TMED2 promotes epithelial ovarian cancer growth

TMED3 stabilizes SMAD2 by counteracting NEDD4-mediated ubiquitination to promote ovarian cancer

Ovarian cancer is a major cause of death among cancer patients. Recent research has shown that the transmembrane emp24 domain (TMED) protein family plays a role in the progression of various types of cancer. In this study, we investigated the expression of TMED3 in ovarian cancer tumors compared to nontumor tissues using immunohistochemical staining. We found that TMED3 was overexpressed in ovarian cancer tumors, and its high expression was associated with poor disease-free and overall survival. To understand the functional implications of TMED3 overexpression in ovarian cancer, we conducted experiments to knockdown TMED3 using short hairpin RNA (shRNA). We observed that TMED3 knockdown resulted in reduced cell viability and migration, as well as increased cell apoptosis. Additionally, in subcutaneous xenograft models in BALB-c nude mice, TMED3 knockdown inhibited tumor growth. Further investigation revealed that SMAD family member 2 (SMAD2) was a downstream target of TMED3, driving ovarian cancer progression. TMED3 stabilized SMAD2 by inhibiting the E3 ligase NEDD4-mediated ubiquitination of SMAD2. To confirm the importance of SMAD2 in TMED3-mediated ovarian cancer, we performed functional rescue experiments and found that SMAD2 played a critical role in this process. Moreover, we discovered that the PI3K-AKT pathway was involved in the promoting effects of TMED3 overexpression on ovarian cancer cells. Overall, our study identifies TMED3 as a prognostic indicator and tumor promoter in ovarian cancer. Its function is likely mediated through the regulation of the SMAD2 and PI3K-AKT signaling pathway. These findings contribute to our understanding of the molecular mechanisms underlying ovarian cancer progression and provide potential targets for therapeutic intervention.

TMED family genes and their roles in human diseases

The members of the transmembrane emp24 domain-containing protein (TMED) family are summarized in human as four subfamilies, α (TMED 4, 9), β (TMED 2), γ (TMED1, 3, 5, 6, 7) and δ (TMED 10), with a total of nine members, which are important regulators of intracellular protein transport and are involved in normal embryonic development, as well as in the pathogenic processes of many human diseases. Here we systematically review the composition, structure and function of TMED family members, and describe the progress of TMED family in human diseases, including malignancies (head and neck tumors, lung cancer, breast cancer, ovarian cancer, endometrial cancer, gastrointestinal tumors, urological tumors, osteosarcomas, etc.), immune responses, diabetes, neurodegenerative diseases, and nonalcoholic fatty liver disease, dilated cardiomyopathy, mucin 1 nephropathy (MKD), and desiccation syndrome (SS). Finally, we discuss and prospect the potential of TMED for disease prognosis prediction and therapeutic targeting, with a view to laying the foundation for therapeutic research based on TMED family causative genes.

TMED2 Induces Cisplatin Resistance in Breast Cancer via Targeting the KEAP1-Nrf2 Pathway

OBJECTIVE

Cisplatin is the first-line treatment for breast cancer, but it faces challenges of drug resistance. This study investigated new molecular mechanisms underlying cisplatin resistance in breast cancer.

METHODS

We analyzed sequencing data from the TCGA database to identify potential associations between transmembrane emp24 protein transport domain containing 2 (TMED2) and breast cancer. Western blotting, real-time PCR, CCK-8, and TUNEL assays were used to measure the effects and molecular mechanism of TMED2 on cisplatin resistance in MCF-7 and MDA-MB-231 cell lines.

RESULTS

TMED2 was overexpressed in breast cancer and associated with poor prognosis. TMED2 increased cisplatin resistance in breast cancer cells in vitro via promoting ubiquitination of Kelch-like ECH-associated protein 1 (KEAP1), relieving inhibition of KEAP1 on nuclear factor erythroid 2-related factor 2 (Nrf2), and increasing expression of downstream drug resistance related genes, such as heme oxygenase 1 (HO-1) and NAD (P) H quinone oxidoreductase 1 (NQO1).

CONCLUSION

We identified a new molecular mechanism by which TMED2 affects cisplatin resistance in breast cancer. Our results provide theoretical guidance for future clinical applications.

VIRMA facilitates intrahepatic cholangiocarcinoma progression through epigenetic augmentation of TMED2 and PARD3B mRNA stabilization

BACKGROUND

N6-methyladenine modification of RNA, a critical component of the regulatory role at the post-transcriptional level, has a crucial effect on tumor development and progression. vir-Like m6A methyltransferase associated (VIRMA) has been recently discovered as an N6-methyladenine methyltransferase; however, its specific role in intrahepatic cholangiocarcinoma (ICC) remains to be investigated in-depth.

METHODS

VIRMA expression and its association with clinicopathological characteristics were evaluated using The Cancer Genome Atlas (TCGA) dataset and tissue microarrays. In vivo and in vitro assays were performed to determine the role of VIRMA in ICC proliferation and metastasis. The underlying mechanism by which VIRMA influences ICC was clarified by RNA sequencing (RNA-seq), methylated RNA immunoprecipitation sequencing (MeRIP-seq), SLAM sequencing (SLAM-seq), RNA immunoprecipitation, a luciferase reporter assay, and chromatin immunoprecipitation assay.

RESULTS

VIRMA showed high expression in ICC tissues, and this finding predicted a dismal prognostic outcome. The high expression of VIRMA in ICC was due to the demethylation of H3K27me3 modification in the promoter region. Functionally, VIRMA is required for the endothelial-mesenchymal transition (EMT) process in ICC cells, as shown by multiple ICC models in in vitro and in vivo experiments. Mechanistically, multi-omics analysis using ICC cells demonstrated that TMED2 and PARD3B were the direct downstream target of VIRMA. The methylated TMED2 and PARD3B transcripts were directly recognized by HuR, which exerted stabilizing effects on its bound RNA. VIRMA-induced expression of TMED2 and PARD3B activated the Akt/GSK/β-catenin and MEK/ERK/Slug signaling pathways, thereby promoting ICC proliferation and metastasis.

CONCLUSIONS

The present study showed that VIRMA plays a critical role in ICC development by stabilizing TMED2 and PARD3B expression through the m6A-HuR-mediated mechanism. Thus, demonstrating VIRMA and its pathway as candidate therapeutic targets for ICC treatment.

TMED3 promotes the development of malignant melanoma by targeting CDCA8 and regulating PI3K/Akt pathway

BACKGROUND

Transmembrane emp24 domain containing (TMED) proteins are known to play pivotal roles in normal development, but have been reported to be implicated in pancreatic disease, immune system disorders, and cancers. As far as TMED3 is concerned, its roles in cancers are controversial. However, evidence describing TMED3 in the context of malignant melanoma (MM) is scarce.

RESULTS

In this study, we characterized the functional significance of TMED3 in MM and identified TMED3 as a tumor-promoting factor in MM development. Depletion of TMED3 arrested the development of MM in vitro and in vivo. Mechanistically, we found that TMED3 could interact with Cell division cycle associated 8 (CDCA8). Knocking down CDCA8 suppressed cell events associated with MM development. On the contrary, elevating CDCA8 augmented cell viability and motility and even reversed the inhibitory effects of TMED3 knockdown on MM development. On the other hand, we found that the levels of P-Akt and P-PI3K were decreased in response to TMED3 downregulation, which was partially abolished following SC79 treatment. Thus, our suspicion was that TMED3 exacerbates MM progression via PI3K/Akt pathway. More notably, previously decreased P-Akt and P-PI3K in TMED3-depleted cells were rescued after overexpressing CDCA8. Also, previously impaired cell events due to CDCA8 depletion were ameliorated after SC79 addition, implying that TMED3 regulates PI3K-AKT pathway via CDCA8, thereby promoting MM development.

CONCLUSIONS

Collectively, this study established the link between TMED3 and MM, and provides a potential therapeutic intervention for patients with MM harboring abundant TMED3.

Screening of the novel immune-suppressive biomarkers of TMED family and whether knockdown of TMED2/3/4/9 inhibits cell migration and invasion in breast cancer

Background

Transmembrane p24 trafficking protein (TMED) family members are implicated in several solid tumors, but their clinical relevance for breast cancer (BC) remains unclear. This study aimed to probe their prognostic values and relations with tumor immunity in BC.

Methods

TMED family mRNA expression was assessed in five microarray datasets (GSE65212, GSE42568, GSE5364, GSE22820 and GSE45827) from Gene Expression Omnibus (GEO) database and invasive breast cancer (BRCA) cohort from The Cancer Genome Atlas (TCGA). Receiver operating characteristic (ROC) curve was performed to determine the predictive values of filtered members of the TMED family. The protein expressions of screen genes were validated by Clinical Proteomic Tumor Analysis Consortium (CPTAC) data from University of ALabama at Birmingham CANcer data analysis portal (UALCAN) and detected in the clinical specimens by western blot assay. Clinicopathologic variables were analyzed with bc-GenExMiner, and patient prognostic data were obtained with Kaplan-Meier Plotter. In vitro wound healing and invasion assays were performed on siRNA-transfected BC cell lines. TIMER 2.0, SangerBox, and ImmPort were used to evaluate tumor immune infiltration, immune checkpoints, and other immune-related genes. CbioPortal, Metascape, Expression2kinases, and LinkedOmics were used to explore gene regulatory network.

Results

BC tissues expressed TMED2/3/4/9 at a higher level than normal tissues, providing diagnostic potential. All the areas under the ROC curve for TMED2/3/4/9 were more than 0.7. TMED2/3/4/9 correlated with numerous clinical variables, including lymph node status, Scarff-Bloom-Richardson score (SBR), Nottingham Prognostic Index (NPI), estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER-2), and triple-negative breast cancer (TNBC) status, and their high expression predicted the poor prognosis of BC patients. TMED2/3/4/9 knockdown drastically inhibited the migratory and invasive capacities of MDA-MB-231 and HCC1937 cells. TMED2/3/4/9 expressions correlated negatively with the infiltration of tumor-suppressive immune cells such as CD8⁺ T cells, dendritic cells, and natural killer cells, and was inversely related to a variety of immune checkpoint genes, including programmed cell death 1 (PD-1) and cytotoxic T-lymphocyte associated protein 4 (CTLA4). A set of kinases, transcription factors, and microRNAs (miRNAs) may regulate TMED2/3/4/9 abnormalities at the genome level.

Conclusions

TMED2/3/4/9 may serve as diagnostic, prognostic, and immune-suppressive biomarkers in BC.

TMED2/9/10 Serve as Biomarkers for Poor Prognosis in Head and Neck Squamous Carcinoma

Background: Head and neck squamous carcinoma (HNSC) is one of the most common malignant tumors with high incidence and poor prognosis. Transmembrane emp24 structural domain (TMED) proteins are involved in protein transport and vesicle budding processes, which have implicated various malignancies’ progression. However, the roles of TMEDs in HNSC, especially in terms of development and prognosis, have not been fully elucidated.

Methods: We applied TIMER 2.0, UALCAN, GEPIA 2, Kaplan-Meier plotter, GEO, The Human Protein Atlas (HPA), cBioPortal, Linkedomics, Metascape, GRNdb, STRING, and Cytoscape to investigate the roles of TMED family members in HNSC.

Results: Compared with normal tissues, the mRNA expression levels of TMED1/2/4/5/7/8/9/10 were significantly increased in the TCGA HNSC dataset. And we combined GEPIA 2 and Kaplan-Meier Plotter to select TMED2/9/10 with prognostic value. Then we detected the levels of mRNA in the GEO HNSC database and the protein expression in HPA. It was found that the mRNA and protein expression levels of TMED2/9/10 were increased in HNSC. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that TMED2/9/10 and their co-expressed genes promoted the malignant behavior of tumors by participating in biological processes such as intracellular transferase complex, protein transport, focal adhesion, intracellular protein processing. Single-cell analysis and immune infiltration analysis suggested that immune responses of cancer-associated fibroblasts and endothelial cells might be associated with prognosis. Finally, the transcription factors-genes network and protein-protein functional interaction network pointed to genes such as X-box binding protein 1 (XBP1) and TMED7, which might cooperate with TMED2/9/10 to change the progression of HNSC.

Conclusions: Our study implied that TMED2/9/10 and related genes mightjointly affect the prognosis of HNSC, providing specific clues for further experimental research, personalized diagnosis strategies, and targeted clinical therapy for HNSC.

Golgi Complex: A Signaling Hub in Cancer

The Golgi Complex is the central hub in the endomembrane system and serves not only as a biosynthetic and processing center but also as a trafficking and sorting station for glycoproteins and lipids. In addition, it is an active signaling hub involved in the regulation of multiple cellular processes, including cell polarity, motility, growth, autophagy, apoptosis, inflammation, DNA repair and stress responses. As such, the dysregulation of the Golgi Complex-centered signaling cascades contributes to the onset of several pathological conditions, including cancer. This review summarizes the current knowledge on the signaling pathways regulated by the Golgi Complex and implicated in promoting cancer hallmarks and tumor progression.

Proteomics-based identification of TMED9 is linked to vascular invasion and poor prognoses in patients with hepatocellular carcinoma

BACKGROUND

Due to the difficulties in early diagnosing and treating hepatocellular carcinoma (HCC), prognoses for patients remained poor in the past decade. In this study, we established a screening model to discover novel prognostic biomarkers in HCC patients.

METHODS

Candidate biomarkers were screened by liquid chromatography with tandem mass spectrometry (LC-MS/MS) analyses of five HCC normal (N)/tumor (T) paired tissues and preliminarily verified them through several in silico database analyses. Expression levels and functional roles of candidate biomarkers were respectively evaluated by immunohistochemical staining in N/T paired tissue (n = 120) and MTS, colony formation, and transwell migration/invasion assays in HCC cell lines. Associations of clinicopathological features and prognoses with candidate biomarkers in HCC patients were analyzed from GEO and TCGA datasets and our recruited cohort.

RESULTS

We found that the transmembrane P24 trafficking protein 9 (TMED9) protein was elevated in HCC tissues according to a global proteomic analysis. Higher messenger (m)RNA and protein levels of TMED9 were observed in HCC tissues compared to normal liver tissues or pre-neoplastic lesions. The TMED9 mRNA expression level was significantly associated with an advanced stage and a poor prognosis of overall survival (OS, p = 0.00084) in HCC patients. Moreover, the TMED9 protein expression level was positively correlated with vascular invasion (p = 0.026), OS (p = 0.044), and disease-free survival (p = 0.015) in our recruited Taiwanese cohort. In vitro, manipulation of TMED9 expression in HCC cells significantly affected cell migratory, invasive, proliferative, and colony-forming abilities.

CONCLUSIONS

Ours is the first work to identify an oncogenic role of TMED9 in HCC cells and may provide insights into the application of TMED9 as a novel predictor of clinical outcomes and a potential therapeutic target in patients with HCC.

Expression and Importance of TMED2 in Multiple Myeloma Cells

Objective

TMED2 is a member of the transmembrane emp24 domain (Tmed)/p24 protein family, which is significantly upregulated in breast cancer, ovarian cancer and other tumour tissues. The purpose of this study was to investigate the expression of TMED2 in MM cell lines and its effect on the biological behaviour of MM cell lines.

Methods

Real-time quantitative PCR (RT-qPCR) was used to detect the expression of TMED2 in MM cell lines, including MM.1S and RPMI 8226 cells, and lentivirus vector-mediated TMED2 gene silencing was used to further study the effect of the downregulation of TMED2 expression on cell viability, the cell cycle, and apoptosis.

Results

Based on the RT-qPCR results, the expression of the TMED2 mRNA was increased in the MM cell lines MM.1S and RPMI 8226 compared with endogenous control GAPDH. The expression of the TMED2 mRNA was substantially reduced after transfection of the shRNA targeting TMED2 (shTMED2) in both MM cell lines. The CCK-8 assay showed significant decreases in the viability of MM.1S and RPMI 8226 cells, suggesting that the TMED2 gene plays an important role in the proliferation of these two cell lines. The cell cycle of MM.1S and RPMI 8226 cells was substantially altered by shTMED2, as evidenced by the increased number of cells in G1 phase and decreased number of cells in S and G2/M phases. The FACS analysis revealed a significant increase in the apoptosis of MM.1S and RPMI 8226 cells due to the increased activity of Caspase 3/7, suggesting that the TMED2 gene is significantly related to the apoptosis of these two cell lines.

Conclusion

Based on these results, TMED2 may play an important role in the pathogenesis of MM. This novel study may contribute to further investigations of useful biomarkers and potential therapeutic targets in patients with MM.

Circular RNA circ_0008305 aggravates hepatocellular carcinoma growth through binding to miR‐186 and inducing TMED2

Dysregulation of circRNAs is reported to exert crucial roles in cancers, including hepatocellular carcinoma (HCC). So far, the function of circRNAs in HCC development remains poorly known. Currently, our data showed that circ_0008305 was highly elevated in HCC cell lines and 30 paired tissue samples of HCC. As evidenced, suppression of circ_0008305 repressed HCC cell growth significantly. Meanwhile, up‐regulation of circ_0008305 significantly reduced HCC cell growth. Mechanistically, we displayed that circ_0008305 could bind with miR‐186 by using bioinformatics analysis. miR‐186 has been reported to be a crucial tumour oncogene in many cancers. In addition, we proved miR‐186 was greatly decreased in HCC. The direct correlation between miR‐186 and circ_0008305 was confirmed in our work. In addition, up‐regulation of miR‐186 obviously restrained HCC progression. Increased expression of transmembrane p24 trafficking protein 2 (TMED2) is significantly related to the unfavourable outcomes in cancer patients. At our present work, we proved that TMED2 could act as a direct target of miR‐186. Mechanistically, we demonstrated that circ_0008305 up‐regulated TMED2 expression by sponging miR‐186, which resulted in significantly induced HCC progression in vitro and in vivo. These revealed the significant role of circ_0008305 in HCC progression, which might indicate a new perspective on circRNAs in HCC development.

TMED3 Promotes Proliferation and Migration in Breast Cancer Cells by Activating Wnt/β-Catenin Signaling

Purpose

Evidence describing TMED3 in the context of breast cancer is scarce, and the effect of TMED3 on Wnt/β-catenin signaling in breast cancer has not been reported. The objective of this study was to determine the potential physiological functions and molecular mechanisms of TMED3 in breast cancer.

Materials and Methods

Quantitative real-time PCR and Western blot analysis were used to analyze the expression of TMED3 mRNA and protein in 182 paraffin-embedded primary breast cancer tissues and 60 paired noncancerous tissues and 25 fresh primary breast cancer tissues and surrounding adjacent noncancerous tissues. Associations between TMED3 expression and clinicopathologic factors or overall survival were determined. The effects of overexpression or knockdown of TMED3 on proliferation, migration, invasion, and cell cycle progression in breast cancer cell lines were investigated with the Cell Counting Kit-8, clone formation assay, transwell assay, wound healing assay, and flow cytometry, respectively. Immunofluorescence and Western blot analysis were used to detect the expression of cell cycle, migration-related, and Wnt/β-catenin signaling proteins.

Results

The expression of TMED3 mRNA and protein were significantly increased in breast cancer tissues and cell lines compared to normal controls. TMED3 upregulation was significantly correlated with clinicopathologic characteristics and predicted poor prognosis in patients with breast cancer. TMED3 overexpression promoted proliferation, migration, invasion, and cell cycle progression compared to controls in breast cancer cell lines. TMED3 knockdown suppressed proliferation, migration, invasion, and cell cycle progression compared to controls in breast cancer cell lines. TMED3 promoted proliferation and migration of breast cancer cells by a mechanism that involved Wnt/β-catenin signaling.

Conclusion

TMED3 behaves as an oncogene that promotes the proliferation and migration of breast cancer cells by a mechanism that involved Wnt/β-catenin signaling. Strategies targeting TMED3 have potential therapeutic implications for patients with breast cancer.

The circular RNA CDR1as regulate cell proliferation via TMED2 and TMED10

Background

Circular RNAs (CircRNAs) are biologically active RNAs. CDR1as is one such circRNA previously reported to be a microRNA-7 (miR-7) sponge, thereby regulating associated gene expression. The specific underlying molecular mechanisms of CDR1as biology, however, remain largely unknown.

Methods

We performed CDR1as knockdown in order to explore its function in cell proliferation, migration, the cell cycle, and tumorigenesis. We further employed quantitative proteomic analyses and associated bioinformatics strategies to globally assess CDR1as-regulated proteins (CRPs). Western blotting and immunofluorescence staining were used to validate the proteomic results. We additionally investigated a specific link between TMED2, TMED10, and miR-7 via a dual-luciferase reporter system, and generated CDR1as knockout cell lines via CRISPR/Cas9 editing.

Results

We identified 353 proteins dysregulated upon CDR1as knockdown in 293 T cells. These CRPs were found to interact with one another and to play key roles in certain cellular pathways. Two such proteins, TMED2 and TMED10, were found to specifically contribute to the influence of CDR1as on cell proliferation. CDR1as may regulate these two TMED proteins through miR-7 sponging. We were able to further confirm these results using both CRISPRi cell lines and nude mouse models.

Conclusion

This study suggested that CDR1as may regulate cell proliferation via serving as a miR-7 sponge, thereby regulating TMED2 and TMED10 expression. These results are an invaluable template for future streamlined studies of circRNAs.

Transmembrane emp24 domain proteins in development and disease

Regulated transport through the secretory pathway is essential for embryonic development and homeostasis. Disruptions in this process impact cell fate, differentiation and survival, often resulting in abnormalities in morphogenesis and in disease. Several congenital malformations are caused by mutations in genes coding for proteins that regulate cargo protein transport in the secretory pathway. The severity of mutant phenotypes and the unclear aetiology of transport protein-associated pathologies have motivated research on the regulation and mechanisms through which these proteins contribute to morphogenesis. This review focuses on the role of the p24/transmembrane emp24 domain (TMED) family of cargo receptors in development and disease.

Increased expression of TMED2 is an unfavorable prognostic factor in patients with breast cancer

Background: We obtained 2 types of clones which were termed SC (sphere-shaped clone) and NSC (non-sphere-shaped clone) from 4T1 cells by monoclonal culture. SC and NSC were distinct in morphology, surface marker, metabolism and proliferation rate. With the transcriptome sequencing data analysis, we found TMED2 expressed higher in SCs. TMED2 was a member of the transmembrane emp24 domain and might play roles in cancer cell proliferation. However, its prognostic roles in breast cancer remained unknown. We aimed to investigate the prognostic values of TMED2 in patients with breast cancer.

Methods: We used UALCAN (http://ualcan.path.uab.edu) and the Human Protein Atlas (www.proteinatlas.org) to explore the TMED2 expression level and DNA methylation data between breast cancer and normal breast tissue. With Oncomine (www.oncomine.org), we investigated the copy number of TMED2 in breast cancer sample and normal breast tissue. We used the Kaplan–Meier Plotter database (http://kmplot.com/analysis) to analyze prognostic values of TMED2 mRNA expression in all breast cancers and in different intrinsic subtypes. Moreover, protein expression levels of TMED2 were confirmed by Western blot in breast cancer tissues and normal mammary tissue as well as SCs and NSCs.

Results: TMED2 significantly upregulated in breast cancer patients compared to normal mammary samples. Meanwhile, the increased expression of TMED2 mRNA was closely associated with reduced overall survival (OS) in all breast cancers, and with reduced OS in patients with ER-positive, Luminal A or Luminal B breast cancer subtypes. Moreover, western blot confirmed that TMED2 increased expressed was correlated with the reduced OS at protein levels.

Conclusion: Increased expression of TMED2 was significantly related to unfavorable outcomes in patients with breast cancer. Thus, we supposed TMED2 is oncogenic and a potential target for breast cancer therapy and these preliminary findings require further study to determine whether TMED2-targeting reagents might be developed for clinical application in breast cancer.

Leptin induces the expression of tumorigenic genes in the gastric mucosa of male Sprague-Dawley rats

Leptin promotes the growth of gastric cancer cells in vitro. It is, however, unknown if leptin induces gastric cancer in vivo. This study therefore investigated the effect of leptin on the histology and expression of tumorigenic genes in the stomach of rats following 40 weeks of leptin treatment. Male Sprague-Dawley rats, aged 6 weeks, were randomized into control and experimental groups ( n = 8 per group). The experimental group was given intraperitoneal injections of leptin (60 µg/kg/day) once daily for 40 weeks, whereas the control group received intraperitoneal injection of an equal volume of normal saline daily. Rats were housed in polypropylene cages for the duration of the study. Body weight was measured weekly. Upon completion of treatment, rats were euthanized and their stomachs were collected for histopathological examination, microarray, and RT-qPCR. Data were analyzed using one-way ANOVA and Fisher’s exact test. On histology, one rat (12.5%) in the leptin-treated group had a large red-colored tumor nodule at the pyloric antrum of the stomach. Microscopically, stomachs of two leptin-treated rats (25%) showed hyperplasia or dysplasia. Microarray analysis revealed significant upregulation of a number of genes in the stomachs of leptin-treated rats that have been shown to be associated with tumorigenesis in other tissues, including Furin (protein maturation), Eef1a1 and Eif4g2 (translation factors), Tmed2 (vesicular trafficking), Rab7a (plasma membrane trafficking), Rfwd2 (protein degradation), Fth1 and Ftl1 (oxygen transport), Tspan8, Tspan1, Fxyd3, and Rack1 (cell migration), Pde4d (signal transduction), Nupr1 and Ybx1 (transcription factors), Ptma and Tmem134 (oncogenes), Srsf2 (mRNA maturation), and Reep5 (cell proliferation). None of the known oncogenes were, however, significantly up-regulated. In conclusion, although the overall effect of leptin on gastric carcinogenesis seems inconclusive, the findings of dysplasia and the up-regulation of some of the cancer-related genes nevertheless warrant further scrutiny on the role of leptin in gastric cancer.

Impact statement

Gastric cancer is the third most common cause of death due to cancer in the world. Obese individuals are at risk of developing gastric cancer, and the reason for this is unknown. Serum leptin levels are high in obese individuals and leptin is known to induce proliferation of gastric cancer cells in vitro. However, to date, no reports exist on the tumorigenic effects of leptin on the stomach in vivo. This study therefore determines if chronic leptin administration induces gastric carcinogenesis in non-obese rats, which might serve as a useful animal model for future studies. Although the findings are somewhat inconclusive, to our knowledge, however, this is the first study to show the up-regulation of numerous potential driver genes that highlight the potential role of leptin in the higher prevalence of gastric cancer among obese individuals. The findings certainly necessitate further scrutiny of leptin gastric cancer.