Sivaramakrishnan V, Bidula S, Campwala H, Katikaneni D, Fountain SJ. Constitutive lysosome exocytosis releases ATP and engages P2Y receptors in human monocytes.
J Cell Sci 2012;
125:4567-75. [PMID:
22767503 DOI:
10.1242/jcs.107318]
[Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Elucidating mechanisms by which Ca(2+) signals are generated by monocytes is important for understanding monocyte function in health and disease. We have investigated mechanisms underlying Ca(2+) signals generated following disruption of lysosomes by exposure to the cathepsin C substrate glycyl-L-phenylalanine-β-napthylamide (GPN). Exposure to 0.2 mM GPN resulted in robust increases in the intracellular Ca(2+) concentration ([Ca(2+)](i)) in the absence of extracellular Ca(2+). The response was antagonised by thapsigargin and evoked capacitative Ca(2+) entry. Dantrolene-sensitive Ca(2+) responses were observed at higher concentrations of GPN (0.4 mM) but not at 0.2 mM. Strikingly, GPN-evoked Ca(2+) responses and β-hexosaminidase secretion were inhibited by the ATPase/ADPase apyrase. Simultaneous measurement of [Ca(2+)](i) and extracellular ATP revealed a concomitant secretion of ATP during GPN-evoked Ca(2+) signalling. Furthermore, the ability of GPN to raise [Ca(2+)](i) was inhibited by P2Y receptor antagonists or by inhibiting vesicular exocytosis with N-ethylmaleimide (NEM). NEM treatment was associated with an inability of GPN to trigger ATP secretion, a drop in baseline [Ca(2+)](i) and reduction in extracellular ATP concentration. Antagonism of purinergic signalling also caused a reduction in baseline [Ca(2+)](i). In summary, these data suggest that P2Y receptor activation contributes significantly to GPN-evoked Ca(2+) signalling, and that constitutive secretion of lysosomal ATP is a major determinant of Ca(2+) homeostasis in monocytes. Lysosomal Ca(2+) stores can communicate with ER Ca(2+) stores either directly through activation of ryanodine receptors, or indirectly through release of ATP and engagement of P2Y receptors.
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