The Notch1/cyclooxygenase-2/Snail/E-cadherin pathway is associated with hypoxia-induced hepatocellular carcinoma cell invasion and migration

COX-2 regulates Snail expression in gastric cancer via the Notch1 signaling pathway

The conversion of arachidonic acid into prostaglandins by cyclooxygenase (COX)-2 contributes to the biological properties of malignant tumours. During the initiation and development of various tumours, the Notch family plays a key role. However, the association between COX‑2 and the Notch family in gastric cancer (GC) remains unclear. The present study aimed to clarify the mechanisms through which COX‑2 participates in the pathogenesis of GC. Quantitative PCR and western blot analysis were used to detect the expression of Notch family members and COX‑2 in human GC and paracancerous tissues, GES‑1 cells and GC cell lines (AGS, SGC‑7901, BGC‑823, and MGC‑803) treated with or without celecoxib, prostaglandin E2 and small interfering RNA (siRNA). A CCK‑8 assay was performed to detect the proliferation of GC cells transfected with siRNA against COX‑2 (si‑COX‑2). A high mRNA expression of Notch1 and a decreased expression of Notch-1 intracellular active domain (N1IC) in GC were found to be related to the depth of invasion and TNM staging. The mRNA levels of Notch2, Notch3, Jagged1 and N2IC were found to be high in GC. A High expression of COX‑2 was associated with poorly differentiated and deeply invasive GC. COX‑2 and Notch1 exhibited an inverse expression pattern in the GES‑1 cells and different GC cell lines; the inhibition of COX‑2 increased Notch1 expression and activated the GC cells, whereas Notch1 downregulation had the opposite effect. Notch1 exhibited varying effects on Snail in the GC cell lines. The downregulation of COX‑2 expression significantly inhibited the proliferation of GC cells. On the whole, the expression of Notch signalling molecules differed in GC. COX‑2 inversely regulated Notch1 in GC and partially depended on the Notch1 signalling pathway in altering the expression of Snail.

Upregulation of PP2Ac predicts poor prognosis and contributes to aggressiveness in hepatocellular carcinoma

Protein phosphatase 2A (PP2A) is a heterotrimeric protein phosphatase consisting of a 36-kD catalytic C subunit (PP2Ac). This study aimed to explore the prognostic and biological significance of PP2Ac in human hepatocellular carcinoma (HCC). High PP2Ac expression was significantly (P < 0.01) associated with serum hepatitis B surface antigen positivity, serum hepatitis B e antigen positivity, liver cirrhosis, moderate to poor differentiation grade, advanced disease stage, intrahepatic metastasis, and early recurrence in HCC. Multivariate analysis revealed PP2Ac as an independent prognostic factor for overall survival. Enforced expression of hepatitis B virus X protein (HBx) and its carboxyl-terminal truncated isoform induced PP2Ac expression in HCC cells. Co-immunoprecipitation assay revealed a direct interaction between PP2Ac and HBx. Small interfering RNA-mediated knockdown of PP2Ac significantly inhibited in vitro cell proliferation, colony formation, migration, and invasion and reduced tumor growth in an xenograft mouse model. In contrast, overexpression of PP2Ac promoted HCC cell proliferation, colony formation, and tumorigenesis. Additionally, silencing of PP2Ac impaired the growth-promoting effects on HepG2 HCC cells elicited by overexpression of carboxyl-terminal truncated HBx. Gene expression profiling analysis showed that PP2Ac downregulation modulated the expression of numerous genes involved in cell cycle and apoptosis regulation. Collectively, PP2Ac upregulation has a poor prognostic impact on the overall survival of HCC patients and contributes to the aggressiveness of HCC. PP2Ac may represent a potential therapeutic target for HCC.

Hypoxia: a key player in antitumor immune response. A Review in the Theme: Cellular Responses to Hypoxia

The tumor microenvironment is a complex system, playing an important role in tumor development and progression. Besides cellular stromal components, extracellular matrix fibers, cytokines, and other metabolic mediators are also involved. In this review we outline the potential role of hypoxia, a major feature of most solid tumors, within the tumor microenvironment and how it contributes to immune resistance and immune suppression/tolerance and can be detrimental to antitumor effector cell functions. We also outline how hypoxic stress influences immunosuppressive pathways involving macrophages, myeloid-derived suppressor cells, T regulatory cells, and immune checkpoints and how it may confer tumor resistance. Finally, we discuss how microenvironmental hypoxia poses both obstacles and opportunities for new therapeutic immune interventions.

Transforming growth factor-β1 induces bronchial epithelial cells to mesenchymal transition by activating the Snail pathway and promotes airway remodeling in asthma

Airway remodeling is characterized by airway wall thickening, subepithelial fibrosis, increased smooth muscle mass, angiogenesis and an increase in mucous glands, which may lead to a chronic and obstinate asthma with pulmonary function depression. In the present study, we observed substantially thickened lung tissue with extensive fibrosis in ovalbumin-sensitized mice, which was interrelated with transforming growth factor-β1 (TGF-β1) expression in bronchoalveolar lavage fluid. In vitro experiments further demonstrated that TGF-β1 resulted in epithelial-mesenchymal transition (EMT) in bronchial epithelial cells, which was characterized by the expected decrease in E-cadherin expression and the increase in vimentin and α-smooth muscle actin expression, as well as the associated increase in Snail expression at mRNA and protein levels. Furthermore, the downregulation of Snail by small interfering RNA (siRNA) attenuated the TGF-β1‑induced EMT-like phenotype. Of note, a significantly increased synthesis of fibronectin was observed following TGF-β1 treatment, which further supported the hypothesis that EMT is a pivotal factor in peribronchial fibrosis. In combination, the results indicated that myofibroblasts deriving from bronchial epithelial cells via EMT may contribute to peribronchial fibrosis and that Snail may be an important factor in this phenomenon.

Snail inhibits Notch1 intracellular domain mediated transcriptional activation via competing with MAML1

Notch1 intracellular domain (NICD) is the transcription factor which controls cell fate and differentiation in embryonic and tumor cells. Snail has a critical role which increases invasion and metastasis of cancer cell as a transcription factor and epigenetic regulator. Recently, we discovered NICD induced Snail degradation by direct binding interaction with Snail. In this experiment, we found that Snail suppressed transcriptional activity of the protein complex formed with NICD and RBPJk in nucleus. Moreover, Snail decreased transcription of NICD target genes via competing with MAML1, co-activator, in NICD complex. In conclusion, Snail inhibited NICD-mediated transcriptional activation of target genes by physical interaction with NICD.