Background Estrogen receptor β (ERβ) has been reported to play an anti-cancer role in breast cancer, but the regulatory mechanism by which ERβ exerts this effect is not clear. Claudin-6 (CLDN6), a tight junction protein, acts as a tumor suppressor gene in breast cancer. Our previous studies have found that 17β-estradiol (E2) induces CLDN6 expression and inhibits MCF-7 cell migration and invasion, but the underlying molecular mechanisms are still unclear. In this study, we aimed to investigate the role of ERβ in this process and the regulatory mechanisms involved. Methods Polymerase chain reaction (PCR) and western blot were used to characterize the effect of E2 on the expression of CLDN6 in breast cancer cells. Chromatin immunoprecipitation (ChIP) assays were carried out to confirm the interaction between ERβ and CLDN6. Dual luciferase reporter assays were used to detect the regulatory role of ERβ on the promoter activity of CLDN6. Wound healing and Transwell assays were used to examine the migration and invasion of breast cancer cells. Western blot, immunofluorescence and transmission electron microscopy (TEM) were performed to detect autophagy. Xenograft mouse models were used to explore the regulatory effect of the CLDN6-beclin1 axis on breast cancer metastasis. Immunohistochemistry (IHC) was used to detect ERβ/CLDN6/beclin1 expression in breast cancer patient samples. Results Here, E2 upregulated the expression of CLDN6, which was mediated by ERβ. ERβ regulated CLDN6 expression at the transcriptional level. ERβ inhibited the migration and invasion of breast cancer cells through CLDN6. Interestingly, this effect was associated with CLDN6-induced autophagy. CLDN6 positively regulated the expression of beclin1, which is a key regulator of autophagy. Beclin1 knockdown reversed CLDN6-induced autophagy and the inhibitory effect of CLDN6 on breast cancer metastasis. Moreover, ERβ and CLDN6 were positively correlated, and the expression of CLDN6 was positively correlated with beclin1 in breast cancer tissues. Conclusion Overall, this is the first study to demonstrate that the inhibitory effect of ERβ on the migration and invasion of breast cancer cells was mediated by CLDN6, which induced the beclin1-dependent autophagic cascade. Electronic supplementary material The online version of this article (10.1186/s13046-019-1359-9) contains supplementary material, which is available to authorized users.

BackgroundClaudin-6 (CLDN6), a member of CLDN family and a key component of tight junction, has been reported to function as a tumor suppressor in breast cancer. However, whether CLDN6 plays any role in breast cancer chemoresistance remains unclear. In this study, we investigated the role of CLDN6 in the acquisition of chemoresistance in breast cancer cells.MethodsWe manipulated the expression of CLDN6 in MCF-7 and MCF-7/MDR cells with lv-CLDN6 and CLDN6-shRNA and investigated whether CLDN6 manipulation lead to different susceptibilities to several chemotherapeutic agents in these cells. The cytotoxicity of adriamycin (ADM), 5-fluorouracil (5-FU), and cisplatin (DDP) was tested by cck-8 assay. Cell death was determined by DAPI nuclear staining. The enzyme activity of glutanthione S-transferase-p1 (GSTP1) was detected by a GST activity kit. Then lv-GSTP1 and GSTP1-shRNA plasmids were constructed to investigate the potential of GSTP1 in regulating chemoresistance of breast cancer. The TP53-shRNA was adopted to explore the regulation mechanism of GSTP1. Finally, immunohistochemistry was used to explore the relationship between CLDN6 and GSTP1 expression in breast cancer tissues.ResultsSilencing CLDN6 increased the cytotoxicity of ADM, 5-FU, and DDP in MCF-7/MDR cells. Whereas overexpression of CLDN6 in MCF-7, the parental cell line of MCF-7/MDR expressing low level of CLDN6, increased the resistance to the above drugs. GSTP1 was upregulated in CLDN6-overexpressed MCF-7 cells. RNAi –mediated silencing of CLDN6 downregulated both GSTP1 expression and GST enzyme activity in MCF-7/MDR cells. Overexpresssion of GSTP1 in CLDN6 silenced MCF-7/MDR cells restored chemoresistance, whereas silencing GSTP1 reduced the chemoresistance due to ectopic overexpressed of CLDN6 in MCF-7 cells. These observations were also repeated in TNBC cells Hs578t. We further confirmed that CLDN6 interacted with p53 and promoted translocation of p53 from nucleus to cytoplasm, and both the expression and enzyme activity of GSTP1 were regulated by p53. Clinicopathologic analysis revealed that GSTP1 expression was positively associated with CLDN6 in human breast cancer samples.ConclusionHigh expression of CLDN6 confers chemoresistance on breast cancer which is mediated by GSTP1, the activity of which is regulated by p53. Our findings provide a new insight into mechanisms and strategies to overcome chemoresistance in breast cancer.Electronic supplementary materialThe online version of this article (10.1186/s13046-017-0627-9) contains supplementary material, which is available to authorized users.

BackgroundSelf-renewal is dependent on an intrinsic gene regulatory network centered on OCT4 and on an atypical cell cycle G1/S transition, which is also regulated by OCT4. p21, a gene negatively associated with self-renewal and a senescence marker, is a member of the universal cyclin-dependent kinase inhibitors (CDKIs) and plays critical roles in the regulation of the G1/S transition. The expression of p21 can be regulated by OCT4-targeted DNA methyltransferases (DNMTs), which play distinct roles in gene regulation and maintaining pluripotency properties. The aim of this study was to determine the role of OCT4 in the regulation of self-renewal and senescence in human hair follicle mesenchymal stem cells (hHFMSCs) and to characterize the molecular mechanisms involved.MethodsA lentiviral vector was used to ectopically express OCT4. The influences of OCT4 on the self-renewal and senescence of hHFMSCs were investigated. Next-generation sequencing (NGS) was performed to identify the downstream genes of OCT4 in this process. Methylation-specific PCR (MSP) analysis was performed to measure the methylation level of the p21 promoter region. p21 was overexpressed in hHFMSCsOCT4 to test its downstream effect on OCT4. The regulatory effect of OCT4 on DNMTs was examined by ChIP assay. 5-aza-dC/zebularine was used to inhibit the expression of DNMTs, and then self-renewal properties and senescence in hHFMSCs were detected.ResultsThe overexpression of OCT4 promoted proliferation, cell cycle progression, and osteogenic differentiation capacity of hHFMSCs. The cell senescence of hHFMSCs was markedly suppressed due to the ectopic expression of OCT4. Through NGS, we identified 2466 differentially expressed genes (DEGs) between hHFMSCsOCT4 and hHFMSCsEGFP, including p21, which was downregulated. The overexpression of p21 abrogated the proliferation and osteogenic differentiation capacity of hHFMSCsOCT4 and promoted cell senescence. OCT4 enhanced the transcription of DNMT genes, leading to an elevation in the methylation of the p21 promoter. The inhibition of DNMTs reversed the OCT4-induced p21 reduction, depleted the self-renewal of hHFMSCsOCT4, and triggered cell senescence.ConclusionsOCT4 maintains the self-renewal ability of hHFMSCs and reverses senescence by suppressing the expression of p21 through the upregulation of DNMTs.Electronic supplementary materialThe online version of this article (10.1186/s13287-018-1120-x) contains supplementary material, which is available to authorized users.

Background: We have previously described CLDN6 as a tumor suppressor gene in breast cancer. Here, a new finding is that CLDN6 was upregulated under hypoxia, a commonly recognized factor that promotes tumor metastasis. In this study, we aim to explain this confusing finding and delineate the role of CLDN6 in the breast cancer metastasis induced by hypoxia. Methods: RNAi and ChIP assays were used to confirm that CLDN6 is transcriptional regulated by HIF-1α. mRNA seq and KEGG analysis were performed to define the downstream pathways of CLDN6. The roles of the CLDN6/SENP1/ HIF-1α signaling on tumor metastasis were evaluated by function experiments and clinical samples. Finally, the possible transcription factor of SENP1 was suspected and then validated by ChIP assay. Results: We demonstrated a previously unrecognized negative feedback loop exists between CLDN6 and HIF-1α. CLDN6 was transcriptionally up-regulated by HIF-1α under hypoxia. On the other hand, in cytoplasm CLDN6 combines and retains β-catenin, a transcription factor of SENP1, causing β-catenin degradation and preventing its nuclear translocation. This process reduced SENP1 expression and prevented the deSUMOylation of HIF-1α, ultimately leading to HIF-1α degradation and breast cancer metastasis suppression. Conclusions: Our data provide a molecular mechanistic insight indicating that CLDN6 loss may lead to elevated HIF-1α-driven breast cancer metastasis in a SUMOylation-dependent manner.

| INTRODUC TI ONOCT4 gene (official symbol POU5F1) is a mammalian POU transcription factor that affects the maintenance of self-renewal and pluripotency, which are the central features of embryonic stem cells.Human OCT4 gene can generate at least three transcripts (OCT4A, OCT4B and OCT4B1) and four protein isoforms (OCT4A, by alternative splicing and translation initiation. OCT4A (often referred to as OCT4) is a transcription factor that regulates stemness. While OCT4B cannot sustain ES cell self-renewal, it may respond to cell stress. However, the function of OCT4B1 is still unclear. 1 There are seven pseudogenes of humanOCT4-pg6 and OCT4-pg7. 2 Studies have revealed that transcription factors related to the maintenance of "stemness," such as Sox-2 and c-Myc, which are involved in the suppression of cancer growth and Abstract Objective: POU5F1 (OCT4) is implicated in cancer stem cell self-renewal. Currently, some studies have shown that OCT4 has a dual function in suppressing or promoting cancer progression. However, the precise molecular mechanism of OCT4 in breast cancer progression remains unclear. Materials and Methods:RT-PCR and Western blot were utilized to investigate OCT4 expression in breast cancer tissues and cells. Cell proliferation assays and mouse models were applied to determine the effects of OCT4 on breast cancer cell proliferation. DNMT1 inhibitors, ChIP, CoIP, IHC and ERα inhibitors were used to explore the molecular mechanism of OCT4 in breast cancer. Results: OCT4 was down-regulated in breast cancer tissues, and the overexpression of OCT4 promoted MDA-MB-231 cell proliferation and inhibited the proliferation of MCF-7 cells in vitro and in vivo, respectively. Two DNMT1 inhibitors (5-aza-dC and zebularine) suppressed OCT4-induced MDA-MB-231 cell proliferation through Ras/ Raf1/ERK inactivation by targeting ISL1, which is the downstream of DNMT1. In contrast, OCT4 interacted with ERα, decreased DNMT1 expression and inactivated the Ras/Raf1/ERK signalling pathway in MCF-7 cells. Moreover, ERα inhibitor (AZD9496) reversed the suppression of OCT4-induced proliferation in MCF-7 cells via the activation of ERK signalling pathway.Conclusions: OCT4 is dependent on ERα to suppress the proliferation of breast cancer cells through DNMT1/ISL1/ERK axis.

Claudin 6 (CLDN6) was found to be a breast cancer suppressor gene, which is lowly expressed in breast cancer and inhibits breast cancer cell proliferation upon overexpression. However, the mechanism by which CLDN6 inhibits breast cancer proliferation is unclear. Here, we investigated this issue and elucidated the molecular mechanisms by which CLDN6 inhibits breast cancer proliferation. First, we verified that CLDN6 was lowly expressed in breast cancer tissues and that patients with lower CLDN6 expression had a worse prognosis. Next, we confirmed that CLDN6 inhibited breast cancer proliferation through in vitro and in vivo experiments. As for the mechanism, we found that CLDN6 inhibited c–MYC–mediated aerobic glycolysis based on a metabolomic analysis of CLDN6 affecting cellular lactate levels. CLDN6 interacted with a transcriptional co–activator with PDZ-binding motif (TAZ) and reduced the level of TAZ, thereby suppressing c–MYC transcription, which led to a reduction in glucose uptake and lactate production. Considered together, our results suggested that CLDN6 suppressed c–MYC–mediated aerobic glycolysis to inhibit the proliferation of breast cancer by TAZ, which indicated that CLDN6 acted as a novel regulator of aerobic glycolysis and provided a theoretical basis for CLDN6 as a biomarker of progression in breast cancer.

Claudins (CLDNs) are the most important tight junction proteins, which are mainly expressed in endothelial cells or epithelial cells in a tissue-specific manner. As a member of the CLDNs family, CLDN6 is highly expressed in fetal tissues such as the stomach, pancreas, lung, and kidney, but is not expressed in corresponding adult tissues. The expression of CLDN6 is regulated by a variety of factors, including but not limited to stimuli and transcription factors, DNA methylation, and post-translational modifications. CLDN6 has been found to have a key role in the formation of barriers, especially the lung epithelial barrier and the epidermal permeability barrier (EPB). Importantly, the roles of CLDN6 in cancers have gained focus and are being investigated in recent years. Strong evidence indicates that the altered expression of CLDN6 is linked to the development of various cancers. Malignant phenotypes of tumors affected by CLDN6 include proliferation and apoptosis, migration and invasion, and drug resistance, which are regulated by CLDN6-mediated key signaling pathways. Given the important role in tumors and its low or no expression in normal tissues, CLDN6 is an ideal target for tumor therapy. This review aims to provide an overview of the structure and regulation of CLDN6, and its traditional barrier function, with a special emphasis on its emerging roles in cancers, including its impact on the malignant phenotypes, signal-modulating effects, the prognosis of tumor patients, and clinical applications in cancers.

Background: Metastatic breast cancer is the major cause of death in breast cancer patients. Activation of epithelial-mesenchymal transition (EMT) induces migration and invasion of breast cancer cells (BCCs). OCT4 (POU5F1) is a key transcription factor for reprograming and plays an important role in self-renewal. Recent studies recovered OCT4 may correlate with cancer progression. However, it is no sufficient proofs to verify how OCT4 plays in metastasis of breast cancer. In this present study, we show the role of OCT4 in the migration and invasion of BCCs in vitro and metastasis in vivo.Methods: PCR, Western Blot and Immunofluorescence staining were performed to determine to OCT4 expression in BCCs. Wound-healing assay and invasion assay were utilized to analyze the mobility of BCCs. Tumor metastasis was assessed with nude mice by subcutaneously injection. IHC assay was used to evaluate phosphorylated signal transducer and activator of transcription 3 (p-STAT3) expression in breast cancer tissues and normal breast tissues. To study whether OCT4 regulate EMT through STAT3 signal, we used shRNA to knockdown STAT3 gene expression in BCCs.Results: OCT4 changed cell morphology of BCCs, decreased cell adhesion, and inhibited migration, invasion and metastatic ability of BCCs. In the meantime, overexpression of OCT4 activated STAT3 signaling and changed EMT-related protein expressions in BCCs. However, knockdown of STAT3 in BCCs with overexpression of OCT4 could facilitate EMT.Conclusion: Our data demonstrate that OCT4 suppresses EMT in BCCs through activation of STAT3 signaling, which is a key mechanism in impeding BCCs migration and invasion. Collectively, these data suggest that elevating OCT4 expression may be an effective method for reducing the metastatic potential of BCCs, which could also contribute to developing new methods for diagnosis and new molecular target therapies in breast cancer metastasis.