Increased lymphocytic aminopeptidase N/CD13 promoter activity after cell-cell contact

Aminopeptidase N (APN)/CD13 is a transmembrane ectoenzyme expressed on a wide variety of cells. With respect to haematopoietic cells, APN/CD13 has been considered specific for the myeloid lineage, because granulocytes and monocytes/macrophages, but not lymphocytes of peripheral blood, show a surface expression of CD13 antigen. However, we could recently show that cell-cell contact of lymphocytes with endothelial cells, monocytes, and fibroblast-like synoviocytes (SFCs) results in an increase of steady-state APN/CD13 mRNA and a rapid expression of cell-surface protein on the lymphocytes. In this study using the Dual-Luciferase reporter assay, we demonstrate that interaction of the T-cell line Jurkat with SFCs results in a higher activity of the APN/CD13 myeloid promoter in T cells. An enhancer located between the myeloid and epithelial APN/CD13 promoter increases the response of the promoter to the cell-cell contact-induced expression of APN/CD13 in lymphocytes. Adhesion of lymphocytes to extracellular matrix did not result in increased promoter activity. The lymphocytic promoter response induced by direct cell-cell contact with SFCs is not affected by mutations of a proximal promoter element (nucleotides -48 to -35), which has a possible functional role in the basal APN/CD13 gene expression in lymphocytes. Upregulated peptidase-promoter activity via cell-cell contact shown in this study for the first time is discussed as a general mechanism in peptidase induction.     

Aminopeptidase N/CD13 induces angiogenesis through interaction with a pro-angiogenic protein, galectin-3

Aminopeptidase N/CD13 is an endothelial cell surface ectoenzyme involved in one of the initial steps of angiogenesis. However, little is known how APN induces angiogenesis in endothelial cells. Using human cDNA library-encoding phage display biopanning method, we here identified a galactoside-specific lectin family protein, galectin-3, as an interacting protein of APN. Galectin-3 specifically binds to APN both in vitro and in human umbilical vein endothelial cells (HUVECs) in a carbohydrate recognition-dependent manner. Immunohistochemical analysis demonstrates that both APN and galectin-3 are exclusively coexpressed during the angiogenic stage of mouse forebrain development. Finally, exogenous addition of galectin-3 into HUVECs induced angiogenesis in an APN-dependent manner, implying that APN is a crucial mediator of galectin-3-induced angiogenesis in endothelial cells.     

Increased lymphocytic aminopeptidase N/CD13 promoter activity after cell‐cell contact

Aminopeptidase N (APN)/CD13 is a transmembrane ectoenzyme expressed on a wide variety of cells. With respect to haematopoietic cells, APN/CD13 has been considered specific for the myeloid lineage, because granulocytes and monocytes/macrophages, but not lymphocytes of peripheral blood, show a surface expression of CD13 antigen. However, we could recently show that cell‐cell contact of lymphocytes with endothelial cells, monocytes, and fibroblast‐like synoviocytes (SFCs) results in an increase of steady‐state APN/CD13 mRNA and a rapid expression of cell‐surface protein on the lymphocytes. In this study using the Dual‐Luciferase reporter assay, we demonstrate that interaction of the T‐cell line Jurkat with SFCs results in a higher activity of the APN/CD13 myeloid promoter in T cells. An enhancer located between the myeloid and epithelial APN/CD13 promoter increases the response of the promoter to the cell‐cell contact‐induced expression of APN/CD13 in lymphocytes. Adhesion of lymphocytes to extracellular matrix did not result in increased promoter activity. The lymphocytic promoter response induced by direct cell‐cell contact with SFCs is not affected by mutations of a proximal promoter element (nucleotides −48 to −35), which has a possible functional role in the basal APN/CD13 gene expression in lymphocytes. Upregulated peptidase‐promoter activity via cell‐cell contact shown in this study for the first time is discussed as a general mechanism in peptidase induction. J. Cell. Biochem. 80:115–123, 2000. © 2000 Wiley‐Liss, Inc.     

Angiotensin II-induced vascular endothelial dysfunction through RhoA/Rho kinase/p38 mitogen-activated protein kinase/arginase pathway

Enhanced vascular arginase activity impairs endothelium-dependent vasorelaxation by decreasing l-arginine availability to endothelial nitric oxide (NO) synthase, thereby reducing NO production. Elevated angiotensin II (ANG II) is a key component of endothelial dysfunction in many cardiovascular diseases and has been linked to elevated arginase activity. We determined signaling mechanisms by which ANG II increases endothelial arginase function. Results show that ANG II (0.1 μM, 24 h) elevates arginase activity and arginase I expression in bovine aortic endothelial cells (BAECs) and decreases NO production. These effects are prevented by the arginase inhibitor BEC (100 μM). Blockade of ANG II AT(1) receptors or transfection with small interfering RNA (siRNA) for Gα12 and Gα13 also prevents ANG II-induced elevation of arginase activity, but siRNA for Gαq does not. ANG II also elevates active RhoA levels and induces phosphorylation of p38 MAPK. Inhibitors of RhoA activation (simvastatin, 0.1 μM) or Rho kinase (ROCK) (Y-27632, 10 μM; H1152, 0.5 μM) block both ANG II-induced elevation of arginase activity and phosphorylation of p38 MAPK. Furthermore, pretreatment of BAECs with p38 inhibitor SB-202190 (2 μM) or transfection with p38 MAPK siRNA prevents ANG II-induced increased arginase activity/expression and maintains NO production. Additionally, inhibitors of p38 MAPK (SB-203580, 5 μg·kg(-1)·day(-1)) or arginase (ABH, 8 mg·kg(-1)·day(-1)) or arginase gene knockout in mice prevents ANG II-induced vascular endothelial dysfunction and associated enhancement of arginase. These results indicate that ANG II increases endothelial arginase activity/expression through Gα12/13 G proteins coupled to AT(1) receptors and subsequent activation of RhoA/ROCK/p38 MAPK pathways leading to endothelial dysfunction.     

The C. elegans G-protein-coupled receptor SRA-13 inhibits RAS/MAPK signalling during olfaction and vulval development

In C. elegans, the RAS/MAPK pathway is used in different tissues to regulate various cell fate decisions. Several positive and negative regulators tightly control the activity of the RAS/MAPK pathway at different steps. We demonstrate a link between a G-protein-coupled receptor signalling pathway and the RAS/MAPK cascade. SRA-13, a member of the SRA family of chemosensory receptors, negatively regulates RAS/MAPK signalling during vulval induction and the olfaction of volatile attractants. Epistasis analysis indicates that SRA-13 inhibits the RAS/MAPK pathway at the level or upstream of MAPK. In both tissues, the vulval precursor cells and the chemosensory neurones, SRA-13 acts through the GPA-5 Galpha protein subunit, suggesting a common mechanism of crosstalk. Moreover, we find that vulval induction is repressed by food withdrawal during larval development and that SRA-13 activity is required for the suppression of vulval induction in response to food starvation. Thus, SRA-13 may serve to adapt the activity of the RAS/MAPK pathway to environmental conditions.