BackgroundThe BMI1 oncogene is overexpressed in several human malignancies including gastric cancer. In addition to BMI1, mammalian cells also express Mel-18, which is closely related to BMI1. We have reported that Mel-18 functions as a potential tumor suppressor by repressing the expression of BMI1 and consequent downregulation of activated AKT in breast cancer cells. However, the mechanisms of BMI1 overexpression and the role of Mel-18 in other cancers are still not clear. The purpose of this study is to investigate the role of BMI1 and Mel-18 in gastric cancer.ResultsBMI1 was found to be overexpressed in gastric cancer cell lines and gastric tumors. Overexpression of BMI1 correlated with advanced clinical stage and lymph node metastasis; while the expression of Mel-18 negatively correlated with BMI1. BMI1 but not Mel-18 was found to be an independent prognostic factor. Downregulation of BMI1 by Mel-18 overexpression or knockdown of BMI1 expression in gastric cancer cell lines led to upregulation of p16 (p16INK4a or CDKN2A) in p16 positive cell lines and reduction of phospho-AKT in both p16-positive and p16-negative cell lines. Downregulation of BMI1 was also accompanied by decreased transformed phenotype and migration in both p16- positive and p16-negative gastric cancer cell lines.ConclusionsIn the context of gastric cancer, BMI1 acts as an oncogene and Mel-18 functions as a tumor suppressor via downregulation of BMI1. Mel-18 and BMI1 may regulate tumorigenesis, cell migration and cancer metastasis via both p16- and AKT-dependent growth regulatory pathways.

Nitidine chloride (NC), a novel benzo[c]phenanthridine alkaloid, induces the growth inhibition of cancer cells. Previously it was demonstrated that SMMC-7721 human hepatocellular carcinoma (HCC) cells are highly susceptible to the antiproliferative effects of NC. However, the specific mechanisms remained unclear. In the present study the pathways of growth inhibition induced by NC in SMMC-7721 cells were investigated. The effects of NC on SMMC-7721 cell proliferation were characterized by MTT and colony formation assays. Additionally, BALB/c nude mice were transplanted with SMMC-7721 cells to verify the inhibition of HCC by NC in vivo. The results showed that NC inhibited the proliferation of SMMC-7721 cells in vitro in a time- and dose-dependent manner and identified efficacy in vivo in a mouse model of HCC. Acridine orange (AO) staining, transmission electron microscopy, Annexin V/PI staining, TUNEL assay and caspase-3 activation assays were used to investigate apoptosis and the cell cycle distribution. Inhibition was mediated in part by cell cycle arrest in G2/M, leading to chromatin condensation, DNA fragmentation and the formation of apoptotic bodies. Apoptosis was also verified by Annexin V/PI staining, TUNEL assay and caspase-3 activation. To assess the levels of the cell cycle and apoptotic regulators, immunohistochemical staining, ELISA, real-time PCR and RNA interference (RNAi) were employed. The apoptotic process triggered by NC involved the upregulation of p53, p21 and Bax, and the downregulation of Bcl-2. These data elucidate a pathway of apoptosis in SMMC‑7721 cells that involves G2/M arrest, upregulation of p53, Bax, caspase-3 and p21, and downregulation of Bcl-2.

A neural field is a continuous version of a neural network model accounting for dynamical pattern forming from populational firing activities in neural tissues. These patterns include standing bumps, moving bumps, traveling waves, target waves, breathers, and spiral waves, many of them observed in various brain areas. They can be categorized into two types: a wave-like activity spreading over the field and a particle-like localized activity. We show through numerical experiments that localized traveling excitation patterns (traveling bumps), which behave like particles, exist in a two-dimensional neural field with excitation and inhibition mechanisms. The traveling bumps do not require any geometric restriction (boundary) to prevent them from propagating away, a fact that might shed light on how neurons in the brain are functionally organized. Collisions of traveling bumps exhibit rich phenomena; they might reveal the manner of information processing in the cortex and be useful in various applications. The trajectories of traveling bumps can be controlled by external inputs.