BACE1 and presenilin/γ‐secretase regulate proteolytic processing of KCNE1 and 2, auxiliary subunits of voltage‐gated potassium channels

Abstract

BACE1 and presenilin (PS)/γ-secretase play a major role in Alzheimer's disease pathogenesis by regulating amyloid-β peptide generation. We recently showed that these secretases also regulate the processing of voltage-gated sodium channel auxiliary β-subunits and thereby modulate membrane excitability. Here, we report that KCNE1 and KCNE2, auxiliary subunits of voltage-gated potassium channels, undergo sequential cleavage mediated by either α-secretase and PS/γ-secretase or BACE1 and PS/γ-secretase in cells. Elevated α-secretase or BACE1 activities increased C-terminal fragment (CTF) levels of KCNE1 and 2 in human embryonic kidney (HEK293T) and rat neuroblastoma (B104) cells. KCNE-CTFs were then further processed by PS/γ-secretase to KCNE intracellular domains. These KCNE cleavages were specifically blocked by chemical inhibitors of the secretases in the same cell models. We also verified our results in mouse cardiomyocytes and cultured primary neurons. Endogenous KCNE1- and KCNE2-CTF levels increased by 2- to 4-fold on PS/γ-secretase inhibition or BACE1 overexpression in these cells. Furthermore, the elevated BACE1 activity increased KCNE1 processing and shifted KCNE1/KCNQ1 channel activation curve to more positive potentials in HEK cells. KCNE1/KCNQ1 channel is a cardiac potassium channel complex, and the positive shift would lead to a decrease in membrane repolarization during cardiac action potential. Together, these results clearly showed that KCNE1 and KCNE2 cleavages are regulated by BACE1 and PS/γ-secretase activities under physiological conditions. Our results also suggest a functional role of KCNE cleavage in regulating voltage-gated potassium channels.

Inhibitory Neuron and Hippocampal Circuit Dysfunction in an Aged Mouse Model of Alzheimer's Disease

“…This work confirms a recent report of mild interneuron dysfunction associated with early-to-mid-level amyloid pathology, whereby neocortical interneurons had reduced action potential amplitude and this could be rescued with overexpression of Nav1.1 in the inhibitory cells [21]. Alternatively, there have been other channelopathies that have been reported to be disturbed in mouse models of aging and AD, including potassium [66], calcium and calcium-dependent potassium channels [67], [68] and muscarinic M current [69]. Our current results reveal that there is a broad degree of hyperexcitability within the dentate gyrus, the hippocampal circuits and that at the advanced stages of Aβ pathology interneuron ability to generate action potentials may be completely lost.…”

The Many Substrates of Presenilin/γ-Secretase

“…We have found that BACE1 and PS/γ-secretase cleavages of Na v β2 release a Na v β2-ICD, which modulates the levels of the pore-forming Na v 1.1 α-subunit intra-cellularly and on the cell surface [108]. Since four auxiliary subunits of the voltage-gated potassium channel are also cleaved by BACE1 and PS/γ-secretase [175], it appears that these two enzymes are involved in the regulation of ion channel function. Interestingly, voltage-gated sodium and potassium channels together are the key components of action potential generation and propagation.…”

Inhibiting BACE1 to reverse synaptic dysfunctions in Alzheimer’s disease

“…In addition to previously identified BACE1 substrates such as neuregulin-1 (Nrg1) (Fleck et al, 2013; Hu et al, 2008; Hu et al, 2006; Luo et al, 2011; Willem et al, 2006), voltage-gated channel proteins such as sodium channel protein β-subunits (Kim et al, 2007; Kim et al, 2011; Wong et al, 2005), the potassium channel proteins KCNE1 and 2 (Hitt et al, 2010; Sachse et al, 2013), neural cell adhesion molecule close homolog of L1 (Hitt et al, 2012; Kuhn et al, 2012; Zhou et al, 2012), Notch ligands Jagged-1 and Jagged-2 (He et al, 2014; Hu et al, 2013), and contactin-2 (Gautam et al, 2014), many more membrane-bound proteins have now been identified as BACE1 substrates by unbiased proteomic or secretome approaches using BACE1-null mouse or zebrafish models (Hemming et al, 2009; Hogl et al, 2011; Hogl et al, 2013). By comparative proteomic analyses of wild-type vs .…”