Chih-Jen Hsieh

Hypermethylation of the CDKN2/p16 Promoter During Neoplastic Progression in Barrett's Esophagus

BACKGROUND & AIMS Inactivation of the CDKN2/p16(INK4A) tumor-suppressor gene is one of the most frequent genetic alterations in human malignancies. In esophageal adenocarcinomas, mutations of the p16 gene or homozygous deletions of the gene locus 9p21 are rare. This study investigated whether p16 promoter hypermethylation is an alternative mechanism for p16 gene inactivation during neoplastic progression in Barretts esophagus. METHODS A methylation-specific polymerase chain reaction protocol was applied. A total of 95 specimens from 14 patients with Barretts esophagus were analyzed longitudinally. The p16 promoter status was compared with histomorphological findings. RESULTS p16 promoter hypermethylation was detected in 9 of the 10 patients who had displayed dysplasia at some time during surveillance, whereas none of the patients who had not displayed dysplasia during surveillance had p16 promoter hypermethylation. p16 promoter hypermethylation was detected in 3% (2 of 67) of the samples without dysplasia, 60% (3 of 5) of the samples with lesions indefinite for dysplasia, 55.6% (10 of 18) of the specimens with low-grade dysplasia, and 75% (3 of 4) of the specimens with high-grade dysplasia. CONCLUSIONS These data suggest that p16 promoter hypermethylation is a common mechanism of p16 gene inactivation during neoplastic progression in Barretts esophagus.

Intestinal Anion Exchanger Down-regulated in Adenoma (DRA) Is Inhibited by Intracellular Calcium

The Na/H exchanger 3 (NHE3) and the Cl/HCO3 exchanger down-regulated in adenoma (DRA) together facilitate intestinal electroneutral NaCl absorption. Elevated Ca2+i inhibits NHE3 through mechanisms involving the PDZ domain proteins NHE3 kinase A regulatory protein (E3KARP) or PDZ kidney 1 (PDZK1). DRA also possesses a PDZ-binding motif, but the roles of interactions with E3KARP or PDZK1 and Ca2+i in DRA regulation are unknown. Wild type DRA and a mutant lacking the PDZ interaction motif (DRA-ETKFminus) were expressed constitutively in human embryonic kidney (HEK) and inducibly in Caco-2/BBE cells. DRA-mediated Cl/HCO3 exchange was measured as intracellular pH changes. Ca2+i was assessed fluorometrically. DRA was induced 8–16-fold and was delivered to the apical surface of polarized Caco-2 cells. Putative anion transporter 1 and cystic fibrosis transmembrane regulator did not contribute to Cl/HCO3 exchange in transfected Caco-2 cells. The calcium ionophore 4Br-A23187 inhibited DRA and DRA-ETKFminus in HEK cells, but only full-length DRA was inhibited in Caco-2 cells. In contrast, 100 μm UTP, which increased Ca2+i, inhibited full-length DRA but not DRA-ETKFminus in Caco-2 and HEK cells. In HEK cells, which express little PDZK1, additional transfection of PDZK1 was required for UTP to inhibit DRA. As HEK cells do not express cystic fibrosis transmembrane regulator or NHE3, the data indicate that Ca2+i-dependent DRA inhibition is not because of modulation of other transport activities. In polarized epithelium, this inhibition requires interaction of DRA with PDZK1. Together with data from PDZK1−/− mice, these data underscore the prominent role of PDZK1 in Ca2+i-mediated inhibition of colonic NaCl absorption.

Quorum sensing in the probiotic bacterium Escherichia coli Nissle 1917 (Mutaflor) - evidence that furanosyl borate diester (AI-2) is influencing the cytokine expression in the DSS colitis mouse model.

Background“Quorum sensing” (QS) is the phenomenon which allows single bacterial cells to measure the concentration of bacterial signal molecules. Two principle different QS systems are known, the Autoinducer 1 system (AI-1) for the intraspecies communication using different Acyl-homoserine lactones (AHL) and AI-2 for the interspecies communication. Aim of this study was to investigate QS of Escherichia coli Nissle 1917 (Mutaflor).ResultsWhile E. coli Nissle is producing AI-2 in a density dependent manner, no AI-1 was produced. To study the effect of AI-2 in the DSS (dextran sulphate sodium) induced mouse model of acute colitis, we silenced the corresponding gene lux S by intron insertion. The mutant bacterium E. coli Nissle::lux S was equally effective in colonizing the colon and the mutation turned out to be 100% stable during the course of the experiment. Isolating RNA from the colon mucosa and performing semiquantitative RT PCR, we were able to show that the expression of the pro-inflammatory cytokine IFN-y was suppressed in mice being infected with the E. coli Nissle wild type. Mice infected with the E. coli Nissle::lux S mutant showed a suppressed expression of IL-10 compared to uninfected mice, while the expression of the pro-inflammatory cytokines IL-6 and TNF-α was higher in these mice. The expression of mBD-1 was suppressed in mice being infected with the mutant in comparison to the mice not infected or infected with the wild type. No differences were seen in the histological examination of the colon sections in the different groups of mice.ConclusionsE. coli Nissle is producing AI-2 molecules, which are influencing the expression of cytokines in the mucosa of the colon in the DSS mice. However, if QS has a direct influence on the probiotic properties of E. coli Nissle remains to be elucidated.

Activity and PI3-kinase dependent trafficking of the intestinal anion exchanger downregulated in adenoma depend on its PDZ interaction and on lipid rafts

The Cl/HCO(3) exchanger downregulated in adenoma (DRA) mediates electroneutral NaCl absorption in the intestine together with the apical Na/H exchanger NHE3. Lipid rafts (LR) modulate transport activity and are involved in phosphatidylinositol 3-kinase (PI3-kinase)-dependent trafficking of NHE3. Although DRA and NHE3 interact via PDZ adaptor proteins of the NHERF family, the role of LR and PDZ proteins in the regulation of DRA is unknown. We examined the association of DRA with LR using the nonionic detergent Triton X-100. DRA cofractionated with LR independently of its PDZ binding motif. Furthermore, DRA interacts with PDZK1, E3KARP, and IKEPP in LR, although their localization within lipid rafts is independent of DRA. Disruption of LR integrity resulted in the disappearance of DRA from LR, in a decrease of its surface expression and in a reduction of its activity. In HEK cells the inhibition of DRA by LR disruption was entirely dependent on the presence of the PDZ interaction motif. In addition, in Caco-2/BBE cells the inhibition by LR disruption was more pronounced in wild-type DRA than in mutated DRA (DRA-ETKFminus; lacking the PDZ binding motif)-expressing cells. Inhibition of PI3-kinase decreased the activity and the cell surface expression of wild-type DRA but not of DRA-ETKFminus; the partitioning into LR was unaffected. Furthermore, simultaneous inhibition of PI3-kinase and disruption of LR did not further decrease DRA activity and cell surface expression compared with LR disruption only. These results suggest that the activity of DRA depends on its LR association, on its PDZ interaction, and on PI3-kinase activity.

NOD2 mutations are associated with the development of intestinal failure in the absence of Crohn's disease

BACKGROUND & AIMS Short bowel syndrome (SBS) and intestinal failure (IF) are multi-factorial conditions which in adults result from extensive intestinal resection. NOD2 is an intracellular pattern recognition receptor associated with CD. An unexpected high frequency of NOD2 mutations has been found in patients undergoing intestinal transplantation (35%). The role of NOD2 in a cohort with SBS/IF not specifically requiring intestinal transplantation has not been studied yet. METHODS The course of 85 patients with non-malignant SBS/IF was characterized. The major NOD2 mutations, as well as ATG16L1 and IL23R were determined. The allele frequencies were compared to the published frequencies of CD patients and controls. RESULTS In non-CD patients (72%) allele frequencies of NOD2 mutations were statistically more frequent than in controls (14% vs 6%, p = 0.006). In CD patients (28%) allele frequencies were not different between SBS and controls (29% vs 22%, p = 0.23). NOD2 mutations were neither associated with parameters potentially heralding the need for transplantation nor with an earlier time to the indication for intestinal transplantation. CONCLUSIONS NOD2 mutations are associated with the development of SBS/IF in the absence of CD, but not with specific complications. NOD2 mutations may increase the risk for more extensive intestinal resection or may impair intestinal adaptation.

The PDZ-interaction of the intestinal anion exchanger downregulated in adenoma (DRA; SLC26A3) facilitates its movement into Rab11a-positive recycling endosomes

Electroneutral NaCl absorption in the ileum and colon is mediated by downregulated in adenoma (DRA) (Cl⁻/HCO₃⁻ exchanger; SLC26A3) and Na⁺/H⁺ exchanger 3 (NHE3, SLC9A3). Surface expression of transport proteins undergoes basal and regulated recycling by endo- and exocytosis. Expression and activity of DRA in the plasma membrane depend on intact lipid rafts, phosphatidylinositol 3-kinase (PI3-kinase), and the PDZ interaction of DRA. However, it is unknown how the PDZ interaction of DRA affects its trafficking to the cell surface. Therefore, the (re)cycling pathway of DRA was investigated in HEK cells stably expressing enhanced green fluorescent protein (EGFP)-DRA or EGFP-DRA-ETKFminus (a mutant lacking the PDZ interaction motif). Early, late, and recycling endosomes were immunoisolated by precipitating stably transfected mCherry-hemagglutinin (HA)-Rab5a, -7a, or -11a. EGFP-DRA and EGFP-DRA-ETKFminus were equally present in early endosomes. In recycling endosomes, wild-type DRA was preferentially present, whereas, in late endosomes, DRA-ETKF-minus dominated. Correspondingly, EGFP-DRA colocalized with mCherry-HA-Rab11a in recycling endosomes, whereas EGFP-DRA-ETKFminus colocalized with mCherry-HA-Rab7a in late endosomes. Functionally, this different distribution was reflected by a shorter half-life of the mutant DRA. Transient expression of dominant-negative Rab11a(S25N) inhibited the activity (-17%, P < 0.05) and the cell surface expression of DRA (-30%, P < 0.05). Transient transfection of Rab4a or its dominant-negative mutant Rab4a(S22N) was without effect and thus excluded participation of the rapid recycling pathway. Taken together, the PDZ interaction of DRA facilitates its movement into Rab11a-positive recycling endosomes, from where it is inserted in the plasma membrane. A scenario emerges where specific PDZ adaptor proteins are present along several compartments of the endocytosis-recycling pathway.

After Intestinal Transplantation Kidney Function Is Impaired by Downregulation of Epithelial Ion Transporters in the Ileum

BACKGROUND Intestinal transplantation is a treatment option for intestinal failure. Although nephrotoxic medication after transplantation is a major cause for posttransplant renal insufficiency, it remains unclear why kidney dysfunction is particularly frequent after intestinal transplantation. METHODS This study analyzed messenger RNA expression of NHE3, DRA, and CFTR in 404 biopsies obtained between day 2 and 1508 from the terminal ileum of 10 adult intestinal transplant recipients. RESULTS The time courses of immunosuppression and glomerular filtration rate were correlated. In the first posttransplant year, expression of NHE3 and DRA, which mediate NaCl absorption, was diminished to a greater degree than that of CFTR, which mediates chloride secretion. Reduced NHE3 and DRA expression was associated with high tacrolimus trough levels. Titration of tacrolimus to low levels by year 2 was paralleled by partially restored NHE3 and DRA expression. In cell culture experiments, similar effects of tacrolimus on transporter expression were detected. In patients, both reduced tacrolimus levels and recovery of NHE3 and DRA expression were associated with stabilization of renal function. CONCLUSIONS Our data strongly suggest that tacrolimus impairs absorption of NaCl and water from the transplanted ileum, leading to volume depletion and impaired renal function. This may be reversible by reduction of tacrolimus to lower levels without increased rates of rejection or chronic graft failure.

Two patients with intestinal failure requiring home parenteral nutrition, a NOD2 mutation and tuberculous lymphadenitis

BackgroundMutations in the NOD2 gene are a significant risk factor to acquire intestinal failure requiring home parenteral nutrition. Tuberculous lymphadenitis is the main manifestation of extrapulmonary tuberculosis. Defects in the innate immunity, including NOD2 mutations, may increase the risk for acquiring infections caused by M. tuberculosis. An association of intestinal failure, mutations in the NOD2 gene and tuberculous lymphadenitis has not been described before.Case presentationWe report of two patients with intestinal failure secondary to mesenteric ischemia. Both patients presented with fever and weight loss while receiving long term home parenteral nutrition. Both of them were found to have mutations in the NOD2 gene. Catheter related infections were ruled out. FDG-PET-CT scans initially obtained in search for another infectious focus that would explain the symptoms unexpectedly showed high FDG uptake in mediastinal lymph nodes. Direct or indirect evidence proved or was highly suggestive for tuberculous lymphadenitis. Intravenous tuberculostatic therapy was started and led to a reversal of symptoms and to resolution of the lesions by FDG-PET-CT.ConclusionMutations in the NOD2 gene may put patients both at an increased risk for acquiring M. tuberculosis infections as well as at an increased risk of intestinal failure after extensive intestinal resection. Thus we suggest to specifically include reactivated and opportunistic infections in the differential diagnosis of suspected catheter related infection in patients with intestinal failure who carry mutations in their NOD2 gene.