Regulation of Neuronal Cav3.1 Channels by Cyclin-Dependent Kinase 5 (Cdk5)

Low voltage-activated (LVA) T-type Ca²⁺ channels activate in response to subthreshold membrane depolarizations and therefore represent an important source of Ca²⁺ influx near the resting membrane potential. In neurons, these proteins significantly contribute to control relevant physiological processes including neuronal excitability, pacemaking and post-inhibitory rebound burst firing. Three subtypes of T-type channels (Ca_v3.1 to Ca_v3.3) have been identified, and using functional expression of recombinant channels diverse studies have validated the notion that T-type Ca²⁺ channels can be modulated by various endogenous ligands as well as by second messenger pathways. In this context, the present study reveals a previously unrecognized role for cyclin-dependent kinase 5 (Cdk5) in the regulation of native T-type channels in N1E-115 neuroblastoma cells, as well as recombinant Ca_v3.1channels heterologously expressed in HEK-293 cells. Cdk5 and its co-activators play critical roles in the regulation of neuronal differentiation, cortical lamination, neuronal cell migration and axon outgrowth. Our results show that overexpression of Cdk5 causes a significant increase in whole cell patch clamp currents through T-type channels in N1E-115 cells, while siRNA knockdown of Cdk5 greatly reduced these currents. Consistent with this, overexpression of Cdk5 in HEK-293 cells stably expressing Ca_v3.1channels upregulates macroscopic currents. Furthermore, using site-directed mutagenesis we identified a major phosphorylation site at serine 2234 within the C-terminal region of the Ca_v3.1subunit. These results highlight a novel role for Cdk5 in the regulation of T-type Ca²⁺ channels.