A secretory-type protein, containing a pentraxin domain, interacts with an A-type K+ channel

Deletion of Stk11 and Fos in mouse BLA projection neurons alters intrinsic excitability and impairs formation of long-term aversive memory

Conditioned taste aversion (CTA) is a form of one-trial learning dependent on basolateral amygdala projection neurons (BLApn). Its underlying cellular and molecular mechanisms remain poorly understood. RNAseq from BLApn identified changes in multiple candidate learning-related transcripts including the expected immediate early gene Fos and Stk11, a master kinase of the AMP-related kinase pathway with important roles in growth, metabolism and development, but not previously implicated in learning. Deletion of Stk11 in BLApn blocked memory prior to training, but not following it and increased neuronal excitability. Conversely, BLApn had reduced excitability following CTA. BLApn knockout of a second learning-related gene, Fos, also increased excitability and impaired learning. Independently increasing BLApn excitability chemogenetically during CTA also impaired memory. STK11 and C-FOS activation were independent of one another. These data suggest key roles for Stk11 and Fos in CTA long-term memory formation, dependent at least partly through convergent action on BLApn intrinsic excitability.

The large conductance calcium-activated K(+) channel interacts with the small GTPase Rab11b

The transduction of sound by the receptor or hair cells of the cochlea leads to the activation of ion channels found in the basal and lateral regions of these cells. Thus, the processing of these transduced signals to the central nervous system is tied to the regulation of baso-lateral ion channels. The large conductance calcium-activated potassium or BK channel was revealed to interact with the small GTPase, Rab11b, which is one of many Rabs found in various endosomal pathways. Immunoelectron microscopy showed the colocalization of these two proteins in receptor cells and auditory neurons. Using Chinese hamster ovary cells as a heterologous expression system, Rab11b increased or decreased BK expression, depending on the overexpression or RNAi knockdown of Rab, respectively. Additional mutation analyses, using a yeast two-hybrid assay, suggested that this GTPase moderately interacts within a region of BK exclusive of the N- or C-terminal tails. These data suggest that this small GTPase regulates BK in a slow recycling process through the endocytic compartment and to the plasmalemma.

Lack of nAChR activity depresses cochlear maturation and up-regulates GABA system components: temporal profiling of gene expression in alpha9 null mice

Background

It has previously been shown that deletion of chrna9, the gene encoding the α9 nicotinic acetylcholine receptor (nAChR) subunit, results in abnormal synaptic terminal structure. Additionally, all nAChR-mediated cochlear activity is lost, as characterized by a failure of the descending efferent system to suppress cochlear responses to sound. In an effort to characterize the molecular mechanisms underlying the structural and functional consequences following loss of α9 subunit expression, we performed whole-transcriptome gene expression analyses on cochleae of wild type and α9 knockout (α9^−/−) mice during postnatal days spanning critical periods of synapse formation and maturation.

Principal Findings

Data revealed that loss of α9 receptor subunit expression leads to an up-regulation of genes involved in synaptic transmission and ion channel activity. Unexpectedly, loss of α9 receptor subunit expression also resulted in an increased expression of genes encoding GABA receptor subunits and the GABA synthetic enzyme, glutamic acid decarboxylase. These data suggest the existence of a previously unrecognized association between the nicotinic cholinergic and GABAergic systems in the cochlea. Computational analyses have highlighted differential expression of several gene sets upon loss of nicotinic cholinergic activity in the cochlea. Time-series analysis of whole transcriptome patterns, represented as self-organizing maps, revealed a disparate pattern of gene expression between α9^−/− and wild type cochleae at the onset of hearing (P13), with knockout samples resembling immature postnatal ages.

Conclusions

We have taken a systems biology approach to provide insight into molecular programs influenced by the loss of nicotinic receptor-based cholinergic activity in the cochlea and to identify candidate genes that may be involved in nicotinic cholinergic synapse formation, stabilization or function within the inner ear. Additionally, our data indicate a change in the GABAergic system upon loss of α9 nicotinic receptor subunit within the cochlea.

The large-conductance Ca(2+)-activated K(+) channel interacts with the apolipoprotein ApoA1

Owing to the multifaceted functions of the large conductance Ca(2+)-activated K(+) channel (BK), identification of protein-protein interactions is essential in determining BK regulation. A yeast two-hybrid screening of a cochlear cDNA library revealed a BK-ApoA1 interaction. Patch clamp recordings of excised membrane patches from transfected HEK293 cells showed that ApoA1 inhibits the BK alpha-subunit by significantly increasing activation and deactivation times, and shifting half-activation voltage to more positive potentials. Reciprocal coimmunoprecipitations verified the BK-ApoA1 interaction using excised sensory epithelium and ganglia. Additionally, immunocolocalization studies revealed BK and ApoA1 expression in both receptor cells and auditory neurons. These data suggest new avenues of investigation, given the importance of apolipoproteins in neurological diseases.

PPTX, a pentraxin domain-containing protein, interacts with the T1 domain of K v 4

Voltage-gated K(+) (K(v)) channels reside as tetramers in the membrane. The events that coordinate folding, trafficking, and tetramerization are mediated by an array of associated proteins and phospholipids whose identification is vital to understanding the dynamic nature of channel expression and activity. An interaction between an A-type K(+) channel, K(v)4.2, and a protein containing a pentraxin domain (PPTX) was demonstrated in the cochlea (Duzhyy et al. [ 2005] J. Biol. Chem. 280:15165-15172). Here, we present results based on fold recognition and homology modeling that revealed the tetramerization (T1) domain of K(v)4.2 as a potential docking site for interacting proteins such as PPTX. By using this model, putative sites were experimentally tested with the yeast two-hybrid system to assay interactions between PPTX and the T1 domain of K(v)4.2 wild type (wt) and mutants (mut). Results showed that amino acid residues 86 and 118 in the T1 domain are essential for interaction, because replacing these negatively charged with neutrally charged amino acids inhibits interactions. Cotransfections of Chinese hamster ovary cells with PPTX and K(v)4.2wt further revealed that PPTX increases K(v)4.2 wt expression in vitro when analyzing total lysates, whereas interactions with K(v)4.2 microt resulted in a decrease. These studies suggest that portions of the T1 domain can act as docking sites for proteins such as PPTX, further underscoring the significance of this domain.

The use of 2-D gels to identify novel protein-protein interactions in the cochlea

Functional proteomics comprises a wide range of technologies for the identification of novel protein-protein interactions and biological markers. Studies of protein-protein interactions have gained from the development of techniques and technologies such as immunoprecipitation, preparative two-dimensional (2-D) gel electrophoresis for peptide mass fingerprinting (PMF), using matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and liquid chromatography-tandem mass spectrometry (LC-MS/MS). These applications enabled the discovery of putative protein partners without a priori knowledge of which one(s) might be relevant. Here, we report the methods by which membrane proteins are isolated from cochlear tissues and prepared for identification by mass spectrometry techniques.

In vivo verification of protein interactions in the inner ear by coimmunoprecipitation

Genomics has provided us with vast amounts of data and thus, the challenge to identify and characterize gene products. Proteomics analysis, using methods such as yeast two-hybrid screenings, isoelectric focusing, and mass spectroscopy, generate potentially useful information. To determine functional relationships between and among proteins, however, the initial data for putative protein interactions must first be validated. One technique, which is considered the gold standard, is coimmunoprecipitation.

Surface expression and distribution of voltage-gated potassium channels in neurons (Review)

The last decade has witnessed an exponential increase in interest in one of the great mysteries of nerve cell biology: Specifically, how do neurons know where to place the ion channels that control their excitability? Many of the most important insights have been gleaned from studies on the voltage-gated potassium channels (Kvs) which underlie the shape, duration and frequency of action potentials. In this review, we gather recent evidence on the expression, trafficking and maintenance mechanisms which control the surface density of Kvs in different subcellular compartments of neurons and how these may be regulated to control cell excitability.

Role of the soluble pattern recognition receptor PTX3 in vascular biology

Pentraxins act as soluble pattern recognition receptors with a wide range of functions in various pathophysiological conditions. The long-pentraxin PTX3 shares the C-terminal pentraxin-domain with short-pentraxins C-reactive protein and serum amyloid P component and possesses an unique N-terminal domain. These structural features suggest that PTX3 may have both overlapping and distinct biological/ligand recognition properties when compared to short-pentraxins. PTX3 serves as a mechanism of amplification of inflammation and innate immunity. Indeed, vessel wall elements produce high amounts of PTX3 during inflammation and the levels of circulating PTX3 increase in several pathological conditions affecting the cardiovascular system. PTX3 exists as a free or extracellular matrix-associated molecule and it binds the complement fraction C1q. PTX3 binds also apoptotic cells and selected pathogens, playing a role in innate immunity processes. In endothelial cells and macrophages, PTX3 upregulates tissue factor expression, suggesting its action as a regulator of endothelium during thrombogenesis and ischaemic vascular disease. Finally, PTX3 binds the angiogenic fibroblast growth factor-2, thus inhibiting its biological activity. Taken together, these properties point to a role for PTX3 during vascular damage, angiogenesis, atherosclerosis, and restenosis.

Interaction of syntaxin 1A with the N-terminus of Kv4.2 modulates channel surface expression and gating

Kv4.2 channels are responsible in the heart for the Ca2+-independent transient outward currents and are important in regulating myocardial excitability and Ca2+ homeostasis. We have identified previously the expression of syntaxin 1A (STX1A) on the cardiac ventricular myocyte plasma membranes, and its modulation of cardiac ATP-sensitive K+ channels. We speculated that STX1A interacts with other cardiac ion channels, thus we examined the interaction of STX1A with Kv4.2 channels. Co-immunoprecipitation and GST pulldown assays demonstrated a direct interaction of STX1A with the Kv4.2 N-terminus. We next investigated the functional alterations of Kv4.2 gating by STX1A in Xenopus oocytes. Coexpression of Kv4.2 with STX1A (1) resulted in a reduction of Kv4.2 current amplitude; (2) caused a depolarizing shift of the steady-state inactivation curve; (3) enhanced the rate of current decay; and (4) accelerated the rate of recovery from inactivation. Additional coexpression of botulinum neurotoxin C, which cleaves STX1A, reversed the effects of STX1A on Kv4.2. STX1A inhibited partially the gating changes by KChIP2, suggesting a competitive interaction of these proteins for an overlapping binding region on the N-terminus of Kv4.2. Indeed, the N-terminal truncation mutants of Kv4.2 (Kv4.2Delta2-40 and Kv4.2Delta7-11), which form part of the KChIP2 binding site, displayed reduced sensitivity to STX1A modulation. Our study suggests that STX1A directly modulates Kv4.2 current amplitude and gating through its interaction with an overlapping region of the KChIP binding motif domain on the Kv4.2 N-terminus.

Gene expression profiling analysis of the inner ear

Recent developments in molecular genetics, including progress in the human genome project, have allowed identification of genes at an unprecedented rate. To date gene expression profiling studies have focused on identifying transcripts that are specifically or preferentially enriched within the inner ear on the assumption that they are more likely to be important for auditory and vestibular function. It is now apparent that some genes preferentially expressed in the cochleo-vestibular system are not crucial for hearing or balance or their functions are compensated for by other genes. In addition, transcripts expressed at low abundance in the inner ear are generally under-represented in gene profiling studies. In this review, we highlight the limitations of current gene expression profiling strategies as a discovery tool for genes involved in cochleo-vestibular development and function. We argue that expression profiling based on hierarchical clustering of transcripts by gene ontology, combined with tissue enrichment data, is more effective for inner ear gene discovery. This approach also provides a framework to assist and direct the functional characterization of gene products.