A Conserved Docking Motif for CK1 Binding Controls the Nuclear Localization of NFAT1

Abstract

In resting cells, the NFAT1 transcription factor is kept inactive in the cytoplasm by phosphorylation on multiple serine residues. These phosphorylated residues are primarily contained within two types of serine-rich motifs, the SRR-1 and SP motifs, which are conserved within the NFAT family. Several different kinases have been proposed to regulate NFAT, but no single candidate displays the specificity required to fully phosphorylate both types of motifs; thus, the identity of the kinase that regulates NFAT activity remains unclear. Here we show that the NFAT1 serine motifs are regulated by distinct kinases that must coordinate to control NFAT1 activation. CK1 phosphorylates only the SRR-1 motif, the primary region required for NFAT1 nuclear import. CK1 exists with NFAT1 in a high-molecular-weight complex in resting T cells but dissociates upon activation. GSK3 does not phosphorylate the SRR-1 region but can target the NFAT1 SP-2 motif, and it synergizes with CK1 to regulate NFAT1 nuclear export. We identify a conserved docking site for CK1 in NFAT proteins and show that mutation of this site disrupts NFAT1-CK1 interaction and causes constitutive nuclear localization of NFAT1. The CK1 docking motif is present in proteins of the Wnt, Hedgehog, and circadian-rhythm pathways, which also integrate the activities of CK1 and GSK3.

PAWS 1 controls Wnt signalling through association with casein kinase 1α

“…Nuclear localisation of NFAT is regulated by CK1α via a SSR‐1 motif in the N‐terminus, in which phosphorylation of the motif by CK1 promotes NFAT1 nuclear export, while its dephosphorylation by calcineurin induces nuclear import. Phospho‐deficient SSR‐1 motif mutants of NFAT1 accumulate in the nucleus 32, as does NFAT in cells treated with a CK1 inhibitor 32, and when overexpressed in Xenopus ventralise embryos 38. In dissociated animal cap cells expressing a NFAT_GFP reporter construct, NFAT_GFP accumulated predominantly in the cytoplasm (Fig EV4A–C).…”

Calcium signaling in lymphocytes

“…Dephosphorylation of cytoplasmic NFAT proteins by calcineurin unmasks the nuclear localization sequence and then NFAT proteins translocate into nucleus [4]. NFAT-driven gene expression is highly dependent on sustained Ca 2+ influx and calcineurin activity, because a decrease in intracellular Ca 2+ levels or treatment with the calcineurin inhibitor cyclosporin A results in the immediate export of NFAT from nucleus by NFAT kinases, which include GSK3 (glycogen synthase kinase 3), CK1 (casein kinase 1) and DYRK1A (dual-specificity tyrosine-phosphorylation regulated kinase 1A) [28][29][30].…”

The first armadillo repeat is involved in the recognition and regulation of β-catenin phosphorylation by protein kinase CK1

“…This result means that ␤-catenin possesses functional element(s) committed to its highaffinity recognition by CK1 independent of the sequence encompassing the phosphoacceptor site (Ser-45). A first choice for this element is a sequence (FSQSF) conforming the CK1 putative docking motif identified in NFAT1 whose mutation disrupts NFAT1-CK1 interaction (39) and that is present in proteins of the Wnt, Hedgehog, and circadian-rhythm pathways.…”