ABSTRACT
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.
Subject(s)
Adenocarcinoma of Lung , Disease Progression , Lung Neoplasms , MAP Kinase Signaling System , Membrane Proteins , STAT3 Transcription Factor , Vascular Endothelial Growth Factor A , Animals , Female , Humans , Male , Mice , Middle Aged , A549 Cells , Adenocarcinoma of Lung/pathology , Adenocarcinoma of Lung/metabolism , Adenocarcinoma of Lung/genetics , Cell Line, Tumor , Cell Movement , Cell Proliferation , Gene Expression Regulation, Neoplastic , Human Umbilical Vein Endothelial Cells/metabolism , Lung Neoplasms/metabolism , Lung Neoplasms/pathology , Lung Neoplasms/genetics , Membrane Proteins/metabolism , Membrane Proteins/genetics , Mice, Inbred BALB C , Mice, Nude , Neovascularization, Pathologic/metabolism , Neovascularization, Pathologic/genetics , STAT3 Transcription Factor/metabolism , Vascular Endothelial Growth Factor A/metabolismABSTRACT
BACKGROUND: Epiplakin1 (EPPK1) has been associated with disease progression and unfavorable prognosis of many cancers, but its functional involvement in esophageal squamous cell carcinoma (ESCC) remains to be uncovered. METHODS: The Quantitative Real-time PCR (qPCR) assay was employed to determine the expression of EPPK1 in ESCC tissues and cells. CCK-8 assay, colony forming assay, wound healing assay, and transwell invasion assay were utilized to evaluate the effects of EPPK1 on cell proliferation, migration, and invasion capacity in ESCC cells using small interfering ribonucleic acids. Flow cytometry was performed to estimate the cell apoptotic rate caused by silencing of EPPK1. The proteins related to epithelial-to-mesenchymal transition (EMT), apoptosis, and activation of the phosphatidylinositol 3-kinase/serine threonine protein kinase 1 (PI3K/AKT) signaling pathway were measured by western blot. RESULTS: The expression of EPPK1 was dramatically increased in ESCC tissues and cells compared to that in relative controls. Additionally, silencing of EPPK1 suppressed ESCC cell growth, colony formation, migration, invasion, and EMT, while promoting ESCC cell apoptosis. Furthermore, EPPK1 induced ESCC cell progression via mediating the PI3K/AKT signaling pathway. CONCLUSION: EPPK1 promotes ESCC progression by modulating the PI3K/AKT signaling pathway and could serve as a potential target for ESCC treatment.
