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Maintenance of intestinal mucosal epithelial integrity requires polyamines that are involved in the multiple signaling pathways controlling gene expression and different epithelial cell functions. Integrity of the intestinal epithelial barrier depends on a complex of proteins composing different intercellular junctions, including tight junctions, adherens junctions, and desmosomes. E-cadherin is primarily found at the adherens junctions and plays a critical role in cell-cell adhesions that are fundamental to formation of the intestinal epithelial barrier. The current study determined whether polyamines regulate intestinal epithelial barrier function by altering E-cadherin expression. Depletion of cellular polyamines by α-difluoromethylornithine (DFMO) reduced intracellular free Ca[sup 2+] concentration ([Ca[sup 2+]][sub cyt]), decreased E-cadherin expression, and increased paracellular permeability in normal intestinal epithelial cells (IEC-6 line). Polyamine depletion did not alter expression of tight junction proteins such as zona occludens (ZO)-1, ZO-2, and junctional adhesion molecule (JAM)-1. Addition of exogenous polyamine spermidine reversed the effects of DFMO on [Ca[sup 2+]][sub cyt] and E-cadherin expression and restored paracellular permeability to near normal. Elevation of [Ca[sup 2+]][sub cyt] by the Ca[sup 2+] ionophore ionomycin increased E-cadherin expression in polyamine-deficient cells. In contrast, reduction of [Ca[sup 2+]][sub cyt] by polyamine depletion or removal of extracellular Ca[sup 2+] not only inhibited expression of E-cadherin mRNA but also decreased the halflife of E-cadherin protein. These results indicate that polyamines regulate intestinal epithelial paracellular barrier function by altering E-cadherin expression and that polyamines are essential for E-cadherin expression at least partially through [Ca[sup 2+]][sub cyt]. [ABSTRACT FROM AUTHOR]

Presents a study where microarrays were hybridized to labeled RNA obtained from several colonic specimens in order to discover global gene expression patterns characterizing subgroups of colon cancer. Information on colorectal cancer; Importance of the early detection of colon cancer in the premalignant stages; Application of the software program Significant Analysis of Microarrays to identify genes whose expression were used to distinguish between normal and cancerous colonic epithelium.

Normal intestinal mucosal growth requires polyamines that regulate expression of various genes through distinct mechanisms. We have recently found that polyamines modulate subcellular distribution of HuR, a critical regulator of post-transcriptional fate of target transcripts, and that decreasing cellular polyamines increases cytoplasmic levels of HuR, leading to stabilization of NPM and p53 mRNAs. ATF-2 is a transcription factor and known to regulate epithelial cell proliferation and apoptosis. Present study tests the hypothesis that polyamines regulate ATF-2 expression through HuR in normal intestinal epithelial cells (IEC-6). Methods: Expression of the ATF-2 gene was examined by measurements of its promoter activity and mRNA and protein levels in the presence or absence of cellular polyamines. HuR binding to 3'-untranslated region (UTR) of ATF-2 mRNA was identified by RNA pull-down and HuR-immunoprecipitation assays. Functions of HuR were investigated by using siRNA that specifically targets HuR (siHuR). Results: Decreasing cellular polyamines by inhibiting ODC (key enzyme for polyamine biosynthesis) increased levels of ATF-2 mRNA and protein, while increasing polyamines through stable transfection of the ODC gene repressed ATF-2 expression. Polyamine depletion stabilized ATF-2 mRNA as indicated by an increase in its mRNA half-life, but had not effect on ATF-2 gene transcription. Increased cytoplasmic HuR specially bound to 3'-UTR of ATF-2 mRNA following polyamine depletion. HuR silencing by siHuR rendered the ATF-2 mRNA unstable and prevented increases in ATF-2 mRNA and protein in polyamine-deficient cells. Conclusions: These results indicate that polyamines destabilized ATF-2 mRNA through modulation of cytoplasmic HuR levels in IECs. [ABSTRACT FROM AUTHOR]