The molecular basis for calcium release by NAADP

Lead Research Organisation: University College London
Department Name: Neuroscience Physiology and Pharmacology

Abstract

All cells of the body are physically separated from their surrounding environment by a membrane. In order for cells to respond to factors in the blood (such as hormones) which normally can not pass through the membrane, special 'messenger' molecules are used that are generated inside the cell upon contact of the stimulus with the cell. One of these molecules, NAADP controls cell function by mediating changes in the concentration of calcium. These calcium changes are important for many processes including, for example, fertilisation. Understanding how NAADP increases calcium levels is important to understand how cells work but at present we do not know the identity of the protein or 'channel' that opens in response to NAADP to allow calcium levels to change. In this proposal, we will study a family of proteins that we know very little about but which our initial experiments suggest are the channels for NAADP. We will define their location within the cell, determine exactly how they respond to NAADP and whether they are needed for hormones which make NAADP to mediate changes in calcium. The results of our experiments will provide urgently needed information on how NAADP functions and experimental tools to further study the effects of NAADP.

Technical Summary

Cytosolic calcium ions form the basis of a ubiquitous signal transduction pathway that controls a huge number of physiological processes. Understanding how changes in cytosolic calcium occur in response to extracellular cues is crucial for understanding how calcium dependent events are regulated, and has major implications for the many diseases in which calcium signals are perturbed. Recent studies have established a new calcium signalling pathway regulated by the potent calcium mobilizing messenger NAADP. Unlike the 'traditional' messenger molecules, IP3 and cyclic ADP-ribose, NAADP mobilizes acidic stores of calcium. Moreover, NAADP has the unique ability to coordinate the activity of other intracellular calcium channels. However, despite the critical importance of NAADP in triggering agonist-evoked calcium signals, the molecular identity of the target channel has yet to be unequivocally defined. This paucity in information is substantially hampering efforts to characterize the physiological roles of NAADP. In this application, we will test whether the target channels for NAADP are a family of proteins that bear homology to voltage-sensitive calcium channels and which in animals are almost completely uncharacterised. Using a combination of molecular and cell biology approaches, and based on substantial preliminary data, we expect to localize the candidate channels to the endo-lysosomal system, demonstrate their sensitivity to NAADP and establish their contribution to physiologically relevant agonist-evoked calcium signals. Determining the molecular basis for NAADP action will represent a major breakthrough in the signal transduction field that will not only substantially further our understanding of how calcium signals are generated but also provide truly novel opportunities for future study of this ubiquitous signalling pathway.

Publications

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Penny C (2014) A computational model of lysosome-ER Ca2+ microdomains in Journal of Cell Science

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Gómez-Suaga P (2012) A link between LRRK2, autophagy and NAADP-mediated endolysosomal calcium signalling. in Biochemical Society transactions

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Patel S (2011) Acidic Ca(2+) stores come to the fore. in Cell calcium

 
Description We have identified and characterized a new class of ion channels known as the two-pore channels (TPCs). Our findings indicate that these proteins are responsible for releasing calcium from acidic organelles such as lysosomes in response to the second messenger NAADP. This is a major breakthrough as a definitive molecular correlate for NAADP action was not known. TPCs are now being studied by many groups worldwide.
Exploitation Route TPCs now present themselves as novel therapeutic targets. See outcomes from independent work funded by Parkinson's UK.
Sectors Healthcare

Pharmaceuticals and Medical Biotechnology

URL http://jcb.rupress.org/content/186/2/164.2.full.pdf+html
 
Description A role for a novel animal endo-lysosomal Ca2+/H+ exchanger in Ca2+ signalling and chemotaxis
Amount £428,461 (GBP)
Funding ID BB/K000942/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 01/2013 
End 01/2016
 
Description Abnormal lysosomal calcium signalling in Parkinson's: Clues from lysosomal storage disorders
Amount £34,798 (GBP)
Funding ID K-1107 
Organisation Parkinson's UK 
Sector Charity/Non Profit
Country United Kingdom
Start 05/2012 
End 03/2014
 
Description Membrane contact sites between endolysosomes and the ER as novel hubs in Ca2+ signalling
Amount £430,122 (GBP)
Funding ID BB/N01524X/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 06/2016 
End 06/2019
 
Description Mis-coordinated Ca2+ signalling in Parkinson's
Amount £92,276 (GBP)
Organisation Parkinson's UK 
Sector Charity/Non Profit
Country United Kingdom
Start 08/2013 
End 09/2016
 
Description Targeting two-pore channel 2 in LRRK2-dependent Parkinson's disease
Amount £34,798 (GBP)
Funding ID K-1412 
Organisation Parkinson's UK 
Sector Charity/Non Profit
Country United Kingdom
Start 01/2015 
End 09/2015