CACHD1 is an α2δ-like protein that modulates CaV3 voltage-gated calcium channel activity

The putative cache (Ca 2+ channel and chemotaxis receptor) domain containing 1 (CACHD1) protein has predicted structural similarities to members of the α2δ voltage-gated Ca 2+ channel (VGCC) auxiliary subunit family. CACHD1 mRNA and protein were highly expressed in the male mammalian CNS, in particular in the thalamus, hippocampus and cerebellum, with a broadly similar tissue distribution to Ca V 3 subunits, in particular, Ca V 3.1. In expression studies, CACHD1 increased cell-surface localization of Ca V 3.1 and these proteins were in close proximity at the cell surface consistent with the formation of CACHD1-Ca V 3.1 complexes. In functional electrophysiological studies, co-expression of human CACHD1 with Ca V 3.1, Ca V 3.2 and Ca V 3.3 caused a significant increase in peak current density and corresponding increases in maximal conductance. By contrast, α2δ-1 had no effect on peak current density or maximal conductance in either Ca V 3.1, Ca V 3.2 or Ca V 3.3. Comparison of CACHD1-mediated increases in Ca V 3.1 current density and gating currents revealed an increase in channel open probability. In hippocampal neurons from male and female E19 rats, CACHD1 overexpression increased Ca V 3-mediated action potential (AP) firing frequency and neuronal excitability. These data suggest that CACHD1 is structurally an α2δ-like protein that functionally modulates Ca V 3 voltage-gated calcium channel activity. SIGNIFICANCE STATEMENT This is the first study to characterise the CACHD1 protein. CACHD1 is widely expressed in the CNS, in particular in the thalamus, hippocampus and cerebellum. CACHD1 distribution is similar to that of low-voltage-activated (Ca V 3, T-type) calcium channels, in particular to Ca V 3.1, a protein which regulates neuronal excitability and is a potential therapeutic target in conditions such as epilepsy and pain. CACHD1 is structurally a α2δ-like protein that functionally increases Ca V 3 calcium current. CACHD1 increases the presence of Ca V 3.1 at the cell surface, forms complexes with Ca V 3.1 at the cell-surface and causes an increase in channel open probability. In hippocampal neurons, CACHD1 causes increases in neuronal firing. Thus, CACHD1 represents a novel protein that modulates Ca V 3 activity.