Effects of synthetic A3 adenosine receptor agonists on cell proliferation and viability are receptor independent at micr
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ORIGINAL PAPER
Effects of synthetic A3 adenosine receptor agonists on cell proliferation and viability are receptor independent at micromolar concentrations Petr Mlejnek & Petr Dolezel & Ivo Frydrych
Received: 11 May 2012 / Accepted: 7 November 2012 / Published online: 27 November 2012 # University of Navarra 2012
Abstract The question as to whether A3 adenosine receptor (A3AR) agonists, N 6 -(3-iodobenzyl)adenosine-5′-N- methyluronamide (IB-MECA) and 2-c hloro-N 6 -(3 -io dobe nzyl)- aden osine-5 ′-N methyluronamide (Cl-IB-MECA), could exert cytotoxic effects at high concentrations with or without the involvement of A3AR has been a controversial issue for a long time. The initial findings suggesting that A3AR plays a crucial role in the induction of cell death upon treatment with micromolar concentrations of IBMECA or Cl-IB-MECA were revised, however, the direct and unequivocal evidence is still missing. Therefore, the sensitivity of Chinese hamster ovary (CHO) cells transfected with human recombinant A3AR (A3-CHO) and their counter partner wild-type CHO cells, which do not express any of adenosine receptors, to micromolar concentrations of IB-MECA and Cl-IB-MECA was studied. We observed that IBMECA and Cl-IB-MECA exhibited a strong inhibitory effect on cell proliferation due to the blockage of cell cycle progression at G1/S and G2/M transitions in both A3-CHO and CHO cells. Further analysis revealed that IB-MECA and Cl-IB-MECA attenuated the Erk1/2 signalling irrespectively to A3AR expression. In addition, Cl-IB-MECA induced massive cell death mainly with hallmarks of a necrosis in both cell lines. P. Mlejnek (*) : P. Dolezel : I. Frydrych Department of Biology, Faculty of Medicine and Dentistry, Palacky University Olomouc, Hnevotinska 3, Olomouc 77515, Czech Republic e-mail: [email protected]
In contrast, IB-MECA affected cell viability only slightly independently of A3AR expression. IB-MECA induced cell death that exhibited apoptotic hallmarks. In general, the sensitivity of A3-CHO cells to micromolar concentrations of IB-MECA and Cl-IB-MECA was somewhat, but not significantly, higher than that observed in the CHO cells. These results strongly suggest that IBMECA and Cl-IB-MECA exert cytotoxic effects at micromolar concentrations independently of A3AR expression. Keywords Cl-IB-MECA . IB-MECA . CHO cells . Erk1/2 . Akt . Apoptosis . Necrosis . A3 adenosine agonist
Introduction Purines are ubiquitously present simple molecules that participate on transducing signals in all eukaryotic cells under both physiological and pathological conditions. Adenosine represents an important intercellular messenger in animals. Upon release from metabolically active or damaged cells, it acts as a regulatory molecule through binding to specific adenosine cell surface receptors, which are subclassed into four groups: A1, A2A, A2B and A3 [1, 12, 13]. Among them, the A3 subtype seems to be rather enigmatic since it exhibits opposite roles under different pathophysiological conditions [4, 10, 19, 21]. Nevertheless, intensive s
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