4585

MUC4

The acquisition of invasiveness in ovarian cancer (OC) is accompanied by the process of epithelial-to-mesenchymal transition (EMT). The MUC4 mucin is overexpressed in ovarian tumors and has a role in the invasiveness of OC cells. The present study was aimed at evaluating the potential involvement of MUC4 in the metastasis of OC cells by inducing EMT. Ectopic overexpression of MUC4 in OC cells (SKOV3-MUC4) resulted in morphological alterations along with a decreased expression of epithelial markers (E-cadherin and cytokeratin (CK)-18) and an increased expression of mesenchymal markers (N-cadherin and vimentin) compared with the control cells (SKOV3-vector). Also, pro-EMT transcription factors TWIST1, TWIST2 and SNAIL showed an upregulation in SKOV3-MUC4 cells. We further investigated the pathways upstream of N-cadherin, such as focal adhesion kinase (FAK), MKK7, JNK1/2 and c-Jun, which were also activated in the SKOV3-MUC4 cells compared with SKOV3-vector cells. Inhibition of phospho-FAK (pFAK) and pJNK1/2 decreased N-cadherin expression in the MUC4-overexpressing cells, which further led to a significant decrease in cellular motility. Knockdown of N-cadherin decreased the activation of extracellular signal-regulated kinase-1/2 (ERK1/2), AKT and matrix metalloproteinase 9 (MMP9), and inhibited the motility in the SKOV3-MUC4 cells. Upon in vivo tumorigenesis and metastasis analysis, the SKOV3-MUC4 cells produced significantly larger tumors and demonstrated a higher incidence of metastasis to distance organs (peritoneal wall, colon, intestine, stomach, lymph nodes, liver and diaphragm). Taken together, our study reveals a novel role for MUC4 in inducing EMT through the upregulation of N-cadherin and promoting metastasis of OC cells.

The mucin MUC4 is a high molecular weight membrane-bound transmembrane glycoprotein that is frequently detected in invasive and metastatic cancer. The overexpression of MUC4 is associated with increased risks for several types of cancer. However, the functional role of MUC4 is poorly understood in lung adenocarcinoma. Using antisense-MUC4-RNA transfected adenocarcinoma cells, we discovered that the loss of MUC4 expression results in epithelial-mesenchymal transition (EMT). We found morphological alterations and the repression of the epithelial marker E-cadherin in transfected cells. Additionally, the loss of MUC4 caused the upregulation of the mesenchymal marker vimentin compared to control cells. Using a MUC4-knockdown versus control LTEP xenograft mice model (129/sv mice), we also found that EMT happened in lung tissues of MUC4-knockdown-LTEP xenograft mice. Moreover, antisense-MUC4-RNA transfected cells had a significantly increased cellular migration ability in vitro. The loss of MUC4 also occurred in lung adenocarcinoma patients with lymph node metastases. We further investigated MUC4 and found that it plays a critical role in regulating EMT by modulating beta-catenin. Taken together, our study reveals a novel role for MUC4 in suppressing EMT and suggests that the assessment of MUC4 may function as a prognostic biomarker and could be a potential therapeutic target for lung adenocarcinoma metastasis.

BACKGROUND: The transcription factor PR domain containing 16 (PRDM16) is known to play a significant role in the determination and function of brown and beige fat. However, the role of PRDM16 in tumor biology has not been well addressed. Here we investigated the impact of PRDM16 on tumor growth and metastasis in lung cancer. METHODS: UALCAN database, immunoblotting and immunohistochemistry analysis were used to assess PRDM16 expression in lung cancer patients. Kaplan-Meier plotter database was used to analyze the overall survival of patients with lung cancer stratified by PRDM16 expression. PRDM16 overexpression and knockdown experiments were conducted to assess the effects of PRDM16 on growth and metastasis in vitro and in vivo, and its molecular mechanism was investigated in lung adenocarcinoma cells by chromatin immunoprecipitation-sequencing (ChIP-Seq), real time-quantitative PCR (RT-qPCR), luciferase assay, xenograft models and rescue experiments. RESULTS: PRDM16 was downregulated in lung adenocarcinomas, and its expression level correlated with key pathological characteristics and prognoses of lung adenocarcinoma patients. Overexpressing PRDM16 inhibited the epithelial-to-mesenchymal transition (EMT) of cancer cells both in vivo and in vitro by repressing the transcription of Mucin-4 (MUC4), one of the regulators of EMT in lung adenocarcinomas. Furthermore, deleting the PR domain from PRDM16 increased the transcriptional repression of MUC4 by exhibiting significant differences in histone modifications on its promoter. CONCLUSIONS: Our findings demonstrate a critical interplay between transcriptional and epigenetic modifications during lung adenocarcinoma progression involving EMT of cancer cells and suggest that PRDM16 is a metastasis suppressor and potential therapeutic target for lung adenocarcinomas.