Coordinate Gene Regulation by Two Different Catenins

Modulation of P-glycoprotein efflux pump: induction and activation as a therapeutic strategy

P-glycoprotein (P-gp) is an ATP-dependent efflux pump encoded by the MDR1 gene in humans, known to mediate multidrug resistance of neoplastic cells to cancer therapy. For several decades, P-gp inhibition has drawn many significant research efforts in an attempt to overcome this phenomenon. However, P-gp is also constitutively expressed in normal human epithelial tissues and, due to its broad substrate specificity, to its cellular polarized expression in many excretory and barrier tissues, and to its great efflux capacity, it can play a crucial role in limiting the absorption and distribution of harmful xenobiotics, by decreasing their intracellular accumulation. Such a defense mechanism can be of particular relevance at the intestinal level, by significantly reducing the intestinal absorption of the xenobiotic and, consequently, avoiding its access to the target organs. In this review, the current knowledge on this important efflux pump is summarized, and a new focus is brought on the therapeutic interest of inducing and/or activating P-gp for limiting the toxicity caused by its substrates. Several in vivo and in vitro studies validating the use of such a therapeutic strategy are discussed. An extensive literature search for reported P-gp inducers/activators and for the experimental models used in their characterization was conducted. Those studies demonstrate that effective antidotal pathways can be achieved by efficiently promoting the P-gp-mediated efflux of deleterious xenobiotics, resulting in a significant reduction in their intracellular levels and, consequently, in a significant reduction of their toxicity.

Evaluation of the Effects of STZ-Induced Diabetes on In Vitro Fertilization and Early Embryogenesis Processes

The aim of this study was to investigate the effects of experimentally induced diabetes on (a) germ cells, (b) in vitro fertilization (IVF) success rate, and (c) gap junction and cell adhesion molecule gene and protein expressions during the early blastocyst period. Germ cells were obtained from healthy and diabetic rats, analyzed for number, motility, and morphology, and used for IVF. After reaching the early blastocyst stage, the expressions of genes encoding gap junction proteins and cell adhesion molecules were analyzed by quantitative RT-PCR. Histomorphologically and immunohistochemically analyses were also performed. Diabetes significantly affected sperm number and motility and the development of oocytes. Gene expressions of β -catenin and connexin family members and protein expressions of E-cadherin and connexin-43 significantly decreased in groups including germ cells isolated from diabetic rats. Connective tissue growth factor expression increased in groups that included sperm cells isolated from diabetic male rats, whereas mucin-1 expression increased in the group that included oocytes isolated from diabetic female rats paired with sperm cells isolated from healthy male rats. In summary, experimentally induced diabetes was found to influence gap junctions, cell adhesion molecules, and associated proteins which all have important roles in germ cell maturation, fertilization, and development.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Evidence for a role of epithelial mesenchymal transition during pathogenesis of fistulae in Crohn's disease

BACKGROUND

The pathogenesis of fistulae in Crohn's disease (CD) patients is barely understood. We recently showed that more than two-thirds of CD fistulae are covered with flat, mesenchymal-like cells (transitional cells [TC]) forming a patchy basement membrane. Epithelial-to-mesenchymal transition (EMT) is a process of reprogramming epithelial cells, allowing them to migrate more effectively and giving epithelial cells an "invasive" potential. EMT has been suggested to be crucial in fibrosis found in different tissues and diseases. We therefore investigated whether EMT could be involved in the pathogenesis of fistulae formation in CD.

METHODS

In all, 18 perianal fistulae, 2 enteroenteric, and 1 enterovesical fistulae from 17 CD patients were analyzed. In addition 2 perianal fistulae of non-CD patients were studied. Hematoxylin and eosin staining, immunohistochemistry for the expression of cytokeratins 8 and 20, beta6-integrin, E-cadherin, beta-catenin, vimentin, and TGF-beta1 and 2 were performed according to standard techniques.

RESULTS

The TC covering perianal or enteroenteric fistulae were strongly positive for cytokeratins 8 and 20 but negative for vimentin, indicating their epithelial origin. beta6-Integrin and TGF-beta had the highest staining intensities in the transitional zone between the epithelium and the TC. Expression of junctional proteins such as E-cadherin was reduced in TC as compared to regular fistulae epithelium. In addition, a translocation of beta-catenin from the membrane to the cytoplasm was observed.

CONCLUSIONS

Our data for the first time indicate an expression pattern of epithelial and mesenchymal markers in TC associated with fistulae formation that is characteristic for EMT. Studying the pathways of EMT during intestinal fistulae formation may help to develop new therapeutic strategies.

Inhibition of N-cadherin and beta-catenin function reduces axon-induced Schwann cell proliferation

N-cadherin and beta-catenin are involved in cell adhesion and cell cycle in tumor cells and neural crest. Both are expressed at key stages of Schwann cell (SC) development, but little is known about their function in the SC lineage. We studied the role of these molecules in adult rat derived SC-embryonic dorsal root ganglion cocultures by using low-Ca(2+) conditions and specific blocking antibodies to interfere with N-cadherin function and by using small interfering RNA (siRNA) to decrease beta-catenin expression in both SC-neuron cocultures and adult rat-derived SC monocultures. N-cadherin blocking conditions decreased SC-axon association and reduced axon-induced SC proliferation. In SC monocultures, beta-catenin reduction diminished the proliferative response of SCs to the mitogen beta1-heregulin, and, in SC-DRG cocultures, beta-catenin reduction inhibited axon-contact-dependent SC proliferation. Stimulation of SC cultures with beta1-heregulin increased total beta-catenin protein amount, phosphorylation of GSK-3beta and beta-catenin presence in nuclear extracts. In conclusion, our findings suggest a previously unrecognized contribution of beta-catenin and N-cadherin to axon-induced SC proliferation.

Frodo Links Dishevelled to the p120-Catenin/Kaiso Pathway: Distinct Catenin Subfamilies Promote Wnt Signals

p120-catenin is an Arm repeat protein that interacts with varied components such as cadherin, small G proteins, kinases, and the Kaiso transcriptional repressor. Despite recent advances in understanding the roles that p120-catenin and Kaiso play in downstream modulation of Wnt/beta-catenin signaling, the identity of the upstream regulators of the p120-catenin/Kaiso pathway have remained unclear. Here, we find that p120-catenin binds Frodo, which itself interacts with the Wnt pathway protein Dishevelled (Dsh). In Xenopus laevis, we demonstrate that Wnt signals result in Frodo-mediated stabilization of p120-catenin, which, in turn, promotes Kaiso sequestration or removal from the nucleus. Our results point to Dsh and Frodo as upstream regulators of the p120-catenin/Kaiso signaling pathway. Importantly, this suggests that Wnt signals acting through Dsh regulate the stability of p120-catenin in addition to that of beta-catenin, and that each catenin promotes its respective signal in parallel to regulate distinct, as well as shared, direct downstream gene targets.