Ancillary Subunits Regulate PKC Mediated Effects on Closed-State Inactivation of Kv4.3

Abstract

Kv4 channels are expressed with a variety of ancillary subunits in vivo. The most prominent of these proteins are the KChIPs, a family of cytoplasmic proteins that modulate channel gating and act as chaperones. We have previously shown that heterologously expressed Kv4.3 is regulated by PKC. After induction of PKC by PMA, current expression level is reduced. PKC also influences closed-state inactivation (CSI) in an isoform dependent manner; CSI is decreased upon PKC induction in Kv4.3-S, and increased in PKC-L. To understand the role of PKC on modulation of Kv4-based currents, we expressed channels in the presence of three KChIP2 isoforms and compared their responses to PKC. Two KChIP2 isoforms, KChIP2a and 2b, negated PKC influence on channel gating, kinetics, and expression levels in both Kv4.3-S and Kv4.3-L. In contrast, 70-amino acid KChIP2d was permissive for PKC modulation with respect to both CSI and current expression, while allowing the fast recovery from open-state inactivation characteristic of other KChIP2 isoforms. Additionally, the KChIP2d effects on CSI in Kv4.3-L were dependent on the presence of a putative PKC phosphorylation site in the C terminus. These data suggest a different physiological role for KChIP2d than the other KChIP2 isoforms, and suggest that the longer forms of KChIP2 interact with the regions of Kv4.3 affected by PKC, while KChIP2d interacts with the channel in a manner that allows PKC modulation while still accelerating recovery.