GSK-3 kinases enhance calcineurin signaling by phosphorylation of RCNs.
The conserved RCN family of proteins can bind and directly regulate calcineurin, a Ca(2+)-activated protein phosphatase involved in immunity, heart growth, muscle development, learning, and other processes. Whereas high levels of RCNs can inhibit calcineurin signaling in fungal and animal cells, RCNs can also stimulate calcineurin signaling when expressed at endogenous levels. Here we show that the stimulatory effect of yeast Rcn1 involves phosphorylation of a conserved serine residue by Mck1, a member of the GSK-3 family of protein kinases. Mutations at the GSK-3 consensus site of Rcn1 and human DSCR1/MCIP1 abolish the stimulatory effects on calcineurin signaling. RCNs may therefore oscillate between stimulatory and inhibitory forms in vivo in a manner similar to the Inhibitor-2 regulators of type 1 protein phosphatase. Computational modeling indicates a biphasic response of calcineurin to increasing RCN concentration such that protein phosphatase activity is stimulated by low concentrations of phospho-RCN and inhibited by high concentrations of phospho- or dephospho-RCN. This prediction was verified experimentally in yeast cells expressing Rcn1 or DSCR1/MCIP1 at different concentrations. Through the phosphorylation of RCNs, GSK-3 kinases can potentially contribute to a positive feedback loop involving calcineurin-dependent up-regulation of RCN expression. Such feedback may help explain the large induction of DSCR1/MCIP1 observed in brain of Down syndrome individuals.
Hilioti
Zoe
Z
Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Gallagher
Deirdre A
DA
Low-Nam
Shalini T
ST
Ramaswamy
Priya
P
Gajer
Pawel
P
Kingsbury
Tami J
TJ
Birchwood
Christine J
CJ
Levchenko
Andre
A
Cunningham
Kyle W
KW
D019703:Calcineurin / Q000378:metabolism*; D017124:Conserved Sequence; D015966:Gene Expression Regulation, Fungal; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics* / Q000378:metabolism*; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D020411:Oligonucleotide Array Sequence Analysis; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D015398:Signal Transduction
D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D038362:Glycogen Synthase Kinase 3; D019703:Calcineurin