Caspase-3-truncated type 1 inositol 1,4,5-trisphosphate receptor enhances intracellular Ca2+ leak and disturbs Ca2+ signalling.
BACKGROUND
The IP(3)R (inositol 1,4,5-trisphosphate receptor) is a tetrameric channel that accounts for a large part of the intracellular Ca(2+) release in virtually all cell types. We have previously demonstrated that caspase-3-mediated cleavage of IP(3)R1 during cell death generates a C-terminal fragment of 95 kDa comprising the complete channel domain. Expression of this truncated IP(3)R increases the cellular sensitivity to apoptotic stimuli, and it was postulated to be a constitutively active channel.


RESULTS
In the present study, we demonstrate that expression of the caspase-3-cleaved C-terminus of IP(3)R1 increased the rate of thapsigargin-mediated Ca(2+) leak and decreased the rate of Ca(2+) uptake into the ER (endoplasmic reticulum), although it was not sufficient by itself to deplete intracellular Ca(2+) stores. We detected the truncated IP(3)R1 in different cell types after a challenge with apoptotic stimuli, as well as in aged mouse oocytes. Injection of mRNA corresponding to the truncated IP(3)R1 blocked sperm factor-induced Ca(2+) oscillations and induced an apoptotic phenotype.


CONCLUSIONS
In the present study, we show that caspase-3-mediated truncation of IP(3)R1 enhanced the Ca(2+) leak from the ER. We suggest a model in which, in normal conditions, the increased Ca(2+) leak is largely compensated by enhanced Ca(2+)-uptake activity, whereas in situations where the cellular metabolism is compromised, as occurring in aging oocytes, the Ca(2+) leak acts as a feed-forward mechanism to divert the cell into apoptosis.
Verbert
Leen
L
Laboratory of Molecular and Cellular Signalling, Division of Physiology, Department of Molecular Cell Biology, K.U. Leuven, Campus Gasthuisberg, O&N1 bus 802, B-3000 Leuven, Belgium.
Lee
Bora
B
Kocks
Sarah L
SL
Assefa
Zerihun
Z
Parys
Jan B
JB
Missiaen
Ludwig
L
Callewaert
Geert
G
Fissore
Rafael A
RA
De Smedt
Humbert
H
Bultynck
Geert
G
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D053148:Caspase 3 / Q000378:metabolism*; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000378:metabolism; D005260:Female; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000235:genetics / Q000378:metabolism*; D008540:Meiosis / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D009865:Oocytes / Q000166:cytology / Q000502:physiology; D019311:Staurosporine / Q000378:metabolism; D019284:Thapsigargin / Q000378:metabolism
D004791:Enzyme Inhibitors; D053496:Inositol 1,4,5-Trisphosphate Receptors; D019284:Thapsigargin; D053148:Caspase 3; D019311:Staurosporine; D002118:Calcium