Akt Activation Is Necessary for Growth Factor–Induced Trafficking of Functional K_CaChannels in Developing Parasympathetic Neurons

Abstract

The protein kinase Akt is a crucial regulator of neuronal survival and apoptosis. Here we show that Akt activation is necessary for mobilization of large-conductance K(Ca) channels in ciliary ganglion (CG) neurons evoked by beta-neuregulin-1 (NRG1) and transforming growth factor-beta1 (TGFbeta1). Application of NRG1 to embryonic day 9 (E9) CG neurons increased Akt phosphorylation, as observed previously for TGF(beta)1. NRG1- and TGF(beta)1-evoked stimulation of K(Ca) is blocked by inhibitors of PI3K by overexpression of a dominant-negative form of Akt, by overexpression of CTMP, an endogenous negative regulator of Akt, and by application of the Akt inhibitor 1L-6-hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate (HIMO). Conversely, overexpression of a constitutively-active form of Akt was sufficient by itself to increase mobilization of functional K(Ca) channels. NRG1 and TGF(beta)1 evoked an Akt-dependent increase in cell-surface SLO alpha-subunits. These procedures have no effect on voltage-activated Ca2+ currents. Thus Akt plays an essential role in the developmental regulation of excitability in CG neurons.

Dominant-Negative Regulation of Cell Surface Expression by a Pentapeptide Motif at the Extreme COOH Terminus of an Slo1 Calcium-Activated Potassium Channel Splice Variant

“…Although Short-QEERL and Short-VEDEC showed similar levels of total expression, the surface expression of Short-VEDEC was markedly reduced compared with that of Short-QEERL (Fig. 4, A and B), although nonlinearities in cell surface biotinylation assays may result in the underestimation of surface expression when signals are faint (Chae et al, 2005a). Consistent with this, the whole-cell current recorded from cells expressing Short-VEDEC was also significantly reduced compared with Short-QEERL (Fig.…”

Complex Regulation of Spiral Ganglion Neuron Firing Patterns by Neurotrophin-3

“…However, from the time courses that we chose to evaluate in the present study, we cannot rule out that more immediate modifications may also be involved, such as those revealed for glutamate receptors (Levine et al, 1998;Arvanov et al, 2000;Balkowiec et al, 2000) as well as in some types of voltage-gated ion channels (Kafitz et al, 1999;Tucker and Fadool, 2002). Moreover, recent studies have shown that growth factors can alter the surface expression of both voltage-and ligand-gated ion channels via extranuclear, Akt-dependent signaling pathways (Blair et al, 1999;Brami-Cherrier et al, 2002;Wang et al, 2003;Ning et al, 2004;Chae et al, 2005). Cytoplasmic activation of signaling cascades has explicitly been demonstrated in spiral ganglion neurons to enhance their survival to depolarizing stimuli via cAMP activation of protein kinase A, possibly via the Akt effector (Bok et al, 2003); therefore, we may expect that similar mechanisms may also be in place to regulate channel surface expression in these cells.…”

Interactions with Filamin A Stimulate Surface Expression of Large-Conductance Ca2+-Activated K+ Channels in the Absence of Direct Actin Binding

“…Previous studies from our laboratory have shown that the steady-state surface expression of BK Ca channels is stimulated by growth factors in developing vertebrate neurons (Cameron et al, 1998(Cameron et al, , 2001Chae et al, 2005) and transformed cell lines (Kim et al, 2007a,b). It is noteworthy that these effects require activation of phosphoinositide 3-kinase and Akt pathways (Lhuillier and Dryer, 2002;Chae et al, 2005).…”

“…It is noteworthy that these effects require activation of phosphoinositide 3-kinase and Akt pathways (Lhuillier and Dryer, 2002;Chae et al, 2005). In this regard, filamin A is a substrate for several proteins that are downstream effectors of phosphoinositide 3-kinase and Akt, including p21-activated protein kinase (Vadlamudi et al, 2002) and ribosomal S6 kinase (Woo et al, 2004).…”