title: The RCAN carboxyl end mediates calcineurin docking-dependent inhibition via a site that dictates binding to substrates and regulators.
abstract: Specificity of signaling kinases and phosphatases toward their targets is usually mediated by docking interactions with substrates and regulatory proteins. Here, we characterize the motifs involved in the physical and functional interaction of the phosphatase calcineurin with a group of modulators, the RCAN protein family. Mutation of key residues within the hydrophobic docking-cleft of the calcineurin catalytic domain impairs binding to all human RCAN proteins and to the calcineurin interacting proteins Cabin1 and AKAP79. A valine-rich region within the RCAN carboxyl region is essential for binding to the docking site in calcineurin. Although a peptide containing this sequence compromises NFAT signaling in living cells, it does not inhibit calcineurin catalytic activity directly. Instead, calcineurin catalytic activity is inhibited by a motif at the extreme C-terminal region of RCAN, which acts in cis with the docking motif. Our results therefore indicate that the inhibitory action of RCAN on calcineurin-NFAT signaling results not only from the inhibition of phosphatase activity but also from competition between NFAT and RCAN for binding to the same docking site in calcineurin. Thus, competition by substrates and modulators for a common docking site appears to be an essential mechanism in the regulation of Ca(2+)-calcineurin signaling.
authors.affiliation: Department of Vascular Biology and Inflammation, Centro Nacional de Investigaciones Cardiovasculares, 28029 Madrid, Spain.
authors.forename: Sara
authors.initials: S
authors.lastname: Martínez-Martínez
authors.forename: Lali
authors.initials: L
authors.lastname: Genescà
authors.forename: Antonio
authors.initials: A
authors.lastname: Rodríguez
authors.forename: Alicia
authors.initials: A
authors.lastname: Raya
authors.forename: Eulàlia
authors.initials: E
authors.lastname: Salichs
authors.forename: Felipe
authors.initials: F
authors.lastname: Were
authors.forename: María Dolores
authors.initials: MD
authors.lastname: López-Maderuelo
authors.forename: Juan Miguel
authors.initials: JM
authors.lastname: Redondo
authors.forename: Susana
authors.initials: S
authors.lastname: de la Luna