Effect of PKCK2 mediated snail phosphorylation on Wnt signaling

Abstract

Protein kinase casein kinase 2 (PKCK2) is a serine/threonine kinase that has been known to play important roles in cell cycle control, cellular differentiation, and proliferation. Recently, PKCK2 is overexpressed in many types of human cancer. It is a positive regulator in Wnt signaling pathway, since the Wnt signaling pathway intermediate Dishevelled, -catenin, and LZTS2 are a PKCK2 phosphorylation substrates and activating the transcription of Wnt target genes. The zinc finger transcription factor, Snail, functions as a potent repressor of E-cadherin expression. Snail is phosphorylated by GSK3-, resulting in -TrCP-mediated ubiquitination and proteasomal degradation. Axin2 levels increase in response to Wnt signaling, GSK3- is exported from the nuclear compartment leaving Snail in its non-phosphorylated, transcriptionally active form. Thus, stabilization of Snail repressed E-cadherin expression is required for cell migration, invasion, and metastasis. However, little is known about PKCK2 mediated regulation of Snail.This study presented the identification of Snail as a novel binding protein to PKCK2, the role of PKCK2-mediated phosphorylation on Snail, and its effect on Wnt signaling. The interaction between Snail and PKCK2 was initially identified by a yeast two-hybrid screening and was further confirmed by GST pull down and co-immunoprecipitation. Mutational analysis and in vitro kinase assay indicate that Snail contains multiple PKCK2 phosphorylation sites. In addition, it is demonstrated that PKCK2 stabilizes Snail by phosphrylation. PKCK2 induced an accumulation of Snail in the nucleus which further bloked phosphorylation by GSK3- and snail active form repressed the E-cadherin level. Further, PKCK2 activity is required for the regulation of Snail-mediated Wnt signaling pathway.Taken together, PKCK2 regulates the Snail stability through its phosphorylation, thereby modulates E-cadherin mediated transcriptional activity.