AP-1 contributes to endosomal targeting of the ubiquitin ligase RNF13 via a secondary and novel non-canonical binding motif.

Cellular trafficking between organelles is typically assured by short motifs that contact carrier proteins to transport them to their destination. The ubiquitin E3 ligase RING finger protein 13 (RNF13), a regulator of proliferation, apoptosis and protein trafficking, localizes to endolysosomal compartments through the binding of a dileucine motif to clathrin adaptor protein complex AP-3. Mutations within this motif reduce the ability of RNF13 to interact with AP-3.

Overview of Sigma-1R Subcellular Specific Biological Functions and Role in Neuroprotection.

For the past several years, fundamental research on Sigma-1R (S1R) protein has unveiled its necessity for maintaining proper cellular homeostasis through modulation of calcium and lipid exchange between the endoplasmic reticulum (ER) and mitochondria, ER-stress response, and many other mechanisms. Most of these processes, such as ER-stress response and autophagy, have been associated with neuroprotective roles. In fact, improving these mechanisms using S1R agonists was beneficial in several brain disorders including neurodegenerative diseases.

Membrane Targeting and GTPase Activity of Rab7 Are Required for Its Ubiquitination by RNF167.

Rab7 is a GTPase that controls late endosome and lysosome trafficking. Recent studies have demonstrated that Rab7 is ubiquitinated, a post-translational modification mediated by an enzymatic cascade. To date, only one ubiquitin E3 ligase and one deubiquitinase have been identified in regulating Rab7 ubiquitination.

From to Human: Biological Function of E3 Ligase Godzilla and Its Role in Disease.

The ubiquitin-proteasome system is of fundamental importance in all fields of biology due to its impact on proteostasis and in regulating cellular processes. Ubiquitination, a type of protein post-translational modification, involves complex enzymatic machinery, such as E3 ubiquitin ligases. The E3 ligases regulate the covalent attachment of ubiquitin to a target protein and are involved in various cellular mechanisms, including the cell cycle, cell division, endoplasmic reticulum stress, and neurotransmission.

RNF13 Dileucine Motif Variants L311S and L312P Interfere with Endosomal Localization and AP-3 Complex Association.

Developmental and epileptic encephalopathies (DEE) are rare and serious neurological disorders characterized by severe epilepsy with refractory seizures and a significant developmental delay. Recently, DEE73 was linked to genetic alterations of the RNF13 gene, which convert positions 311 or 312 in the RNF13 protein from leucine to serine or proline, respectively (L311S and L312P). Using a fluorescence microscopy approach to investigate the molecular and cellular mechanisms affected by RNF13 protein variants, the current study shows that wild-type RNF13 localizes extensively with endosomes and lysosomes, while L311S and L312P do not extensively colocalize with the lysosomal marker Lamp1.

Functional interaction of ubiquitin ligase RNF167 with UBE2D1 and UBE2N promotes ubiquitination of AMPA receptor.

Protein ubiquitination has been historically associated with protein degradation, but recent studies have demonstrated other cellular functions associated with substrate ubiquitination. Among the RING-type ubiquitin E3 ligase enzymes present in the human genome, RNF167 is a transmembrane protein located in endosomes and lysosomes and is implicated in controlling the endolysosomal pathway. Substrates of RNF167 have been identified, but the ubiquitin-conjugating E2 enzymes involved in the mechanism remain unknown.

Quantitative Immunoblotting Analyses Reveal that the Abundance of Actin, Tubulin, Synaptophysin and EEA1 Proteins is Altered in the Brains of Aged Mice.

Optimal synaptic activity is essential for cognitive function, including memory and learning. Evidence indicates that cognitive decline in elderly individuals is associated with altered synaptic function. However, the impact of aging on the expression of neurotransmitter receptors and accessory proteins in brain synapses remains unclear.

Identification of a conformational heparin-recognition motif on the peptide hormone secretin: key role for cell surface binding.

Secretin is a peptide hormone that exerts pleiotropic physiological functions by specifically binding to its cognate membrane-bound receptor. The membrane catalysis model of peptide-receptor interactions states that soluble peptidic ligands initially interact with the plasma membrane. This interaction increases the local concentration and structures the peptide, enhancing the rate of receptor binding.

GSG1L suppresses AMPA receptor-mediated synaptic transmission and uniquely modulates AMPA receptor kinetics in hippocampal neurons.

Regulation of AMPA receptor (AMPAR)-mediated synaptic transmission is a key mechanism for synaptic plasticity. In the brain, AMPARs assemble with a number of auxiliary subunits, including TARPs, CNIHs and CKAMP44, which are important for AMPAR forward trafficking to synapses. Here we report that the membrane protein GSG1L negatively regulates AMPAR-mediated synaptic transmission.

Dynamic Regulation of N-Methyl-d-aspartate (NMDA) and α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors by Posttranslational Modifications.

Many molecular mechanisms underlie the changes in synaptic glutamate receptor content that are required by neuronal networks to generate cellular correlates of learning and memory. During the last decade, posttranslational modifications have emerged as critical regulators of synaptic transmission and plasticity. Notably, phosphorylation, ubiquitination, and palmitoylation control the stability, trafficking, and synaptic expression of glutamate receptors in the central nervous system.

Casein kinase 2 phosphorylates GluA1 and regulates its surface expression.

Controlling the density of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) at synapses is essential for regulating the strength of excitatory neurotransmission. In particular, the phosphorylation of AMPARs is important for defining both synaptic expression and intracellular routing of receptors. Phosphorylation is a post-translational modification known to regulate many cellular events and the C-termini of glutamate receptors are important targets.

Ubiquitin ligase RNF167 regulates AMPA receptor-mediated synaptic transmission.

AMPA receptors (AMPARs) mediate the majority of fast excitatory neurotransmission, and their density at postsynaptic sites determines synaptic strength. Ubiquitination is a posttranslational modification that dynamically regulates the synaptic expression of many proteins. However, very few of the ubiquitinating enzymes implicated in the process have been identified.

Activity-dependent ubiquitination of the AMPA receptor subunit GluA2.

AMPA receptors (AMPARs) are postsynaptic glutamate-gated ion channels that mediate fast excitatory neurotransmission in the mammalian brain. Synaptic activity modulates the density of synaptic AMPARs, thereby affecting synaptic function, learning, and memory. Consequently, there is intense interest in defining the molecular mechanisms regulating AMPAR trafficking.

TRUSS, TNF-R1, and TRPC ion channels synergistically reverse endoplasmic reticulum Ca2+ storage reduction in response to m1 muscarinic acetylcholine receptor signaling.

Although most signaling responses initiated by tumor necrosis factor-alpha (TNF-alpha) occur in a Ca(2+)-independent fashion, TNF-alpha receptor signaling augments Ca(2+) entry induced by Galpha(q/11) G-protein coupled receptors (GPCRs) in endothelial cells and increases trans-endothelial permeability. The signaling events involved in GPCR-induced Ca(2+) influx have been characterized and involve store-operated Ca(2+) entry facilitated by the Ca(2+) permeable ion channel, transient receptor potential canonical 4 (TRPC4). Little is known about the mechanisms by which TNF-alpha receptor signaling augments GPCR-induced Ca(2+) entry.

The self-association of two N-terminal interaction domains plays an important role in the tetramerization of TRPC4.

Transient receptor potential canonical (TRPC) channels function as cation channels. In a previous study, we identified the molecular determinants involved in promoting TRPC subunit assembly. In the present study, we used size-exclusion chromatography assays to show that the N-terminus of TRPC4 can self-associate and form a tetramer in cellulo.

RNF24, a new TRPC interacting protein, causes the intracellular retention of TRPC.

TRPCs function as cation channels in non-excitable cells. The N-terminal tails of all TRPCs contain an ankyrin-like repeat domain, one of the most common protein-protein interaction motifs. Using a yeast two-hybrid screening approach, we found that RNF24, a new membrane RING-H2 protein, interacted with the ankyrin-like repeat domain of TRPC6.

Identification of two domains involved in the assembly of transient receptor potential canonical channels.

Transient receptor potential canonical (TRPC) channels are associated with calcium entry activity in nonexcitable cells. TRPCs can form homo- or heterotetrameric channels, in which case they can assemble together within a subfamily groups. TRPC1, 4, and 5 represent one group, and TRPC3, 6, and 7 represent the other.

MxA, a member of the dynamin superfamily, interacts with the ankyrin-like repeat domain of TRPC.

Mammalian transient receptor potential canonical channels have been proposed as the molecular entities associated with calcium entry activity in nonexcitable cells. Amino acid sequence analyses of TRPCs revealed the presence of ankyrin-like repeat domains, one of the most common protein-protein interaction motifs. Using a yeast two-hybrid interaction assay, we found that the second ankyrin-like repeat domain of TRPC6 interacted with MxA, a member of the dynamin superfamily.

The overexpression of presenilin2 and Alzheimer's-disease-linked presenilin2 variants influences TRPC6-enhanced Ca2+ entry into HEK293 cells.

Mutations in the presenilin (PS) genes are linked to the development of early-onset Alzheimer's disease by a gain-of-function mechanism that alters proteolytic processing of the amyloid precursor protein (APP). Recent work indicates that Alzheimer's-disease-linked mutations in presenilin1 and presenilin2 attenuate calcium entry and augment calcium release from the endoplasmic reticulum (ER) in different cell types. However, the regulatory mechanisms underlying the altered profile of Ca(2+) signaling are unknown.

Exocytotic insertion of TRPC6 channel into the plasma membrane upon Gq protein-coupled receptor activation.

TRPC proteins are the mammalian homologues of the Drosophila transient receptor potential channel and are involved in calcium entry after agonist stimulation of non-excitable cells. Seven mammalian TRPCs have been cloned, and their mechanisms of activation and regulation are still the subject of intense research. TRPC proteins interact with the inositol 1,4,5-trisphosphate receptor, and the conformational coupling plays a critical role in the activation of calcium entry.