Kelch-like 1 protein upregulates T-type currents by an actin-F dependent increase in α_1H channels via the recycling endosome

The neuronal protein Kelch-like 1 (KLHL1) is a novel actin-binding protein that modulates neuronal structure and function. KLHL1 knockout mice exhibit dendritic atrophy in cerebellar Purkinje neurons and motor dysfunction. Interestingly, KLHL1 upregulates high and low voltage-gated calcium currents (Ca_V2.1 and Ca_V3.2) and interacts with their respective principal subunits, α_1A and α_1H. We reported the mechanism of enhanced Ca_V3.2 (α_1H) current density (and calcium influx) by KLHL1 is due to an increase in channel number (N) that requires the binding of actin. In this report we further elucidate the role of the actin cytoskeleton in this process using pharmacological tools to disrupt or stabilize actin filaments and to prevent protein trafficking and vesicle recycling. Disruption of the cytoskeleton did not affect the basal activity of α_1H, but did eliminate its modulation by KLHL1. In contrast, actin-F stabilization on its own increased basal α_1H activity similar to KLHL1 but without synergy in its presence, suggesting KLHL1 requires actin-polymerization to increase α_1H currents. Noise analysis revealed that actin polymerization induced an increase in N and P _o, in contrast to increased N in the presence of KLHL1. Interestingly, pharmacological or genetic disruption of endosomal recycling eliminated the increase in channel number by KLHL1 demonstrating this effect occurs via enhanced α_1H re-insertion through the recycling endosome. Our findings afford insight on a novel mechanism of T-type channel modulation that could have overall functional implications for T-type channel function in the brain.