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  • Title: Binding of "AT4 receptor" ligands to insulin regulated aminopeptidase (IRAP) in intact Chinese hamster ovary cells.
    Author: Demaegdt H, Gard P, De Backer JP, Lukaszuk A, Szemenyei E, Tóth G, Tourwé D, Vauquelin G.
    Journal: Mol Cell Endocrinol; 2011 Jun 06; 339(1-2):34-44. PubMed ID: 21457753.
    Abstract:
    Insulin regulated aminopeptidase (IRAP) recognises "AT(4)-receptor" ligands like angiotensin IV (Ang IV) and peptidomimetics like AL-11. The metabolic stability and high affinity of [(3)H]AL-11 for catalytically active IRAP allowed its detection in Chinese hamster ovary (CHO-K1) cell membranes in the absence of chelators (Demaegdt et al., 2009). Here, we show that, contrary to [(3)H]Ang IV, [(3)H]AL-11 displays high affinity and specificity for IRAP in intact CHO-K1 cells as well. After binding to IRAP at the surface, [(3)H]AL-11 is effectively internalized by an endocytotic process. Unexpectedly, surface binding and internalization of [(3)H]AL-11 was not affected by pretreating the cells with Ang IV but declined with AL-11. In the latter case surface expression of IRAP even increased. After elimination of simpler explanations, it is proposed that metabolically stable "AT(4)-receptor" ligands undergo semi-continuous cycling between the cell surface and endosomal compartments. The in vivo efficacy of stable and unstable "AT(4)-receptor" ligands could therefore differ.
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