Function Of Transmembrane Proteins Research Articles

Overexpression of transmembrane protein 2 (TMEM2), a novel hyaluronidase, predicts poor prognosis in pancreatic ductal adenocarcinoma

BackgroundAbnormal metabolism of hyaluronan (HA), a major component of extracellular matrix, is a hallmark of cancer. Our previous studies have shown the importance of enzymes responsible for HA degradation in the aggressive phenotype of pancreatic ductal adenocarcinoma (PDAC). In the present study, we investigated the expression and function of transmembrane protein 2 (TMEM2), a recently identified HA-degrading enzyme, in PDAC. Materials & methodsWe used immunohistochemistry to investigate expression patterns of TMEM2 in archival tissues obtained from 100 patients with PDAC who underwent surgical resection from 1982 to 2012. The correlations between TMEM2 expression and clinicopathological variables, including survival, were determined using univariate and multivariate analyses. The effect of TMEM2 on proliferation and migratory ability (measured using transwell cell migration assay) of PDAC cells was determined by TMEM2 knockdown with small-interfering RNA (siRNA). ResultsImmunohistochemical analysis revealed high expression of TMEM2 in 22 (22%) of 100 patients. The overall survival was significantly shorter in patients with high TMEM2 expression than in those with low expression (P = 0.013). Multivariate analysis identified high TMEM2 expression as an independent factor predicting poor prognosis (P = 0.011). Unexpectedly, knockdown of TMEM2 resulted in increased migratory ability of PDAC cells, which was associated with increased expression of KIAA1199, a potent HA-degrading enzyme shown to enhance cell migration. ConclusionTMEM2 overexpression is associated with poor prognosis in PDAC patients. Targeted disruption of this molecule, however, could enhance the aggressiveness of PDAC cells through a possible interaction with KIAA1199.

Lipid sponge droplets as programmable synthetic organelles.

Living cells segregate molecules and reactions in various subcellular compartments known as organelles. Spatial organization is likely essential for expanding the biochemical functions of synthetic reaction systems, including artificial cells. Many studies have attempted to mimic organelle functions using lamellar membrane-bound vesicles. However, vesicles typically suffer from highly limited transport across the membranes and an inability to mimic the dense membrane networks typically found in organelles such as the endoplasmic reticulum. Here, we describe programmable synthetic organelles based on highly stable nonlamellar sponge phase droplets that spontaneously assemble from a single-chain galactolipid and nonionic detergents. Due to their nanoporous structure, lipid sponge droplets readily exchange materials with the surrounding environment. In addition, the sponge phase contains a dense network of lipid bilayers and nanometric aqueous channels, which allows different classes of molecules to partition based on their size, polarity, and specific binding motifs. The sequestration of biologically relevant macromolecules can be programmed by the addition of suitably functionalized amphiphiles to the droplets. We demonstrate that droplets can harbor functional soluble and transmembrane proteins, allowing for the colocalization and concentration of enzymes and substrates to enhance reaction rates. Droplets protect bound proteins from proteases, and these interactions can be engineered to be reversible and optically controlled. Our results show that lipid sponge droplets permit the facile integration of membrane-rich environments and self-assembling spatial organization with biochemical reaction systems.

Aromatic interactions with membrane modulate human BK channel activation.

Large-conductance potassium (BK) channels are transmembrane (TM) proteins that can be synergistically and independently activated by membrane voltage and intracellular Ca2+. The only covalent connection between the cytosolic Ca2+ sensing domain and the TM pore and voltage sensing domains is a 15-residue 'C-linker'. To determine the linker's role in human BK activation, we designed a series of linker sequence scrambling mutants to suppress potential complex interplay of specific interactions with the rest of the protein. The results revealed a surprising sensitivity of BK activation to the linker sequence. Combining atomistic simulations and further mutagenesis experiments, we demonstrated that nonspecific interactions of the linker with membrane alone could directly modulate BK activation. The C-linker thus plays more direct roles in mediating allosteric coupling between BK domains than previously assumed. Our results suggest that covalent linkers could directly modulate TM protein function and should be considered an integral component of the sensing apparatus.

Membrane-Ion Interactions Modify the Lipid Flip-Flop Dynamics of Biological Membranes: A Molecular Dynamics Study.

The asymmetric distribution of lipids in the cell membrane is maintained by protein transporters, and in the absence of proteins, by spontaneous flip-flop of lipids that involve the formation of transient pores in the membrane. The composition of the cell membranes influences the metabolism of the cell by modulating the function of transmembrane proteins, and flip-flop processes are therefore of key importance. Membranes are in direct contact with aqueous solutions, containing ions of different compositions that interact with the lipid head groups or cross the cell membrane through transmembrane channels. The impact of the ions on the lipid flip-flop rates is, however, an outstanding question. Here, we show that the flip-flop rate slows down significantly with the increasing valence of the cation, from minutes for monovalent cations (Na+, K+) to hours for divalent (Mg2+, Ca2+) or days for trivalent cations (Yb3+).

Self-Assembly of Mammalian-Cell Membranes on Bioelectronic Devices with Functional Transmembrane Proteins.

Transmembrane proteins (TMPs) regulate processes occurring at the cell surface and are essential gatekeepers of information flow across the membrane. TMPs are difficult to study, given the complex environment of the membrane and its influence on protein conformation, mobility, biomolecule interaction, and activity. For the first time, we create mammalian biomembranes supported on a transparent, electrically conducting polymer surface, which enables dual electrical and optical monitoring of TMP function in its native membrane environment. Mammalian plasma membrane vesicles containing ATP-gated P2X2 ion channels self-assemble on a biocompatible polymer cushion that transduces the changes in ion flux during ATP exposure. This platform maintains the complexity of the native plasma membrane, the fluidity of its constituents, and protein orientation critical to ion channel function. We demonstrate the dual-modality readout using microscopy to characterize protein mobility by single-particle tracking and sensing of ATP gating of P2X2 using electrical impedance spectroscopy. This measurement of TMP activity important for pain sensing, neurological activity, and sensory activity raises new possibilities for drug screening and biosensing applications.

In Situ Fluorescent and Photoacoustic Imaging of Golgi pH to Elucidate the Function of Transmembrane Protein 165

Golgi pH homeostasis affects many different biological processes, including glycosylation. Recent studies have demonstrated that transmembrane protein 165 (TMEM165) deficiency leads to Golgi glycosylation abnormalities by disturbing Golgi pH homeostasis. However, due to the lack of specific tools to measure Golgi pH in situ, evidence for TMEM165 involvement in H+ transport in the Golgi apparatus is still absent. Herein, the photoacoustic and fluorescent dual-mode probe CPH was developed for ratiometric detection of Golgi pH. CPH was proved to accumulate in the Golgi apparatus and reversibly image Golgi pH in real-time with high sensitivity in cells. Furthermore, we found that the absence of TMEM165 influenced H+ equilibrium and caused Golgi apparatus acidification. Our work provides strong evidence that TMEM165 regulates Golgi pH homeostasis. Moreover, we believe that CPH has the potential to be a practical tool to monitor Golgi pH in various biological processes.

Real-Time Analysis of Individual Ebola Virus Glycoproteins Reveals Pre-Fusion, Entry-Relevant Conformational Dynamics.

The Ebola virus (EBOV) envelope glycoprotein (GP) mediates the fusion of the virion membrane with the membrane of susceptible target cells during infection. While proteolytic cleavage of GP by endosomal cathepsins and binding of the cellular receptor Niemann-Pick C1 protein (NPC1) are essential steps for virus entry, the detailed mechanisms by which these events promote membrane fusion remain unknown. Here, we applied single-molecule Förster resonance energy transfer (smFRET) imaging to investigate the structural dynamics of the EBOV GP trimeric ectodomain, and the functional transmembrane protein on the surface of pseudovirions. We show that in both contexts, pre-fusion GP is dynamic and samples multiple conformations. Removal of the glycan cap and NPC1 binding shift the conformational equilibrium, suggesting stabilization of conformations relevant to viral fusion. Furthermore, several neutralizing antibodies enrich alternative conformational states. This suggests that these antibodies neutralize EBOV by restricting access to GP conformations relevant to fusion. This work demonstrates previously unobserved dynamics of pre-fusion EBOV GP and presents a platform with heightened sensitivity to conformational changes for the study of GP function and antibody-mediated neutralization.

Fe65 is the sole member of its family that mediates transcription regulated by the amyloid precursor protein.

The amyloid precursor protein (APP), a central molecule in Alzheimer's disease (AD), has physiological roles in cell adhesion and signaling, migration, neurite outgrowth and synaptogenesis. Intracellular adapter proteins mediate the function of transmembrane proteins. Fe65 (also known as APBB1) is a major APP-binding protein. Regulated intramembrane proteolysis (RIP) by γ-secretase releases the APP intracellular domain (AICD), together with the interacting proteins, from the membrane. We studied the impact of the Fe65 family (Fe65, and its homologs Fe65L1 and Fe65L2, also known as APBB2 and APBB3, respectively) on the nuclear signaling function of the AICD. All Fe65 family members increased amyloidogenic processing of APP, generating higher levels of β-cleaved APP stubs and AICD. However, Fe65 was the only family member supporting AICD translocation to nuclear spots and its transcriptional activity. Using a recently established transcription assay, we dissected the transcriptional activity of Fe65 and provide strong evidence that Fe65 represents a transcription factor. We show that Fe65 relies on the lysine acetyltransferase Tip60 (also known as KAT5) for nuclear translocation. Furthermore, inhibition of APP cleavage reduces nuclear Tip60 levels, but this does not occur in Fe65-knockout cells. The rate of APP cleavage therefore regulates the nuclear translocation of AICD-Fe65-Tip60 (AFT) complexes, to promote transcription by Fe65.

Age‑associated variation in the expression and function of TMEM16A calcium‑activated chloride channels in the cochlear stria vascularis of guinea pigs.

The present study was designed to investigate the expression and function of transmembrane protein 16 (TMEM16A), a calcium-activated chloride channel (CaCC), in the stria vascularis (SV) of the cochlea of guinea pigs at different ages, and to understand the role of CaCCs in the pathogenesis of presbycusis (age-related hearing loss), the most common type of sensorineural hearing loss that occurs with natural aging. Guinea pigs were divided into the following groups: 2 weeks (young group), 3 months (youth group), 1 year (adult group), D-galactose intervention (D-gal group; aging model induced by subcutaneous injection of D-galactose) and T16Ainh-A01 (intraperitoneal injection of 50 µg/kg/day TMEM16A inhibitor T16Ainh-A01 for 2 weeks). Differences in the hearing of guinea pigs between the various age groups were analyzed using auditory brainstem response (ABR), and immunofluorescence staining was performed to detect TMEM16A expression in the SV and determine the distribution. Reverse transcription-quantitative PCR and western blot analyses were conducted to detect the mRNA and protein levels of TMEM16A in SV in the different age groups. Morris water maze behavior analysis demonstrated that spatial learning ability and memory were damaged in the D-gal group. Superoxide dismutase activity and malondialdehyde content assays indicated that there was oxidative stress damage in the D-gal group. The ABR thresholds gradually increased with age, and the increase in the T16Ainh-A01 group was pronounced. Immunofluorescence analysis in the cochlear SV of guinea pigs in different groups revealed that expression of TMEM16A increased with increasing age (2 weeks to 1 year); fluorescence intensity was reduced in the D-gal model of aging. As the guinea pigs continued to mature, the protein and mRNA contents of TMEM16A in the cochlea SV increased gradually, but were decreased in the D-gal group. The findings indicated that CaCCs in the cochlear SV of guinea pigs were associated with the development of hearing in guinea pigs, and that downregulation of TMEM16A may be associated with age-associated hearing loss.

Directed Insertion of Light-Activated Proteorhodopsin into Asymmetric Polymersomes from an ABC Block Copolymer.

Nanoscopic artificial vesicles containing functional protein transporters are fundamental for synthetic biology. Energy-providing modules, such as proton pumps, are a basis for simple nanoreactors. We report on the first insertion of a functional transmembrane protein into asymmetric polymersomes from an ABC triblock copolymer. The polymer with the composition poly(ethylene glycol)-poly(diisopropylaminoethyl methacrylate)-poly(styrenesulfonate) (PEG-PDPA-PSS) was synthesized by sequential controlled radical polymerization. PEG and PSS are two distinctively different hydrophilic blocks, allowing for a specific orientation of our protein, the light-activated proton pump proteorhodopsin (PR), into the final proteopolymersome. A very interesting aspect of the PEG-PDPA-PSS triblock copolymers is that it allowed for simultaneous vesicle formation and oriented insertion of PR simply by adjusting the pH. The intrinsic positive charge of PR's intracellular surface was enhanced by a His-tag, which aligns readily with the negative charges of the PSS on the outside of the polymersomes. The directed insertion of PR was confirmed by a light-dependent pH change of the proteopolymersome solution, indicating the intended orientation. We have hereby demonstrated the first successful oriented insertion of a proton pump into an artificial asymmetric membrane.

Tools for Low-Dimensional Chemistry.

Many biological mechanisms can be considered to be low-dimensional systems: their function is determined by molecular objects of reduced dimensionality. Bacterial photosynthesis is a very good example: the photosynthetic pathway is contained within nano-objects (vesicles) whose function is determined by the numbers and nanoscale organization of membrane proteins and by the ratios of the different types of protein that they contain. Systems biology has provided computational models for studying these processes, but there is a need for experimental platforms with which to test their predictions. This Invited Feature Article reviews recent work on the development of tools for the reconstruction of membrane processes on solid surfaces. Photochemical methods provide a powerful, versatile means for the organization of molecules and membranes across length scales from the molecular to the macroscopic. Polymer brushes are highly effective supports for model membranes and versatile functional and structural components in low-dimensional systems. The incorporation of plasmonic elements facilitates enhanced measurement of spectroscopic properties and provides an additional design strategy via the exploitation of quantum optical phenomena. A low-dimensional system that incorporates functional transmembrane proteins and a mechanism for the in situ measurement of proton transport is described.

Ricardo Miledi - an outstanding neurophysiologist of 20th-21st centuries (1927-2017)

Ricardo Miledi (16.09.1927-18.12.2017) is an outstanding neurophysiologist and biophysicist who made a great contribution to the study of synaptic transmission functions. He proved the key role of сalcium ions in the release of neuromediators, developed methods of receptor expression and membrane fragments integration into large oocytes that provided huge possibilities for thousands of researchers to study subtle mechanisms of transmembrane proteins function in norm and pathology. Ricardo Miledi received his MD degree in the National Autonomous University of Mexico and in 1954 he defensed his dissertation on the study of electrical nature of cardiac fibrillation in the National Institute of Cardiology (Mexico). In 1956-1958 he underwent training in Canberra Health Research Institute (Australia) in the laboratory headed by John Eccles (Nobel Prize 1963). In 1958 R. Miledi was invited to the Department of biophysics of University College London where in cooperation with Bernard Katz (Nobel Prize 1970) made a number of important discoveries in the analysis of acetylcholine receptor expression in denervated mucle; determination of the role of calcium in neuromediators release; analysis of membrane noise on neuromediator application to neuromuscular synapses; study of the effect of antibodies from patients with myasthenia gravis on neuromuscular transmission. In the early 1980s Ricardo Miledi implemented the method of functional expression in Xenopus frog oocytes of receptors and ion channels from messenger ribonucleic acid (mRNA). His heritage running the gamut is presented in more than 500 articles.

Role of the Lipid Membrane on the Oligomeric Assembly and Function of Proteorhodopsin

Transmembrane proteins are biomolecules in the lipid bilayers of cells that accomplish critical tasks such as sensing, transport, and enzymatic catalysis. Previous studies indicated that transmembrane proteins could tune their function by forming oligomeric complexes. However, it remains unclear whether oligomerization modulates function significantly more than other factors in native-like lipid bilayer environments. In this study, we aim to elucidate how protein oligomerization and other environmental factors tune the function of transmembrane proteins in lipid membrane systems. Proteorhodopsin (PR), a model transmembrane protein, was used to examine this functional modulation because of its assessable light-responsive proton transferring functions. Our results showed that oligomerization remained an important factor in tuning PR's functions in a liposome environment. Analyses of PR photocycle kinetics measured by a time-resolved optical absorbance technique indicated that faster photocycle kinetics can be observed with the monomeric PR E50Q mutant than with the pentameric/hexameric wild type PR in a liposome environment. These results concur with what has been observed for surfactant-solubilized PR. Interestingly, the pKa of the PR D97 residue that determines the pH at which proton transport switches direction was insensitive to oligomeric distribution in the lipid bilayer environment, but was sensitive to changes in the hydration gradient across lipid bilayers. Therefore, our work suggested that besides oligomerization, the lipid hydration gradient could play a role in modulating PR's function. The new understanding developed here is expected to yield guidelines for functional studies of other therapeutically relevant transmembrane proteins.

DNA Origami Scaffolds as Templates for Functional Tetrameric Kir3 K+ Channels.

In native systems, scaffolding proteins play important roles in assembling proteins into complexes to transduce signals. This concept is yet to be applied to the assembly of functional transmembrane protein complexes in artificial systems. To address this issue, DNA origami has the potential to serve as scaffolds that arrange proteins at specific positions in complexes. Herein, we report that Kir3 K+ channel proteins are assembled through zinc-finger protein (ZFP)-adaptors at specific locations on DNA origami scaffolds. Specific binding of the ZFP-fused Kir3 channels and ZFP-based adaptors on DNA origami were confirmed by atomic force microscopy and gel electrophoresis. Furthermore, the DNA origami with ZFP binding sites nearly tripled the K+ channel current activity elicited by heterotetrameric Kir3 channels in HEK293T cells. Thus, our method provides a useful template to control the oligomerization states of membrane protein complexes in vitro and in living cells.

DNA Origami Scaffolds as Templates for Functional Tetrameric Kir3 K+ Channels

AbstractIn native systems, scaffolding proteins play important roles in assembling proteins into complexes to transduce signals. This concept is yet to be applied to the assembly of functional transmembrane protein complexes in artificial systems. To address this issue, DNA origami has the potential to serve as scaffolds that arrange proteins at specific positions in complexes. Herein, we report that Kir3 K+ channel proteins are assembled through zinc‐finger protein (ZFP)‐adaptors at specific locations on DNA origami scaffolds. Specific binding of the ZFP‐fused Kir3 channels and ZFP‐based adaptors on DNA origami were confirmed by atomic force microscopy and gel electrophoresis. Furthermore, the DNA origami with ZFP binding sites nearly tripled the K+ channel current activity elicited by heterotetrameric Kir3 channels in HEK293T cells. Thus, our method provides a useful template to control the oligomerization states of membrane protein complexes in vitro and in living cells.

Molecular physiology and pathophysiology of stromal interaction molecules.

Ca2+ release from the endoplasmic reticulum is an important component of Ca2+ signal transduction that controls numerous physiological processes in eukaryotic cells. Release of Ca2+ from the endoplasmic reticulum is coupled to the activation of store-operated Ca2+ entry into cells. Store-operated Ca2+ entry provides Ca2+ for replenishing depleted endoplasmic reticulum Ca2+ stores and a Ca2+ signal that regulates Ca2+-dependent intracellular biochemical events. Central to connecting discharge of endoplasmic reticulum Ca2+ stores following G protein-coupled receptor activation with the induction of store-operated Ca2+ entry are stromal interaction molecules (STIM1 and STIM2). These highly homologous endoplasmic reticulum transmembrane proteins function as sensors of the Ca2+ concentration within the endoplasmic reticulum lumen and activators of Ca2+ release-activated Ca2+ channels. Emerging evidence indicates that in addition to their role in Ca2+ release-activated Ca2+ channel gating and store-operated Ca2+ entry, STIM1 and STIM2 regulate other cellular signaling events. Recent studies have shown that disruption of STIM expression and function is associated with the pathogenesis of several diseases including autoimmune disorders, cancer, cardiovascular disease, and myopathies. Here, we provide an overview of the latest developments in the molecular physiology and pathophysiology of STIM1 and STIM2. Impact statement Intracellular Ca2+ signaling is a fundamentally important regulator of cell physiology. Recent studies have revealed that Ca2+-binding stromal interaction molecules (Stim1 and Stim2) expressed in the membrane of the endoplasmic reticulum (ER) are essential components of eukaryote Ca2+ signal transduction that control the activity of ion channels and other signaling effectors present in the plasma membrane. This review summarizes the most recent information on the molecular physiology and pathophysiology of stromal interaction molecules. We anticipate that the work presented in our review will provide new insights into molecular interactions that participate in interorganelle signaling crosstalk, cell function, and the pathogenesis of human diseases.

Cell membranes. Molecular lipid therapy

Membrane lipids, due to diverse molecular structures, electric charge and different functional characteristic, have a profound role in multiple cytophysiological processes. A better understanding of the membrane structure and changes of its function in a wide range of diseases gave rise to a new approach termed membrane lipid therapy and directed to modifying the membranes. The strategies directed to membrane involve a direct regulation of membrane lipid composition that causes a change of the transmembrane protein function and modifies the organization of membrane microdomains, or regulation of enzyme activity and gene expression to alter membrane lipid composition. Membrane therapy assumes the use of new molecules specifically designed to modify lipid composition and function of abnormal signaling proteins. Therefore, modifications of the lipid composition and organization of membrane microdomains become pharmacological targets to reverse pathological changes in the profile of enzymatically and non-enzymatically generated lipid derivatives or to modify signaling pathways in the cell. The present monography is an update of the canonical membrane model by Singer-Nicolson and describes the therapeutic targets related to the regulation of the composition and organization of the lipids in the plasma membrane.

ω-3 Long Chain Polyunsaturated Fatty Acids as Sensitizing Agents and Multidrug Resistance Revertants in Cancer Therapy.

Chemotherapy efficacy is strictly limited by the resistance of cancer cells. The ω-3 long chain polyunsaturated fatty acids (ω-3 LCPUFAs) are considered chemosensitizing agents and revertants of multidrug resistance by pleiotropic, but not still well elucidated, mechanisms. Nowadays, it is accepted that alteration in gene expression, modulation of cellular proliferation and differentiation, induction of apoptosis, generation of reactive oxygen species, and lipid peroxidation are involved in ω-3 LCPUFA chemosensitizing effects. A crucial mechanism in the control of cell drug uptake and efflux is related to ω-3 LCPUFA influence on membrane lipid composition. The incorporation of docosahexaenoic acid in the lipid rafts produces significant changes in their physical-chemical properties affecting content and functions of transmembrane proteins, such as growth factors, receptors and ATP-binding cassette transporters. Of note, ω-3 LCPUFAs often alter the lipid compositions more in chemoresistant cells than in chemosensitive cells, suggesting a potential adjuvant role in the treatment of drug resistant cancers.

Membrane curvature regulates ligand-specific membrane sorting of GPCRs in living cells.

The targeted spatial organization (sorting) of Gprotein-coupled receptors (GPCRs) is essential for their biological function and often takes place in highly curved membrane compartments such as filopodia, endocytic pits, trafficking vesicles or endosome tubules. However, the influence of geometrical membrane curvature on GPCR sorting remains unknown. Here we used fluorescence imaging to establish a quantitative correlation between membrane curvature and sorting of three prototypic class A GPCRs (the neuropeptide Y receptor Y2, the β1 adrenergic receptor and the β2 adrenergic receptor) in living cells. Fitting of a thermodynamic model to the data enabled us to quantify how sorting is mediated by an energetic drive to match receptor shape and membrane curvature. Curvature-dependent sorting was regulated by ligands in a specific manner. We anticipate that this curvature-dependent biomechanical coupling mechanism contributes to the sorting, trafficking and function of transmembrane proteins in general.

Upregulation and biological function of transmembrane protein 119 in osteosarcoma

Osteosarcoma is suggested to be caused by genetic and molecular alterations that disrupt osteoblast differentiation. Recent studies have reported that transmembrane protein 119 (TMEM119) contributes to osteoblast differentiation and bone development. However, the level of TMEM119 expression and its roles in osteosarcoma have not yet been elucidated. In the present study, TMEM119 mRNA and protein expression was found to be up-regulated in osteosarcoma compared with normal bone cyst tissues. The level of TMEM119 protein expression was strongly associated with tumor size, clinical stage, distant metastasis and overall survival time. Moreover, gene set enrichment analysis (GSEA) of the Gene Expression Omnibus (GEO) GSE42352 dataset revealed TMEM119 expression in osteosarcoma tissues to be positively correlated with cell cycle, apoptosis, metastasis and TGF-β signaling. We then knocked down TMEM119 expression in U2OS and MG63 cells using small interfering RNA, which revealed that downregulation of TMEM119 could inhibit the proliferation of osteosarcoma cells by inducing cell cycle arrest in G0/G1 phase and apoptosis. We also found that TMEM119 knockdown significantly inhibited cell migration and invasion, and decreased the expression of TGF-β pathway-related factors (BMP2, BMP7 and TGF-β). TGF-β application rescued the inhibitory effects of TMEM119 knockdown on osteosarcoma cell migration and invasion. Further in vitro experiments with a TGF-β inhibitor (SB431542) or BMP inhibitor (dorsomorphin) suggested that TMEM119 significantly promotes cell migration and invasion, partly through TGF-β/BMP signaling. In conclusion, our data support the notion that TMEM119 contributes to the proliferation, migration and invasion of osteosarcoma cells, and functions as an oncogene in osteosarcoma.