Ca2+/calmodulin-dependent protein kinase IIalpha clusters are associated with stable lipid rafts and their formation traps PSD-95.

Relatively large number of post-synaptic density (PSD) proteins, including Ca2+/calmodulin-dependent protein kinase II (CaMKII), have the potential to associate with lipid rafts. We in this study demonstrate that the CaMKIIalpha clusters induced by ionomycin in human embryonic kidney 293 cells, as well as unclustered CaMKIIalpha (Du F., Saitoh F., Tian Q. B., Miyazawa S., Endo S. and Suzuki T, 2006, Biochem. Biophys. Res. Commun 347, 814-820), were associated with lipid rafts. The CaMKIIalpha clusters associated with lipid raft fraction became resistant to treatment with methyl-beta-cyclodextrin and subsequent cold Triton X-100, which suggests the stabilization of CaMKIIalpha cluster-associated lipid rafts. Next, we found that PSD-95, which is also a component of lipid raft fraction and does not interact directly with CaMKII, was trapped by stable CaMKIIalpha cluster-containing structure. Association of PSD-95 with CaMKIIalpha clusters was also observed in cultured neuronal cells. These results suggest the CaMKIIalpha clusters associated with the lipid rafts in the cytoplasmic region play a role in the assembly and stabilization of certain PSD proteins that have the potential to associate with lipid rafts.