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Two pore channel 2 (TPC2) inhibits autophagosomal-lysosomal fusion by alkalinizing lysosomal pH

Yingying Lu1, Bai-Xia Hao, Richard Graeff

  • 1Department of Physiology, University of Hong Kong, Hong Kong, China.

The Journal of Biological Chemistry
|July 10, 2013
PubMed

Insights

Nicotinic acid adenine dinucleotide phosphate (NAADP) signaling via TPC2 channels inhibits autophagy by increasing lysosomal pH. This disrupts autophagosomal-lysosomal fusion, leading to autophagosome accumulation and impaired degradation.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Physiology

Background:

  • Autophagy is a critical cellular process for degrading damaged components via lysosomes.
  • The precise molecular mechanisms regulating autophagy, particularly autophagosomal-lysosomal fusion, are not fully understood.
  • Nicotinic acid adenine dinucleotide phosphate (NAADP) is a key calcium (Ca2+) signaling molecule involved in cellular processes.

Purpose of the Study:

  • To investigate the role of TPC2 channels and NAADP signaling in regulating autophagy.
  • To elucidate the specific stage of autophagy affected by TPC2/NAADP signaling.
  • To determine the impact of TPC2 overexpression on lysosomal function and autophagy progression.

Main Methods:

  • Overexpression and knockdown of TPC2 in HeLa and mouse embryonic stem cells.
  • Treatment with NAADP agonists (NAADP-AM) and antagonists (Ned-19).
  • Assessment of autophagosomal-lysosomal fusion, autophagosome accumulation, lysosomal pH, and Rab-7 recruitment.

Main Results:

  • TPC2 overexpression inhibited autophagosomal-lysosomal fusion, causing autophagosome accumulation.
  • NAADP agonists exacerbated TPC2-induced autophagosome accumulation, while antagonists and TPC2 knockdown reduced it.
  • TPC2 overexpression alkalinized lysosomal pH, and re-acidification reversed the autophagosome accumulation; Rab-7 recruitment was impaired.

Conclusions:

  • TPC2/NAADP/Ca2+ signaling specifically inhibits the later stages of basal autophagy.
  • Lysosomal alkalinization induced by TPC2 activity is the mechanism underlying autophagy inhibition.
  • This pathway provides a novel regulatory mechanism for controlling autophagic flux.
Keywords:
AutophagyCalciumCalcium ChannelsCalcium Intracellular ReleaseCalcium SignalingLysosomesNAADPTPC2pH

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