Gs Protein-Coupled Adenosine Receptor Signaling and Lytic Function of Activated NK Cells

Abstract

The effect of adenosine and its analogues on the cytotoxic activity of IL-2-activated NK cells was investigated. Adenosine is an endogenous ligand for four different adenosine receptor (AdoR) subtypes (AdoRA1, AdoRA2A, AdoRA2B, and AdoRA3). Increased concentrations of adenosine were found in ascites of MethA sarcoma or in culture medium of 3LL Lewis lung carcinoma growing under hypoxic conditions. We hypothesize that intratumor adenosine impairs the ability of lymphokine-activated killer (LAK) cells to kill tumor cells. The effect of AdoR engagement on LAK cells cytotoxic activity was analyzed using AdoR agonists and antagonists as well as LAK cells generated from AdoR knockout mice. Adenosine and its analogues efficiently inhibited the cytotoxic activity of LAK cells. CGS21680 (AdoRA2A agonist) and 5-N-ethylcarboxamide adenosine (NECA) (AdoRA2A/ADoRA2B agonist) inhibited LAK cell cytotoxicity in parallel with their ability to increase cAMP production. The inhibitory effects of stable adenosine analog 2-chloroadenosine (CADO) and AdoRA2 agonists were blocked by AdoRA2 antagonist ZM 241385. Adenosine and its analogues impair LAK cell function by interfering with both perforin-mediated and Fas ligand-mediated killing pathways. Studies with LAK cells generated from AdoRA1−/− and AdoRA3−/− mice ruled out any involvement of these AdoRs in the inhibitory effects of adenosine. LAK cells with genetically disrupted AdoRA2A were resistant to the inhibitory effects of adenosine, CADO and NECA. However, with extremely high concentrations of CADO or NECA, mild inhibition of LAK cytotoxicity was observed that was probably mediated via AdoRA2B signaling. Thus, by using pharmacological and genetic blockage of AdoRs, our results clearly indicate the prime importance of cAMP elevating AdoR2A in the inhibitory effect of adenosine on LAK cell cytotoxicity. The elevated intratumor levels of adenosine might inhibit the antitumor effects of activated NK cells.

In vitro atrazine-exposure inhibits human natural killer cell lytic granule release

“…PDE is responsible for the conversion of the signaling molecule cyclic adenosine monophosphate (cAMP) to five prime adenosine monophosphate (5'-AMP), and inhibition of PDE can cause increases in the levels of cellular cAMP. This is significant in that Goto et al 1983 and Raskovalova et al 2005 established that increases in cellular cAMP levels either through the increased production of or the addition of exogenous cAMP caused a decrease in the NK cell mediated lysis of NK cell specific targets (Goto et al 1983;Raskovalova et al 2005). Thus a potential target through which atrazine may effect on NK cell lytic function is the PDE protein (Roberge et al 2004).…”

Growth Factor Regulation of Prostaglandin-Endoperoxide Synthase 2 (Ptgs2) Expression in Colonic Mesenchymal Stem Cells

“…Two of these are activin receptors (Acvrl1 and Acvr2a) that recognize this member of the transforming growth factor-␤ superfamily, a factor that may be secreted by Th2 cells (69) and by dendritic cells (70). The expressed adenosine receptor, Adora2b, can receive signals important to NK cell activity and regulation (71). A receptor capable of sensing extracellular nucleotides released in inflammation is also present (P2ry6) (72).…”

Adenosine as an endogenous immunoregulator in cancer pathogenesis: where to go?

“…As earlier mentioned, hypoxia is one of the major causes for production of adenosine; therefore, adenosine is found at higher concentration in these hypoxic sites associated with tumor. In vitro studies with 3LL Lewis lung carcinoma cells have shown that hypoxia stimulates adenosine production by tumor cells [61] (Fig. 3).…”

“…Williams Adenosine, CADO, and A 2A receptor agonists CGS, and 5-N-ethylcarboxamide adenosine (CGS21680 and NECA) inhibit both the perforin-and FasL-mediated lysis of tumor cells by lymphokine-activated killer (LAK) cells [61]. Various similar studies, in which LAK cells were isolated from deficient A 1 and A 3 receptors have confirmed that these adenosine receptors do not play any role in the adenosinemediated suppression of NK cell activity in tumor environment [143].…”