Adenosine deaminase affects ligand‐induced signalling by interacting with cell surface adenosine receptors

Abstract

Adenosine deaminase (ADA) is not only a cytosolic enzyme but can be found as an ecto-enzyme. At the plasma membrane, an adenosine deaminase binding protein (CD26, also known as dipeptidylpeptidase IV) has been identified but the functional role of this ADMCD26 complex is unclear. Here by confocal microscopy, affinity chromatography and coprecipitation experiments we show that A 1 adenosine receptor (AIR) is a second ecto-ADA binding protein. Binding of ADA to AtR increased its affinity for the ligand thus suggesting that ADA was needed for an effective coupling between A~R and heterotrimeric G proteins. This was confirmed by the fact that ASA, independently of its catalytic behaviour, enhanced the ligand-induced second messenger production via AtR. These findings demonstrate that, apart from the cleavage of adenosine, a further role of ecto-adenosine deaminase on the cell surface is to facilitate the signal transduction via AIR.

Regulation of L‐Type Calcium Channels in GH4 Cells via A1 Adenosine Receptors

“…ADA and A1Rs could be functionally coupled in GH4 cells because both proteins colocalize at the cell surface level (authors' manuscript in preparation). In recent reports we have presented results demonstrating a functional interaction between A1Rs and ecto-ADA Saura et al, 1996). Thus, ecto-ADA, irrespective of its catalytic behavior, facilitates signaling via ARs in the smooth muscle cell line DDT1MF-2 .…”

“…The characterization of these antibodies, their specificity, and their ability to recognize the A1Rs from many sources, have been described elsewhere (Ciruela et al, 1995Saura et al, 1996). Conjugated secondary antibodies were from Boehringer Mannheim Biochemica.…”

CD26, adenosine deaminase, and adenosine receptors mediate costimulatory signals in the immunological synapse

“…To obtain ADA without enzymatic activity, desalted ADA was treated with HgCl 2 as described in ref. 6 and passed again through a PD-10 column to eliminate remaining HgCl 2 . The enzymatic activity of Hg 2ϩ -treated ADA (ADA-Hg 2ϩ ) was completely abolished.…”

“…The first type, with only one member, is CD26, a multifunctional protein of 110 KDa strongly expressed on epithelial cells (kidney proximal tubules, intestine, and bile duct) and on several types of endothelial cells and fibroblasts and on leukocyte subsets (3)(4)(5). The second type of ecto-ADA-binding proteins includes the adenosine receptors (AR) A 1 (A 1 R) (6) and A 2B (A 2B R) (7). The association between ADA and CD26 on the T cell surface has been proposed to have a costimulatory function during T cell antigen receptor-CD3 complex engagement (2).…”

“…At present, it is not known whether ADA generates a signal when it binds to AR. However, we have previously demonstrated that ADA binding to A 1 R or A 2B R is required for high efficiency affinity binding of the agonist and for efficient agonist-dependent signaling (6,7).…”