Cell Surface Adenosine Deaminase Binds and Stimulates Plasminogen Activation on 1-LN Human Prostate Cancer Cells

Abstract

Adenosine deaminase (ADA) is expressed intracellularly by all cells, but in some tissues, it is also associated with the cell surface multifunctional glycoprotein CD26/ dipeptidyl peptidase IV. By modulating extracellular adenosine, this "ecto-ADA" may regulate adenosine receptor signaling implicated in various cellular functions. CD26 is expressed on the surface of human prostate cancer 1-LN cells acting as a receptor for plasminogen (Pg). Since ADA and Pg bind to CD26 at distinct but nearby sites, we investigated a possible interaction between these two proteins on the surface of 1-LN cells. Human ADA binds to CD26 on the surface 1-LN cells and immobilized CD26 isolated from the same cells with similar affinity. In both cases, ADA binding is diminished by mutation of ADA residues known to interact with CD26. ADA was also found to bind Pg 2 in the absence of CD26 via the Pg kringle 4 (K4) domain. In the presence of 1-LN cells or immobilized CD26, exogenous ADA enhances conversion of Pg 2 to plasmin by 1-LN endogenous urinary plasminogen activator (u-PA), as well as by added tissue Pg Activator (t-PA), suggesting that ADA and Pg bind simultaneously to CD26 in a ternary complex that stimulates the Pg activation by its physiologic activators. Consistent with this, in melanoma A375 cells that bind Pg, but do not express CD26, the rate of Pg activation was not affected by ADA. Thus, ADA may be a factor regulating events in prostate cancer cells that occur when Pg binds to the cell surface and is activated.

Molecular Evidence of Adenosine Deaminase Linking Adenosine A2A Receptor and CD26 Proteins

“…This is in agreement with the affinity constants of ADA to bind to these two proteins. It has been reported that the affinity of 125 I-ADA by CD26 is around 18 nM ( Gonzalez-Gronow et al, 2004 ) (equivalent to 0.7 μg/ml), and its affinity by A 1 R is around 230 nM ( Saura et al, 1996 ) (equivalent to 9 μg/ml). These values indicate that first ADA binds to CD26 and then to AR, so that a balance of ADA concentrations occurs between the bars of 0.1 and 10 μg/ml in Figure 4A to form a trimeric complex, where ADA has enough concentration to bridge CD26 and AR, but higher concentrations shift the equilibrium toward dimeric ADA-CD26 and ADA-AR complexes.…”

Angiostatin directly inhibits human prostate tumor cell invasion by blocking plasminogen binding to its cellular receptor, CD26

“…Pg binds via its 2,3-linked sialic acid residues attached to Thr 345 O-linked carbohydrate chains to CD26 [12]. Pg also binds via its kringle 4 to adenosine deaminase in complex with CD26 [13]. Both these interactions with CD26 result in an augmented Pm generation which, in addition to facilitating cell invasion, may also stimulate generation of angiostatin directly on the cell surface.…”

Relatively Small Increases in the Steady-State Levels of Nucleobase Deamination Products in DNA from Human TK6 Cells Exposed to Toxic Levels of Nitric Oxide

“…That this artifact was due to contaminating dA deaminase activity was confirmed by the absence of dI formation when coformycin, a specific inhibitor of dA/A deaminase, was added during DNA processing steps (14). The presence of dA deaminase activity is not surprising given the role of adenine deaminase in purine metabolism, the adenosine deaminase (ADA) associated with cell surface glycoproteins to regulate adenosine receptor signaling (46), and the adenosine deaminases termed ADARs that mediate RNA editing (47)(48)(49)(50). Among the known ADARs, ADAR1 was found to recognize Z-DNA when flanked by B-DNA (51).…”