CK2 activity is required for the interaction of FGF14 with voltage‐gated sodium channels and neuronal excitability

Abstract

Recent data shows that fibroblast growth factor 14 (FGF14) binds to and controls the function of the voltage-gated sodium (Nav) channel with phenotypic outcomes on neuronal excitability. Mutations in the FGF14 gene in humans have been associated with brain disorders that are partially recapitulated in Fgf14 2/2 mice. Thus, signaling pathways that modulate the FGF14:Nav channel interaction may be important therapeutic targets. Bioluminescence-based screening of small molecule modulators of the FGF14:Nav1.6 complex identified 4,5,6,7-tetrabromobenzotriazole (TBB), a potent casein kinase 2 (CK2) inhibitor, as a strong suppressor of FGF14:Nav1.6 interaction. Inhibition of CK2 through TBB reduces the interaction of FGF14 with Nav1.6 and Nav1.2 channels. Mass spectrometry confirmed direct phosphorylation of FGF14 by CK2 at S228 and S230, and mutation to alanine at these sites modified FGF14 modulation of Nav1.6-mediated currents. In 1 d in vitro hippocampal neurons, TBB induced a reduction in FGF14 expression, a decrease in transient Na + current amplitude, and a hyperpolarizing shift in the voltage dependence of Nav channel steady-state inactivation. In mature neurons, TBB reduces the axodendritic polarity of FGF14. In cornu ammonis area 1 hippocampal slices from wild-type mice, TBB impairs neuronal excitability by increasing action potential threshold and lowering firing frequency. Importantly, these changes in excitability are recapitulated in Fgf14 2/2 mice, and deletion of Fgf14 occludes TBB-dependent phenotypes observed in wild-type mice. These results suggest that a CK2-FGF14 axis may regulate Nav channels and neuronal

PPARgamma agonists rescue increased phosphorylation of FGF14 at S226 in the Tg2576 mouse model of Alzheimer's disease

“…In previous studies, we showed that FGF14 forms a complex with neuronal Nav1.6 channel, and this interaction is controlled by S/T kinases (Hsu et al, 2015, 2016; Shavkunov et al, 2013). The S226 residue of FGF14 is located in the C-terminal tail of the protein in a region enriched with other S/T sites (Fig.…”

“…5A–B) (Hsu et al, 2015, 2016; Ali et al, 2016; Ali et al, 2014; Shavkunov et al, 2013; Shavkunov et al, 2012; Shavkunov et al, 2015). HEK293 cells were transiently transfected with CLuc-FGF14 and CD4-Nav1.6 -C-tail- NLuc plasmids expressing the coding sequence of FGF14 and the C-terminal tail of Nav1.6 fused to the single transmembrane domain protein CD4, respectively.…”

“…Recent studies have identified highly clustered areas containing phosphorylation sites on the voltage-gated Na + (Nav) Nav1.2 isoform, particularly at the I–II linker and the C-terminal intracellular regions (Baek et al, 2011; Berendt et al, 2010). These phosphorylation sites control channel gating, expression, and sub-cellular localization, which impact Nav channel function and consequently affect excitability (Berendt et al, 2010; Hsu et al, 2015, 2016; Wildburger et al, 2015). Previous studies have identified alterations in the phosphoproteome concomitant with neurologic disease: studies in humans with AD as well as an early onset mouse model of AD reveal significant alterations in global phosphorylation profiles with critical alterations in multiple cellular signaling pathways (Wang et al, 2013; Zahid et al, 2012), and phosphorylation as well as other post-translational modifications of Nav1.2 channels (James et al, 2015), such as methylation, are reciprocally modulated in epilepsy (Baek et al, 2014).…”

“…Among these, fibroblast growth factor 14 (FGF14) stands out for its specific modulatory roles on neuronal Nav channels. Recent studies highlight the importance of FGF14, a multivalent accessory protein of the Nav channel, in animal as well as human studies (Hsu et al, 2015, 2016; James et al, 2015; Ali et al, 2016; Alshammari et al, 2016a, b, c; Tempia et al, 2015; Ali et al, 2014; Shavkunov et al, 2013). Through direct monomeric binding to the Nav channel C-terminal tail, FGF14 forms a complex with the channel that is required for proper gating, expression and trafficking of the channel to the AIS as well as the control of neuronal excitability (Ali et al, 2014, 2016; Alshammari et al, 2016a; Laezza et al, 2007, 2009; Lou et al, 2005; Wang et al, 2000, 2002; Xiao et al, 2007; Goetz et al, 2009).…”

“…Inhibition of GSK–3 reduces the assembly of the FGF14:Nav channel complex, modifies FGF14-dependent regulation of Na + currents, and induces dissociation and subcellular redistribution of the native FGF14:Nav channel complex (Shavkunov et al, 2013). Furthermore, CK2 is a known priming kinase of GSK–3, and recent studies have shown that inhibition of CK2 induces similar alterations in assembly and distribution of the FGF14:Nav complex (Hsu et al, 2016). …”