Wnt5a controls Notch1 signaling through CaMKII-mediated degradation of the SMRT corepressor protein

Area of Science:

• Molecular Biology
• Cell Signaling
• Signal Transduction

Background:

• Serine-threonine Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is crucial in noncanonical Wnt5a signaling.
• The silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) acts as a co-repressor for Notch signaling.

Purpose of the Study:

• To investigate the role of CaMKII in Wnt5a-mediated regulation of Notch signaling.
• To elucidate the mechanism by which CaMKII affects SMRT protein stability and Notch signaling components.

Main Methods:

• Western blotting to assess protein stability.
• Pharmacological inhibition of CaMKII using KN93.
• Co-immunoprecipitation assays to study protein interactions.
• Reporter assays to measure transcriptional activity.
• Site-directed mutagenesis and in vitro kinase assays to identify phosphorylation sites.

Main Results:

• Wnt5a-induced CaMKII promotes proteasomal degradation of SMRT, reducing its protein stability.
• CaMKII activation enhances Notch1 intracellular domain (Notch1-IC) transcription activity.
• CaMKII facilitates the association between Notch1-IC and RBP-Jk.
• CaMKII disrupts the physical association between RBP-Jk and SMRT.
• CaMKII directly phosphorylates SMRT at Ser-1407, leading to its nuclear export and degradation.

Conclusions:

• CaMKII plays a key role in Wnt5a-mediated Notch signaling activation.
• CaMKII down-regulates SMRT protein stability through direct phosphorylation and subsequent proteasomal degradation.
• This mechanism highlights a novel regulatory pathway linking Wnt5a, CaMKII, SMRT, and Notch signaling.