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Adenosine uptake is the major effector of extracellular ATP toxicity in human cervical cancer cells.

Mello Pde A, Filippi-Chiela EC, Nascimento J, Beckenkamp A, Santana DB, Kipper F, Casali EA, Nejar Bruno A, Paccez JD, Zerbini LF, Wink MR, Lenz G, Buffon A - Mol. Biol. Cell (2014)

Bottom Line: Corroborating these data, blockage or knockdown of P2 × 7 only slightly reduced ATP cytotoxicity.Moreover, ATP-induced apoptosis and signaling-p53 increase, AMPK activation, and PARP cleavage-as well as autophagy induction were also inhibited by dipyridamole.In addition, inhibition of adenosine conversion into AMP also blocked cell death, indicating that metabolization of intracellular adenosine originating from extracellular ATP is responsible for the main effects of the latter in human cervical cancer cells.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Biochemical and Cytological Analysis, Faculty of Pharmacy, Federal University of Rio Grande do Sul, Porto Alegre, RS 90610-000, Brazil.

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Schematic illustration of how adenosine uptake induces SiHa cervical tumor cell death in response to high levels of extracellular ATP. (A) A small subpopulation that expresses high levels of P2×7 died after being exposed to high levels of extracellular ATP via P2×7 activation by an unknown intracellular mechanism. The P2×7 antagonist oATP and receptor knockdown partially blocked ATP-induced cell death. (B) A major subpopulation of cells that express low levels of P2×7 died after being exposed to ATP metabolites such as ADP, AMP, adenosine, inosine, and hypoxanthine. In these cells, adenosine is taken up and partially converted to inosine through adenosine deaminase (ADA) activity. Concomitantly, adenosine is also phosphorylated to AMP by adenosine kinase (ADK), which leads to dATP accumulation, AMPK phosphorylation, p53 activation, autophagy induction, and finally cell death through apoptosis. Dipyridamole (DIP), an adenosine transporter inhibitor, and ABT-702, an adenosine kinase inhibitor, completely blocked cell death induction by these pathways. →, stimulation; –/, inhibition. ADO, adenosine; ADP, adenosine 5´-diphosphate; AMP, adenosine 5´-monophosphate; ATP, adenosine 5´-triphosphate; dADP, deoxyadenosine 5´-diphosphate; dATP, deoxyadenosine 5´-triphospate; HYPO, hypoxanthine; INO, inosine.
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Figure 8: Schematic illustration of how adenosine uptake induces SiHa cervical tumor cell death in response to high levels of extracellular ATP. (A) A small subpopulation that expresses high levels of P2×7 died after being exposed to high levels of extracellular ATP via P2×7 activation by an unknown intracellular mechanism. The P2×7 antagonist oATP and receptor knockdown partially blocked ATP-induced cell death. (B) A major subpopulation of cells that express low levels of P2×7 died after being exposed to ATP metabolites such as ADP, AMP, adenosine, inosine, and hypoxanthine. In these cells, adenosine is taken up and partially converted to inosine through adenosine deaminase (ADA) activity. Concomitantly, adenosine is also phosphorylated to AMP by adenosine kinase (ADK), which leads to dATP accumulation, AMPK phosphorylation, p53 activation, autophagy induction, and finally cell death through apoptosis. Dipyridamole (DIP), an adenosine transporter inhibitor, and ABT-702, an adenosine kinase inhibitor, completely blocked cell death induction by these pathways. →, stimulation; –/, inhibition. ADO, adenosine; ADP, adenosine 5´-diphosphate; AMP, adenosine 5´-monophosphate; ATP, adenosine 5´-triphosphate; dADP, deoxyadenosine 5´-diphosphate; dATP, deoxyadenosine 5´-triphospate; HYPO, hypoxanthine; INO, inosine.

Mentions: We propose that human cervical cancer cells comprise a heterogeneous population that responds differently to extracellular ATP toxicity according to the level of P2×7 receptor present in the cell membrane. Our hypothesis is that ATP per se is responsible for the elimination of a small subpopulation of cells (∼20%) that express a high level of P2×7 and are killed through P2×7 activation, whereas adenosine acts in the remaining subpopulation, which is ATP resistant, expresses low levels of P2×7, and dies through adenosine uptake, AMPK phosphorylation, dATP accumulation, p53 activation, and autophagy induction (Figure 8). Thus cooperation among ATP and its metabolites seems to be important for cytotoxicity, with adenosine being necessary, but not sufficient, to induce cell death in the whole population of cells, which is of fundamental importance in cancer therapeutics. In conclusion, here we shed light on how cervical cancer cells respond to high extracellular ATP, which is a context commonly present in solid tumors and can be exploited to improve our understanding of tumor biology, as well as to increase therapy efficiency and overcome cell resistance.


Adenosine uptake is the major effector of extracellular ATP toxicity in human cervical cancer cells.

Mello Pde A, Filippi-Chiela EC, Nascimento J, Beckenkamp A, Santana DB, Kipper F, Casali EA, Nejar Bruno A, Paccez JD, Zerbini LF, Wink MR, Lenz G, Buffon A - Mol. Biol. Cell (2014)

Schematic illustration of how adenosine uptake induces SiHa cervical tumor cell death in response to high levels of extracellular ATP. (A) A small subpopulation that expresses high levels of P2×7 died after being exposed to high levels of extracellular ATP via P2×7 activation by an unknown intracellular mechanism. The P2×7 antagonist oATP and receptor knockdown partially blocked ATP-induced cell death. (B) A major subpopulation of cells that express low levels of P2×7 died after being exposed to ATP metabolites such as ADP, AMP, adenosine, inosine, and hypoxanthine. In these cells, adenosine is taken up and partially converted to inosine through adenosine deaminase (ADA) activity. Concomitantly, adenosine is also phosphorylated to AMP by adenosine kinase (ADK), which leads to dATP accumulation, AMPK phosphorylation, p53 activation, autophagy induction, and finally cell death through apoptosis. Dipyridamole (DIP), an adenosine transporter inhibitor, and ABT-702, an adenosine kinase inhibitor, completely blocked cell death induction by these pathways. →, stimulation; –/, inhibition. ADO, adenosine; ADP, adenosine 5´-diphosphate; AMP, adenosine 5´-monophosphate; ATP, adenosine 5´-triphosphate; dADP, deoxyadenosine 5´-diphosphate; dATP, deoxyadenosine 5´-triphospate; HYPO, hypoxanthine; INO, inosine.
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Related In: Results  -  Collection

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Figure 8: Schematic illustration of how adenosine uptake induces SiHa cervical tumor cell death in response to high levels of extracellular ATP. (A) A small subpopulation that expresses high levels of P2×7 died after being exposed to high levels of extracellular ATP via P2×7 activation by an unknown intracellular mechanism. The P2×7 antagonist oATP and receptor knockdown partially blocked ATP-induced cell death. (B) A major subpopulation of cells that express low levels of P2×7 died after being exposed to ATP metabolites such as ADP, AMP, adenosine, inosine, and hypoxanthine. In these cells, adenosine is taken up and partially converted to inosine through adenosine deaminase (ADA) activity. Concomitantly, adenosine is also phosphorylated to AMP by adenosine kinase (ADK), which leads to dATP accumulation, AMPK phosphorylation, p53 activation, autophagy induction, and finally cell death through apoptosis. Dipyridamole (DIP), an adenosine transporter inhibitor, and ABT-702, an adenosine kinase inhibitor, completely blocked cell death induction by these pathways. →, stimulation; –/, inhibition. ADO, adenosine; ADP, adenosine 5´-diphosphate; AMP, adenosine 5´-monophosphate; ATP, adenosine 5´-triphosphate; dADP, deoxyadenosine 5´-diphosphate; dATP, deoxyadenosine 5´-triphospate; HYPO, hypoxanthine; INO, inosine.
Mentions: We propose that human cervical cancer cells comprise a heterogeneous population that responds differently to extracellular ATP toxicity according to the level of P2×7 receptor present in the cell membrane. Our hypothesis is that ATP per se is responsible for the elimination of a small subpopulation of cells (∼20%) that express a high level of P2×7 and are killed through P2×7 activation, whereas adenosine acts in the remaining subpopulation, which is ATP resistant, expresses low levels of P2×7, and dies through adenosine uptake, AMPK phosphorylation, dATP accumulation, p53 activation, and autophagy induction (Figure 8). Thus cooperation among ATP and its metabolites seems to be important for cytotoxicity, with adenosine being necessary, but not sufficient, to induce cell death in the whole population of cells, which is of fundamental importance in cancer therapeutics. In conclusion, here we shed light on how cervical cancer cells respond to high extracellular ATP, which is a context commonly present in solid tumors and can be exploited to improve our understanding of tumor biology, as well as to increase therapy efficiency and overcome cell resistance.

Bottom Line: Corroborating these data, blockage or knockdown of P2 × 7 only slightly reduced ATP cytotoxicity.Moreover, ATP-induced apoptosis and signaling-p53 increase, AMPK activation, and PARP cleavage-as well as autophagy induction were also inhibited by dipyridamole.In addition, inhibition of adenosine conversion into AMP also blocked cell death, indicating that metabolization of intracellular adenosine originating from extracellular ATP is responsible for the main effects of the latter in human cervical cancer cells.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Biochemical and Cytological Analysis, Faculty of Pharmacy, Federal University of Rio Grande do Sul, Porto Alegre, RS 90610-000, Brazil.

Show MeSH
Related in: MedlinePlus