Regulation of the intestinal anion exchanger DRA (downregulated in adenoma).

Barrier function and transepithelial transport are intimately linked and are sometimes disturbed in parallel. DRA (downregulated in adenoma) is an intestinal chloride/bicarbonate exchanger that is functionally coupled to CFTR (cystic fibrosis transmembrane regulator) in the upper gastrointestinal tract to mediate chloride and bicarbonate secretion and to NHE3 (Na/H exchanger- isoform 3) in the lower gastrointestinal tract to mediate electroneutral NaCl absorption. All three transport proteins possess PDZ domain binding motifs that facilitate binding to members of the NHERF (Na/H exchanger regulatory factor) family of adapter proteins [NHERF, E3KARP (NHE3 kinase A regulatory protein), PDZK1 (PDZ protein kidney 1) and IKEPP (intestinal and kidney enriched PDZ protein)]. Regulation of DRA appears to depend on the presence of a partner transport protein, and this may involve the assembly of different complexes of transporters, adapter proteins, and signaling molecules. We have established stable expression of DRA in HEK cells. In these cells, that do not express significant amounts of CFTR or NHE3, DRA is inhibited by intracellular calcium but not by protein kinase C or protein kinase A. At high calcium concentrations induced by 4Br-A23187 this inhibition is independent of the PDZ interaction of DRA. These data show that DRA can be individually regulated and may be confirmed in a more physiologically relevant expression system (i.e., Caco-2/BBE cells) using natural agonists of the intracellular calcium signal.

Prognostic implications of BAX protein expression and microsatellite instability in all non-metastatic stages of primary colon cancer treated by surgery alone.

PURPOSE: This study examined whether the apoptosis-related protein, BAX, or the microsatellite-instability phenotype provide prognostic information in patients with resected colon cancer. METHODS: A total of 371 stage I-III patients that previously underwent radical surgery were included (mean follow-up 51.8 months). BAX expression was examined by immunohistochemical staining; high-frequency microsatellite instability (MSI+) was determined by assessing the specific marker, BAT26, using single-strand conformation polymorphism (SSCP)-based analysis. RESULTS: High BAX expression was found in 66.4% of patients. MSI+ tumors were observed in 14.8% of 344 patients. Univariate analysis showed that unlike MSI, low BAX expression was significantly correlated with poor disease-specific overall survival (OS) in stages I-III (p = 0.04). Multivariate subgroup analyses revealed that unlike MSI, low BAX was an independent predictor for OS in stage II (p = 0.009); however, in stages I or III, BAX or MSI were not independent predictors of OS. CONCLUSIONS: In stage II colon cancer treated with surgery alone, BAX protein expression may be a predictor for prognosis.

Low BAX protein expression correlates with disease recurrence in preoperatively irradiated rectal carcinoma.

PURPOSE: To determine the prognostic impact of BAX in correlation to its upstream effector p53 as well as clinicopathologic variables and patient outcome in preoperatively irradiated rectal carcinoma. METHODS AND MATERIALS: We investigated 92 rectal carcinoma patients treated by preoperative radiotherapy to a total dose of 30 Gy followed by surgery. Median follow-up was 71 months. Immunohistochemistry was performed on paraffin sections of pretreatment biopsy samples for BAX protein. Also, we considered the previously determined p53 expression data from this cohort. RESULTS: BAX protein expression was classified as high and low in 63 (68.5%) and 29 (31.5%) tumors, respectively. Unlike clinicopathologic variables, high BAX expression was significantly associated with improved disease-free survival by univariate analysis (p = 0.048). Moreover, in multivariate analyses, high BAX expression was an independent prognostic indicator for both improved local recurrence-free interval and improved disease-free survival (p = 0.03 and 0.047, respectively). Concerning the p53/BAX pathway, subgroup analysis yielded no association between p53 immunonegative/BAX high vs. p53 immunopositive/BAX low expressing tumors with regard to overall, disease-free, or local recurrence-free survival in either univariate (p = 0.88, 0.54, and 0.16, respectively) or multivariate analysis. CONCLUSIONS: This study demonstrates that BAX protein expression might help to predict disease recurrence in preoperatively irradiated rectal carcinoma, whereas determination of p53, the proposed upstream regulator of BAX-induced apoptosis, did not provide additional prognostic information.