CRL4ACRBN E3 ubiquitin ligase restricts BK channel activity and prevents epileptogenesis

Abstract

Ion channels regulate membrane excitation, and mutations of ion channels often cause serious neurological disorders including epilepsy. Compared with extensive analyses of channel protein structure and function, much less is known about the fine tuning of channel activity by post-translational modification. Here we report that the large conductance, Ca 2 þ -and voltage-activated K þ (BK) channels are targeted by the E3 ubiquitin ligase CRL4A CRBN for polyubiquitination and retained in the endoplasmic reticulum (ER). Inactivation of CRL4A CRBN releases deubiquitinated BK channels from the ER to the plasma membrane, leading to markedly enhanced channel activity. Mice with CRL4A CRBN mutation in the brain or treated with a CRL4A CRBN inhibitor are very sensitive to seizure induction, which can be attenuated by blocking BK channels. Finally, the mutant mice develop spontaneous epilepsy when aged. Therefore, ubiquitination of BK channels before their cell surface expression is an important step to prevent systemic neuronal excitability and epileptogenesis.

A missense mutation in theCRBNgene that segregates with intellectual disability and self-mutilating behaviour in a consanguineous Saudi family

“…8 The CRBN gene is highly expressed in the hippocampus, consistent with its role in the pathogenesis of limbic seizures. 9 Compelling evidence suggests that BK Ca channel loss-of-function mutations contribute to neuronal hyperexcitability that leads to enhanced seizure susceptibility, 20 although the mechanistic link between increased BK Ca expression and ARNS-ID remains undefined. Kyle and Braun 21 explain that CRBN, as a substrate of the CRL4A CRBN complex, interacts with BK Ca in the central nervous system (CNS), leading to the ubiquitylation of the BK Ca α subunit and retention of the channels in the ER.…”

“…Any changes that affect the CRL4A CRBN complex could prevent ubiquitylation of the BK Ca channels, which increases trafficking of these channels to neuronal cell membrane and increases the incidence of seizures and epilepsy in mice. 9 Hence, the elevated BK Ca channel expression in the CNS is closely linked with epilepsy, strongly suggesting that increased BK Ca current density can lead to neurological disorders and possibly synaptic dysfunction/degeneration. Ultimately, how the CRBN mutation reported in this study leads to ID with additional features at a mechanistic level remains unsolved and requires further investigation.…”

BKCachannel dysfunction in neurological diseases

“…BK Ca channels can also be regulated by acidification (Brelidze and Magleby, 2004; Hou et al, 2008), ethanol (Liu et al, 2008), protein kinase phosphorylation (Tian et al, 2001; Zhou et al, 2010), ubiquitination (Liu et al, 2014) and palmitoylation (Shipston, 2013; Zhou et al, 2012). Of particular importance, protein S-palmitoylation (or palmitoylation) and ubiquitination control the cell surface expression and activity of BK Ca , thereby critically contributing to BK Ca channel functions (Shipston, 2013; Liu et al, 2014). Notably, the palmitoylation of BK Ca channel β subunits promotes the exit of the pore-forming α subunit from the endoplasmic reticulum and promotes BK Ca channel surface expression (Chen et al, 2013).…”

“…Potential mechanisms underlying neuronal hyperexcitability following BK Ca channels loss-of-function include reduced fAHP conductances. BK Ca channel gain-of-function is characterized by the release of ubiquitinated BK Ca channels from the ER and their insertion into the membrane surface (Liu et al, 2014). Thus, impairing ubiquitination may lead to overexpression of BK Ca channels relative to control conditions.…”

Activation of c-Abl Kinase Potentiates the Anti-myeloma Drug Lenalidomide by Promoting DDA1 Protein Recruitment to the CRL4 Ubiquitin Ligase

“…Based on these results, novel chemicals conjugating glutarimide to other protein-interacting chemical structures are designed to control protein stability and thus enable targeting of previously intractable proteins (23). CRBN by itself mediates the ubiquitination of several putative substrates, including the large conductance, Ca 2ϩ -and voltage-activated K ϩ (BK) channels (24), MEIS2 (20) and glutamine synthetase (25), suggesting that the CRL4 CRBN ubiquitin ligase activity is diverted by IMiDs or its derived chemicals from its physiological functions.…”