Knockdown of Sec6 improves cell-cell adhesion by increasing α-E-catenin in oral cancer cells

EXOC4 Promotes Diffuse-Type Gastric Cancer Metastasis via Activating FAK Signal

In comparison with intestinal-type gastric cancer, diffuse-type gastric cancer (DGC) is more likely to recur, metastasize, and exhibit worse clinical outcomes; however, the underlying mechanism of DGC recurrence remains elusive. By employing an LC/MS-MS proteomic approach, we identified that exocyst complex component 4 (EXOC4) was significantly upregulated in DGC with recurrence, compared to those with nonrecurrence. High expression of EXOC4 was correlated with tumor metastasis and poor prognosis in patients with DGC. Moreover, EXOC4 promoted cell migration and invasion as well as the tumor metastasis of DGC cells. Mechanistically, EXOC4 regulated the phosphorylation of focal adhesion kinase (FAK) at Y397 sites by stimulating the secretion of integrin α5/β1/EGF and enhancing the interaction of FAK and integrin or EGFR. The FAK inhibitor VS-4718 reversed the metastasis mediated by EXOC4 overexpression and suppressed the tumor growth of patient-derived xenografts derived from DGC with high EXOC4 expression. The EXOC4-FAK axis could be a potential therapeutic target for patients with DGC with high expression of EXOC4.

IMPLICATIONS

The EXOC4-FAK axis promoted DGC metastasis and could be a potential therapeutic target for patients with DGC.

Molecular cloning, inducible expression and function analysis of Epinephelus coioides Sec6 response to SGIV infection

Exocyst complex component 3 Sec6 of mammals, one of the components of the exocyst complex, participates in numerous cellular functions, such as promoting cell migration and inhibiting apoptosis. In this study, the Sec6 was obtained from Epinephelus coioides, an economically important cultured fish. The full length of E. coioides Sec6 was 2655 bp including a 245 bp 5' UTR, a 154 bp 3' UTR, and a 2256 bp open reading frame (ORF) encoding 751 amino acids, with a molecular mass of 86.76 kDa and a theoretical pI of 5.57. Sec6 mRNA was detected in all the tissues examined, but the expression level is different in these tissues. Using fluorescence microscopy, Sec6 were distributed in both the nucleus and the cytoplasm. After SGIV infection, the expression of E. coioides Sec6 was significantly up-regulated in both trunk kidney and spleen response to Singapore grouper iridovirus (SGIV), an important pathogens of E. coioides. Sec6 could increase the SGIV-induced cytopathic effects (CPE), the expression of the SGIV genes VP19, LITAF, MCP, ICP18 and MCP, and the viral titers. Besides, E. coioides Sec6 significantly downregulated the promoter of NF-κB and AP-1, and inhibited the SGIV-induced apoptosis. The results demonstrated that E. coioides Sec6 might play important roles in SGIV infection.

High expression of oncogene cadherin-6 correlates with tumor progression and a poor prognosis in gastric cancer

Background

Gastric cancer (GC) is one of the most common and fatal cancers worldwide. Effective biomarkers to aid the early diagnosis of GC, as well as predict the course of disease, are urgently needed. Hence, we explored the role and function of cadherin-6 (CDH6) in the diagnosis and prognosis of gastric cancer.

Methods

The expression levels of CDH6 in cancerous and normal gastric tissue were analyzed using multiple public databases. Gene set enrichment analysis (GSEA) was performed using The Cancer Genome Atlas (TCGA) dataset. The diagnostic efficiency of CDH6 expression in GC patients was determined through receiver operating characteristic (ROC) curve analysis. The associations between clinical variables and CDH6 expression were evaluated statistically, and the prognostic factors for overall survival were analyzed by univariate and multivariate Cox regression. 44 GC tissue samples, 20 donor-matched adjacent normal tissue samples, and associated detailed clinical information, were collected from the Tianjin Medical University General Hospital. CDH6 expression levels were determined for further validation.

Results

CDH6 was upregulated in GC samples compared to normal gastric tissue. Furthermore, GSEA identified the tricarboxylic acid (TCA) cycle, extracellular matrix (ECM) receptor interaction, glyoxylate and dicarboxylate metabolism, oxidative phosphorylation, and the pentose phosphate pathway as differentially enriched in GC tissue samples. According to the area under the ROC curve (AUC) values (AUC = 0.829 in the TCGA and 0.966 in the GSE54129 dataset), CDH6 expression was associated with high diagnostic efficacy. Patients with high CDH6 levels in their GC tissues had a higher T number (according to the TNM classification) and a worse prognosis than those with low CDH6 expression. Univariate and multivariate Cox regression analysis showed that CDH6 was an independent risk factor for overall survival (univariate: HR = 1.305, P = 0.002, multivariate: HR = 1.481, P < 0.001).

Conclusion

CDH6 was upregulated in GC, and high CDH6 expression was indicative of a higher T number and a worse prognosis. Therefore, CDH6 represents a potentially independent molecular biomarker for the diagnostic and prognostic prediction of GC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02071-y.

Role of Cadherins in Cancer-A Review

Cadherins play an important role in tissue homeostasis, as they are responsible for cell-cell adhesion during embryogenesis, tissue morphogenesis, differentiation and carcinogenesis. Cadherins are inseparably connected with catenins, forming cadherin-catenin complexes, which are crucial for cell-to-cell adherence. Any dysfunction or destabilization of cadherin-catenin complex may result in tumor progression. Epithelial mesenchymal transition (EMT) is a mechanism in which epithelial cadherin (E-cadherin) expression is lost during tumor progression. However, during tumorigenesis, many processes take place, and downregulation of E-cadherin, nuclear β-catenin and p120 catenin (p120) signaling are among the most critical. Additional signaling pathways, such as Receptor tyrosine kinase (RTK), Rho GTPases, phosphoinositide 3-kinase (PI3K) and Hippo affect cadherin cell-cell adhesion and also contribute to tumor progression and metastasis. Many signaling pathways may be activated during tumorigenesis; thus, cadherin-targeting drugs seem to limit the progression of malignant tumor. This review discusses the role of cadherins in selected signaling mechanisms involved in tumor growth. The clinical importance of cadherin will be discussed in cases of human and animal cancers.

Changes in cell junctions induced by inhibition of epidermal growth factor receptor in oral squamous cell carcinoma cells

The benefits of epidermal growth factor receptor (EGFR) targeting in the treatment of head and neck cancer, have been documented. However, a minority of patients with head and neck cancer are unresponsive to EGFR targeting therapies. The present study evaluated the effects and limitations of an EGFR inhibitor on oral squamous cell carcinoma cells, particularly on cell-cell junctions mediated by epithelial (E)-cadherin. HSC-3 oral squamous cell carcinoma cells were treated with the EGFR inhibitor, AG1478 (0, 0.5, 2, 10 and 50 µM), and the effects of EGFR inhibition in HSC-3 cells were evaluated by wound healing assays, E-cadherin immunostaining and measurement of transepithelial electrical resistance in vitro. It was observed that treatment of oral squamous cell carcinoma cells with AG1478 suppressed cell motility, altered cell morphology and increased the number of cell-cell junctions compared with untreated control cells. Knockdown of EGFR induced a similar phenotype to that observed by the inhibition of EGFR. Furthermore, in oral squamous cell carcinoma cells treated with high-dose EGFR inhibitor (50 µM), the small number of cells that survived formed cell-cell junctions that were positive for E-cadherin expression. In cells treated with low concentrations of EGFR inhibitor (2 µM), recovery of epithelial properties was observed. The retention of E-cadherin expression in cells that survived high-dose EGFR inhibitor treatment may be a survival mechanism of cancer cells.

Exo70 is transcriptionally up-regulated by hepatic nuclear factor 4α and contributes to cell cycle control in hepatoma cells

Exo70, a member of the exocyst complex, is involved in cell exocytosis, migration, invasion and autophagy. However, the expression regulation and function of Exo70 in hepatocellular carcinoma are still poorly understood. In this study, we found Exo70 expression in human hepatoma cells was greatly reduced after knocking down hepatic nuclear factor 4α (HNF4α), the most important and abundant transcription factor in liver. This regulation occurred at the transcriptional level but not post-translational level. HNF4α transactivated Exo70 promoter through directly binding to the HNF4α-response element in this promoter. Cell cycle analysis further revealed that down-regulation of HNF4α and Exo70 was essential to berberine-stimulated G2/M cell cycle arrest in hepatoma cells. Moreover, knocking down either Exo70 or HNF4α induced G2/M phase arrest of hepatoma cells. Exo70 acted downstream of HNF4α to stimulate G2/M transition via increasing Cdc2 expression. Together, our results identify Exo70 as a novel transcriptional target of HNF4α to promote cell cycle progression in hepatoma, thus provide a basis for the development of therapeutic strategies for hepatocellular carcinoma.

Nuclear Translocation of p65 is Controlled by Sec6 via the Degradation of IκBα

Nuclear factor-κB (NF-κB) is an inducible transcription factor that mediates immune and inflammatory responses. NF-κB pathways are also involved in cell adhesion, differentiation, proliferation, autophagy, senescence, and protection against apoptosis. The deregulation of NF-κB activity is found in a number of disease states, including cancer, arthritis, chronic inflammation, asthma, neurodegenerative diseases, and heart disease. The 90 kDa ribosomal S6 kinase (p90RSK) family, which is serine/threonine kinases, is phosphorylated by extracellular signal-regulated kinase1/2 (ERK1/2) and is related to NF-κB pathways. Our previous studies revealed that Sec6, a component of the exocyst complex, plays specific roles in cell-cell adhesion and cell cycle arrest. However, the mechanism by which Sec6 regulates the NF-κB signaling pathway is unknown. We demonstrated that Sec6 knockdown inhibited the degradation of IκBα and delayed the nucleus-cytoplasm translocation of p65 in HeLa cells transfected with Sec6 siRNAs after treatment with tumor necrosis factor alpha (TNF-α). Furthermore, the binding of p65 and cAMP response element binding protein (CREB) binding protein (CBP) or p300 decreased and NF-κB related genes which were inhibitors of NF-κB alpha (IκBα), A20, B cell lymphoma protein 2 (Bcl-2), and monocyte chemoattractant protein-1 (MCP-1) were low in cells transfected with Sec6 siRNAs in response to TNF-α stimulation. Sec6 knockdown decreased the expression of p90RSKs and the phosphorylation of ERK or p90RSK1 at Ser380 or IκBα at Ser32. The present study suggests that Sec6 regulates NF-κB transcriptional activity via the control of the phosphorylation of IκBα, p90RSK1, and ERK.

Knockdown of Sec8 enhances the binding affinity of c-Jun N-terminal kinase (JNK)-interacting protein 4 for mitogen-activated protein kinase kinase 4 (MKK4) and suppresses the phosphorylation of MKK4, p38, and JNK, thereby inhibiting apoptosis

The exocyst complex, also called the Sec6/8 complex, is important for targeting exocytic vesicles to specific docking sites on the plasma membrane in yeast and mammalian cells. In addition to these original findings, recent results of studies suggest that Sec8 is also involved in oncogenesis, although the functional implications of Sec8 in cancer cells are not well understood. c-Jun N-terminal kinase-interacting protein 4 (JIP4) is a scaffold protein that plays a crucial role in the regulation of mitogen-activated protein kinase (MAPK) signaling cascades. The present study examined how Sec8 is involved in JIP4-mediated MAPK signaling under apoptotic conditions. It was found that Sec8 binds to and regulates JIP4, and that knockdown of Sec8 enhances the binding of JIP4 to MAPK kinase 4, thereby decreasing the phosphorylation of MAPK kinase 4, JNK, and p38. These results raise the possibility that Sec8 serves as an important regulator of MAPK signaling cascades.

Knockdown of Sec8 promotes cell-cycle arrest at G1/S phase by inducing p21 via control of FOXO proteins

p21(Cip1) protein inhibits the activity of cyclins at the G(1) checkpoint and influences transition of cells from the G(1) to the S phase of the cell cycle. Moreover, expression of members of the FOXO family (active form of forkhead transcription factors of the O class) in dividing cells promotes cell-cycle arrest at the G(1)/S boundary via regulation of p21(Cip1). Recently, the exocyst complex, including Sec8, has been implicated in various roles independent of its role in secretion, such as cell migration, invadopodia formation, cytokinesis, glucose uptake and neural development. Given the essential roles of the exocyst complex in cellular and developmental processes, disruption of its function may be involved in various diseases such as cancer, diabetes and neuronal disorders. However, the relationship between Sec8 and the cell cycle remains to be elucidated. In this study, knockdown of Sec8 inhibited cell growth and promoted cell-cycle arrest at the G(1)/S phase by control of p21 expression and retinoblastoma protein phosphorylation. Furthermore, Sec8 regulated FOXO family proteins via ubiquitin-proteasome degradation by regulating the expression of the murine double minute 2 (Mdm2) protein but not S-phase kinase-associated protein 2 (Skp2).

Phenotypic and Molecular Characterization of MCF10DCIS and SUM Breast Cancer Cell Lines

We reviewed the phenotypic and molecular characteristics of MCF10DCIS.com and the SUM cell lines based on numerous studies performed over the years. The major signaling pathways that give rise to the phenotype of these cells may serve as a good resource of information when researchers in drug discovery and development use these cells to identify novel targets and biomarkers. Major signaling pathways and mutations affecting the coding sequence are also described providing important information when using these cells as a model in a variety of studies.