Voltage-Dependent Regulation of Intracellular Signaling by Ether À go-go K⁺Channels.

Abstract

Voltage-gated ion channels play a key role neuronal function by regulating ion flux. My research has shown that the Drosophila Ether à-go-go (EAG) potassium channel has a distinct conductance-independent role as an upstream activator of intracellular signaling pathways. Heterologous expression of EAG in NIH 3T3 fibroblasts results in increased proliferation and p38 mitogen-activated protein kinase activity, an effect that occurs even when the channel is rendered nonconducting by mutation of the selectivity filter. Importantly, analysis of mutations that shift the voltage-dependence of channel gating reveals that EAG signaling activity is regulated by the voltage sensor. Targeted mutation of key residues in the intracellular EAG carboxyl terminal shows that signaling requires an intact calcium/calmodulin-dependent protein kinase II (CaMKII) binding domain, and biochemical assays confirm that the activity of membrane-associated CaMKII is modulated by voltage-dependent conformations of EAG. Conductance-independent, CaMKII-mediated EAG signaling activity is also observed with the mammalian isoform of EAG. Finally, in recordings at the Drosophila larval neuromuscular junction, EAG channels with mutations in the CaMKII binding domain largely failed to rescue the high levels of spontaneous activity characteristic of eag mutants, whereas nonconducting EAG channels rescued spontaneous activity with an efficiency nearly overlapping that observed for the wild type channel. These results suggest that voltage-dependent, conductance-independent EAG signaling activity plays a role in synaptic homeostasis in vivo and implicate EAG signaling as a novel mechanism for linking neuronal activity to the state of intracellular messenger pathways. EAG signaling activity may contribute to the learning defects observed in Drosophila eag mutants, as well as to the oncogenic effects observed following abnormal expression of human EAG.