Leptin transcriptionally enhances peptide transporter (hPepT1) expression and activity via the cAMP-response element-binding protein and Cdx2 transcription factors.

PepT1 is an intestinal epithelial apical membrane transporter that is expressed in the small intestine, with little or no expression in the normal colon. However, we previously demonstrated that colonic PepT1 may be expressed during chronic inflammation. To begin elucidating inflammatory hPepT1 signaling, we herein investigated the long term leptin treatments, on PepT1 expression and activity in Caco2-BBE cells, and began to reveal the involved signaling pathways. We successfully cloned the 723-bp hPepT1 promoter region and identified the human transcription initiation site 86 bp upstream from the translation start site. Leptin treatment dose- and time-dependently increased hPepT1 promoter and transport activities in Caco2-BBE cells, with maximal activity observed in cells treated with 100 nM leptin for 8 h. Under these conditions, we observed 2-fold increases in hPepT1 mRNA and protein expression, as well as increased transport activity. Our molecular analyses of possible signal-transduction pathways revealed that leptin treatment enhanced the intracellular levels of cAMP and phosphorylated cAMP-response element-binding protein (CREB) protein in Caco2-BBE cells, whereas our deletion, mutation, and CDX2 overexpression analyses demonstrated that interaction of the Cdx2 and phosphorylated CREB transcription factors was essential for leptin-induced hPepT1 transcription in Caco2-BBE cells. Our results indicate that leptin, which is increased in inflamed colonic mucosa, triggers colonic expression of hPepT1 via the CREB and Cdx2 transcription factors. These findings provide important new insights into the mechanisms of intestinal inflammation and may suggest new therapeutic modalities in the future.

hPepT1 mediates bacterial tripeptide fMLP uptake in human monocytes.

Here, we examined hPepT1 expression in the monocytic cell line, KG-1. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that hPepT1 is expressed in KG-1 cells, while cDNA cloning and direct sequencing confirmed the sequence of KG-1 hPepT1 (accession number, AY634368). Immunoblotting of cell lysates from KG-1 cells or macrophages isolated from human peripheral blood revealed a approximately 100 kDa immunoreactive band mainly present in the membrane fraction. Uptake experiments showed that the transport of 20 microM radiolabeled Gly-Sarcosine ([14C]Gly-Sar) in KG-1 cells was Na+, Cl- dependent and disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS)-sensitive. In addition, hPepT1 activity was likely to be coupled to a Na+/H+ exchanger, as evidenced by the fact that [14C]Gly-Sar uptake was not affected by the absence of Na+ when cells were incubated at low pH (5.2). Interestingly, hPepT1-mediated transport was reduced in KG-1 cells incubated at low pH as it was also observed in nonpolarized Caco2-BBE cells. This pattern of pH-dependence is due to a disruption of the driving force of hPepT1-mediated transport events. This was supported by our finding that nonpolarized cells, Caco2-BBE cells and KG-1 cells, have an increased permeability to H+ when compared to polarized Caco2-BBE cells. Finally, we showed that hPepT1 is responsible for transporting fMLP into undifferentiated and differentiated (macrophage-like) KG-1 cells. Together, these results show that hPepT1 is expressed in nonpolarized immune cells, such as macrophages, where the transporter functions best at the physiological pH 7.2. Furthermore, we provide evidence for hPepT1-mediated fMLP transport, which might constitute a novel immune cell activation pathway during intestinal inflammation.

Dystroglycan receptor is involved in integrin activation in intestinal epithelia.

The dystroglycans (alpha-DG and beta-DG), which play important roles in the formation of basement membranes, have been well studied in skeletal muscle and nerve, but their expression and localization in intestinal epithelial cells has not been previously investigated. Here, we demonstrated that the DG complex, composed of alpha-DG, beta-DG, and utrophin, is specifically expressed in the basolateral membrane of the Caco-2-BBE monolayer. The DG complex coprecipitated with beta(1)-integrin, suggesting a possible interaction among these proteins. In addition, we observed that activation of DG receptors by laminin-1 enhanced the interaction between beta(1)-integrin and laminin-1, whereas activation of DG receptors by laminin-2 reduced the interaction between beta(1)-integrin and laminin-2. Finally, we demonstrated that the intracellular COOH-terminal tail of beta-DG and its binding to the DG binding domain of utrophin are crucial for the interactions between laminin-1/-2 and beta(1)-integrin. Collectively, these novel results indicate that dystroglycans play important roles in the regulation of interactions between intestinal epithelial cells and the extracellular matrix.

Synteny perturbations between wheat homoeologous chromosomes caused by locus duplications and deletions correlate with recombination rates.

Loci detected by Southern blot hybridization of 3,977 expressed sequence tag unigenes were mapped into 159 chromosome bins delineated by breakpoints of a series of overlapping deletions. These data were used to assess synteny levels along homoeologous chromosomes of the wheat A, B, and D genomes, in relation to both bin position on the centromere-telomere axis and the gradient of recombination rates along chromosome arms. Synteny level decreased with the distance of a chromosome region from the centromere. It also decreased with an increase in recombination rates along the average chromosome arm. There were twice as many unique loci in the B genome than in the A and D genomes, and synteny levels between the B genome chromosomes and the A and D genome homoeologues were lower than those between the A and D genome homoeologues. These differences among the wheat genomes were attributed to differences in the mating systems of wheat diploid ancestors. Synteny perturbations were characterized in 31 paralogous sets of loci with perturbed synteny. Both insertions and deletions of loci were detected and both preferentially occurred in high recombination regions of chromosomes.