Disruption of CTCF/cohesin-mediated high-order chromatin structures by DNA methylation downregulates PTGS2 expression

The CCCTC-binding factor (CTCF)/cohesin complex regulates gene transcription via high-order chromatin organization of the genome. De novo methylation of CpG islands in the promoter region is an epigenetic hallmark of gene silencing in cancer. Although the CTCF/cohesin complex preferentially targets hypomethylated DNA, it remains unclear whether the CTCF/cohesin-mediated high-order chromatin structure is affected by DNA methylation during tumorigenesis. We found that DNA methylation downregulates the expression of prostaglandin-endoperoxide synthase 2 (PTGS2), which is an inducible, rate-limiting enzyme for prostaglandin synthesis, by disrupting CTCF/cohesin-mediated chromatin looping. We show that the CTCF/cohesin complex is enriched near a CpG island associated with PTGS2 and that the PTGS2 locus forms chromatin loops through methylation-sensitive binding of the CTCF/cohesin complex. DNA methylation abolishes the association of the CTCF/cohesin complex with the PTGS2 CpG island. Disruption of chromatin looping by DNA methylation abrogates the enrichment of transcriptional components, such as positive elongation factor b, at the transcriptional start site of the PTGS2 locus. These alterations result in the downregulation of PTGS2. Our results provide evidence that CTCF/cohesin-mediated chromatin looping of the PTGS2 locus is dynamically influenced by the DNA methylation status.

Acute ectopic pancreatitis occurring after endoscopic biopsy in a gastric ectopic pancreas

Ectopic pancreas is a congenital anomaly and the most common type of ectopic tissue in the gastrointestinal tract. Most patients with an ectopic pancreas are asymptomatic and rarely have complications. Ectopic pancreatitis after an endoscopic biopsy has not been reported. We report a patient who developed acute ectopic pancreatitis in the stomach after an endoscopic biopsy. A 71-year-old male patient presented with a subepithelial tumor (SET) in the stomach and had no symptoms. Endoscopic ultrasonography demonstrated a 30-mm hypoechoic mural mass, lobulated margins, and anechoic duct-like lesions. To obtain proper tissue specimen, endoscopic biopsy was performed through the opening on the surface of the mass. The pathologic results confirmed an ectopic pancreas. One day after the endoscopic biopsy, he developed persistent epigastric pain. His serum amylase and lipase elevated. Computed tomography of the abdomen showed swelling of the SET and diffuse edema of the gastric wall. His condition was diagnosed as acute ectopic pancreatitis occurring after endoscopic biopsy.

A case of squamous metaplasia of the stomach

Intestinal metaplasia of the stomach is a common metaplastic lesion associated with chronic gastritis and mucosal atrophy. However, squamous metaplasia is a comparatively rare condition. On endoscopy, squamous metaplasia is usually observed as a whitish mucosal lesion in the lesser curvature of the cardiac region of the stomach. When Lugol's iodine solution is applied, the lesion stains brown in the same way as normal esophageal mucosa. We report a case of 79-year-old man with a whitish flat lesion in the lesser curvature of the cardiac region on surveillance endoscopy after endoscopic treatment of gastric adenoma. The endoscopic biopsy showed stratified squamous epithelial mucosa.

Endoscopic resection of granular cell tumors in the gastrointestinal tract: a single center experience

BACKGROUND

The frequency of granular cell tumors (GCTs) identified in the gastrointestinal tract has recently increased with the increased use of routine endoscopy. Endoscopic treatment is increasingly used as an alternative to traditional surgical resection, but there are few reports on the efficacy, safety, and long-term prognosis of endoscopic treatment for GCTs. The aim of this study was to assess the efficacy, safety, and long-term prognosis of endoscopic resection for the gastrointestinal GCTs.

METHODS

We examined a total of 27 GCTs in 25 patients who were treated by endoscopic resection from January 2007 to February 2011. For endoscopic resection, endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD) was used.

RESULTS

Twenty GCTs were located in the esophagus, 5 in the stomach, and 2 in the colon. The median size of the GCTs was 10 mm; the largest size, located in the ascending colon, measured 18 mm. EMR with a ligation device was performed in 20 cases, conventional EMR in 5 cases, and ESD in 2 cases. En bloc resection was performed in 25 cases (92.6%), and endoscopic complete resection piecemeal resection was achieved in 25 cases (92.6%). Pathologic complete resection was achieved in 22 lesions (81.5%). Intraprocedural bleeding was noted in three patients, with no occurrence of perforation or postprocedure stricture. No recurrence was observed during the mean follow-up period of 15 months (range 9-31 months).

CONCLUSIONS

Endoscopic resection appears to be a safe and effective treatment for GCTs in the gastrointestinal tract.

The murine IL-2 promoter contains distal regulatory elements responsive to the Ah receptor, a member of the evolutionarily conserved bHLH-PAS transcription factor family

Signaling through the TCR and costimulatory signals primarily control transcription of the IL-2 gene in naive T cells. The minimal promoter necessary for this expression lies proximal, between -300 and the transcription start site. We had previously shown that activation of the arylhydrocarbon receptor (AHR), a member of the bHLH-PAS family of transcription factors, leads to increased mRNA expression of IL-2 in murine fetal thymocytes. The AHR is abundant in the thymus and may play a role for the development of the immune system. Moreover, its overactivation by chemicals such as dioxins leads to immunosuppression and thymic involution. Binding motifs for the liganded AHR can be identified in the distal region -1300 to -800 of the mouse IL-2 promoter. We show here that these DNA motifs, the so-called dioxin response elements, after binding to the liganded AHR are sufficient to transactivate luciferase expression in a reporter gene system. The IL-2 gene can be induced by the AHR also in thymocytes in vivo after injection of 2,3,7, 8-tetrachlorodibenzo-p-dioxin, a potent ligand of the AHR. The AHR mediates the IL-2 induction as shown with AHR-deficient mice. However, in spleen cells in vitro costimulation via the TCR is necessary for optimal IL-2 gene induction. Thus, the IL-2 promoter region contains novel distal regulatory elements that can be addressed by the AHR to induce IL-2 and can cooperate with the proximal promoter in this.

Constitutive expression in gal7 mutants of Kluyveromyces lactis is due to internal production of galactose as an inducer of the Gal/Lac regulon

The induction process of the galactose regulon has been intensively studied, but until now the nature of the inducer has remained unknown. We have analyzed a delta gal7 mutant of the yeast Kluyveromyces lactis, which lacks the galactotransferase activity and is able to express the genes of the Gal/Lac regulon also in the absence of galactose. We found that this expression is semiconstitutive and undergoes a strong induction during the stationary phase. The gal1-209 mutant, which has a reduced kinase activity but retains its positive regulatory function, also shows a constitutive expression of beta-galactosidase, suggesting that galactose is the inducer. A gal10 deletion in delta gal7 or gal1-209 mutants reduces the expression to under wild-type levels. The presence of the inducer could be demonstrated in both delta gal7 crude extracts and culture medium by means of a bioassay using the induction in gal1-209 cells. A mutation in the transporter gene LAC12 decreases the level of induction in gal7 cells, indicating that galactose is partly released into the medium and then retransported into the cells. Nuclear magnetic resonance analysis of crude extracts from delta gal7 cells revealed the presence of 50 microM galactose. We conclude that galactose is the inducer of the Gal/Lac regulon and is produced via UDP-galactose through a yet-unknown pathway.

Endosymbiosis in amoebae: recently established endosymbionts have become required cytoplasmic components

A strain of large, free-living amoeba that became dependent on bacterial endosymbionts which had infected the amoebae initially as intracellular parasites, was studied by micrurgy and electron microscopy. The results show that the infected host cells require the presence of live endosymbionts for their survival.Thus, the nucleus of an infected amoeba can form a viable cell with the cytoplasm of a noninfected amoeba only when live endosymbionts are present. The endosymbiotic bacteria are not digested by the host amoebae and are not themselves used as nutritional supplement. While the host amoebae are dependent specifically on the endosymbionts, the latter can live inside amoebae of different strains, indicating that their dependence on the host cells is not yet strain specific.

Scanning electron microscope observations of Amoeba proteus during phagocytosis

Phagocytosing Amoeba proteus at different stages of forming foodcups have been observed by scanning electron microscopy. A nonphagocytosing ameba is characterized by dorsal and lateral ridges running longitudinally over the posterior half of the cell and its attachment to the substrate over small areas. When stimulated by prey organisms, the ameba loses polarity and ridges, and adheres to the substrate more firmly over a wider area of contact. Then it forms broad pseudopods to surround its prey and this results in the formation of foodcups. The surface of all ameba is covered with small projections, and membranous blebs are often seen on the surface of phagocytosing organisms.

Cytoplasmic filaments and cellular wound healing in Amoeba proteus

The flexibility and self-healing properties of animal cell surface membranes are well known. These properties have been best exploited in various micrurgical studies on living cells (2, 3), especially in amoebae (7, 20). During nuclear transplantation in amoebae, the hole in the membrane through which a nucleus passes can have a diameter of 20-30 mum, and yet such holes are quickly sealed, although some cytoplasm usually escapes during the transfer. While enucleating amoebae in previous studies, we found that if a very small portion of a nucleus was pushed through the membrane and exposed to the external medium, the amoeba expelled such a nucleus on its own accord. When this happened, a new membrane appeared to form around the embedded portion of the nucleus and no visible loss of cytoplasm occurred during nuclear extrusion. In the present study, we examined amoebae that were at different stages of expelling partially exposed nuclei, to follow the sequence of events during the apparent new membrane formation. Unexpectedly, we found that a new membrane is not formed around the nucleus from inside but a hole is sealed primarily by a constriction of the existing membrane, and that cytoplasmic filaments are responsible for the prevention of the loss of cytoplasm.