Calcium-Calmodulin-Dependent Protein Kinase II Isoforms Differentially Impact the Dynamics and Structure of the Actin Cytoskeleton

Abstract

Calcium-calmodulin-dependent protein kinase II (CaMKII) has been implicated in a wide variety of cellular processes, which include a critical regulatory role in actin cytoskeletal assembly. CaMKII is ubiquitous in cells, expressed as one of four isoforms referred to as α, β, γ, and δ. Characterization of the CaMKII-actin interaction has been mainly focused on the β isoform, which has been shown to bundle actin filaments and sequester actin monomers in an activity dependent manner. Much less is known about the interactions of other CaMKII isoforms with actin. In the present report, isoform specific interactions of CaMKII with actin are described and reveal that the δ isoform of CaMKII bundles F-actin filaments similarly to the β isoform while the γ isoform induces a novel layered structure to filaments. Using electron tomography, CaMKII holoenzymes are clearly identified in the complexes bridging the actin filaments, allowing direct visualization of the interactions between CaMKII isoforms and actin. In addition, we determined the isoform specificity of CaMKII-mediated inhibition of actin polymerization and discovered that all isoforms inhibit polymerization to varying degrees with β > γ ≈ δ > α (from most to least effective). Ca2+/CaM activation of all kinase isoforms produced a robust increase in actin polymerization that surpassed the rates of polymerization in the absence of kinase inhibition. These results indicate that diversity exists between the types of CaMKII-actin interactions mediated by the different isoforms and that CaMKII isoform composition differentially impacts the formation and maintenance of the actin cytoskeleton.

Control of cell mechanics by RhoA and calcium fluxes during epithelial scattering

“…20,89,90 Actin bundling activity has also been reported with d, and g isoforms, the latter of which creates a novel layered bundle structure. 91 Whether CaMKII's actin bundling activity occurs in epithelial cells and whether negative regulation of this activity by calcium might facilitate epithelial scattering, perhaps by releasing actin bundling prior to rearrangement of actin at cell-cell junctions into transcellular networks, remains unclear.…”

Relative Cosolute Size Influences the Kinetics of Protein-Protein Interactions

“…Wild-type mammalian calmodulin (CaM) (31)(32)(33), T34C/T110C CaM (17), K75C CaM (34), D2C CaM (35,36), and 15 N-isotope-labeled CaM (31,37,38) were expressed and purified as previously described in the cited works. The target peptide representing the CaM recognition motif for CaMKI (AKSKWKQAFNATAVVRHMRKLQ) was purchased from LifeTein (Somerset, NJ).…”

Phosphorylation of CEACAM1 Molecule by Calmodulin Kinase IID in a Three-dimensional Model of Mammary Gland Lumen Formation

“…One clue to the answer is that CaMKII proteins, including CaMKIID, have been recently shown to bind to G-actin in the absence of Ca 2ϩ and to bundle actin when activated by Ca 2ϩ /CaM (22). Given that new information, one can envision a stepwise series of events that start with Ca 2ϩ release and proceeds all the way to actin binding, polymerization, and bundling at the site of CEACAM1 activation (Fig.…”

“…Expression of CaMKIID was implicated in apoptosis of myocardiocytes during ischemia (17), regulation of vascular smooth muscle polarization and migration (20), and down-regulation in breast cancer tumor cells (21). In addition, CAMKII in the absence of CaM can bind G-actin and bundle F-actin (22). Intrigued by the functional relevance of CaMKIID to apoptosis and cancer, its up-regulation in our comparative gene chip analysis, and the fact that CEACAM1 binds CaM (23,24) and G-actin (15), we decided to explore the possibility that CaMKIID may be responsible for the phosphorylation of Thr-457 in CEACAM1-SF and may play an essential role in lumen formation.…”