REGULATION OF CARDIAC NAV1.5 CHANNELS BY FHF2 PHOSPHORYLATION
Résumé
The voltage-gated Na+ channels NaV1.5 are responsible for the upstroke of cardiac
action potentials, and dysregulations of this channel underlie inherited or acquired
cardiac disease. While phosphorylation of NaV1.5 is extensive, the regulation of
NaV1.5 by phosphorylation of its accessory proteins remains unexplored.
Phosphoproteomics of mouse ventricular NaV1.5 channel complexes showed
phosphorylation of the FHF2 accessory protein at 9 specific sites. To determine the
functional roles of these sites, two cardiac cellular models were developed. Patchclamp
analyses demonstrated that FHF2 knockdown accelerates the rates of closedstate
and open-state inactivation of NaV channels in both neonatal and adult
ventricular cardiomyocytes, and shifts the voltage-dependence of NaV channel
activation towards hyperpolarized potentials in neonatal cardiomyocytes. Although
the rescue of FHF2 with the WT FHF2-VY isoform restored the inactivation properties
of NaV channels in both neoanatal and adult cells, no restoration of the activation
properties was obtained in neonatal cells, suggesting involvement of another FHF2
isoform in regulating NaV channel activation in neonatal cells. Similar to WT FHF2-
VY, however, each of the analyzed FHF2-VY phosphomutants restored the
inactivation properties of NaV channels in both models, preventing to identify roles
for FHF2 phosphosites. FHF2 knockdown also increased the late Na+ current in
adult cardiomyocytes, which was restored similarly by WT and phosphosilent FHF2-
VY. Together, our results demonstrate that ventricular FHF2 is highly
phosphorylated, implicate differential roles for FHF2 in regulating NaV1.5 channels in
neonatal and adult cardiomyocytes, and suggest that the regulation of NaV1.5 by
FHF2 phosphorylation is highly complex.
Domaines
Sciences du Vivant [q-bio]
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