T606-phosphorylated Kaiso interacting with 14-3-3 and p120ctn is sequestered in the cytoplasm of human cells

Kaiso is a transcription factor in the nucleus and p120ctn-binding protein in the cytoplasm. Although it is known that p120ctn is involved in Kaiso cytoplasmic-nuclear transportation, regulatory mechanisms of Kaiso transportation remain to be explored. We firstly found that Kaiso could directly interact with 14-3-3 family proteins, depending on the phosphorylation at the 606 threonine residue (606) within the RSSIP motif of Kaiso. AKT1 could phosphorylate Kaiso at T606. T606A mutation abolished most Kaiso-14-3-3 interaction. Notably, we found that the phosphorylated Kaiso (pT606-Kaiso) could also bind to p120ctn in the cytoplasm and block the cytoplasmic-nuclear transportation of Kaiso. The present study indicates, for the first time, that Kaiso can be phosphorylated by AKT1 at T606 and that pT606-Kaiso can bind both 14-3-3 and p120ctn proteins in the cytoplasm. The pT606-Kaiso-p120ctn (and 14-3-3) complexes cannot shift to the nucleus and accumulate in the cytoplasm. T606 phosphorylation regulates intracellular transportation of Kaiso.