Kv3.3 Channels Bind Hax-1 and Arp2/3 to Assemble a Stable Local Actin Network that Regulates Channel Gating

Mutations in the Kv3.3 potassium channel (KCNC3) cause cerebellar neurodegeneration and impair auditory processing. The cytoplasmic C terminus of Kv3.3 contains a proline-rich domain conserved in proteins that activate actin nucleation through Arp2/3. We found that Kv3.3 recruits Arp2/3 to the plasma membrane, resulting in formation of a relatively stable cortical actin filament network resistant to cytochalasin D that inhibits fast barbed end actin assembly. These Kv3.3-associated actin structures are required to prevent very rapid N-type channel inactivation during short depolarizations of the plasma membrane. The effects of Kv3.3 on the actin cytoskeleton are mediated by the binding of the cytoplasmic C terminus of Kv3.3 to Hax-1, an anti-apoptotic protein that regulates actin nucleation through Arp2/3. A human Kv3.3 mutation within a conserved proline-rich domain produces channels that bind Hax-1 but are impaired in recruiting Arp2/3 to the plasma membrane, resulting in growth cones with deficient actin veils in stem cell-derived neurons. [Display omitted] •Kv3.3 ion channels coordinate assembly of Arp2/3-dependent cortical actin networks•These actin networks slow the rate of Kv3.3 channel closing during depolarization•Network assembly is coordinated by Hax-1, a Rac- and cortactin-binding protein•Cerebellar ataxia is correlated with a channel mutation that blocks network assembly Kv3.3 channels coordinate assembly of cortical Arp2/3-dependent actin networks that in turn interact with channels to slow their rate of closing during sustained depolarization, suggesting a basis for how known channel mutations result in abnormal neuronal growth during development and cause cerebellar ataxia in human patients.