSIONS

Our results reveal that TMEM9 hyperactivates Wnt signaling for liver regeneration and tumorigenesis through lysosomal degradation of APC.

MicroRNA-346-5p Regulates Differentiation of Bone Marrow-Derived Mesenchymal Stem Cells by Inhibiting Transmembrane Protein 9

The molecular mechanisms how bone marrow-derived mesenchymal stem cells (BMSCs) differentiate into osteoblast need to be investigated. MicroRNAs (miRNAs) contribute to the osteogenic differentiation of BMSCs. However, the effect of miR-346-5p on osteogenic differentiation of BMSCs is not clear. This study is aimed at elucidating the underlying mechanism by which miR-346-5p regulates osteogenic differentiation of human BMSCs. Results of alkaline phosphatase (ALP) and Alizarin Red S (ARS) staining indicated that upregulation of miR-346-5p suppressed osteogenic differentiation of BMSCs, whereas downregulation of miR-346-5p enhanced this process. The protein levels of the osteoblastic markers Osterix and Runt-related transcription factor 2 (Runx2) were decreased in cells treated with miR-346-5p mimic at day 7 and day 14 after being differentiated. By contrast, downregulation of miR-346-5p elevated the protein levels of Osterix and Runx2. Moreover, a dual-luciferase reporter assay revealed that Transmembrane Protein 9 (TMEM9) was a target of miR-346-5p. In addition, the Western Blot results demonstrated that the TMEM9 protein level was significantly reduced by the miR-346-5p mimic whereas downregulation of miR-346-5p improved the protein level of TMEM9. These results together demonstrated that miR-346-5p served a key role in BMSC osteogenic differentiation of through targeting TMEM9, which may provide a novel target for clinical treatments of bone injury.

TMEM9 mediates IL-6 and IL-1β secretion and is modulated by the Wnt pathway

Novel studies have shown that the Transmembrane protein 9 (TMEM9) gene is localized at 1q41 and encodes a protein consisting of 183 amino acids with an N-terminus containing many important domains. As a novel human transmembrane protein, TMEM9 is highly conserved in species from Caenorhabditis elegans to humans and is widely expressed in many tissues and cells. Moreover, TMEM9 may play an important role in intracellular transport and the growth of hepatoma cells. However, evidence for the function of TMEM9 in inflammation is still limited. We studied the expression of TMEM9 and its effect on cytokine secretion in tumor necrosis factor-alpha (TNF-α)-induced LX-2 cells. We proved that overexpression of TMEM9 by transfection with pEGFP-C2-TMEM9 may increase the expression of IL-6 and IL-1β in LX-2 cells. At the same time, knockdown of TMEM9 expression by transfection with a TMEM9-siRNA decreased IL-6 and IL-1β secretion in LX-2 cells. Additionally, our results proved that overexpression of TMEM9 enhanced the protein expression levels of the canonical Wnt/β-catenin accompanied by an upregulation of wnt2b, wnt3a and β-catenin protein levels in LX-2 cells treated with TNF-α. These results indicate that TMEM9 plays a significant role in TNF-α-enhanced cytokines (IL-6 and IL-1β) secretion in LX-2 cells and that the canonical Wnt/β-catenin signaling pathway is involved in the induction of these cytokine expressions.

Genetic Networks in Mouse Retinal Ganglion Cells

Retinal ganglion cells (RGCs) are the output neuron of the eye, transmitting visual information from the retina through the optic nerve to the brain. The importance of RGCs for vision is demonstrated in blinding diseases where RGCs are lost, such as in glaucoma or after optic nerve injury. In the present study, we hypothesize that normal RGC function is transcriptionally regulated. To test our hypothesis, we examine large retinal expression microarray datasets from recombinant inbred mouse strains in GeneNetwork and define transcriptional networks of RGCs and their subtypes. Two major and functionally distinct transcriptional networks centering around Thy1 and Tubb3 (Class III beta-tubulin) were identified. Each network is independently regulated and modulated by unique genomic loci. Meta-analysis of publically available data confirms that RGC subtypes are differentially susceptible to death, with alpha-RGCs and intrinsically photosensitive RGCs (ipRGCs) being less sensitive to cell death than other RGC subtypes in a mouse model of glaucoma.

Effects of TMEM9 gene on cell progression in hepatocellular carcinoma by RNA interference

Hepatocellular carcinoma (HCC) is a malignant tumor that has become a global health issue. The aim of the present study was to examine the role of transmembrane protein 9 (TMEM9) in cell progression, such as cell growth, cell cycle, cell metastasis of hepatoma cells, and to discuss the TMEM9 gene‑encoding protein as a potential therapy target of hepatoma. RT-qPCR was performed to examine TMEM9 expression in tumor tissues and adjacent tissues of patients with liver cancer. siRNAs were used to interfere TMEM9 in HepG2 and 7721 cells. A CCK-8 assay was performed to evaluate cell growth at 24, 48 and 72 h. Cell cycle and apoptosis were analyzed using flow cytometry. Transwell assays were used to determine cell invasion, migration and adhesion. The results showed that TMEM9 was expressed abnormally in liver cancers. TMEM9 expression increased significantly in the 34 examined patients. TMEM9 knockdown inhibited proliferation in the HepG2 and 7721 cells. The flow cytometric analysis revealed that TMEM9 knockdown by RNA interference resulted in G1 arrest and induced apoptosis. Cell invasion, migration and adhesion ability were also decreased. Western blotting indicated that expression of the cell cycle‑related proteins CDK1, EIF3H, RPL10L, S100A10, CCNB1 and CCNB2 was significantly decreased. In conclusion, TMEM9 plays an important role in the cell growth of hepatoma cells.

The mouse IAPE endogenous retrovirus can infect cells through any of the five GPI-anchored Ephrin A proteins

The IAPE (Intracisternal A-type Particles elements with an Envelope) family of murine endogenous retroelements is present at more than 200 copies in the mouse genome. We had previously identified a single copy that proved to be fully functional, i.e. which can generate viral particles budding out of the cell and infectious on a series of cells, including human cells. We also showed that IAPE are the progenitors of the highly reiterated IAP elements. The latter are now strictly intracellular retrotransposons, due to the loss of the envelope gene and re-localisation of the associated particles in the course of evolution. In the present study we searched for the cellular receptor of the IAPE elements, by using a lentiviral human cDNA library and a pseudotype assay on transduced cells. We identified Ephrin A4, a GPI-anchored molecule involved in several developmental processes, as a receptor for the IAPE pseudotypes. We also found that the other 4 members of the Ephrin A family -but not those of the closely related Ephrin B family- were also able to mediate IAPE cell entry, thus significantly increasing the amount of possible cell types susceptible to IAPE infection. We show that these include mouse germline cells, as illustrated by immunohistochemistry experiments, consistent with IAPE genomic amplification by successive re-infection. We propose that the uncovered properties of the identified receptors played a role in the accumulation of IAPE elements in the mouse genome, and in the survival of a functional copy.

Wegener's granuloma harbors B lymphocytes with specificities against a proinflammatory transmembrane protein and a tetraspanin

Wegener's granulomatosis (WG) is a severe autoimmune disorder ranging from localized granulomatous disease to generalised anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis. A previous analysis of immunoglobulin heavy chain genes derived from tissue, i.e. Wegener's granuloma indicated selection and affinity maturation towards local antigen(s). The current study focused on determining the specificity of immunoglobulins from distinct B lymphocytes out of Wegener's granuloma. Four pairs of variable region immunoglobulin light and heavy chain genes, isolated before, were recombinantly expressed using the baculovirus/insect cell system. These immunoglobulins were then analysed for their antigenic target employing a protein macroarray based upon a human fetal brain tissue cDNA expression library. The lysosomal transmembrane protein 9B, a key regulator for TNFα activation, was identified as the putative antigenic target of two immunoglobulins and a tetraspanin, which might play a role in leukocyte activation and motility, was identified as the putative antigenic target of another one. Recombinant monoclonal antibodies out of Wegener's granuloma represent a new tool aiding in elucidation of its and WG immunopathogenesis.

The lysosomal transmembrane protein 9B regulates the activity of inflammatory signaling pathways

The intracellular signaling pathway by which tumor necrosis factor (TNF) induces its pleiotropic actions is well characterized and includes unique components as well as modules shared with other signaling pathways. In addition to the currently known key effectors, further molecules may however modulate the biological response to TNF. In our attempt to characterize novel regulators of the TNF signaling cascade, we have identified transmembrane protein 9B (TMEM9B, c11orf15) as an important component of TNF signaling and a module shared with the interleukin 1beta (IL-1beta) and Toll-like receptor (TLR) pathways. TMEM9B is a glycosylated protein localized in membranes of the lysosome and partially in early endosomes. The expression of TMEM9B is required for the production of proinflammatory cytokines induced by TNF, IL-1beta, and TLR ligands but not for apoptotic cell death triggered by TNF or Fas ligand. TMEM9B is essential in TNF activation of both the NF-kappaB and MAPK pathways. It acts downstream of RIP1 and upstream of the MAPK and IkappaB kinases at the level of the TAK1 complex. These findings indicate that TMEM9B is a key component of inflammatory signaling pathways and suggest that endosomal or lysosomal compartments regulate these pathways.