Coordination between Rac1 and Rab Proteins: Functional Implications in Health and Disease

Genetic Variants in the TBC1D2B Gene Are Associated with Ramon Syndrome and Hereditary Gingival Fibromatosis

Ramon syndrome (MIM 266270) is an extremely rare genetic syndrome, characterized by gingival fibromatosis, cherubism-like lesions, epilepsy, intellectual disability, hypertrichosis, short stature, juvenile rheumatoid arthritis, and ocular abnormalities. Hereditary or non-syndromic gingival fibromatosis (HGF) is also rare and considered to represent a heterogeneous group of disorders characterized by benign, slowly progressive, non-inflammatory gingival overgrowth. To date, two genes, ELMO2 and TBC1D2B, have been linked to Ramon syndrome. The objective of this study was to further investigate the genetic variants associated with Ramon syndrome as well as HGF. Clinical, radiographic, histological, and immunohistochemical examinations were performed on affected individuals. Exome sequencing identified rare variants in TBC1D2B in both conditions: a novel homozygous variant (c.1879_1880del, p.Glu627LysfsTer61) in a Thai patient with Ramon syndrome and a rare heterozygous variant (c.2471A>G, p.Tyr824Cys) in a Cambodian family with HGF. A novel variant (c.892C>T, p.Arg298Cys) in KREMEN2 was also identified in the individuals with HGF. With support from mutant protein modeling, our data suggest that TBC1D2B variants contribute to both Ramon syndrome and HGF, although variants in additional genes might also contribute to the pathogenesis of HGF.

Lysosomal biogenesis and function in osteoclasts: a comprehensive review

Lysosomes serve as catabolic centers and signaling hubs in cells, regulating a multitude of cellular processes such as intracellular environment homeostasis, macromolecule degradation, intracellular vesicle trafficking and autophagy. Alterations in lysosomal level and function are crucial for cellular adaptation to external stimuli, with lysosome dysfunction being implicated in the pathogenesis of numerous diseases. Osteoclasts (OCs), as multinucleated cells responsible for bone resorption and maintaining bone homeostasis, have a complex relationship with lysosomes that is not fully understood. Dysregulated function of OCs can disrupt bone homeostasis leading to the development of various bone disorders. The regulation of OC differentiation and bone resorption for the treatment of bone disease have received considerable attention in recent years, yet the role and regulation of lysosomes in OCs, as well as the potential therapeutic implications of intervening in lysosomal biologic behavior for the treatment of bone diseases, remain relatively understudied. This review aims to elucidate the mechanisms involved in lysosomal biogenesis and to discuss the functions of lysosomes in OCs, specifically in relation to differentiation, bone resorption, and autophagy. Finally, we explore the potential therapeutic implication of targeting lysosomes in the treatment of bone metabolic disorders.

Molecular dynamic simulation reveals the inhibiting impact of Rhein on wild-type and P29S-mutated Rac1

Ras-related C3 botulinum toxin substrate 1 (Rac1) is a small GTPase belonging to the Rho family. It acts as a binary molecular switch regulating several cellular functions, including cell adhesion and migration. Malfunctions due to the P29S mutation in Rac1 increase the stability of the activated form of Rac1. This sustained activation can drive aberrant cellular processes associated with cancer, such as cell proliferation, survival, and migration. Therefore, finding an inhibitor that can inhibit the mutant form of the protein is very important. Rhein, a natural compound with diverse pharmacological properties, has been studied in relation to Rac1. However, specific interactions between Rhein and Rac1 have not been examined. In this study, we investigated the potential of Rhein, a natural compound, as an inhibitor of two forms of Rac1: the wild type and the P29S mutation, using molecular dynamics simulations. Results indicated that the P29S mutation led to structural changes in the Rac1 protein, which resulted in greater accessibility of the Rhein to the active site. In addition, the binding energy of Rhein to mutant Rac1 was more negative than the native protein. Therefore, it seems that the Rhein has a better inhibitory effect on the P29S-mutated form of the Rac1 protein.

HMGB1 promotes mitochondrial transfer between hepatocellular carcinoma cells through RHOT1 and RAC1 under hypoxia

Mitochondrial transfer plays an important role in various diseases, and many mitochondrial biological functions can be regulated by HMGB1. To explore the role of mitochondrial transfer in hepatocellular carcinoma (HCC) and its relationship with HMGB1, field emission scanning electron microscopy, immunofluorescence, and flow cytometry were used to detect the mitochondrial transfer between HCC cells. We found that mitochondrial transfer between HCC cells was confirmed using tunnel nanotubes (TNTs). The transfer of mitochondria from the highly invasive HCC cells to the less invasive HCC cells could enhance the migration and invasion ability of the latter. The hypoxic conditions increased the mitochondrial transfer between HCC cells. Then the mechanism was identified using co-immunoprecipitation, luciferase reporter assay, and chromatin immunoprecipitation. We found that RHOT1, a mitochondrial transport protein, promoted mitochondrial transfer and the migration and metastasis of HCC cells during this process. Under hypoxia, HMGB1 further regulated RHOT1 expression by increasing the expression of NFYA and NFYC subunits of the NF-Y complex. RAC1, a protein associated with TNTs formation, promoted mitochondrial transfer and HCC development. Besides, HMGB1 regulated RAC1 aggregation to the cell membrane under hypoxia. Finally, the changes and significance of related molecules in clinical samples of HCC were analyzed using bioinformatics and tissue microarray analyses. We found that HCC patients with high HMGB1, RHOT1, or RAC1 expression exhibited a relatively shorter overall survival period. In conclusion, under hypoxic conditions, HMGB1 promoted mitochondrial transfer and migration and invasion of HCC cells by increasing the expression of mitochondrial transport protein RHOT1 and TNTs formation-related protein RAC1.

Crosstalk between the Rho and Rab family of small GTPases in neurodegenerative disorders

Neurodegeneration is associated with defects in cytoskeletal dynamics and dysfunctions of the vesicular trafficking and sorting systems. In the last few decades, studies have demonstrated that the key regulators of cytoskeletal dynamics are proteins from the Rho family GTPases, meanwhile, the central hub for vesicle sorting and transport between target membranes is the Rab family of GTPases. In this regard, the role of Rho and Rab GTPases in the induction and maintenance of distinct functional and morphological neuronal domains (such as dendrites and axons) has been extensively studied. Several members belonging to these two families of proteins have been associated with many neurodegenerative disorders ranging from dementia to motor neuron degeneration. In this analysis, we attempt to present a brief review of the potential crosstalk between the Rab and Rho family members in neurodegenerative pathologies such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington disease, and amyotrophic lateral sclerosis (ALS).

Kalirin mediates Rac1 activation downstream of calcium/calmodulin-dependent protein kinase II to stimulate glucose uptake during muscle contraction

In this study, we investigated the role of calcium/calmodulin-dependent protein kinase II (CaMKII) in contraction-stimulated glucose uptake in skeletal muscle. C2C12 myotubes were contracted by electrical pulse stimulation (EPS), and treadmill running was used to exercise mice. The activities of CaMKII, the small G protein Rac1, and the Rac1 effector kinase PAK1 were elevated in muscle by running exercise or EPS, while they were lowered by the CaMKII inhibitor KN-93 and/or small interfering RNA (siRNA)-mediated knockdown. EPS induced the mRNA and protein expression of the Rac1-GEF Kalirin in a CaMKII-dependent manner. EPS-induced Rac1 activation was lowered by the Kalirin inhibitor ITX3 or siRNA-mediated Kalirin knockdown. KN-93, ITX3, and siRNA-mediated Kalirin knockdown reduced EPS-induced glucose uptake. These findings define a CaMKII-Kalirin-Rac1 signaling pathway that contributes to contraction-stimulated glucose uptake in skeletal muscle myotubes and tissue.

ARL11 correlates with the immunosuppression and poor prognosis in breast cancer: A comprehensive bioinformatics analysis of ARL family members

ADP-ribosylation factor-like protein (ARL) family members (ARLs) may regulate the malignant phenotypes of cancer cells. However, relevant studies on ARLs in breast cancer (BC) are limited. In this research, the expression profiles, genetic variations, and prognostic values of ARLs in BC have been systematically analyzed for the first time using various databases. We find that ARLs are significantly dysregulated in BC according to the TCGA database, which may result from DNA methylation and copy number alteration. Prognostic analysis suggests that ARL11 is the most significant prognostic indicator for BC, and higher ARL11 predicts worse clinical outcomes for BC patients. Further functional enrichment analysis demonstrates that ARL11 enhances the immunosuppression in BC, and dysregulation of ARL11 is significantly associated with immune infiltration in various types of cancer. Our results demonstrate the potential of ARL11 as an immune therapeutic target for BC.

The Rab GTPase in the heart: Pivotal roles in development and disease

Rab proteins are a family of small GTPases that function as molecular switches of intracellular vesicle formation and membrane trafficking. As a key factor, Rab GTPase participates in autophagy and protein transport and acts as the central hub of membrane trafficking in eukaryotes. The role of Rab GTPase in neurodegenerative disorders, such as Alzheimer's and Parkinson's, has been extensively investigated; however, its implication in cardiovascular embryogenesis and diseases remains largely unknown. In this review, we summarize previous findings and reveal their importance in the onset and progression of cardiac diseases, as well as their emergence as potential therapeutic targets for cardiovascular disease.

Overexpressed or hyperactivated Rac1 as a target to treat hepatocellular carcinoma

Despite novel targeted and immunotherapies, the prognosis remains bleak for patients with hepatocellular carcinoma (HCC), especially for advanced and/or metastatic forms. The rapid emergence of drug resistance is a major obstacle in the success of chemo-, targeted-, immuno-therapies of HCC. Novel targets are needed. The prominent roles of the small GTPase Rac1 in the development and progression of HCC are discussed here, together with its multiple protein partners, and the targeting of Rac1 with RNA-based regulators and small molecules. We discuss the oncogenic functions of Rac1 in HCC, including the contribution of Rac1 mutants and isoform Rac1b. Rac1 is a ubiquitous target, but the protein is frequently overexpressed and hyperactivated in HCC. It contributes to the aggressivity of the disease, with key roles in cancer cell proliferation, tumor metastasis and resistance to treatment. Small molecule targeting Rac1, indirectly or directly, have shown anticancer effects in HCC experimental models. Rac1-binding agents such as EHT 1864 and analogues offer novel opportunities to combat HCC. We discuss the different modalities to repress Rac1 overactivation in HCC with small molecules and the combination with reference drugs to promote cancer cell death and to repress cell invasion. We highlight the necessity to combine Rac1-targeted approach with appropriate biomarkers to select Rac1 activated tumors. Our analysis underlines the prominent oncogenic functions of Rac1 in HCC and discuss the modalities to target this small GTPase. Rac1 shall be considered as a valid target to limit the acquired and intrinsic resistance of HCC tumors and their metastatic potential.

Chemokine CCL18 Promotes Phagocytosis Through Its Receptor CCR8 Rather than PITPNM3 in Human Microglial Cells

CCL18 is a CC chemokine that exhibits diverse functions through interaction with various cell subsets with both proinflammatory anti-inflammatory properties through its receptors CCR8 (CC chemokine receptor 8) and PITPNM3 (phosphatidylinositol transfer protein 3). However, the function of CCL18 in microglia remains unclear. In this study, we show that CCL18 did not change the expression of the inflammatory factors, interleukin (IL)-1β, IL-6, tumor necrosis factor alpha (TNF-α), or inducible nitric oxide synthase (iNOS), but significantly induced expression of the macrophage markers, MRC-1 and ARG-1 M2, in a human microglial clone 3 cell line (HMC3). Phagocytosis by HMC3 cells was significantly enhanced in the presence of CCL18, indicated by uptake of amyloid-β and dextran. CCR8 and PITPNM3 were both expressed on HMC3 cells, but selective knockdown of CCR8 and PITPNM3 showed that only the former played a dominant role in phagocytosis of HMC3 through the nuclear factor kappa B (NF-κB)/Src signaling pathway. Our results suggest that CCL18 could have anti-inflammatory activity and activate the phagocytic function of microglia, which is involved in neural development, homeostasis, and repair mechanisms.

Autophagy and Mitophagy-Related Pathways at the Crossroads of Genetic Pathways Involved in Familial Sarcoidosis and Host-Pathogen Interactions Induced by Coronaviruses

Sarcoidosis is a multisystem disease characterized by the development and accumulation of granulomas, the hallmark of an inflammatory process induced by environmental and/or infectious and or genetic factors. This auto-inflammatory disease mainly affects the lungs, the gateway to environmental aggressions and viral infections. We have shown previously that genetic predisposition to sarcoidosis occurring in familial cases is related to a large spectrum of pathogenic variants with, however, a clustering around mTOR (mammalian Target Of Rapamycin)-related pathways and autophagy regulation. The context of the COVID-19 pandemic led us to evaluate whether such genetic defects may increase the risk of a severe course of SARS-CoV2 infection in patients with sarcoidosis. We extended a whole exome screening to 13 families predisposed to sarcoidosis and crossed the genes sharing mutations with the list of genes involved in the SARS-CoV2 host-pathogen protein-protein interactome. A similar analysis protocol was applied to a series of 100 healthy individuals. Using ENRICH.R, a comprehensive gene set enrichment web server, we identified the functional pathways represented in the set of genes carrying deleterious mutations and confirmed the overrepresentation of autophagy- and mitophagy-related functions in familial cases of sarcoidosis. The same protocol was applied to the set of genes common to sarcoidosis and the SARS-CoV2-host interactome and found a significant enrichment of genes related to mitochondrial factors involved in autophagy, mitophagy, and RIG-I-like (Retinoic Acid Inducible Gene 1) Receptor antiviral response signaling. From these results, we discuss the hypothesis according to which sarcoidosis is a model for studying genetic abnormalities associated with host response to viral infections as a consequence of defects in autophagy and mitophagy processes.

Rabphilin silencing causes dilated cardiomyopathy in a Drosophila model of nephrocyte damage

Heart failure (HF) and the development of chronic kidney disease (CKD) have a direct association. Both can be cause and consequence of the other. Many factors are known, such as diabetes or hypertension, which can lead to the appearance and/or development of these two conditions. However, it is suspected that other factors, namely genetic ones, may explain the differences in the manifestation and progression of HF and CKD among patients. One candidate factor is Rph, a gene expressed in the nervous and excretory system in mammals and Drosophila, encoding a Rab small GTPase family effector protein implicated in vesicular trafficking. We found that Rph is expressed in the Drosophila heart, and the silencing of Rph gene expression in this organ had a strong impact in the organization of fibers and functional cardiac parameters. Specifically, we observed a significant increase in diastolic and systolic diameters of the heart tube, which is a phenotype that resembles dilated cardiomyopathy in humans. Importantly, we also show that silencing of Rabphilin (Rph) expression exclusively in the pericardial nephrocytes, which are part of the flies' excretory system, brings about a non-cell-autonomous effect on the Drosophila cardiac system. In summary, in this work, we demonstrate the importance of Rph in the fly cardiac system and how silencing Rph expression in nephrocytes affects the Drosophila cardiac system.

Small Rab GTPases in Intracellular Vesicle Trafficking: The Case of Rab3A/Raphillin-3A Complex in the Kidney

Small Rab GTPases, the largest group of small monomeric GTPases, regulate vesicle trafficking in cells, which are integral to many cellular processes. Their role in neurological diseases, such as cancer and inflammation have been extensively studied, but their implication in kidney disease has not been researched in depth. Rab3a and its effector Rabphillin-3A (Rph3A) expression have been demonstrated to be present in the podocytes of normal kidneys of mice rats and humans, around vesicles contained in the foot processes, and they are overexpressed in diseases with proteinuria. In addition, the Rab3A knockout mice model induced profound cytoskeletal changes in podocytes of high glucose fed animals. Likewise, RphA interference in the Drosophila model produced structural and functional damage in nephrocytes with reduction in filtration capacities and nephrocyte number. Changes in the structure of cardiac fiber in the same RphA-interference model, open the question if Rab3A dysfunction would produce simultaneous damage in the heart and kidney cells, an attractive field that will require attention in the future.

Strict network analysis of evolutionary conserved and brain-expressed genes reveals new putative candidates implicated in Intellectual Disability and in Global Development Delay

OBJECTIVES

Intellectual Disability (ID) and Global Development Delay (GDD) are frequent reasons for referral to genetic services and although they present overlapping phenotypes concerning cognitive, motor, language, or social skills, they are not exactly synonymous. Aiming to better understand independent or shared mechanisms related to these conditions and to identify new candidate genes, we performed a highly stringent protein-protein interaction network based on genes previously related to ID/GDD in the Human Phenotype Ontology portal.

METHODS

ID/GDD genes were searched for reliable interactions through STRING and clustering analysis was applied to detect biological complexes through the MCL algorithm. Six coding hub genes (TP53, CDC42, RAC1, GNB1, APP, and EP300) were recognised by the Cytoscape NetworkAnalyzer plugin, interacting with 1625 proteins not yet associated with ID or GDD. Genes encoding these proteins were explored by gene ontology, associated diseases, evolutionary conservation, and brain expression.

RESULTS

One hundred and seventy-two new putative genes playing a role in enriched processes/pathways previously related to ID and GDD were revealed, some of which were already postulated to be linked to ID/GDD in additional databases.

CONCLUSIONS

Our findings expanded the aetiological genetic landscape of ID/GDD and showed evidence that both conditions are closely related at the molecular and functional levels.

The Significant Role of the Microfilament System in Tumors

Actin is the structural protein of microfilaments, and it usually exists in two forms: monomer and polymer. Among them, monomer actin is a spherical molecule composed of a polypeptide chain, also known as spherical actin. The function of actin polymers is to produce actin filaments, so it is also called fibroactin. The actin cytoskeleton is considered to be an important subcellular filament system. It interacts with numerous relevant proteins and regulatory cells, regulating basic functions, from cell division and muscle contraction to cell movement and ensuring tissue integrity. The dynamic reorganization of the actin cytoskeleton has immense influence on the progression and metastasis of cancer as well. This paper explores the significance of the microfilament network, the dynamic changes of its structure and function in the presence of a tumor, the formation process around the actin system, and the relevant proteins that may be target molecules for anticancer drugs so as to provide support and reference for interlinked cancer treatment research in the future.

ARL4C might serve as a prognostic factor and a novel therapeutic target for gastric cancer: bioinformatics analyses and biological experiments

The ADP‐ribosylation factor‐like proteins (ARLs) have been proved to regulate the malignant phenotypes of several cancers. However, the exact role of ARLs in gastric cancer (GC) remains elusive. In this study, we systematically investigate the expression status, interactive relations, potential pathways, genetic variations and clinical values of ARLs in GC. We find that ARLs are significantly dysregulated in GC and involved in various cancer‐related pathways. Subsequently, machine learning models identify ARL4C as one of the two most significant clinical indicators among ARLs for GC. Furthermore, ARL4C silencing remarkably inhibits the growth and metastasis of GC cells both in vitro and in vivo. Moreover, enrichment analysis indicates that ARL4C is highly correlated with TGF‐β1 signalling. Correspondingly, TGF‐β1 treatment dramatically increases ARL4C expression and ARL4C knockdown inhibits the phosphorylation level of Smads, downstream factors of TGF‐β1. Meanwhile, the coexpression of ARL4C and TGF‐β1 worsens the prognosis of GC patients. Our work comprehensively demonstrates the crucial role of ARLs in the carcinogenesis of GC and the specific mechanisms underlying the GC‐promoting effects of TGF‐β1. More importantly, we uncover the great promise of ARL4C‐targeted therapy in improving the efficacy of TGF‐β1 inhibitors for GC patients.

Contributions of the Four Essential Entry Glycoproteins to HSV-1 Tropism and the Selection of Entry Routes

Herpes simplex viruses (HSV-1 and HSV-2) encode up to 16 envelope proteins, four of which are essential for entry. However, whether these four proteins alone are sufficient to dictate the broad cellular tropism of HSV-1 and the selection of different cell type-dependent entry routes is unknown. To begin addressing this, we previously pseudotyped vesicular stomatitis virus (VSV), lacking its native glycoprotein G, with only the four essential entry glycoproteins of HSV-1: gB, gH, gL, and gD. This novel VSVΔG-BHLD pseudotype recapitulated several important features of HSV-1 entry: the requirement for gB, gH, gL, gD, and a cellular receptor and sensitivity to anti-gB and anti-gH/gL neutralizing antibodies. However, due to the use of a single cell type in that study, the tropism of the VSVΔG-BHLD pseudotype was not investigated. Here, we show that the cellular tropism of the pseudotype is severely limited compared to that of wild-type HSV-1 and that its entry pathways differ from the native HSV-1 entry pathways. To test the hypothesis that other HSV-1 envelope proteins may contribute to HSV-1 tropism, we generated a derivative pseudotype containing the HSV-1 glycoprotein C (VSVΔG-BHLD-gC) and observed a gC-dependent increase in entry efficiency in two cell types. We propose that the pseudotyping platform developed here has the potential to uncover functional contributions of HSV-1 envelope proteins to entry in a gain-of-function manner.IMPORTANCE Herpes simplex viruses (HSV-1 and HSV-2) contain up to 16 different proteins in their envelopes. Four of these, glycoproteins gB, gD, gH, and gL, are termed essential with regard to entry, whereas the rest are typically referred to as nonessential based on the entry phenotypes of the respective single genetic deletions. However, the single-gene deletion approach, which relies on robust loss-of-function phenotypes, may be confounded by functional redundancies among the many HSV-1 envelope proteins. We have developed a pseudotyping platform in which the essential four entry glycoproteins are isolated from the rest, which can be added back individually for systematic gain-of-function entry experiments. Here, we show the utility of this platform for dissecting the contributions of HSV envelope proteins, both the essential four and the remaining dozen (using gC as an example), to HSV entry.

Role of the V1G1 subunit of V-ATPase in breast cancer cell migration

V-ATPase is a large multi-subunit complex that regulates acidity of intracellular compartments and of extracellular environment. V-ATPase consists of several subunits that drive specific regulatory mechanisms. The V1G1 subunit, a component of the peripheral stalk of the pump, controls localization and activation of the pump on late endosomes and lysosomes by interacting with RILP and RAB7. Deregulation of some subunits of the pump has been related to tumor invasion and metastasis formation in breast cancer. We observed a decrease of V1G1 and RAB7 in highly invasive breast cancer cells, suggesting a key role of these proteins in controlling cancer progression. Moreover, in MDA-MB-231 cells, modulation of V1G1 affected cell migration and matrix metalloproteinase activation in vitro, processes important for tumor formation and dissemination. In these cells, characterized by high expression of EGFR, we demonstrated that V1G1 modulates EGFR stability and the EGFR downstream signaling pathways that control several factors required for cell motility, among which RAC1 and cofilin. In addition, we showed a key role of V1G1 in the biogenesis of endosomes and lysosomes. Altogether, our data describe a new molecular mechanism, controlled by V1G1, required for cell motility and that promotes breast cancer tumorigenesis.

GAA deficiency promotes angiogenesis through upregulation of Rac1 induced by autophagy disorder

Angiogenesis, the formation of new blood vessels from pre-existing ones, is vital for vertebrate development and adult homeostasis. Acid α-glucosidase (GAA) is a glycoside hydrolase involved in the lysosomal breakdown of glycogen. Our previous study showed that GAA was highly expressed in mouse pulmonary veins. While whether GAA was involved in angiogenesis remained largely unknown, thus, we performed knockdown experiments both in vivo and in vitro and endothelial cell function experiments to clarify this concern point. We identified that GAA expressed widely at different levels during zebrafish embryonic development and GAA morphants showed excessive angiogenesis of ISV at later stage. In GAA knockdown HUVECs, the migration and tube formation capacity were increased, resulted from the formation of large lamellipodia-like protrusions at the edge of cells. By analyzing autophagic flux, we found that autophagy disorder was the mechanism of GAA knockdown-induced excessive angiogenesis. The block of autophagic flux caused upregulation of Rac1, a small GTPase, and the latter promoted excessive sprouts in zebrafish and enhanced angiogenic behavior in HUVECs. In addition, overexpression of transcription factor E3, a master regulator of autophagy, rescued upregulation of RAC1 and enhanced angiogenic function in GAA-knockdown HUVECs. Also, inhibition of Rac1 partly restored enhanced angiogenic function in GAA-knockdown HUVECs. Taken together, our study firstly reported a novel function of GAA in angiogenesis which is mediated by upregulation of Rac1 induced by autophagy disorder.

Biological insights in the pathogenesis of hypermobile Ehlers-Danlos syndrome from proteome profiling of patients' dermal myofibroblasts

Hypermobile Ehlers-Danlos syndrome (hEDS), mainly characterized by generalized joint hypermobility and its complications, minor skin changes, and apparently segregating with an autosomal dominant pattern, is still without a known molecular basis. Hence, its diagnosis is only clinical based on a strict set of criteria defined in the revised EDS nosology. Moreover, the hEDS phenotypic spectrum is wide-ranging and comprises multiple associated signs and symptoms shared with other heritable or acquired connective tissue disorders and chronic inflammatory diseases. In this complex scenario, we previously demonstrated that hEDS patients' skin fibroblasts show phenotypic features of myofibroblasts, widespread extracellular matrix (ECM) disarray, perturbation of ECM-cell contacts, and dysregulated expression of genes involved in connective tissue architecture and related to inflammatory and pain responses. Herein, the cellular proteome of 6 hEDS dermal myofibroblasts was compared to that of 12 control fibroblasts to deepen the knowledge on mechanisms involved in the disease pathogenesis. Qualitative and quantitative differences were assessed based on top-down and bottom-up approaches and some differentially expressed proteins were proofed by biochemical analyses. Proteomics disclosed the differential expression of proteins principally implicated in cytoskeleton organization, energy metabolism and redox balance, proteostasis, and intracellular trafficking. Our findings offer a comprehensive view of dysregulated protein networks and related pathways likely associated with the hEDS pathophysiology. The present results can be regarded as a starting point for future in-depth investigations aimed to decipher the functional impact of potential bioactive molecules for the development of targeted management and therapies.

Cross Talk at the Cytoskeleton-Plasma Membrane Interface: Impact on Neuronal Morphology and Functions

The cytoskeleton and its associated proteins present at the plasma membrane not only determine the cell shape but also modulate important aspects of cell physiology such as intracellular transport including secretory and endocytic pathways. Continuous remodeling of the cell structure and intense communication with extracellular environment heavily depend on interactions between cytoskeletal elements and plasma membrane. This review focuses on the plasma membrane-cytoskeleton interface in neurons, with a special emphasis on the axon and nerve endings. We discuss the interaction between the cytoskeleton and membrane mainly in two emerging topics of neurobiology: (i) production and release of extracellular vesicles and (ii) local synthesis of new proteins at the synapses upon signaling cues. Both of these events contribute to synaptic plasticity. Our review provides new insights into the physiological and pathological significance of the cytoskeleton-membrane interface in the nervous system.

The Small GTPase RAC1B: A Potent Negative Regulator of-and Useful Tool to Study-TGFβ Signaling

RAC1 and its alternatively spliced isoform, RAC1B, are members of the Rho family of GTPases. Both isoforms are involved in the regulation of actin cytoskeleton remodeling, cell motility, cell proliferation, and epithelial-mesenchymal transition (EMT). Compared to RAC1, RAC1B exhibits a number of distinctive features with respect to tissue distribution, downstream signaling and a role in disease conditions like inflammation and cancer. The subcellular locations and interaction partners of RAC1 and RAC1B vary depending on their activation state, which makes RAC1 and RAC1B ideal candidates to establish cross-talk with cancer-associated signaling pathways-for instance, interactions with signaling by transforming growth factor β (TGFβ), a known tumor promoter. Although RAC1 has been found to promote TGFβ-driven tumor progression, recent observations in pancreatic carcinoma cells surprisingly revealed that RAC1B confers anti-oncogenic properties, i.e., through inhibiting TGFβ-induced EMT. Since then, an unexpected array of mechanisms through which RAC1B cross-talks with TGFβ signaling has been demonstrated. However, rather than being uniformly inhibitory, RAC1B interacts with TGFβ signaling in a way that results in the selective blockade of tumor-promoting pathways, while concomitantly allowing tumor-suppressive pathways to proceed. In this review article, we are going to discuss the specific interactions between RAC1B and TGFβ signaling, which occur at multiple levels and include various components such as ligands, receptors, cytosolic mediators, transcription factors, and extracellular inhibitors of TGFβ ligands.

Roles of GTP and Rho GTPases in pancreatic islet beta cell function and dysfunction

A growing body of evidence implicates requisite roles for GTP and its binding proteins (Rho GTPases) in the cascade of events leading to physiological insulin secretion from the islet beta cell. Interestingly, chronic exposure of these cells to hyperglycaemic conditions appears to result in sustained activation of specific Rho GTPases (e.g. Rac1) leading to significant alterations in cellular functions including defects in mitochondrial function and nuclear collapse culminating in beta cell demise. One of the objectives of this review is to highlight our current understanding of the regulatory roles of GTP and Rho GTPases in normal islet function (e.g. proliferation and insulin secretion) as well potential defects in these signalling molecules and metabolic pathways that could contribute islet beta cell dysfunction and loss of functional beta cell mass leading to the onset of diabetes. Potential knowledge gaps in this field and possible avenues for future research are also highlighted.

ABBREVIATIONS

ARNO: ADP-ribosylation factor nucleotide binding site opener; CML: carboxyl methylation; Epac: exchange protein directly activated by cAMP; ER stress: endoplasmic reticulum stress; FTase: farnesyltransferase; GAP: GTPase activating protein; GDI: GDP dissociation inhibitor; GEF: guanine nucleotide exchange factor; GGTase: geranylgeranyltransferase; GGpp: geranylgeranylpyrophosphate; GGPPS: geranylgeranyl pyrophosphate synthase; GSIS: glucose-stimulated insulin secretion; HGPRTase: hypoxanthine-guanine phosphoribosyltransferase; IMPDH: inosine monophosphate dehydrogenase; α-KIC: α-ketoisocaproic acid; MPA: mycophenolic acid; MVA: mevalonic acid; NDPK: nucleoside diphosphate kinase; NMPK: nucleoside monophosphate kinase; Nox2: phagocyte-like NADPH oxidase; PAK-I: p21-activated kinase-I; β-PIX: β-Pak-interacting exchange factor; PRMT: protein arginine methyltransferase; Rac1: ras-related C3 botulinum toxin substrate 1; Tiam1: T-cell lymphoma invasion and metastasis-inducing protein 1; Trx-1: thioredoxin-1; Vav2: vav guanine nucleotide exchange factor 2.

Kalirin Interacts with TRAPP and Regulates Rab11 and Endosomal Recycling

Coordinated actions of Rab and Rho are necessary for numerous essential cellular processes ranging from vesicle budding to whole cell movement. How Rab and Rho are choreographed is poorly understood. Here, we report a protein complex comprised of kalirin, a Rho guanine nucleotide exchange factor (GEF) activating Rac1, and RabGEF transport protein particle (TRAPP). Kalirin was identified in a mass spectrometry analysis of proteins precipitated by trappc4 and detected on membranous organelles containing trappc4. Acute knockdown of kalirin did not affect trappc4, but significantly reduced overall and membrane-bound levels of trappc9, which specifies TRAPP toward activating Rab11. Trappc9 deficiency led to elevated expression of kalirin in neurons. Co-localization of kalirin and Rab11 occurred at a low frequency in NRK cells under steady state and was enhanced upon expressing an inactive Rab11 mutant to prohibit the dissociation of Rab11 from the kalirin-TRAPP complex. The small RNA-mediated depletion of kalirin diminished activities in cellular membranes for activating Rab11 and resulted in a shift in size of Rab11 positive structures from small to larger ones and tubulation of recycling endosomes. Our study suggests that kalirin and TRAPP form a dual GEF complex to choreograph actions of Rab11 and Rac1 at recycling endosomes.