Ca²⁺-Dependent Facilitation of Ca_v1.3 Ca²⁺Channels by Densin and Ca²⁺/Calmodulin-Dependent Protein Kinase II

Abstract

Cav1 (L-type) channels and calmodulin-dependent protein kinase II (CaMKII) are key regulators of Ca2+signaling in neurons. CaMKII directly potentiates the activity of Cav1.2 and Cav1.3 channels, but the underlying molecular mechanisms are incompletely understood. Here, we report that the CaMKII-associated protein densin is required for Ca2+-dependent facilitation of Cav1.3 channels. While neither CaMKII nor densin independently affects Cav1.3 properties in transfected HEK293T cells, the two together augment Cav1.3 Ca2+currents during repetitive, but not sustained, depolarizing stimuli. Facilitation requires Ca2+, CaMKII activation, and its association with densin, as well as densin binding to the Cav1.3 α1subunit C-terminal domain. Cav1.3 channels and densin are targeted to dendritic spines in neurons and form a complex with CaMKII in the brain. Our results demonstrate a novel mechanism for Ca2+-dependent facilitation that may intensify postsynaptic Ca2+signals during high-frequency stimulation.

Characterization of a Central Ca2+/Calmodulin-dependent Protein Kinase IIα/β Binding Domain in Densin That Selectively Modulates Glutamate Receptor Subunit Phosphorylation

“…Because there are no detectable interactions of CaMKII␣ with the N-terminal LRR domain of densin (densin-T482 splice variant) (9), CaMKII may also interact somewhere between the LRR and C-terminal domains. Consistent with this hypothesis, deletion of a large central domain (residues 483-1377) in a naturally occurring densin splice variant substantially reduced the binding of CaMKII␣ even though this variant retains the C-terminal CaMKII␣ binding domain (12). Therefore, we expressed a family of GST fusion proteins spanning the large central domain of densin in bacteria (Fig.…”

“…For example, although densin-FLC may be expressed only in the perinatal period (6), before CaMKII␣ expression, the IN domain may allow densin-FLC to modulate CaMKII␤. In addition, we previously showed that a natural densin splice variant lacking a large central region containing the densin-IN domain is unable to support CaMKII␣-dependent facilitation of Ca V 1.3 L-type calcium channels (12). A deeper understanding of the expression of densin splice variants in different cell types during development is required to fully appreciate the implications of these findings for CaMKII isoform regulation.…”

“…Moreover, densin-dependent facilitation of Ca V 1.3 L-type calcium channels by CaMKII␣ is ablated by deletion of a large intracellular domain in densin (⌬483-1377) even though this protein retained the LRR, C-terminal CaMKII␣ binding, and PDZ domains. Surprisingly, this internal deletion also reduced the association of densin with CaMKII␣ (12).…”

The Physiology, Pathology, and Pharmacology of Voltage-Gated Calcium Channels and Their Future Therapeutic Potential

“…Fast presynaptic neurotransmitter release in neurons depends on the close coupling of presynaptic Ca V 2 channels to the release machinery. By contrast, Ca V 1.3 and Ca V 1.2 are located postsynaptically predominantly on the cell soma and in the spines and shafts of dendrites in neurons (Di Biase et al, 2008;Jenkins et al, 2010). There they shape neuronal firing and activate Ca 2+ -dependent pathways involved in control of gene expression, termed excitation-transcription coupling .…”

Voltage-Gated Calcium Channels

“…The distal carboxy-terminal domain plays an autoregulatory role in both Ca V 1.3 and Ca V 1.4 channels (Singh et al 2006(Singh et al , 2008, but it is not known whether it is subject to proteolytic processing in vivo. Ca V 1.3 channels are regulated by multiple interacting proteins (Cui et al 2007;Jenkins et al 2010), which may be important in tuning their activity to fit the specific requirements of hair cells transmitting auditory information at different frequencies.…”