Transcriptional activity of the phosphoenolpyruvate carboxykinase gene decreases in regenerating rat liver

AbstractRat cytosolic phosphoenolpyruvate carboxykinase (PEPCK) gene expression and enzyme activity in liver were studied in rats fasted for 12 hours before and after partial hepatectomy, sham operation or no operation. Transcriptional activity and mRNA levels decreased in regenerating liver compared to sham-operated and unoperated controls. In contrast, PEPCK enzyme activity in regenerating liver was similar to that in livers of sham-operated and unoperated controls. Since all the animals were fasted the decrease in transcription is probably caused by some factor other than insulin, the known repressor of PEPCK gene expression

Humans Lack iGb3 Due to the Absence of Functional iGb3-Synthase: Implications for NKT Cell Development and Transplantation

The glycosphingolipid isoglobotrihexosylceramide, or isogloboside 3 (iGb3), is believed to be critical for natural killer T (NKT) cell development and self-recognition in mice and humans. Furthermore, iGb3 may represent an important obstacle in xenotransplantation, in which this lipid represents the only other form of the major xenoepitope Galα(1,3)Gal. The role of iGb3 in NKT cell development is controversial, particularly with one study that suggested that NKT cell development is normal in mice that were rendered deficient for the enzyme iGb3 synthase (iGb3S). We demonstrate that spliced iGb3S mRNA was not detected after extensive analysis of human tissues, and furthermore, the iGb3S gene contains several mutations that render this product nonfunctional. We directly tested the potential functional activity of human iGb3S by expressing chimeric molecules containing the catalytic domain of human iGb3S. These hybrid molecules were unable to synthesize iGb3, due to at least one amino acid substitution. We also demonstrate that purified normal human anti-Gal immunoglobulin G can bind iGb3 lipid and mediate complement lysis of transfected human cells expressing iGb3. Collectively, our data suggest that iGb3S is not expressed in humans, and even if it were expressed, this enzyme would be inactive. Consequently, iGb3 is unlikely to represent a primary natural ligand for NKT cells in humans. Furthermore, the absence of iGb3 in humans implies that it is another source of foreign Galα(1,3)Gal xenoantigen, with obvious significance in the field of xenotransplantation

Recognition of a carbohydrate xenoepitope by human NKRP1A (CD161)

Background: Many immunologically important interactions are mediated by leukocyte recognition of carbohydrates via cell surface receptors. Uncharacterized receptors on human natural killer (NK) cells interact with ligands containing the terminal Gal alpha(1,3)Gal xenoepitope. The aim of this work was to isolate and characterize carbohydrate binding proteins from NK cells that bind alpha Gal or other potential xenoepitopes, such as N-acetyllactosamine (NAcLac), created by the deletion of alpha 1,3galactosyltransferase (GT) in animals. Methods and results: Initial analysis suggested the human C-type lectin NKRP1A bound to a pool of glycoconjugates, the majority of which contained the terminal Gal alpha(1,3)Gal epitope. This was confirmed by high level binding of cells expressing NKRP1A to mouse laminin, which contains a large number of N-linked oligosaccharides with the Gal alpha(1,3)Gal structure. The consequence of removing the terminal alpha Gal was then investigated. Elevated NAcLac levels were observed on thymocytes from GT(-/-) mice. Exposing NAcLac on laminin, by alpha-galactosidase treatment, resulted in a significant increase in NKRP1A binding. Conclusions: NKRPIA binds to the alpha Gal epitope. Moreover, exposing NAcLac by removal of alpha Gal resulted in an increase in binding. This may be relevant in the later phases of xenotransplant rejection if GT(-/-) pigs, like GT(-/-) mice, display increased NAcLac expression

Transgenic expression of a CD46 (membrane cofactor protein) minigene: Studies of xenotransplantation and measles virus infection

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