Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a serine/threonine kinase that is best known for its role in synaptic plasticity and memory. Multiple roles of CaMKII have been identified in the hippocampus, yet its role in developing neurons is less well understood. We show here that endogenous CaMKIIß, but not CaMKIIa, localized to prominent F-actin-rich structures at the soma in embryonic cortical neurons. Fluorescence recovery after photo-bleaching analyses of GFP-CaMKIIß binding interactions with F-actin in this CaMKIIa-free system indicated CaMKIIß binding depended upon a putative F-actin binding domain in the variable region of CaMKIIß. Furthermore, CaMKIIa decreased CaMKIIß binding to F-actin. We examined the interaction of CaMKIIß with stable and dynamic actin and show that CaMKIIß binding to F-actin was dramatically prolonged when F-actin was stabilized. CaMKIIß binding to stable F-actin was disrupted when it was bound by Ca2+/calmodulin or when it was highly phosphorylated, but not by kinase inactivity. Whereas CaMKIIß over-expression increased the prevalence of the F-actin-rich structures, disruption of CaMKIIß binding to F-actin reduced them. Taken together, these data suggest that CaMKIIß binding to stable F-actin is important for the in vivo maintenance of polymerized F-actin.
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