The Kv3.4 voltage-dependent K + channel is present in the growth cones of elongating axons in all major fiber tracts during neuronal development and loss of Kv3.4 results in errors of migration and pathfinding. We have found that the cytoplasmic C-terminal domain of Kv3.4 directly binds PCDH9 (protocadherin-9), a Ca 2+ -dependent adhesion molecule. This prevents degradation of Kv3.4 and is essential for expression in the plasma membrane. We have now tested whether Kv3.4 simply acts a protein scaffold or if Kv3.4 voltage-dependent gating alters PCDH9-depedent actin nucleation by the WAVE complex. Expression of Kv3.4 in CHO cells hyperpolarizes their membrane potential and stimulates the outgrowth of filopodia, an effect that is reversed by PCDH9 knockout of by overexpression of a peptide that specifically blocks the interaction of PCDH9 with the WAVE complex. To differentiate the effects of Kv3.4 open and closed states on filopodial extension, we used two- photon live-imaging of actin combined with patch clamp recording. Depolarizations that open the channel acutely stimulated filopodial extension, while hyperpolarization had no effect and depolarizations that inactivate Kv3.4 caused retraction. Our data support the hypothesis that gating of Kv3.4 channels to the open state suggest promotes the interaction of PCDH9 with the WAVE complex to trigger actin nucleation, and that this interaction is required for normal neuronal development.
Zhang et al. (Sun,) studied this question.