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Published online 7 August 2006. doi:10.1083/jcb.200604033
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 174, Number 4, 521-533
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Article

 PKC{alpha}: a versatile key for decoding the cellular calcium toolkit

Gregor Reither1, Michael Schaefer2, and Peter Lipp1

1 Institute for Molecular Cell Biology, Medical Faculty of the Saarland University, D-66421 Homburg/Saar, Germany
2 Institute for Pharmacology, Campus Benjamin Franklin, Charité-Universitätsmedizin Berlin, 14195 Berlin, Germany

Correspondence to Peter Lipp: peter.lipp{at}uniklinikum-saarland.de

Conventional protein kinases C (cPKCs) play an essential role in signal transduction and are believed to integrate both global Ca2+ transients and diacylglycerol signals. We provide evidence that PKC{alpha} is a ubiquitous readout sensor for the cellular Ca2+ toolkit, including highly restricted elementary Ca2+ release.

Threshold stimulations of cells with Ca2+-mobilizing agonists resulted in PKC{alpha} translocation events with limited spatial spreads (<4 µm) comprising two groups of lifetimes; brief events (400–1,500 ms) exclusively mediated by Ca2+–C2 domain membrane interactions and long-lasting events (>4 s) resulting from longer DAG-C1a domain–mediated membrane interactions.

Although upon uncaging NP-EGTA, which is a caged Ca2+ compound, WT-PKC{alpha} displayed rapid membrane translocations within <250 ms, PKC{alpha} constructs with C2 domains mutated in their Ca2+-binding region lacked any Ca2+-dependent translocation. Flash photolysis of diazo-2, a photosensitive caged Ca2+ buffer, revealed a biphasic membrane dissociation (slow and fast period) of WT-PKC{alpha}. The slow phase was absent in cells expressing PKC{alpha}-constructs containing mutated C1a-domains with largely reduced DAG binding. Thus, two groups of PKC{alpha} membrane interactions coexist; C2- and C1a-mediated interactions with different lifetimes but rapid interconversion.

We conclude that PKC{alpha} can readout very fast and, spatially and temporally, very complex cellular Ca2+ signals. Therefore, cPKCs are important transducers for the ubiquitous cellular Ca2+ signaling toolkit.

Abbreviations used in this paper: cPKC, conventional PKC; DAG, diacylglycerol; HEK, human embryonic kidney; LTE, local translocation event; PIP2, phosphatidyl-4,5-bisphosphate; PMA, phorbol 12-myristate 13-acetate; PS, phosphatidylserine; ROI, region of interest; WT, wild-type.


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