Spectrins: a structural platform for stabilization and activation of membrane channels, receptors and transporters

Dysregulated gene subnetworks in breast invasive carcinoma reveal novel tumor suppressor genes

Breast invasive carcinoma (BRCA) is the most malignant and leading cause of death in women. Global efforts are ongoing for improvement in early detection, prevention, and treatment. In this milieu, a comprehensive analysis of RNA-sequencing data of 1097 BRCA samples and 114 normal adjacent tissues is done to identify dysregulated genes in major molecular classes of BRCA in various clinical stages. Significantly enriched pathways in distinct molecular classes of BRCA have been identified. Pathways such as interferon signaling, tryptophan degradation, granulocyte adhesion & diapedesis, and catecholamine biosynthesis were found to be significantly enriched in Estrogen/Progesterone Receptor positive/Human Epidermal Growth Factor Receptor 2 negative, pathways such as RAR activation, adipogenesis, the role of JAK1/2 in interferon signaling, TGF-β and STAT3 signaling intricated in Estrogen/Progesterone Receptor negative/Human Epidermal Growth Factor Receptor 2 positive and pathways as IL-1/IL-8, TNFR1/TNFR2, TWEAK, and relaxin signaling were found in triple-negative breast cancer. The dysregulated genes were clustered based on their mutation frequency which revealed nine mutated clusters, some of which were well characterized in cancer while others were less characterized. Each cluster was analyzed in detail which led to the identification of NLGN3, MAML2, TTN, SYNE1, ANK2 as candidate genes in BRCA. They are central hubs in the protein-protein-interaction network, indicating their important regulatory roles. Experimentally, the Real-Time Quantitative Reverse Transcription PCR and western blot confirmed our computational predictions in cell lines. Further, immunohistochemistry corroborated the results in ~ 100 tissue samples. We could experimentally show that the NLGN3 & ANK2 have tumor-suppressor roles in BRCA as shown by cell viability assay, transwell migration, colony forming and wound healing assay. The cell viability and migration was found to be significantly reduced in MCF7 and MDA-MB-231 cell lines in which the selected genes were over-expressed as compared to control cell lines. The wound healing assay also demonstrated a significant decrease in wound closure at 12 h and 24 h time intervals in MCF7 & MDA-MB-231 cells. These findings established the tumor suppressor roles of NLGN3 & ANK2 in BRCA. This will have important ramifications for the therapeutics discovery against BRCA.

Multi-omics pan-cancer study of SPTBN2 and its value as a potential therapeutic target in pancreatic cancer

SPTBN2 is a protein-coding gene that is closely related to the development of malignant tumors. However, its prognostic value and biological function in pan-cancer, especially pancreatic cancer (PAAD), have not been reported. In the present study, a novel exploration of the value and potential mechanism of SPTBN2 in PAAD was conducted using multi-omics in the background of pan-cancer. Via various database analysis, up-regulated expression of SPTBN2 was detected in most of the tumor tissues examined. Overexpression of SPTBN2 in PAAD and kidney renal clear cell cancer patients potentially affected overall survival, disease-specific survival, and progression-free interval. In PAAD, SPTBN2 can be used as an independent factor affecting prognosis. Mutations and amplification of SPTBN2 were detected, with abnormal methylation of SPTBN2 affecting its expression and the survival outcome of PAAD patients. Immunoassay results demonstrate that SPTBN2 was a potential biomarker for predicting therapeutic response in PAAD, and may influence the immunotherapy efficacy of PAAD by regulating levels of CD8 + T cells and neutrophil infiltration. Results from an enrichment analysis indicated that SPTBN2 may regulate the development of PAAD via immune pathways. Thus, SPTBN2 is a potential prognostic biomarker and immunotherapy target based on its crucial role in the development of PAAD.

The T-type calcium channelosome

T-type calcium channels perform crucial physiological roles across a wide spectrum of tissues, spanning both neuronal and non-neuronal system. For instance, they serve as pivotal regulators of neuronal excitability, contribute to cardiac pacemaking, and mediate the secretion of hormones. These functions significantly hinge upon the intricate interplay of T-type channels with interacting proteins that modulate their expression and function at the plasma membrane. In this review, we offer a panoramic exploration of the current knowledge surrounding these T-type channel interactors, and spotlight certain aspects of their potential for drug-based therapeutic intervention.

A Systematic Compilation of Human SH3 Domains: A Versatile Superfamily in Cellular Signaling

SRC homology 3 (SH3) domains are fundamental modules that enable the assembly of protein complexes through physical interactions with a pool of proline-rich/noncanonical motifs from partner proteins. They are widely studied modular building blocks across all five kingdoms of life and viruses, mediating various biological processes. The SH3 domains are also implicated in the development of human diseases, such as cancer, leukemia, osteoporosis, Alzheimer's disease, and various infections. A database search of the human proteome reveals the existence of 298 SH3 domains in 221 SH3 domain-containing proteins (SH3DCPs), ranging from 13 to 720 kilodaltons. A phylogenetic analysis of human SH3DCPs based on their multi-domain architecture seems to be the most practical way to classify them functionally, with regard to various physiological pathways. This review further summarizes the achievements made in the classification of SH3 domain functions, their binding specificity, and their significance for various diseases when exploiting SH3 protein modular interactions as drug targets.

Competition between myosin II and βH-spectrin regulates cytoskeletal tension

Spectrins are membrane cytoskeletal proteins generally thought to function as heterotetramers comprising two α-spectrins and two β-spectrins. They influence cell shape and Hippo signaling, but the mechanism by which they influence Hippo signaling has remained unclear. We have investigated the role and regulation of the Drosophila β-heavy spectrin (β_H-spectrin, encoded by the karst gene) in wing imaginal discs. Our results establish that β_H-spectrin regulates Hippo signaling through the Jub biomechanical pathway due to its influence on cytoskeletal tension. While we find that α-spectrin also regulates Hippo signaling through Jub, unexpectedly, we find that β_H-spectrin localizes and functions independently of α-spectrin. Instead, β_H-spectrin co-localizes with and reciprocally regulates and is regulated by myosin. In vivo and in vitro experiments support a model in which β_H-spectrin and myosin directly compete for binding to apical F-actin. This competition can explain the influence of β_H-spectrin on cytoskeletal tension and myosin accumulation. It also provides new insight into how β_H-spectrin participates in ratcheting mechanisms associated with cell shape change.

Apical-basal polarity of the spectrin cytoskeleton in the C. elegans vulva

The C. elegans vulva is a polarized epithelial tube that has been studied extensively as a model for cell-cell signaling, cell fate specification, and tubulogenesis. Here we used endogenous fusions to show that the spectrin cytoskeleton is polarized in this organ, with conventional beta-spectrin ( UNC-70 ) found only at basolateral membranes and beta heavy spectrin ( SMA-1 ) found only at apical membranes. The sole alpha-spectrin ( SPC-1 ) is present at both locations but requires SMA-1 for its apical localization. Thus, beta spectrins are excellent markers for vulva cell membranes and polarity.

Endothelial tip/stalk cell selection requires BMP9-induced βIV-spectrin expression during sprouting angiogenesis

βIV-Spectrin is a membrane cytoskeletal protein with specialized roles in the nervous system and heart. Recent evidence also indicates a fundamental role for βIV-spectrin in angiogenesis as its endothelial-specific gene deletion in mice enhances embryonic lethality due to hypervascularization and hemorrhagic defects. During early vascular sprouting, βIV-spectrin is believed to inhibit tip cell sprouting in favor of the stalk cell phenotype by mediating VEGFR2 internalization and degradation. Despite these essential roles, mechanisms governing βIV-spectrin expression remain unknown. Here we identify bone morphogenetic protein 9 (BMP9) as a major inducer of βIV-spectrin gene expression in the vascular system. We show that BMP9 signals through the ALK1/Smad1 pathway to induce βIV-spectrin expression, which then recruits CaMKII to the cell membrane to induce phosphorylation-dependent VEGFR2 turnover. Although BMP9 signaling promotes stalk cell behavior through activation of hallmark stalk cell genes ID-1/3 and Hes-1 and Notch signaling cross-talk, we find that βIV-spectrin acts upstream of these pathways as loss of βIV-spectrin in neonate mice leads to retinal hypervascularization due to excessive VEGFR2 levels, increased tip cell populations, and strong Notch inhibition irrespective of BMP9 treatment. These findings demonstrate βIV-spectrin as a BMP9 gene target critical for tip/stalk cell selection during nascent vessel sprouting.

Clinical significance of nonerythrocytic spectrin Beta 1 (SPTBN1) in human kidney renal clear cell carcinoma and uveal melanoma: a study based on Pan-Cancer Analysis

BACKGROUND

Nonerythrocytic spectrin beta 1 (SPTBN1) is an important cytoskeletal protein that involves in normal cell growth and development via regulating TGFβ/Smad signaling pathway, and is aberrantly expressed in various cancer types. But, the exact role of SPTBN1 in pan-cancer is still unclear. This report aimed to display expression patterns and prognostic landscapes of SPTBN1 in human cancers, and further assess its prognostic/therapeutic value and immunological role in kidney renal carcinoma (KIRC) and uveal melanoma (UVM).

METHODS

We firstly analyzed expression patterns and prognostic landscapes of SPTBN1 in human cancers using various databases and web-based tools. The relationships between SPTBN1 expression and survival/tumor immunity in KIRC and UVM were further investigated via R packages and TIMER 2.0 platform. The therapeutic roles of SPTBN1 in KIRC and UVM were also explored via R software. Following this, the prognostic value and cancer immunological role of SPTBN1 in KIRC and UVM were validated in our cancer patients and GEO database.

RESULTS

Overall, cancer tissue had a lower expression level of SPTBN1 frequently in pan-cancer, compared with those in adjacent nontumor one. SPTBN1 expression often showed a different effect on survival in pan-cancer; upregulation of SPTBN1 was protective to the survival of KIRC individuals, which was contrary from what was found in UVM patients. In KIRC, there were significant negative associations between SPTBN1 expression and pro-tumor immune cell infiltration, including Treg cell, Th2 cell, monocyte and M2-macrophage, and expression of immune modulator genes, such as tumor necrosis factor superfamily member 9 (TNFSF9); while, in UVM, these correlations exhibited opposite patterns. The following survival and expression correlation analysis in our cancer cohorts and GEO database confirmed these previous findings. Moreover, we also found that SPTBN1 was potentially involved in the resistance of immunotherapy in KIRC, and the enhance of anti-cancer targeted treatment in UVM.

CONCLUSIONS

The current study presented compelling evidence that SPTBN1 might be a novel prognostic and therapy-related biomarker in KIRC and UVM, shedding new light on anti-cancer strategy.

Cytoskeletal orchestration of glucose uptake in Sertoli cell to support efferocytosis of apoptotic germ cells

Efferocytosis of non-viable germ cells by Sertoli cells (SCs) constitutes a sentinel for testis homeostasis, yet how SCs signal for the metabolic and cytoskeletal adaption to this energetically costly process remains unexplored. Spectrin is membrane-associated periodic skeleton assembled into an actin-spectrin-based cytoskeletal structure with an interaction with glucose transporter Glut1. The contribution of spectrin to glucose uptake and efferocytosis is unknown. In this study, we identified a cross-regulation between glucose metabolism and efferocytosis in SCs. Pharmacological or genetic inhibition of glucose uptake or glycolysis compromises efferocytosis activity. We further found that βII-spectrin is a hitherto unappreciated regulator of glucose metabolism and cytoskeletal architecture. βII-spectrin deficiency impairs glucose uptake and lactate production in SCs. Moreover, a defective assembly of cytoskeleton and a loss of blood-testis barrier integrity are also featured by SCs deficient in βII-spectrin. The disruption in glucose metabolism and cytoskeletal organization synergistically lead to a defective efferocytosis. In vivo siRNA-mediated targeting of βII-spectrin in testis causes an obvious morphological aberration in seminiferous epithelium with the presence of exfoliated germ cells and multinucleated giant cells. Importantly, a decrease in expression of αII/βII-spectrin was observed in testes of Adjudin-induced infertility model. By exploring the functional relevance of βII-spectrin to the metabolic and cytoskeletal regulation of efferocytosis, our study proposes a potential link between βII-spectrin deregulation and male infertility.

TMEM30A is essential for hair cell polarity maintenance in postnatal mouse cochlea

BACKGROUND

Phosphatidylserine is translocated to the inner leaflet of the phospholipid bilayer membrane by the flippase function of type IV P-tape ATPase (P4-ATPase), which is critical to maintain cellular stability and homeostasis. Transmembrane protein 30A (TMEM30A) is the β-subunit of P4-ATPase. Loss of P4-ATPase function causes sensorineural hearing loss and visual dysfunction in human. However, the function of TMEM30A in the auditory system is unclear.

METHODS

P4-ATPase subtype expression in the cochlea was detected by immunofluorescence staining and quantitative real-time polymerase chain reaction (qRT-PCR) at different developmental stages. Hair cell specific TMEM30A knockout mice and wild-type littermates were used for the following functional and morphological analysis. Auditory function was evaluated by auditory brainstem response. We investigated hair cell and stereocilia morphological changes by immunofluorescence staining. Scanning electron microscopy was applied to observe the stereocilia ultrastructure. Differentially expressed transcriptomes were analyzed based on RNA-sequencing data from knockout and wild-type mouse cochleae. Differentially expressed genes were verified by qRT-PCR.

RESULTS

TMEM30A and subtypes of P4-ATPase are expressed in the mouse cochlea in a temporal-dependent pattern. Deletion of TMEM30A in hair cells impaired hearing onset due to progressive hair cell loss. The disrupted kinocilia placement and irregular distribution of spectrin-α in cuticular plate indicated the hair cell planar polarity disruption in TMEM30A deletion hair cells. Hair cell degeneration begins at P7 and finishes around P14. Transcriptional analysis indicates that the focal adhesion pathway and stereocilium tip-related genes changed dramatically. Without the TMEM30A chaperone, excessive ATP8A2 accumulated in the cytoplasm, leading to overwhelming endoplasmic reticulum stress, which eventually contributed to hair cell death.

CONCLUSIONS

Deletion of TMEM30A led to disrupted planar polarity and stereocilia bundles, and finally led to hair cell loss and auditory dysfunction. TMEM30A is essential for hair cell polarity maintenance and membrane homeostasis. Our study highlights a pivotal role of TMEM30A in the postnatal development of hair cells and reveals the possible mechanisms underlying P4-ATPase-related genetic hearing loss.

Protein Susceptibility to Peroxidation by 4-Hydroxynonenal in Hereditary Hemochromatosis

Iron overload caused by hereditary hemochromatosis (HH) increases free reactive oxygen species that, in turn, induce lipid peroxidation. Its 4-hydroxynonenal (HNE) by-product is a well-established marker of lipid peroxidation since it reacts with accessible proteins with deleterious consequences. Indeed, elevated levels of HNE are often detected in a wide variety of human diseases related to oxidative stress. Here, we evaluated HNE-modified proteins in the membrane of erythrocytes from HH patients and in organs of Hfe^-/- male and female mice, a mouse model of HH. For this purpose, we used one- and two-dimensional gel electrophoresis, immunoblotting and MALDI-TOF/TOF analysis. We identified cytoskeletal membrane proteins and membrane receptors of erythrocytes bound to HNE exclusively in HH patients. Furthermore, kidney and brain of Hfe^-/- mice contained more HNE-adducted protein than healthy controls. Our results identified main HNE-modified proteins suggesting that HH favours preferred protein targets for oxidation by HNE.

SPTBN1 abrogates renal clear cell carcinoma progression via glycolysis reprogramming in a GPT2-dependent manner

BACKGROUND

Renal clear cell carcinoma (ccRCC) is the most prevalent tumors worldwide. Discovering effective biomarkers is essential to monitor the prognosis and provide alternative clinical options. SPTBN1 is implicated in various cancerous processes. However, its role in ccRCC remains unelucidated. This study intends to explore the biological function and mechanism of SPTBN1 in ccRCC.

METHODS

Single-cell and bulk RNA-seq, tissue microarray, real-time quantitative PCR, and western blotting were applied to verify the expression and predictive value of SPTBN1 in ccRCC. Gain or loss of functional ccRCC cell line models were constructed, and in vitro and in vivo assays were performed to elucidate its tumorigenic phenotypes. Actinomycin D experiment, RNA immunoprecipitation (RIP), specific inhibitors, and rescue experiments were carried out to define the molecular mechanisms.

RESULTS

SPTBN1 was down-regulated in ccRCC and knockdown of SPTBN1 displayed a remarkably oncogenic role both in vitro and in vivo; while overexpressing SPTBN1 reversed this effect. SPTBN1 mediated ccRCC progression via the pathway of glutamate pyruvate transaminase 2 (GPT2)-dependent glycolysis. The expression of GPT2 was significantly negatively correlated with that of SPTBN1. As an RNA binding protein SPTBN1, regulated the mRNA stability of GPT2.

CONCLUSION

Our research demonstrated that SPTBN1 is significantly down-regulated in ccRCC. SPTBN1 knockdown promotes ccRCC progression via activating GPT2-dependent glycolysis. SPTBN1 may serve as a therapeutic target for the treatment of ccRCC.

PI(4,5)P2: signaling the plasma membrane

In the almost 70 years since the first hints of its existence, the phosphoinositide, phosphatidyl-D-myo-inositol 4,5-bisphosphate has been found to be central in the biological regulation of plasma membrane (PM) function. Here, we provide an overview of the signaling, transport and structural roles the lipid plays at the cell surface in animal cells. These include being substrate for second messenger generation, direct modulation of receptors, control of membrane traffic, regulation of ion channels and transporters, and modulation of the cytoskeleton and cell polarity. We conclude by re-evaluating PI(4,5)P2's designation as a signaling molecule, instead proposing a cofactor role, enabling PM-selective function for many proteins.

The Regulation of the Hippo Pathway by Intercellular Junction Proteins

The Hippo pathway is an evolutionarily conserved pathway that serves to promote cell death and differentiation while inhibiting cellular proliferation across species. The downstream effectors of this pathway, yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), are considered vital in promoting the output of the Hippo pathway, with activation of upstream kinases negatively regulating YAP/TAZ activity. The upstream regulation of the Hippo pathway is not entirely understood on a molecular level. However, several studies have shown that numerous cellular and non-cellular mechanisms such as cell polarity, contact inhibition, soluble factors, mechanical forces, and metabolism can convey external stimuli to the intracellular kinase cascade, promoting the activation of key components of the Hippo pathway and therefore regulating the subcellular localisation and protein activity of YAP/TAZ. This review will summarise what we have learnt about the role of intercellular junction-associated proteins in the activation of this pathway, including adherens junctions and tight junctions, and in particular our latest findings about the desmosomal components, including desmoglein-3 (DSG3), in the regulation of YAP signalling, phosphorylation, and subcellular translocation.

β-heavy-spectrin stabilizes the constricting contractile ring during cytokinesis

Cytokinesis requires the constriction of an actomyosin-based contractile ring and involves multiple F-actin crosslinkers. We show that partial depletion of the C. elegans cytokinetic formin generates contractile rings with low F-actin levels that constrict but are structurally fragile, and we use this background to investigate the roles of the crosslinkers plastin/PLST-1 and β-heavy-spectrin/SMA-1 during ring constriction. We show that the removal of PLST-1 or SMA-1 has opposite effects on the structural integrity of fragile rings. PLST-1 loss reduces cortical tension that resists ring constriction and makes fragile rings less prone to ruptures and regressions, whereas SMA-1 loss exacerbates structural defects, leading to frequent ruptures and cytokinesis failure. Fragile rings without SMA-1 or containing a shorter SMA-1, repeatedly rupture at the same site, and SMA-1::GFP accumulates at repair sites in fragile rings and in rings cut by laser microsurgery. These results establish that β-heavy-spectrin stabilizes the constricting ring and reveals the importance of β-heavy-spectrin size for network connectivity at low F-actin density.

Analyzing the mechanisms that facilitate the subtype-specific assembly of γ-aminobutyric acid type A receptors

Impaired inhibitory signaling underlies the pathophysiology of many neuropsychiatric and neurodevelopmental disorders including autism spectrum disorders and epilepsy. Neuronal inhibition is regulated by synaptic and extrasynaptic γ-aminobutyric acid type A receptors (GABA _A Rs), which mediate phasic and tonic inhibition, respectively. These two GABA _A R subtypes differ in their function, ligand sensitivity, and physiological properties. Importantly, they contain different α subunit isoforms: synaptic GABA _A Rs contain the α1-3 subunits whereas extrasynaptic GABA _A Rs contain the α4-6 subunits. While the subunit composition is critical for the distinct roles of synaptic and extrasynaptic GABA _A R subtypes in inhibition, the molecular mechanism of the subtype-specific assembly has not been elucidated. To address this issue, we purified endogenous α1- and α4-containing GABA _A Rs from adult murine forebrains and examined their subunit composition and interacting proteins using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and quantitative analysis. We found that the α1 and α4 subunits form separate populations of GABA _A Rs and interact with distinct sets of binding proteins. We also discovered that the β3 subunit, which co-purifies with both the α1 and α4 subunits, has different levels of phosphorylation on serines 408 and 409 (S408/9) between the two receptor subtypes. To understand the role S408/9 plays in the assembly of α1- and α4-containing GABA _A Rs, we examined the effects of S408/9A (alanine) knock-in mutation on the subunit composition of the two receptor subtypes using LC-MS/MS and quantitative analysis. We discovered that the S408/9A mutation results in the formation of novel α1α4-containing GABA _A Rs. Moreover, in S408/9A mutants, the plasma membrane expression of the α4 subunit is increased whereas its retention in the endoplasmic reticulum is reduced. These findings suggest that S408/9 play a critical role in determining the subtype-specific assembly of GABA _A Rs, and thus the efficacy of neuronal inhibition.

Mechanical role of the submembrane spectrin scaffold in red blood cells and neurons

Spectrins are large, evolutionarily well-conserved proteins that form highly organized scaffolds on the inner surface of eukaryotic cells. Their organization in different cell types or cellular compartments helps cells withstand mechanical challenges with unique strategies depending on the cell type. This Review discusses our understanding of the mechanical properties of spectrins, their very distinct organization in red blood cells and neurons as two examples, and the contribution of the scaffolds they form to the mechanical properties of these cells.

Effect of primary lesions in cytoskeleton proteins on red cell membrane stability in patients with hereditary spherocytosis

We investigated by targeted next generation sequencing the genetic bases of hereditary spherocytosis in 25 patients and compared the molecular results with the biochemical lesion of RBC membrane obtained by SDS-PAGE analysis. The HS diagnosis was based on available guidelines for diagnosis of congenital hemolytic anemia, and patients were selected because of atypical clinical presentation or intra-family variability, or because presented discrepancies between laboratory investigation and biochemical findings. In all patients but 5 we identified pathogenic variants in SPTA1, SPTB, ANK1, SLC4A1, EPB42 genes able to justify the clinical phenotype. Interestingly, a correspondence between the biochemical lesion and the molecular defect was identified in only 11/25 cases, mostly with band 3 deficiency due to SLC4A1 mutations. Most of the mutations in SPTB and ANK1 gene didn’t hesitate in abnormalities of RBC membrane protein; conversely, in two cases the molecular lesion didn’t correspond to the biochemical defect, suggesting that a mutation in a specific cytoskeleton protein may result in a more complex RBC membrane damage or suffering. Finally, in two cases the HS diagnosis was maintained despite absence of both protein defect and molecular lesion, basing on clinical and family history, and on presence of clear laboratory markers of HS. The study revealed complex relationships between the primary molecular lesion and the final effect in the RBC membrane cytoskeleton, and further underlines the concept that there is not a unique approach to the diagnosis of HS.

Involvement of membrane palmitoylated protein 2 (MPP2) in the synaptic molecular complex at the mouse cerebellar glomerulus

We previously reported that the membrane skeletal protein 4.1G in the peripheral nervous system transports membrane palmitoylated protein 6 (MPP6), which interacts with the synaptic scaffolding protein Lin7 and cell adhesion molecule 4 (CADM4) in Schwann cells that form myelin. In the present study, we investigated the localization of and proteins related to MPP2, a highly homologous family protein of MPP6, in the cerebellum of the mouse central nervous system, in which neurons are well organized. Immunostaining for MPP2 was observed at cerebellar glomeruli (CG) in the granular layer after postnatal day 14. Using the high-resolution Airyscan mode of a confocal laser-scanning microscope, MPP2 was detected as a dot pattern and colocalized with CADM1 and Lin7, recognized as small ring/line patterns, as well as with calcium/calmodulin-dependent serine protein kinase (CASK), NMDA glutamate receptor 1 (GluN1), and M-cadherin, recognized as dot patterns, indicating the localization of MPP2 in the excitatory postsynaptic region and adherens junctions of granule cells. An immunoprecipitation analysis revealed that MPP2 formed a molecular complex with CADM1, CASK, M-cadherin, and Lin7. Furthermore, the Lin7 staining pattern showed small rings surrounding mossy fibers in wild-type CG, while it changed to the dot/spot pattern inside small rings detected with CADM1 staining in MPP2-deficient CG. These results indicate that MPP2 influences the distribution of Lin7 to synaptic cell membranes at postsynaptic regions in granule cells at CG, at which electric signals enter the cerebellum.

Paracetamol perturbs neuronal arborization and disrupts the cytoskeletal proteins SPTBN1 and TUBB3 in both human and chicken in vitro models

Epidemiological studies have linked long-term/high-dose usage of paracetamol (N-acetyl-para-aminophenol, APAP) during pregnancy to adverse neuropsychiatric outcomes, primarily attention-deficit hyperactive disorder (ADHD), in the offspring. Though variable, ADHD has been associated with phenotypic alterations characterized by reductions in grey matter densities and aberrations in structural connectivity, effects which are thought to originate in neurodevelopment. We used embryonic chicken cerebellar granule neurons (CGNs) and neuronally differentiating human NTERA2 cells (NT2Ns) to investigate the in vitro effects of APAP on cell viability, migration, neuritogenesis, and the intracellular levels of various proteins involved in neurodevelopment as well as in the maintenance of the structure and function of neurites. Exposure to APAP ranging from 100 to 1600 μM yielded concentration- and time-dependent reductions in cell viability and levels of neurite arborization, as well as reductions in the levels of the cytoskeletal protein β2-spectrin, with the highest APAP concentration resulting in between 50 and 75% reductions in the aforementioned metrics over the course of 72 h. Exposure to APAP also reduced migration in the NT2Ns but not CGNs. Moreover, we found concentration- and time-dependent increases in punctate aggregation of the cytoskeletal protein β3-tubulin following exposure to APAP in both cell model systems, with the highest APAP concentration approximately doubling the number of aggregates over 72-120 h. Our findings demonstrate that APAP negatively perturbs neurite arborization degree, with concurrent reductions in the protein levels of β2-spectrin and disruption of the integrity of β3-tubulin, both proteins of which play important roles in neuronal structure and function.

Secreted Amyloid Precursor Protein Alpha, a Neuroprotective Protein in the Brain Has Widespread Effects on the Transcriptome and Proteome of Human Inducible Pluripotent Stem Cell-Derived Glutamatergic Neurons Related to Memory Mechanisms

Secreted amyloid precursor protein alpha (sAPPα) processed from a parent human brain protein, APP, can modulate learning and memory. It has potential for development as a therapy preventing, delaying, or even reversing Alzheimer’s disease. In this study a comprehensive analysis to understand how it affects the transcriptome and proteome of the human neuron was undertaken. Human inducible pluripotent stem cell (iPSC)-derived glutamatergic neurons in culture were exposed to 1 nM sAPPα over a time course and changes in the transcriptome and proteome were identified with RNA sequencing and Sequential Window Acquisition of All THeoretical Fragment Ion Spectra-Mass Spectrometry (SWATH-MS), respectively. A large subset (∼30%) of differentially expressed transcripts and proteins were functionally involved with the molecular biology of learning and memory, consistent with reported links of sAPPα to memory enhancement, as well as neurogenic, neurotrophic, and neuroprotective phenotypes in previous studies. Differentially regulated proteins included those encoded in previously identified Alzheimer’s risk genes, APP processing related proteins, proteins involved in synaptogenesis, neurotransmitters, receptors, synaptic vesicle proteins, cytoskeletal proteins, proteins involved in protein and organelle trafficking, and proteins important for cell signalling, transcriptional splicing, and functions of the proteasome and lysosome. We have identified a complex set of genes affected by sAPPα, which may aid further investigation into the mechanism of how this neuroprotective protein affects memory formation and how it might be used as an Alzheimer’s disease therapy.

Spectrins and human diseases

Spectrin, as one of the major components of a plasma membrane-associated cytoskeleton, is a cytoskeletal protein composed of the modular structure of α and β subunits. The spectrin-based skeleton is essential for preserving the integrity and mechanical characteristics of the cell membrane. Moreover, spectrin regulates a variety of cell processes including cell apoptosis, cell adhesion, cell spreading, and cell cycle. Dysfunction of spectrins is implicated in various human diseases including hemolytic anemia, neurodegenerative diseases, ataxia, heart diseases, and cancers. Here, we briefly discuss spectrins function as well as the clinical manifestations and currently known molecular mechanisms of human diseases related to spectrins, highlighting that strategies for targeting regulation of spectrins function may provide new avenues for therapeutic intervention for these diseases.

APP and DYRK1A regulate axonal and synaptic vesicle protein networks and mediate Alzheimer's pathology in trisomy 21 neurons

Trisomy 21 (T21) causes Down syndrome and an early-onset form of Alzheimer's disease (AD). Here, we used human induced pluripotent stem cells (hiPSCs) along with CRISPR-Cas9 gene editing to investigate the contribution of chromosome 21 candidate genes to AD-relevant neuronal phenotypes. We utilized a direct neuronal differentiation protocol to bypass neurodevelopmental cell fate phenotypes caused by T21 followed by unbiased proteomics and western blotting to define the proteins dysregulated in T21 postmitotic neurons. We show that normalization of copy number of APP and DYRK1A each rescue elevated tau phosphorylation in T21 neurons, while reductions of RCAN1 and SYNJ1 do not. To determine the T21 alterations relevant to early-onset AD, we identified common pathways altered in familial Alzheimer's disease neurons and determined which of these were rescued by normalization of APP and DYRK1A copy number in T21 neurons. These studies identified disruptions in T21 neurons in both the axonal cytoskeletal network and presynaptic proteins that play critical roles in axonal transport and synaptic vesicle cycling. These alterations in the proteomic profiles have functional consequences: fAD and T21 neurons exhibit dysregulated axonal trafficking and T21 neurons display enhanced synaptic vesicle release. Taken together, our findings provide insights into the initial molecular alterations within neurons that ultimately lead to synaptic loss and axonal degeneration in Down syndrome and early-onset AD.

A particle-based computational model to analyse remodelling of the red blood cell cytoskeleton during malaria infections

Red blood cells can withstand the harsh mechanical conditions in the vasculature only because the bending rigidity of their plasma membrane is complemented by the shear elasticity of the underlying spectrin-actin network. During an infection by the malaria parasite Plasmodium falciparum, the parasite mines host actin from the junctional complexes and establishes a system of adhesive knobs, whose main structural component is the knob-associated histidine rich protein (KAHRP) secreted by the parasite. Here we aim at a mechanistic understanding of this dramatic transformation process. We have developed a particle-based computational model for the cytoskeleton of red blood cells and simulated it with Brownian dynamics to predict the mechanical changes resulting from actin mining and KAHRP-clustering. Our simulations include the three-dimensional conformations of the semi-flexible spectrin chains, the capping of the actin protofilaments and several established binding sites for KAHRP. For the healthy red blood cell, we find that incorporation of actin protofilaments leads to two regimes in the shear response. Actin mining decreases the shear modulus, but knob formation increases it. We show that dynamical changes in KAHRP binding affinities can explain the experimentally observed relocalization of KAHRP from ankyrin to actin complexes and demonstrate good qualitative agreement with experiments by measuring pair cross-correlations both in the computer simulations and in super-resolution imaging experiments.

Malaria is one of the deadliest infectious diseases and its symptoms are related to the blood stage, when the parasite multiplies within red blood cells. In order to avoid clearance by the spleen, the parasite produces specific factors like the adhesion receptor PfEMP1 and the multifunctional protein KAHRP that lead to the formation of adhesive knobs on the surface of the red blood cells and thus increase residence time in the vasculature. We have developed a computational model for the parasite-induced remodelling of the actin-spectrin network to quantitatively predict the dynamical changes in the mechanical properties of the infected red blood cells and the spatial distribution of the different protein components of the membrane skeleton. Our simulations show that KAHRP can relocate to actin junctions due to dynamical changes in binding affinities, in good qualitative agreement with super-resolution imaging experiments. In the future, our simulation framework can be used to gain further mechanistic insight into the way malaria parasites attack the red blood cell cytoskeleton.

Genome-Wide Association of New-Onset Hypertension According to Renin Concentration: The Korean Genome and Epidemiology Cohort Study

The renin-angiotensin system (RAS) is a crucial regulator of vascular resistance and blood volume in the body. This study aimed to examine the genetic predisposition of the plasma renin concentration influencing future hypertension incidence. Based on the Korean Genome and Epidemiology Cohort dataset, 5211 normotensive individuals at enrollment were observed over 12 years, categorized into the low-renin and high-renin groups. We conducted genome-wide association studies for the total, low-renin, and high-renin groups. Among the significant SNPs, the lead SNPs of each locus were focused on for further interpretation. The effect of genotypes was determined by logistic regression analysis between controls and new-onset hypertension, after adjusting for potential confounding variables. During a mean follow-up period of 7.6 years, 1704 participants (32.7%) developed hypertension. The low-renin group showed more incidence rates of new-onset hypertension (35.3%) than the high-renin group (26.5%). Among 153 SNPs in renin-related gene regions, two SNPs (rs11726091 and rs8137145) showed an association in the high-renin group, four SNPs (rs17038966, rs145286444, rs2118663, and rs12336898) in the low-renin group, and three SNPs (rs1938859, rs7968218, and rs117246401) in the total population. Most significantly, the low-renin SNP rs12336898 in the SPTAN1 gene, closely related to vascular wall remodeling, was associated with the development of hypertension (p-value = 1.3 × 10−6). We found the candidate genetic polymorphisms according to blood renin concentration. Our results might be a valuable indicator for hypertension risk prediction and preventive measure, considering renin concentration with genetic susceptibility.

βIV-spectrin as a stalk cell-intrinsic regulator of VEGF signaling

Defective angiogenesis underlies over 50 malignant, ischemic and inflammatory disorders yet long-term therapeutic applications inevitably fail, thus highlighting the need for greater understanding of the vast crosstalk and compensatory mechanisms. Based on proteomic profiling of angiogenic endothelial components, here we report β_IV-spectrin, a non-erythrocytic cytoskeletal protein, as a critical regulator of sprouting angiogenesis. Early loss of endothelial-specific β_IV-spectrin promotes embryonic lethality in mice due to hypervascularization and hemorrhagic defects whereas neonatal depletion yields higher vascular density and tip cell populations in developing retina. During sprouting, β_IV-spectrin expresses in stalk cells to inhibit their tip cell potential by enhancing VEGFR2 turnover in a manner independent of most cell-fate determining mechanisms. Rather, β_IV-spectrin recruits CaMKII to the plasma membrane to directly phosphorylate VEGFR2 at Ser984, a previously undefined phosphoregulatory site that strongly induces VEGFR2 internalization and degradation. These findings support a distinct spectrin-based mechanism of tip-stalk cell specification during vascular development.

Defective angiogenesis remains a high source of morbidity in multiple disorders. Here they show that β_IV-spectrin, a membrane-associated cytoskeletal protein, is essential for regulation of endothelial tip cell populations and VEGF signaling during sprouting angiogenesis.

Spatial proteomic alterations detected via MALDI-MS imaging implicate neuronal loss in a Huntington's disease mouse (YAC128) brain

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder that occurs with the increase of CAG trinucleotide repeats in the huntingtin gene. To understand the mechanisms of HD, powerful proteomics techniques, such as liquid chromatography-tandem mass spectrometry (LC-MS/MS) were employed. However, one major drawback of these methods is loss of the region-specific quantitative information of the proteins due to analysis of total tissue lysates. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a MS-based label-free technique that works directly on tissue sections and gathers m/z values with their respective regional information. In this study, we established a data processing protocol that includes several software programs and methods to determine spatial protein alterations between the brain samples of a 12 month-old YAC128 HD mouse model and their non-transgenic littermates. 22 differentially expressed proteins were revealed with their respective regional information, and possible relationships of several proteins were discussed. As a validation of the MALDI-MSI analysis, a differentially expressed protein (GFAP) was verified using immunohistochemical staining. Furthermore, since several proteins detected in this study have previously been associated with neuronal loss, neuronal loss in the cortical region was demonstrated using an anti-NeuN immunohistochemical staining method. In conclusion, the findings of this research have provided insights into the spatial proteomic changes between HD transgenic and non-transgenic littermates and therefore, we suggest that MALDI-MSI is a powerful technique to determine spatial proteomic alterations between biological samples, and the data processing that we present here can be employed as a complementary tool for the data analysis.

A cryo-ET survey of microtubules and intracellular compartments in mammalian axons

The neuronal axon is packed with cytoskeletal filaments, membranes, and organelles, many of which move between the cell body and axon tip. Here, we used cryo-electron tomography to survey the internal components of mammalian sensory axons. We determined the polarity of the axonal microtubules (MTs) by combining subtomogram classification and visual inspection, finding MT plus and minus ends are structurally similar. Subtomogram averaging of globular densities in the MT lumen suggests they have a defined structure, which is surprising given they likely contain the disordered protein MAP6. We found the endoplasmic reticulum in axons is tethered to MTs through multiple short linkers. We surveyed membrane-bound cargos and describe unexpected internal features such as granules and broken membranes. In addition, we detected proteinaceous compartments, including numerous virus-like capsid particles. Our observations outline novel features of axonal cargos and MTs, providing a platform for identification of their constituents.

Signal Amplification in Highly Ordered Networks Is Driven by Geometry

Here, we hypothesize that, in biological systems such as cell surface receptors that relay external signals, clustering leads to substantial improvements in signaling efficiency. Representing cooperative signaling networks as planar graphs and applying Euler’s polyhedron formula, we can show that clustering may result in an up to a 200% boost in signaling amplitude dictated solely by the size and geometry of the network. This is a fundamental relationship that applies to all clustered systems regardless of its components. Nature has figured out a way to maximize the signaling amplitude in receptors that relay weak external signals. In addition, in cell-to-cell interactions, clustering both receptors and ligands may result in maximum efficiency and synchronization. The importance of clustering geometry in signaling efficiency goes beyond biological systems and can inform the design of amplifiers in nonbiological systems.

Nanoscale Dynamics of Actin Filaments in the Red Blood Cell Membrane Skeleton

Red blood cell (RBC) shape and deformability are supported by a planar network of short actin filament (F-actin) nodes (∼37 nm length, 15–18 subunits) interconnected by long spectrin strands at the inner surface of the plasma membrane. Spectrin-F-actin network structure underlies quantitative modeling of forces controlling RBC shape, membrane curvature, and deformation, yet the nanoscale organization and dynamics of the F-actin nodes in situ are not well understood. We examined F-actin distribution and dynamics in RBCs using fluorescent-phalloidin labeling of F-actin imaged by multiple microscopy modalities. Total internal reflection fluorescence and Zeiss Airyscan confocal microscopy demonstrate that F-actin is concentrated in multiple brightly stained F-actin foci ∼200–300 nm apart interspersed with dimmer F-actin staining regions. Single molecule stochastic optical reconstruction microscopy imaging of Alexa 647-phalloidin-labeled F-actin and computational analysis also indicates an irregular, nonrandom distribution of F-actin nodes. Treatment of RBCs with latrunculin A and cytochalasin D indicates that F-actin foci distribution depends on actin polymerization, while live cell imaging reveals dynamic local motions of F-actin foci, with lateral movements, appearance and disappearance. Regulation of F-actin node distribution and dynamics via actin assembly/disassembly pathways and/or via local extension and retraction of spectrin strands may provide a new mechanism to control spectrin-F-actin network connectivity, RBC shape, and membrane deformability.

Hypothesis Relating the Structure, Biochemistry and Function of Active Zone Material Macromolecules at a Neuromuscular Junction

This report integrates knowledge of in situ macromolecular structures and synaptic protein biochemistry to propose a unified hypothesis for the regulation of certain vesicle trafficking events (i.e., docking, priming, Ca²⁺-triggering, and membrane fusion) that lead to neurotransmitter secretion from specialized “active zones” of presynaptic axon terminals. Advancements in electron tomography, to image tissue sections in 3D at nanometer scale resolution, have led to structural characterizations of a network of different classes of macromolecules at the active zone, called “Active Zone Material’. At frog neuromuscular junctions, the classes of Active Zone Material macromolecules “top-masts”, “booms”, “spars”, “ribs” and “pins” direct synaptic vesicle docking while “pins”, “ribs” and “pegs” regulate priming to influence Ca²⁺-triggering and membrane fusion. Other classes, “beams”, “steps”, “masts”, and “synaptic vesicle luminal filaments’ likely help organize and maintain the structural integrity of active zones. Extensive studies on the biochemistry that regulates secretion have led to comprehensive characterizations of the many conserved proteins universally involved in these trafficking events. Here, a hypothesis including a partial proteomic atlas of Active Zone Material is presented which considers the common roles, binding partners, physical features/structure, and relative positioning in the axon terminal of both the proteins and classes of macromolecules involved in the vesicle trafficking events. The hypothesis designates voltage-gated Ca²⁺ channels and Ca²⁺-gated K⁺ channels to ribs and pegs that are connected to macromolecules that span the presynaptic membrane at the active zone. SNARE proteins (Syntaxin, SNAP25, and Synaptobrevin), SNARE-interacting proteins Synaptotagmin, Munc13, Munc18, Complexin, and NSF are designated to ribs and/or pins. Rab3A and Rabphillin-3A are designated to top-masts and/or booms and/or spars. RIM, Bassoon, and Piccolo are designated to beams, steps, masts, ribs, spars, booms, and top-masts. Spectrin is designated to beams. Lastly, the luminal portions of SV2 are thought to form the bulk of the observed synaptic vesicle luminal filaments. The goal here is to help direct future studies that aim to bridge Active Zone Material structure, biochemistry, and function to ultimately determine how it regulates the trafficking events in vivo that lead to neurotransmitter secretion.

Plastin and spectrin cooperate to stabilize the actomyosin cortex during cytokinesis

Cytokinesis, the process that partitions the mother cell into two daughter cells, requires the assembly and constriction of an equatorial actomyosin network. Different types of non-motor F-actin crosslinkers localize to the network, but their functional contribution remains poorly understood. Here, we describe a synergy between the small rigid crosslinker plastin and the large flexible crosslinker spectrin in the C. elegans one-cell embryo. In contrast to single inhibitions, co-inhibition of plastin and the βH-spectrin (SMA-1) results in cytokinesis failure due to progressive disorganization and eventual collapse of the equatorial actomyosin network. Cortical localization dynamics of non-muscle myosin II in co-inhibited embryos mimic those observed after drug-induced F-actin depolymerization, suggesting that the combined action of plastin and spectrin stabilizes F-actin in the contractile ring. An in silico model predicts that spectrin is more efficient than plastin at stabilizing the ring and that ring formation is relatively insensitive to βH-spectrin length, which is confirmed in vivo with a sma-1 mutant that lacks 11 of its 29 spectrin repeats. Our findings provide the first evidence that spectrin contributes to cytokinesis and highlight the importance of crosslinker interplay for actomyosin network integrity.

Comparative Analysis of Tryptophan Dynamics in Spectrin and Its Constituent Domains: Insights from Fluorescence

Spectrin is a cytoskeletal protein ubiquitous in metazoan cells that acts as a liaison between the plasma membrane and the cellular interior and imparts mechanical stability to the plasma membrane. Spectrin is known to be highly dynamic, with an appreciable degree of torsional and segmental mobility. In this context, we have earlier utilized the red edge excitation shift (REES) approach to report the retention of restricted solvation dynamics and local structure in the vicinity of spectrin tryptophans on urea denaturation and loss of spectrin secondary structure. As a natural progression of our earlier work, in this work, we carried out a biophysical dissection of tryptophan solvation and rotational dynamics in spectrin and its constituent domains, in order to trace the origin of local structure retention observed in denatured spectrin. Our results show that the ankyrin binding domain (and, to a lesser extent, the β-tetramerization domain) is capable of retention of local structure, similar to that observed for intact spectrin. However, all α-chain domains studied exhibit negligible retention of local structure on urea denaturation. Such a stark chain-specific retention of local structure could originate from the fact that the β-chain domains possess specialized functions, where conservation of local (structural) integrity may be a prerequisite for optimum cellular function. To the best of our knowledge, these observations represent one of the first systematic biophysical dissections of spectrin dynamics in terms of its constituent domains and add to emerging literature on comprehensive domain-based analysis of spectrin organization, dynamics, and function.

SPTBN2, a New Biomarker of Lung Adenocarcinoma

Objectives

The roles played by β-III-spectrin, also known as spectrin beta, non-erythrocytic 2 (SPTBN2), in the occurrence and development of lung adenocarcinoma (LUAD) have not been previously examined. Our study aimed to reveal the relationship between the SPTBN2 expression and LUAD.

Materials and Methods

Twenty pairs of LUAD tissues and adjacent tissues were collected from patients diagnosed and treated at the Thoracic Surgery Department of The First Affiliated Hospital of Zhengzhou University from July 2019 to September 2020. RNA sequencing (RNA-seq) analysis determined that the expression of SPTBN2 was higher in LUAD samples than in adjacent normal tissues. The expression levels of SPTBN2 were examined in various databases, including the Cancer Cell Line Encyclopedia (CCLE), Gene Expression Omnibus (GEO), and Human Protein Atlas (HPA). The Search Tool for the Retrieval of Interacting Genes (STRING) online website was used to examine protein–protein interactions involving SPTBN2, and the results were visualized by Cytoscape software. The Molecular Complex Detection (MCODE) plug-in for Cytoscape software was used to identify functional modules of the obtained protein–protein interaction (PPI) network. Gene enrichment analysis was performed, and survival analysis was conducted using the Kaplan–Meier plotter. The online prediction website TargetScan was used to predict SPTBN2-targeted miRNA sequences by searching for SPTBN2 sequences. Finally, we verified the expression of SPTBN2 in the obtained tissue samples using real-time fluorescence quantitative polymerase chain reaction (RT-qPCR). The human lung cancer cell lines A549 and H1299 were selected for the transfection of small interfering RNA (siRNA) targeting SPTBN2 (si-SPTBN2), and the knockdown efficiency was evaluated by RT-qPCR. The cellular proliferation, migration, and invasion capacities of A549 and H1299 cells were determined using the cell counting kit-8 (CCK-8) proliferation assay; the wound-healing assay and the Transwell migration assay; and the Matrigel invasion assay, respectively.

Results

The expression of SPTBN2 in non–small cell lung cancer (NSCLC) ranked 13th among cancer cell lines based on the CCLE database. At the mRNA and protein levels, the expression levels of SPTBN2 were higher in LUAD tissues than in normal lung tissues. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that proteins related to SPTBN2 were enriched in apoptotic and phagosomal pathways. Kaplan–Meier survival analysis revealed that SPTBN2 expression was significantly related to the prognosis of patients with LUAD. The TargetScan database verified that miR-16 was a negative regulator of SPTBN2 mRNA expression. The results of the CCK-8 cell proliferation assay revealed that SPTBN2 knockdown significantly inhibited the cell proliferation abilities of A549 and H1299 cells. The wound-healing assay indicated that SPTBN2 knockdown resulted in reduced migration after 48 h compared with the control group. The Transwell migration and invasion test revealed that the migration and invasion abilities were greatly decreased by SPTBN2 knockdown compared with control conditions.

Conclusion

We uncovered a novel gene, SPTBN2, that was significantly upregulated in LUAD tissues relative to normal tissue expression. SPTBN2 is highly expressed in LUAD, positively correlated with poor prognosis, and can promote the proliferation, migration, and invasion of LUAD cells.

Loss of SPTBN1 Suppresses Autophagy Via SETD7-mediated YAP Methylation in Hepatocellular Carcinoma Initiation and Development

BACKGROUND & AIMS

Loss of Spectrin beta, non-erythrocytic 1 (SPTBN1) plays an important role in the carcinogenesis of hepatocellular carcinoma (HCC); however, the mechanisms underlying its involvement remain poorly understood. Defects in autophagy contribute to hepatic tumor formation. Hence, in this study, we explored the role and mechanism of SPTBN1 in the autophagy of hepatic stem cells (HSCs) and HCC cells.

METHODS

Expansion, autophagy, and malignant transformation of HSCs were detected in the injured liver of Sptbn1^+/- mice induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine treatment. Hippo pathway and Yes-associated protein (YAP) stabilization were examined in isolated HSCs, Huh-7, and PLC/PRF/5 HCC cells and hepatocytes with or without loss of SPTBN1.

RESULTS

We found that heterozygous SPTBN1 knockout accelerated liver tumor development with 3,5-diethoxycarbonyl-1,4-dihydrocollidine induction. Rapamycin promoted autophagy in murine HSCs and reversed the increased malignant transformation induced by heterozygous SPTBN1 deletion. Loss of SPTBN1 also decreased autophagy and increased YAP stability and nuclear localization in human HCC cells and tissues, whereas YAP inhibition attenuated the effects of SPTBN1 deficiency on autophagy. Finally, we found that SPTBN1 positively regulated the expression of suppressor of variegation 3-9-enhancer of zeste-trithorax domain containing lysine methyltransferase 7 to promote YAP methylation, which may lead to YAP degradation and inactivation.

CONCLUSIONS

Our findings provide the first demonstration that loss of SPTBN1 impairs autophagy of HSCs to promote expansion and malignant transformation during hepatocarcinogenesis. SPTBN1 also cooperates with suppressor of variegation 3-9-enhancer of zeste-trithorax domain containing lysine methyltransferase 7 to inactive YAP, resulting in enhanced autophagy of HCC cells. These results may open new avenues targeting SPTBN1 for the prevention and treatment of HCC.

Identification of a Novel Mutation of β-Spectrin in Hereditary Spherocytosis Using Whole Exome Sequencing

Hereditary spherocytosis (HS), the most commonly inherited hemolytic anemia in northern Europeans, comprises a group of diseases whose heterogeneous genetic basis results in a variable clinical presentation. High-throughput genome sequencing methods have made a leading contribution to the recent progress in research on and diagnostics of inherited diseases and inspired us to apply whole exome sequencing (WES) to identify potential mutations in HS. The data presented here reveal a novel mutation probably responsible for HS in a single Polish family. Patients with clinical evidence of HS (clinical symptoms, hematological data, and EMA test) were enrolled in the study. The examination of the resulting WES data showed a number of polymorphisms in 71 genes associated with known erythrocyte pathologies (including membranopathies, enzymopathies, and hemoglobinopathies). Only a single SPTB gene variant indicated the possible molecular mechanism of the disease in the studied family. The new missense mutation p.C183Y was identified using WES in the SPTB gene, which is most likely the cause of clinical symptoms typical of hereditary spherocytosis (membranopathy) due to structural and functional impairments of human β-spectrin. This mutation allows for a better understanding of the molecular mechanism(s) of one of the membranopathies, hereditary spherocytosis.

KAHRP dynamically relocalizes to remodeled actin junctions and associates with knob spirals in Plasmodium falciparum-infected erythrocytes

The knob-associated histidine-rich protein (KAHRP) plays a pivotal role in the pathophysiology of Plasmodium falciparum malaria by forming membrane protrusions in infected erythrocytes, which anchor parasite-encoded adhesins to the membrane skeleton. The resulting sequestration of parasitized erythrocytes in the microvasculature leads to severe disease. Despite KAHRP being an important virulence factor, its physical location within the membrane skeleton is still debated, as is its function in knob formation. Here, we show by super-resolution microscopy that KAHRP initially associates with various skeletal components, including ankyrin bridges, but eventually colocalizes with remnant actin junctions. We further present a 35 Å map of the spiral scaffold underlying knobs and show that a KAHRP-targeting nanoprobe binds close to the spiral scaffold. Single-molecule localization microscopy detected ~60 KAHRP molecules/knob. We propose a dynamic model of KAHRP organization and a function of KAHRP in attaching other factors to the spiral scaffold.

Biallelic SYNE2 Missense Mutations Leading to Nesprin-2 Giant Hypo-Expression Are Associated with Intellectual Disability and Autism

Autism spectrum disorder (ASD) is a group of neurological and developmental disabilities characterised by clinical and genetic heterogeneity. The current study aimed to expand ASD genotyping by investigating potential associations with SYNE2 mutations. Specifically, the disease-causing variants of SYNE2 in 410 trios manifesting neurodevelopmental disorders using whole-exome sequencing were explored. The consequences of the identified variants were studied at the transcript level using quantitative polymerase chain reaction (qPCR). For validation, immunofluorescence and immunoblotting were performed to analyse mutational effects at the protein level. The compound heterozygous variants of SYNE2 (NM_182914.3:c.2483T>G; p.(Val828Gly) and NM_182914.3:c.2362G>A; p.(Glu788Lys)) were identified in a 4.5-year-old male, clinically diagnosed with autism spectrum disorder, developmental delay and intellectual disability. Both variants reside within the nesprin-2 giant spectrin repeat (SR5) domain and are predicted to be highly damaging using in silico tools. Specifically, a significant reduction of nesprin-2 giant protein levels is revealed in patient cells. SYNE2 transcription and the nuclear envelope localisation of the mutant proteins was however unaffected as compared to parental control cells. Collectively, these data provide novel insights into the cardinal role of the nesprin-2 giant in neurodevelopment and suggest that the biallelic hypomorphic SYNE2 mutations may be a new cause of intellectual disability and ASD.

Heterozygous variants in SPTBN1 cause intellectual disability and autism

Spectrins are common components of cytoskeletons, binding to cytoskeletal elements and the plasma membrane, allowing proper localization of essential membrane proteins, signal transduction, and cellular scaffolding. Spectrins are assembled from α and β subunits, encoded by SPTA1 and SPTAN1 (α) and SPTB, SPTBN1, SPTBN2, SPTBN4, and SPTBN5 (β). Pathogenic variants in various spectrin genes are associated with erythroid cell disorders (SPTA1, SPTB) and neurologic disorders (SPTAN1, SPTBN2, and SPTBN4), but no phenotypes have been definitively associated with variants in SPTBN1 or SPTBN5. Through exome sequencing and case matching, we identified seven unrelated individuals with heterozygous SPTBN1 variants: two with de novo missense variants and five with predicted loss-of-function variants (found to be de novo in two, while one was inherited from a mother with a history of learning disabilities). Common features include global developmental delays, intellectual disability, and behavioral disturbances. Autistic features (4/6) and epilepsy (2/7) or abnormal electroencephalogram without overt seizures (1/7) were present in a subset. Identification of loss-of-function variants suggests a haploinsufficiency mechanism, but additional functional studies are required to fully elucidate disease pathogenesis. Our findings support the essential roles of SPTBN1 in human neurodevelopment and expand the knowledge of human spectrinopathy disorders.

Identification of differentially expressed proteins in the locoregional recurrent esophageal squamous cell carcinoma by quantitative proteomics

Background

This study aimed to identify potential biomarkers associated with locoregional recurrence in patients with esophageal squamous cell carcinoma (ESCC) after radical resection.

Methods

We performed a quantitative proteomics analysis using isobaric tags for relative and absolute quantification (iTRAQ) with reversed-phase liquid chromatography-mass spectrometry (RPLC-MS) to identify differential expression proteins (DEPs) between a locoregional recurrence group and good prognosis group of ESCC after radical esophagectomy. The bioinformatics analysis was performed with ingenuity pathway analysis software (IPA) and Gene Ontology (GO) database using the software of MAS 3.0. Kaplan-Meier (KM) Plotter Online Tool (http://www.kmplot.com) was used to evaluate the relationship between the differential expression of proteins and survival in patients with ESCC.

Results

More than 400 proteins were quantitated of which 27 proteins had upregulated expression and 55 proteins had downregulated expression in the locoregional recurrence group compared to the good prognosis group. These 82 DEPs were associated with biological procession of cancer development including cellular movement, cellular assembly and organization, cellular function and maintenance, cellular growth and proliferation, cell death and survival, DNA replication recombination and repair, and so on. Of these DEPs, SPTAN1 and AGT proteins were identified to be associated with RFS in ESCC. SPTAN1 was positively associated with RFS and AGT was negatively associated with RFS. Expression of SPTAN1 tended to have favorable OS while expression of AGT tended to have poor OS.

Conclusions

Our results demonstrated that quantitative proteomics is an effective discovery tool to identify biomarkers for prognosis prediction in ESCC. However, it needs more studies with large populations of ESCC to validate these potential biomarkers.

Erythrocytes: Central Actors in Multiple Scenes of Atherosclerosis

The development and progression of atherosclerosis (ATH) involves lipid accumulation, oxidative stress and both vascular and blood cell dysfunction. Erythrocytes, the main circulating cells in the body, exert determinant roles in the gas transport between tissues. Erythrocytes have long been considered as simple bystanders in cardiovascular diseases, including ATH. This review highlights recent knowledge concerning the role of erythrocytes being more than just passive gas carriers, as potent contributors to atherosclerotic plaque progression. Erythrocyte physiology and ATH pathology is first described. Then, a specific chapter delineates the numerous links between erythrocytes and atherogenesis. In particular, we discuss the impact of extravasated erythrocytes in plaque iron homeostasis with potential pathological consequences. Hyperglycaemia is recognised as a significant aggravating contributor to the development of ATH. Then, a special focus is made on glycoxidative modifications of erythrocytes and their role in ATH. This chapter includes recent data proposing glycoxidised erythrocytes as putative contributors to enhanced atherothrombosis in diabetic patients.

Membrane to cytosol redistribution of αII-spectrin drives extracellular vesicle biogenesis in malignant breast cells

Spectrin is a ubiquitous cytoskeletal protein that provides structural stability and supports membrane integrity. In erythrocytes, spectrin proteolysis leads to the biogenesis of plasma membrane extracellular vesicles (EVs). However, its role in non-erythroid or cancer-derived plasma membrane EVs biogenesis is unknown. This study aims to examine the role of αII-spectrin in malignant and non-malignant plasma membrane vesiculation. We developed a custom, automated cell segmentation plugin for the image processor, Fiji, that provides an unbiased assessment of high resolution confocal microscopy images of the subcellular distribution of αII-spectrin. We show that, in low vesiculating non-malignant MBE-F breast cells, prominent cortical spectrin localises to the cell periphery at rest. In comparison, cortical spectrin is diminished in high vesiculating malignant MCF-7 breast cells at rest. A cortical distribution of spectrin correlates with increased biomechanical stiffness as measured by Atomic Force Microscopy. Furthermore, cortical spectrin can be induced in malignant MCF-7 cells by treatment with known vesiculation modulators including the calcium chelator, BAPTA-AM or the calpain inhibitor II (ALLM). These results demonstrate that the subcellular localisation of spectrin is distinctly different in malignant and non-malignant cells at rest and shows that the redistribution of cortical αII-spectrin to the cytoplasm supports plasma membrane-derived EV biogenesis in malignant cells.

A novel essential splice site variant in SPTB in a large hereditary spherocytosis family

BACKGROUND

We studied a large family with 22 individuals affected with autosomal dominant hereditary spherocytosis (HS).

METHODS

Genome-wide linkage, whole-genome sequencing (WGS), Sanger sequencing, RT-PCR, and ToPO TA cloning analyses were performed.

RESULTS

We revealed a heterozygous G>A transition in the 14q23 locus, at position +1 of the intron 8 donor splice site of the spectrin beta, erythrocytic (SPTB) gene. This splice variant (SPTB c.1064+1G>A) was confirmed by Sanger sequencing and showed complete co-segregation with HS in the family. Further RT-PCR reactions and sequencing analysis indicated that the variant leads to the exclusion of exon 8 and subsequent frameshift in exon 9 and a premature stop codon in SPTB. Translation of the altered allele would lead to a truncation with a loss of all spectrin repeat domains in SPTB protein.

CONCLUSION

This variant is novel and has not been found in any databases. We propose that this splice variant explains the spherocytosis phenotype observed in this large family.

Erythrocyte membrane proteins involved in the immune response to Plasmodium falciparum and Plasmodium vivax infection

Invasion of Plasmodium into the red blood cell involves the interactions of a substantial number of proteins, with red cell membrane proteins as the most involved throughout the process from entry to exit. The objective of this work was to identify proteins of the human erythrocyte membrane capable of generating an antigenic response to P. falciparum and P. vivax infection, with the goal of searching for new molecular targets of interest with an immunological origin to prevent Plasmodium infection. To identify these proteins, an immunoproteomic technique was carried out in four stages: protein separation (electrophoresis), detection of antigenic proteins (western blotting), identification of proteins of interest (mass spectrometry), and interpretation of the data (bioinformatic analysis). Four proteins were identified from extracts of membrane proteins from erythrocytes infected with P. falciparum: Spectrin, Ankyrin-1, Band 3 and band 4.2, and a single protein was identified from erythrocytes infected with P. vivax: Band 3. These results demonstrate that modifications in the red blood cell membrane during infection with P. falciparum and P. vivax can generate an immune response, altering proteins of great structural and functional importance.

Molecular and Diffusion Tensor Imaging Biomarkers of Traumatic Brain Injury: Principles for Investigation and Integration

The last 20 years have seen the advent of new technologies that enhance the diagnosis and prognosis of traumatic brain injury (TBI). There is recognition that TBI affects the brain beyond initial injury, in some cases inciting a progressive neuropathology that leads to chronic impairments. Medical researchers are now searching for biomarkers to detect and monitor this condition. Perhaps the most promising developments are in the biomolecular and neuroimaging domains. Molecular assays can identify proteins indicative of neuronal injury and/or degeneration. Diffusion imaging now allows sensitive evaluations of the brain's cellular microstructure. As the pace of discovery accelerates, it is important to survey the research landscape and identify promising avenues of investigation. In this review, we discuss the potential of molecular and diffusion tensor imaging (DTI) biomarkers in TBI research. Integration of these technologies could advance models of disease prognosis, ultimately improving care. To date, however, few studies have explored relationships between molecular and DTI variables in patients with TBI. Here, we provide a short primer on each technology, review the latest research, and discuss how these biomarkers may be incorporated in future studies.

Cytoskeletal Transport, Reorganization, and Fusion Regulation in Mast Cell-Stimulus Secretion Coupling

Mast cells are well known for their role in allergies and many chronic inflammatory diseases. They release upon stimulation, e.g., via the IgE receptor, numerous bioactive compounds from cytoplasmic secretory granules. The regulation of granule secretion and its interaction with the cytoskeleton and transport mechanisms has only recently begun to be understood. These studies have provided new insight into the interaction between the secretory machinery and cytoskeletal elements in the regulation of the degranulation process. They suggest a tight coupling of these two systems, implying a series of specific signaling effectors and adaptor molecules. Here we review recent knowledge describing the signaling events regulating cytoskeletal reorganization and secretory granule transport machinery in conjunction with the membrane fusion machinery that occur during mast cell degranulation. The new insight into MC biology offers novel strategies to treat human allergic and inflammatory diseases targeting the late steps that affect harmful release from granular stores leaving regulatory cytokine secretion intact.