Constitutive lysosome exocytosis releases ATP and engages P2Y receptors in human monocytes

Sivaramakrishnan, Venketesh; Bidula, Stefan; Campwala, Hinnah; Katikaneni, Divya S.; Fountain, Samuel J.

doi:10.1242/jcs.107318

Cited by 43 publications

(52 citation statements)

References 58 publications

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“…In addition, previous studies have demonstrated that Dictyostelium can condition growth medium with ATP (10). This suggests that Dictyostelium amoebas secrete ATP constitutively, as do some mammalian cells (15,18). Our own bulk phase measurements suggest a relatively high basal level of extracellular ATP, between 2 and 4 M. In this study, inhibition of vesicular secretion with NEM or by drainin knockout did not affect the level of basal ATP, though NEM strongly inhibited ATP release during swelling.…”

Section: Discussionmentioning

confidence: 40%

“…Furthermore, vesicular ATP release is one of numerous mechanisms proposed as modes of ATP secretion in mammalian cells (18). Therefore, we sought to employ N-ethylmaleimide (NEM), which blocks vesicular exocytosis and ATP release in mammalian cells (15). NEM caused profound swelling and loss of regulatory cell volume decrease under hypotonic conditions ( Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Our own bulk phase measurements suggest a relatively high basal level of extracellular ATP, between 2 and 4 M. In this study, inhibition of vesicular secretion with NEM or by drainin knockout did not affect the level of basal ATP, though NEM strongly inhibited ATP release during swelling. Exocytosis of ATP-containing vesicles, such as lysosomes, has been shown to contribute to constitutive ATP secretion in mammalian cells (15), though this appears not to be the case for Dictyostelium. Our current study suggests that constitutively secreted ATP does not influence cell volume, as apyrase had no effect on cell size under isotonic conditions.…”

Section: Discussionmentioning

confidence: 99%

“…The samples were spun immediately at 500 ϫ g for 5 min at 4°C to produce a cell-free supernatant and to limit celldependent ATP breakdown. ATP was quantified by luciferase-luciferin assay as described previously (15). NO assay.…”

Section: Methodsmentioning

confidence: 99%

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Evidence for Extracellular ATP as a Stress Signal in a Single-Celled Organism

Sivaramakrishnan

Fountain

2015

Eukaryot Cell

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ATP is omnipresent in biology and acts as an extracellular signaling molecule in mammals. Information regarding the signaling function of extracellular ATP in single-celled eukaryotes is lacking. Here, we explore the role of extracellular ATP in cell volume recovery during osmotic swelling in the amoeba Dictyostelium. Release of micromolar ATP could be detected during cell swelling and regulatory cell volume decrease (RVD) phases during hypotonic challenge. Scavenging ATP with apyrase caused profound cell swelling and loss of RVD. Apyrase-induced swelling could be rescued by 100 M ␤␥-imidoATP. N-Ethylmalemide (NEM), an inhibitor of vesicular exocytosis, caused heightened cell swelling, loss of RVD, and inhibition of ATP release. Amoebas with impaired contractile vacuole (CV) fusion (drainin knockout [KO] cells) displayed increased swelling but intact ATP release. One hundred micromolar Gd 3؉ caused cell swelling while blocking any recovery by ␤␥-imidoATP. ATP release was 4-fold higher in the presence of Gd 3؉ . Cell swelling was associated with an increase in intracellular nitric oxide (NO), with NO-scavenging agents causing cell swelling. Swelling-induced NO production was inhibited by both apyrase and Gd 3؉ , while NO donors rescued apyrase-and Gd 3؉ -induced swelling. These data suggest extracellular ATP released during cell swelling is an important signal that elicits RVD. Though the cell surface receptor for ATP in Dictyostelium remains elusive, we suggest ATP operates through a Gd 3؉ -sensitive receptor that is coupled with intracellular NO production.T he ability to control cell volume is an essential function for cell survival in the face of osmotic challenge. Perturbations in cell volume evoke wide-ranging signaling events leading to acute protective responses (e.g., rearrangement of the cytoskeleton) and longer-term adaptive responses (e.g., alterations in osmolyte transport and gene expression) (1). During acute swelling, cells can respond by a process of regulatory cell volume decrease (RVD). Under normal physiological conditions, mammalian cells are exposed to extracellular fluid osmolarity of approximately 285 mosmol, which is kept constant by normal body fluid homeostasis. Cell swelling often occurs as a consequence of changes to the intracellular composition of osmolytes, which results in intracellular hypotonicity and the influx of water. Compositional changes may occur during increased cellular transport or accumulation of nutrients or metabolic waste. Osmotically swollen mammalian cells release K ϩ , Cl Ϫ , and nonessential organic osmolytes in an effort to reverse the flow of water by osmosis. In contrast to mammalian cells, free-living single eukaryotic cells can be subjected to rapid and harsh changes in the osmolarity of the extracellular environment. As a consequence, the majority of single-celled organisms have evolved a specialized organelle called the contractile vacuole, a bladder-like structure that plays a major role in extruding water from the cytoplasm and expelling it into the ex...

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Section: Discussionmentioning

confidence: 40%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Evidence for Extracellular ATP as a Stress Signal in a Single-Celled Organism

Sivaramakrishnan

Fountain

2015

Eukaryot Cell

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“…How A␤1-42 induces ATP release from glial cells is largely unknown. Lysosomal exocytosis of ATP has been reported for several types of glial cells or monocytes induced under various conditions (11,35,(49)(50)(51). Whether the A␤1-42-induced ATP release in glial cells is also through lysosomal exocytosis needs further clarification.…”

Section: Discussionmentioning

confidence: 97%