Epithelial membrane protein 2 regulates sphingosylphosphorylcholine-induced keratin 8 phosphorylation and reorganization: Changes of PP2A expression by interaction with alpha4 and caveolin-1 in lung cancer cells

Gene knockout inference with variational graph autoencoder learning single-cell gene regulatory networks

In this paper, we introduce Gene Knockout Inference (GenKI), a virtual knockout (KO) tool for gene function prediction using single-cell RNA sequencing (scRNA-seq) data in the absence of KO samples when only wild-type (WT) samples are available. Without using any information from real KO samples, GenKI is designed to capture shifting patterns in gene regulation caused by the KO perturbation in an unsupervised manner and provide a robust and scalable framework for gene function studies. To achieve this goal, GenKI adapts a variational graph autoencoder (VGAE) model to learn latent representations of genes and interactions between genes from the input WT scRNA-seq data and a derived single-cell gene regulatory network (scGRN). The virtual KO data is then generated by computationally removing all edges of the KO gene-the gene to be knocked out for functional study-from the scGRN. The differences between WT and virtual KO data are discerned by using their corresponding latent parameters derived from the trained VGAE model. Our simulations show that GenKI accurately approximates the perturbation profiles upon gene KO and outperforms the state-of-the-art under a series of evaluation conditions. Using publicly available scRNA-seq data sets, we demonstrate that GenKI recapitulates discoveries of real-animal KO experiments and accurately predicts cell type-specific functions of KO genes. Thus, GenKI provides an in-silico alternative to KO experiments that may partially replace the need for genetically modified animals or other genetically perturbed systems.

Epithelial membrane protein 2 (EMP2): A systematic review of its implications in pathogenesis

OBJECTIVES

Epithelial membrane protein 2 (EMP2) is a cell surface protein composed of approximately 160 amino acids and encoded by the growth arrest-specific 3 (GAS3)/peripheral myelin protein 22 kDa (PMP22) gene family. Although EMP2 expression has been investigated in several diseases, much remains unknown regarding its mechanism of action and the extent of its role in pathogenesis. Our aim was to perform a systematic review on the involvement of EMP2 in disease processes and the current usage of anti-EMP2 therapies.

METHODS

A Boolean search of the English-language medical literature was performed. PubMed, Scopus, Cochrane, and Web of Science were used to identify relevant citations. This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

52 studies met the inclusion criteria for qualitative analysis. Of those, 28 (53.8%) were human-only studies, 11 (21.2%) were animal-only studies, and 13 (25%) studies included both human and animal models. Furthermore, 34 (65.4%) studies focused on EMP2's role in neoplasms, while the remaining 18 (34.6%) articles evaluated its role in other pathologies.

CONCLUSION

Overall, the evidence suggests the mechanisms of action of EMP2 are context dependent. Promising results have been produced by utilizing EMP2 as a biomarker and therapeutic target. More studies are warranted to better understand the mechanism and comprehend the role of EMP2 in the pathogenesis of diseases.

Unraveling the structures, functions and mechanisms of epithelial membrane protein family in human cancers

Peripheral myelin protein 22 (PMP22) and epithelial membrane proteins (EMP-1, -2, and -3) belong to a small hydrophobic membrane protein subfamily, with four transmembrane structures. PMP22 and EMPs are widely expressed in various tissues and play important roles in cell growth, differentiation, programmed cell death, and metastasis. PMP22 presents its highest expression in the peripheral nerve and participates in normal physiological and pathological processes of the peripheral nervous system. The progress of molecular genetics has shown that the genetic changes of the PMP22 gene, including duplication, deletion, and point mutation, are behind various hereditary peripheral neuropathies. EMPs have different expression patterns in diverse tissues and are closely related to the risk of malignant tumor progression. In this review, we focus on the four members in this protein family which are related to disease pathogenesis and discuss gene mutations and post-translational modification of them. Further research into the interactions between structural alterations and function of PMP22 and EMPs will help understand their normal physiological function and role in diseases and might contribute to developing novel therapeutic tools.

Loss of EMP2 Inhibits Melanogenesis of MNT1 Melanoma Cells via Regulation of TRP-2

Melanogenesis is the production of melanin from tyrosine by a series of enzyme-catalyzed reactions, in which tyrosinase and DOPA oxidase play key roles. The melanin content in the skin determines skin pigmentation. Abnormalities in skin pigmentation lead to various skin pigmentation disorders. Recent research has shown that the expression of EMP2 is much lower in melanoma than in normal melanocytes, but its role in melanogenesis has not yet been elucidated. Therefore, we investigated the role of EMP2 in the melanogenesis of MNT1 human melanoma cells. We examined TRP-1, TRP-2, and TYR expression levels during melanogenesis in MNT1 melanoma cells by gene silencing of EMP2. Western blot and RT-PCR results confirmed that the expression levels of TYR and TRP-2 were decreased when EMP2 expression was knocked down by EMP2 siRNA in MNT1 cells, and these changes were reversed when EMP2 was overexpressed. We verified the EMP2 gene was knocked out of the cell line (EMP2 CRISPR/Cas9) by using a CRISPR/Cas9 system and found that the expression levels of TRP-2 and TYR were significantly lower in the EMP2 CRISPR/Cas9 cell lines. Loss of EMP2 also reduced migration and invasion of MNT1 melanoma cells. In addition, the melanosome transfer from the melanocytes to keratinocytes in the EMP2 KO cells cocultured with keratinocytes was reduced compared to the cells in the control coculture group. In conclusion, these results suggest that EMP2 is involved in melanogenesis via the regulation of TRP-2 expression.

Epithelial Membrane Protein 2 Suppresses Non-Small Cell Lung Cancer Cell Growth by Inhibition of MAPK Pathway

Epithelial membrane proteins (EMP1-3) are involved in epithelial differentiation and carcinogenesis. Dysregulated expression of EMP2 was observed in various cancers, but its role in human lung cancer is not yet clarified. In this study, we analyzed the expression of EMP1-3 and investigated the biological function of EMP2 in non-small cell lung cancer (NSCLC). The results showed that lower expression of EMP1 was significantly correlated with tumor size in primary lung tumors (p = 0.004). Overexpression of EMP2 suppressed tumor cell growth, migration, and invasion, resulting in a G1 cell cycle arrest, with knockdown of EMP2 leading to enhanced cell migration, related to MAPK pathway alterations and disruption of cell cycle regulatory genes. Exosomes isolated from transfected cells were taken up by tumor cells, carrying EMP2-downregulated microRNAs (miRNAs) which participated in regulation of the tumor microenvironment. Our data suggest that decreased EMP1 expression is significantly related to increased tumor size in NSCLC. EMP2 suppresses NSCLC cell growth mainly by inhibiting the MAPK pathway. EMP2 might further affect the tumor microenvironment by regulating tumor microenvironment-associated miRNAs.

Ethacrynic acid, a loop diuretic, suppresses epithelial-mesenchymal transition of A549 lung cancer cells via blocking of NDP-induced WNT signaling

Lung cancer is one of the leading causes of death in cancer patients. Epithelial-mesenchymal transition (EMT) plays an important role in lung cancer progression. Therefore, for lung cancer treatment, it is crucial to find substances that inhibit EMT. Ethacrynic acid (ECA) is a diuretic that inhibits cellular ion flux and exerts anticancer effects. However, the effects of ECA on EMT in lung cancer remain unclear. We examined the effects of ECA on sphingosylphosphorylcholine (SPC) or TGF-β1-induced EMT process in A549 and H1299 cells via reverse transcription polymerase chain reaction and Western blotting. We found that ECA inhibited SPC-induced EMT and SPC-induced WNT signalling in EMT. We observed that SPC induces the expression of NDP [Norrie disease protein] and WNT-2, whereas ECA suppressed their expression. SPC-induced WNT activation, EMT, migration, and invasion were suppressed by NDP small-interfering RNA (siNDP), but NDP overexpression (pNDP) enhanced these events in A549 and H1299 cells. Accordingly, NDP expression may influence lung cancer prognosis. In summary, our results revealed that ECA inhibited SPC or TGF-β1-induced EMT in A549 and H1299 lung cancer cells by downregulating NDP expression and inhibiting WNT activation. Therefore, ECA might be a new drug candidate for lung cancer treatment.

Role of Sphingosylphosphorylcholine in Tumor and Tumor Microenvironment

Sphingosylphosphorylcholine (SPC) is a unique type of lysosphingolipid found in some diseases, and has been studied in cardiovascular, neurological, and inflammatory phenomena. In particular, SPC’s studies on cancer have been conducted mainly in terms of effects on cancer cells, and relatively little consideration has been given to aspects of tumor microenvironment. This review summarizes the effects of SPC on cancer and tumor microenvironment, and presents the results and prospects of modulators that regulate the various actions of SPC.

Transcriptional control of lung alveolar type 1 cell development and maintenance by NK homeobox 2-1

The extraordinarily thin alveolar type 1 (AT1) cell constitutes nearly the entire gas exchange surface and allows passive diffusion of oxygen into the blood stream. Despite such an essential role, the transcriptional network controlling AT1 cells remains unclear. Using cell-specific knockout mouse models, genomic profiling, and 3D imaging, we found that NK homeobox 2-1 (Nkx2-1) is expressed in AT1 cells and is required for the development and maintenance of AT1 cells. Without Nkx2-1, developing AT1 cells lose 3 defining features-molecular markers, expansive morphology, and cellular quiescence-leading to alveolar simplification and lethality. NKX2-1 is also cell-autonomously required for the same 3 defining features in mature AT1 cells. Intriguingly, Nkx2-1 mutant AT1 cells activate gastrointestinal (GI) genes and form dense microvilli-like structures apically. Single-cell RNA-seq supports a linear transformation of Nkx2-1 mutant AT1 cells toward a GI fate. Whole lung ChIP-seq shows NKX2-1 binding to 68% of genes that are down-regulated upon Nkx2-1 deletion, including 93% of known AT1 genes, but near-background binding to up-regulated genes. Our results place NKX2-1 at the top of the AT1 cell transcriptional hierarchy and demonstrate remarkable plasticity of an otherwise terminally differentiated cell type.

Genetic Deletion of Emp2 Does Not Cause Proteinuric Kidney Disease in Mice

Nephrotic syndrome is one of the most common glomerular diseases in children and can be classified on the basis of steroid responsiveness. While multiple genetic causes have been discovered for steroid resistant nephrotic syndrome, the genetics of steroid sensitive nephrotic syndrome remains elusive. Mutations in Epithelial Membrane Protein 2 (EMP2), a member of the GAS3/PMP22 tetraspan family of proteins, were recently implicated as putative monogenic cause of steroid sensitive nephrotic syndrome. We investigated this hypothesis by developing Emp2 reporter and knockout mouse models. In lacZ reporter mice (engineered to drive expression of the enzyme β-galactosidase under the control of the endogenous murine Emp2 promoter), Emp2 promoter activity was not observed in podocytes but was particularly prominent in medium- and large-caliber arterial vessels in the kidney and other tissues where it localizes specifically in vascular smooth muscle cells (vSMCs) but not in the endothelium. Strong Emp2 expression was also found in non-vascular smooth muscle cells found in other organs like the stomach, bladder, and uterus. Global and podocyte-specific Emp2 knockout mice were viable and did not develop nephrotic syndrome showing no evidence of abnormal glomerular histology or ultrastructure. Altogether, our results do not support that loss of function of EMP2 represent a monogenic cause of proteinuric kidney disease. However, the expression pattern of Emp2 indicates that it may be relevant in smooth muscle function in various organs and tissues including the vasculature.

YDJC Induces Epithelial-Mesenchymal Transition via Escaping from Interaction with CDC16 through Ubiquitination of PP2A

Lung cancer is the number 1 cause of cancer-related casualties in the world. Appropriate diagnostic markers and novel targets for lung cancer are needed. Chitooligosaccharide deacetylase homolog (YDJC) catalyzes the deacetylation of acetylated carbohydrates; however, the role of YDJC in lung cancer progression has yet to be studied. A549 lung cancer orthotopic mouse model was used for mice experiments. We found that YDJC overexpression contributes to lung cancer progression in an orthotopic mouse model. Long-term treatment (48 h) induces YDJC expression in sphingosylphosphorylcholine (SPC)-induced epithelial-mesenchymal transition (EMT). Gene silencing of YDJC (siYDJC) reduced N-cadherin expression and increased E-cadherin expression in SPC-induced EMT. Overexpression of YDJC reverses them but overexpression of the deacetylase deficient mutant YDJCD13A could not. Interestingly, overexpression of CDC16, a YDJC binding partner, suppressed EMT. ERK2 is activated in siCDC16-induced EMT. YDJC overexpression reduces expression of protein phosphatase 2A (PP2A), whereas CDC16 overexpression induces PP2A expression. YDJC overexpression induced ubiquitination of PP2A but YDJCD13A could not. CDC16 overexpression increased the ubiquitination of YDJC. These results suggest that YDJC contributes to the progression of lung cancer via enhancing EMT by inducing the ubiquitination of PP2A. Therefore, YDJC might be a new target for antitumor therapy against lung cancer.

Novel involvement of RhebL1 in sphingosylphosphorylcholine-induced keratin phosphorylation and reorganization: Binding to and activation of AKT1

Sphingosylphosphorylcholine induces keratin phosphorylation and reorganization, and increases viscoelasticity of metastatic cancer cells such as PANC-1 cells. However, the mechanism involved in sphingosylphosphorylcholine-induced keratin phosphorylation and reorganization is largely unknown. Sphingosylphosphorylcholine dose- and time-dependently induces the expression of RhebL1. The involvement of RhebL1 in sphingosylphosphorylcholine-induced events including keratin 8 (K8) phosphorylation, reorganization, migration and invasion was examined. Gene silencing of RhebL1 suppressed the sphingosylphosphorylcholine-induced events and overexpression of RhebL1 enhanced those events even without sphingosylphosphorylcholine treatment. We examined whether the G protein function of RhebL1 induces K8 phosphorylation using constitutively active RhebL1Q64L and dominant negative RhebL1D60K. G protein activity of RhebL1 is involved in sphingosylphosphorylcholine-induced K8 phosphorylation. We found that RhebL1 binds and activates AKT1. G protein activity of RhebL1 is involved in the binding and activation of AKT1. MK2206 (AKT inhibitor) and gene silencing of AKT1 inhibited the sphingosylphosphorylcholine-induced events, whereas overexpression of activated-AKT1 induced K8 phosphorylation, reorganization, migration and invasion even without sphingosylphosphorylcholine treatment.

The collective results indicate that RhebL1 is involved in sphingosylphosphorylcholine-induced events in A549 lung cancer cells via binding to AKT1 leading to activation of it. These results suggest that suppression of RhebL1 or inhibition of RhebL1′s binding to AKT1 might be a novel way that prevents changes in the physical properties of metastatic cancer cells.

Epithelial membrane protein 2: Molecular interactions and clinical implications

Epithelial membrane protein 2 (EMP2) is a cell surface protein that has recently emerged as an object of neuro-oncological interest due to its potential to be utilized as a biomarker and target for antibody therapies. Preclinical studies have demonstrated that EMP2 is associated with disease prognosis in a number of human cancers, including glioblastoma. The four large extracellular domains of EMP2 and its association with the extracellular matrix makes it an attractive target for future cancer therapies. Translational research suggests that EMP2 may be targeted with antibodies to improve tumor control and survival in a variety of murine models and cancer types. However, in order to translate these preclinical findings into the clinic, future research will need to focus on elucidating the role EMP2 in the normal human body by better understanding its molecular and chemical interactions. The focus of this review is to provide a comprehensive insight into current research endeavors, discuss the potential for clinically translatable applications, and predict the future directions of such research.