Calcineurin and intracellular Ca2+-release channels:: regulation or association?

The Ca2+- and calmodulin-dependent phosphatase calcineurin was reported to interact with the inositol 1,4,5-trisphosphate receptor (IP3R) and the ryanodine receptor (RyR) and to modulate their phosphorylation status and activity. However, controversial data on the molecular mechanisms involved and on the functional relevance of calcineurin for these channel-complexes have been described. Hence, we will focus on the functional importance of calcineurin for IP3R and RyR function and on the different mechanisms by which Ca2+-dependent dephosphorylation can affect the gating of those intracellular Ca2+-release channels. Since many studies made use of immunosuppressive drugs that are inhibiting calcineurin activity, we will also have to take the different side effects of these drugs into account for the proper interpretation of the effects of calcineurin on intracellular Ca2+-release channels. In addition, it became recently known that various other phosphatases and kinases can associate with these channels, thereby forming macromolecular complexes. The relevance of these enzymes for IP3R and RyR functioning will be reviewed since in some cases they could interfere with the effects ascribed to calcineurin. Finally, we will discuss the downstream effects of calcineurin on the regulation of the expression levels of intracellular Ca2+-release channels as well as the relation between IP3R- and RyR-mediated Ca2+ release and calcineurin-dependent gene expression. (C) 2003 Elsevier Inc. All rights reserved.