Editors' ChoiceApoptosis

Channeling Death

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Science Signaling  19 Oct 2010:
Vol. 3, Issue 144, pp. ec318
DOI: 10.1126/scisignal.3144ec318

Apoptotic cells release the nucleotides ATP and UTP to attract phagocytic cells, which in turn clear the apoptotic cells. Chekeni et al. found that carbenoxolone (CBX), which inhibits connexins (which form gap junctions) and pannexins (which form plasma membrane channels), and probenicid, which is thought to be more specific for pannexins, reduced ATP release from apoptotic Jurkat cells to a similar extent as the caspase inhibitor zVAD (which blocks the release of ATP from apoptotic cells). Small interfering RNAs (siRNAs) directed against pannexin 1 (PANX1) decreased the release of ATP and UTP from apoptotic Jurkat cells but did not prevent apoptosis. Supernatant from PANX1 siRNA-transfected apoptotic cells recruited fewer monocytes in an in vitro assay of cell migration and when placed in a subcutaneous air pouch in mice. In contrast, Jurkat cells stably overexpressing PANX1 released more ATP and UTP, and supernatants from these cells (after apoptosis had been induced) recruited more monocytes in vitro. Apoptotic cells take up dyes such as YO-PRO-1, a process the authors showed required PANX1 in Jurkat cells and was blocked by CBX in thymocytes. PANX1 currents were detected only in cells that showed morphological signs of undergoing apoptosis and were reduced by CBX. Immunoprecipitated PANX1 was cleaved at two different sites (called sites A and B by the authors) by caspase-3 and caspase-7 in vitro. Cells expressing a PANX1 mutant that could not be cleaved at site B took up less YO-PRO-1 than those expressing wild-type PANX1 or a mutant that could not be cleaved at site A. In addition, apoptotic cells expressing the PANX1 site B mutant had smaller PANX1 currents, released less ATP, and took up less TO-PRO-3. In contrast, cells expressing a PANX1 mutant that mimicked cleavage at site B took up more YO-PRO-1 and had larger PANX1 currents. Thus, PANX1 is cleaved by caspases during apoptosis, thereby activating this channel to release ATP and UTP to attract phagocytic cells.

F. B. Chekeni, M. R. Elliott, J. K. Sandilos, S. F. Walk, J. M. Kinchen, E. R. Lazarowski, A. J. Armstrong, S. Penuela, D. W. Laird, G. S. Salvesen, B. E. Isakson, D. A. Bayliss, K. S. Ravichandran, Pannexin 1 channels mediate ‘find-me’ signal release and membrane permeability during apoptosis. Nature 467, 863–867 (2010). [PubMed]

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