Oligomerization of Ca2+/calmodulin-dependent protein kinase kinase

Ca2+/calmodulin-dependent protein kinase kinases (CaMKKα and β) are regulatory kinases for multiple downstream kinases, including CaMKI, CaMKIV, PKB/Akt, and AMP-activated protein kinase (AMPK) through phosphorylation of each activation-loop Thr residue. In this report, we biochemically characterize the oligomeric structure of CaMKK isoforms through a heterologous expression system using COS-7 cells. Oligomerization of CaMKK isoforms was readily observed by treating CaMKK transfected cells with cell membrane permeable crosslinkers. In addition, His-tagged CaMKKα (His–CaMKKα) pulled down with FLAG-tagged CaMKKα (FLAG–CaMKKα) in transfected cells. The oligomerization of CaMKKα was confirmed by the fact that GST–CaMKKα/His–CaMKKα complex from transiently expressed COS-7 cells extracts was purified to near homogeneity by the sequential chromatography using glutathione-sepharose/Nisepharose and was observed in a Ca2+/CaM-independent manner by reciprocal pulldown assay, suggesting the direct interaction between monomeric CaMKKα. Furthermore, the His-CaMKKα kinase-dead mutant (D293A) complexed with FLAG–CaMKKα exhibited significant CaMKK activity, indicating the active CaMKKα multimeric complex. Collectively, these results suggest that CaMKKα can self-associate in the cells, constituting a catalytically active oligomer that might be important for the efficient activation of CaMKK-mediated intracellular signaling.

© 2021 Elsevier Inc. This manuscript version is made available under the CC-BY-NC-ND 4.0 License. http://creativecommons.org/licenses/by-nc-nd/4.0/. This is the accepted manuscript version. The formal published version is available at [https://doi.org/10.1016/j.bbrc.2021.11.105] .