Multifaceted Rho GTPase Signaling at the Endomembranes

Unravelling molecular dynamics in living cells: Fluorescent protein biosensors for cell biology

Genetically encoded, fluorescent protein (FP)-based Förster resonance energy transfer (FRET) biosensors are microscopy imaging tools tailored for the precise monitoring and detection of molecular dynamics within subcellular microenvironments. They are characterised by their ability to provide an outstanding combination of spatial and temporal resolutions in live-cell microscopy. In this review, we begin by tracing back on the historical development of genetically encoded FP labelling for detection in live cells, which lead us to the development of early biosensors and finally to the engineering of single-chain FRET-based biosensors that have become the state-of-the-art today. Ultimately, this review delves into the fundamental principles of FRET and the design strategies underpinning FRET-based biosensors, discusses their diverse applications and addresses the distinct challenges associated with their implementation. We place particular emphasis on single-chain FRET biosensors for the Rho family of guanosine triphosphate hydrolases (GTPases), pointing to their historical role in driving our understanding of the molecular dynamics of this important class of signalling proteins and revealing the intricate relationships and regulatory mechanisms that comprise Rho GTPase biology in living cells.

Rabenosyn-5 suppresses non-small cell lung cancer metastasis via inhibiting CDC42 activity

Metastasis, the primary cause of death in lung cancer patients, is facilitated by cytoskeleton remodeling, which plays a crucial role in cancer cell migration and invasion. However, the precise regulatory mechanisms of intracellular trafficking proteins involved in cytoskeleton remodeling remain unclear. In this study, we have identified Rabenosyn-5 (Rbsn) as an inhibitor of filopodia formation and lung cancer metastasis. Mechanistically, Rbsn interacts with CDC42 and functions as a GTPase activating protein (GAP), thereby inhibiting CDC42 activity and subsequent filopodia formation. Furthermore, we have discovered that Akt phosphorylates Rbsn at the Thr253 site, and this phosphorylation negates the inhibitory effect of Rbsn on CDC42 activity. Additionally, our analysis reveals that Rbsn expression is significantly downregulated in lung cancer, and this decrease is associated with a worse prognosis. These findings provide strong evidence supporting the role of Rbsn in suppressing lung cancer progression through the inhibition of metastasis.

Regulation of the DLC3 tumor suppressor by a novel phosphoswitch

Deleted in liver cancer 3 (DLC3) is a Rho GTPase-activating protein (RhoGAP) that plays a crucial role in maintaining adherens junction integrity and coordinating polarized vesicle transport by modulating Rho activity at the plasma membrane and endomembranes. By employing bioinformatical sequence analysis, in vitro experiments, and in cellulo assays we here identified a polybasic region (PBR) in DLC3 that facilitates the association of the protein with cellular membranes. Within the PBR, we mapped two serines whose phosphorylation can alter the electrostatic character of the region. Consequently, phosphomimetic mutations of these sites impaired the membrane association of DLC3. Furthermore, we found a new PBR-dependent localization of DLC3 at the midbody region, where the protein locally controlled Rho activity. Here, the phosphorylation-dependent regulation of DLC3 appeared to be required for proper cytokinesis. Our work thus provides a novel mechanism for spatiotemporal termination of Rho signaling by the RhoGAP protein DLC3.

The role of programmed cell death in osteosarcoma: From pathogenesis to therapy

Osteosarcoma (OS) is a prevalent bone solid malignancy that primarily affects adolescents, particularly boys aged 14-19. This aggressive form of cancer often leads to deadly lung cancer due to its high migration ability. Experimental evidence suggests that programmed cell death (PCD) plays a crucial role in the development of osteosarcoma. Various forms of PCD, including apoptosis, ferroptosis, autophagy, necroptosis, and pyroptosis, contribute significantly to the progression of osteosarcoma. Additionally, different signaling pathways such as STAT3/c-Myc signal pathway, JNK signl pathway, PI3k/AKT/mTOR signal pathway, WNT/β-catenin signal pathway, and RhoA signal pathway can influence the development of osteosarcoma by regulating PCD in osteosarcoma cell. Therefore, targeting PCD and the associated signaling pathways could offer a promising therapeutic approach for treating osteosarcoma.

Ceramide-1-phosphate is a regulator of Golgi structure and is co-opted by the obligate intracellular bacterial pathogen Anaplasma phagocytophilum

Many intracellular pathogens structurally disrupt the Golgi apparatus as an evolutionarily conserved promicrobial strategy. Yet, the host factors and signaling processes involved are often poorly understood, particularly for Anaplasma phagocytophilum, the agent of human granulocytic anaplasmosis. We found that A. phagocytophilum elevated cellular levels of the bioactive sphingolipid, ceramide-1-phosphate (C1P), to promote Golgi fragmentation that enables bacterial proliferation, conversion from its non-infectious to infectious form, and productive infection. A. phagocytophilum poorly infected mice deficient in ceramide kinase, the Golgi-localized enzyme responsible for C1P biosynthesis. C1P regulated Golgi morphology via activation of a PKCα/Cdc42/JNK signaling axis that culminates in phosphorylation of Golgi structural proteins, GRASP55 and GRASP65. siRNA-mediated depletion of Cdc42 blocked A. phagocytophilum from altering Golgi morphology, which impaired anterograde trafficking of trans-Golgi vesicles into and maturation of the pathogen-occupied vacuole. Cells overexpressing phosphorylation-resistant versions of GRASP55 and GRASP65 presented with suppressed C1P- and A. phagocytophilum-induced Golgi fragmentation and poorly supported infection by the bacterium. By studying A. phagocytophilum, we identify C1P as a regulator of Golgi structure and a host factor that is relevant to disease progression associated with Golgi fragmentation.IMPORTANCECeramide-1-phosphate (C1P), a bioactive sphingolipid that regulates diverse processes vital to mammalian physiology, is linked to disease states such as cancer, inflammation, and wound healing. By studying the obligate intracellular bacterium Anaplasma phagocytophilum, we discovered that C1P is a major regulator of Golgi morphology. A. phagocytophilum elevated C1P levels to induce signaling events that promote Golgi fragmentation and increase vesicular traffic into the pathogen-occupied vacuole that the bacterium parasitizes. As several intracellular microbial pathogens destabilize the Golgi to drive their infection cycles and changes in Golgi morphology is also linked to cancer and neurodegenerative disorder progression, this study identifies C1P as a potential broad-spectrum therapeutic target for infectious and non-infectious diseases.

Implication of Rac1 GTPase in molecular and cellular mitochondrial functions

Rac1 is a member of the Rho GTPase family which plays major roles in cell mobility, polarity and migration, as a fundamental regulator of actin cytoskeleton. Signal transduction by Rac1 occurs through interaction with multiple effector proteins, and its activity is regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). The small protein is mainly anchored to the inner side of the plasma membrane but it can be found in endocellular compartments, notably endosomes and cell nuclei. The protein localizes also into mitochondria where it contributes to the regulation of mitochondrial dynamics, including both mitobiogenesis and mitophagy, in addition to signaling processes via different protein partners, such as the proapoptotic protein Bcl-2 and chaperone sigma-1 receptor (σ-1R). The mitochondrial form of Rac1 (mtRac1) has been understudied thus far, but it is as essential as the nuclear or plasma membrane forms, via its implication in regulation of oxidative stress and DNA damages. Rac1 is subject to diverse post-translational modifications, notably to a geranylgeranylation which contributes importantly to its mitochondrial import and its anchorage to mitochondrial membranes. In addition, Rac1 contributes to the mitochondrial translocation of other proteins, such as p53. The mitochondrial localization and functions of Rac1 are discussed here, notably in the context of human diseases such as cancers. Inhibitors of Rac1 have been identified (NSC-23766, EHT-1864) and some are being developed for the treatment of cancer (MBQ-167) or central nervous system diseases (JK-50561). Their effects on mtRac1 warrant further investigations. An overview of mtRac1 is provided here.

Co-Expression Network Analysis Unveiled lncRNA-mRNA Links Correlated to Epidermal Growth Factor Receptor-Tyrosine Kinase Inhibitor Resistance and/or Intermediate Epithelial-to-Mesenchymal Transition Phenotypes in a Human Non-Small Cell Lung Cancer Cellular Model System

We investigated mRNA-lncRNA co-expression patterns in a cellular model system of non-small cell lung cancer (NSCLC) sensitive and resistant to the epithelial growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) erlotinib/gefitinib. The aim of this study was to unveil insights into the complex mechanisms of NSCLC targeted therapy resistance and epithelial-to-mesenchymal transition (EMT). Genome-wide RNA expression was quantified for weighted gene co-expression network analysis (WGCNA) to correlate the expression levels of mRNAs and lncRNAs. Functional enrichment analysis and identification of lncRNAs were conducted on modules associated with the EGFR-TKI response and/or intermediate EMT phenotypes. We constructed lncRNA-mRNA co-expression networks and identified key modules and their enriched biological functions. Processes enriched in the selected modules included RHO (A, B, C) GTPase and regulatory signaling pathways, apoptosis, inflammatory and interleukin signaling pathways, cell adhesion, cell migration, cell and extracellular matrix organization, metabolism, and lipid metabolism. Interestingly, several lncRNAs, already shown to be dysregulated in cancer, are connected to a small number of mRNAs, and several lncRNAs are interlinked with each other in the co-expression network.

Functional Conservation of the Small GTPase Rho5/Rac1-A Tale of Yeast and Men

Small GTPases are molecular switches that participate in many essential cellular processes. Amongst them, human Rac1 was first described for its role in regulating actin cytoskeleton dynamics and cell migration, with a close relation to carcinogenesis. More recently, the role of Rac1 in regulating the production of reactive oxygen species (ROS), both as a subunit of NADPH oxidase complexes and through its association with mitochondrial functions, has drawn attention. Malfunctions in this context affect cellular plasticity and apoptosis, related to neurodegenerative diseases and diabetes. Some of these features of Rac1 are conserved in its yeast homologue Rho5. Here, we review the structural and functional similarities and differences between these two evolutionary distant proteins and propose yeast as a useful model and a device for high-throughput screens for specific drugs.

Characterizing transcriptomic responses to sediment stress across location and morphology in reef-building corals

Anthropogenic activities increase sediment suspended in the water column and deposition on reefs can be largely dependent on colony morphology. Massive and plating corals have a high capacity to trap sediments, and active removal mechanisms can be energetically costly. Branching corals trap less sediment but are more susceptible to light limitation caused by suspended sediment. Despite deleterious effects of sediments on corals, few studies have examined the molecular response of corals with different morphological characteristics to sediment stress. To address this knowledge gap, this study assessed the transcriptomic responses of branching and massive corals in Florida and Hawai'i to varying levels of sediment exposure. Gene expression analysis revealed a molecular responsiveness to sediments across species and sites. Differential Gene Expression followed by Gene Ontology (GO) enrichment analysis identified that branching corals had the largest transcriptomic response to sediments, in developmental processes and metabolism, while significantly enriched GO terms were highly variable between massive corals, despite similar morphologies. Comparison of DEGs within orthogroups revealed that while all corals had DEGs in response to sediment, there was not a concerted gene set response by morphology or location. These findings illuminate the species specificity and genetic basis underlying coral susceptibility to sediments.

RhoU forms homo-oligomers to regulate cellular responses

RhoU is an atypical member of the Rho family of small G-proteins, which has N- and C-terminal extensions compared to the classic Rho GTPases RhoA, Rac1 and Cdc42, and associates with membranes through C-terminal palmitoylation rather than prenylation. RhoU mRNA expression is upregulated in prostate cancer and is considered a marker for disease progression. Here, we show that RhoU overexpression in prostate cancer cells increases cell migration and invasion. To identify RhoU targets that contribute to its function, we found that RhoU homodimerizes in cells. We map the region involved in this interaction to the C-terminal extension and show that C-terminal palmitoylation is required for self-association. Expression of the isolated C-terminal extension reduces RhoU-induced activation of p21-activated kinases (PAKs), which are known downstream targets for RhoU, and induces cell morphological changes consistent with inhibiting RhoU function. Our results show for the first time that the activity of a Rho family member is stimulated by self-association, and this is important for its activity.

The Anticancer Effects of Marine Carotenoid Fucoxanthin through Phosphatidylinositol 3-Kinase (PI3K)-AKT Signaling on Triple-Negative Breast Cancer Cells

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer that lacks specific targets such as estrogen, progesterone, and HER2 receptors. TNBC affects one in eight women in the United States, making up 15-20% of breast cancer cases. Patients with TNBC can develop resistance to chemotherapy over time, leading to treatment failure. Therefore, finding other options like natural products is necessary for treatment. The advantages of using natural products sourced from plants as anticancer agents are that they are less toxic, more affordable, and have fewer side effects. These products can modulate several cellular processes of the tumor microenvironment, such as proliferation, migration, angiogenesis, cell cycle arrest, and apoptosis. The phosphatidyl inositol 3-kinase (PI3K)-AKT signaling pathway is an important pathway that contributes to the survival and growth of the tumor microenvironment and is associated with these cellular processes. This current study examined the anticancer effects of fucoxanthin, a marine carotenoid isolated from brown seaweed, in the MDA-MB-231 and MDA-MB-468 TNBC cell lines. The methods used in this study include a cytotoxic assay, PI3K-AKT signaling pathway PCR arrays, and Wes analysis. Fucoxanthin (6.25 µM) + TNF-α (50 ng/mL) and TNF-α (50 ng/mL) showed no significant effect on cell viability compared to the control in both MDA-MB-231 and MDA-MB-468 cells after a 24 h treatment period. PI3K-AKT signaling pathway PCR array studies showed that in TNF-α-stimulated (50 ng/mL) MDA-MB-231 and MDA-MB-468 cells, fucoxanthin (6.25 µM) modulated the mRNA expression of 12 genes, including FOXO1, RASA1, HRAS, MAPK3, PDK2, IRS1, EIF4EBP1, EIF4B, PTK2, TIRAP, RHOA, and ELK1. Additionally, fucoxanthin significantly downregulated the protein expression of IRS1, EIF4B, and ELK1 in MDA-MB-231 cells, and no change in the protein expression of EIF4B and ELK1 was shown in MDA-MB-468 cells. Fucoxanthin upregulated the protein expression of RHOA in both cell lines. The modulation of the expression of genes and proteins of the PI3K-AKT signaling pathway may elucidate fucoxanthin's effects in cell cycle progression, apoptotic processes, migration, and proliferation, which shows that PI3K-AKT may be the possible molecular mechanism for fucoxanthin's effects. In conclusion, the results obtained in this study elucidate fucoxanthin's molecular mechanisms and indicate that fucoxanthin may be considered a promising candidate for breast cancer-targeted therapy.

Local adaptation and future climate vulnerability in a wild rodent

As climate change continues, species pushed outside their physiological tolerance limits must adapt or face extinction. When change is rapid, adaptation will largely harness ancestral variation, making the availability and characteristics of that variation of critical importance. Here, we used whole-genome sequencing and genetic-environment association analyses to identify adaptive variation and its significance in the context of future climates in a small Palearctic mammal, the bank vole (Clethrionomys glareolus). We found that peripheral populations of bank vole in Britain are already at the extreme bounds of potential genetic adaptation and may require an influx of adaptive variation in order to respond. Analyses of adaptive loci suggest regional differences in climate variables select for variants that influence patterns of population adaptive resilience, including genes associated with antioxidant defense, and support a pattern of thermal/hypoxic cross-adaptation. Our findings indicate that understanding potential shifts in genomic composition in response to climate change may be key to predicting species' fate under future climates.

MiniBAR/GARRE1 is a dual Rac and Rab effector required for ciliogenesis

Cilia protrude from the cell surface and play critical roles in intracellular signaling, environmental sensing, and development. Reduced actin-dependent contractility and intracellular trafficking are both required for ciliogenesis, but little is known about how these processes are coordinated. Here, we identified a Rac1- and Rab35-binding protein with a truncated BAR (Bin/amphiphysin/Rvs) domain that we named MiniBAR (also known as KIAA0355/GARRE1), which plays a key role in ciliogenesis. MiniBAR colocalizes with Rac1 and Rab35 at the plasma membrane and on intracellular vesicles trafficking to the ciliary base and exhibits fast pulses at the ciliary membrane. MiniBAR depletion leads to short cilia, resulting from abnormal Rac-GTP/Rho-GTP levels and increased acto-myosin-II-dependent contractility together with defective trafficking of IFT88 and ARL13B into cilia. MiniBAR-depleted zebrafish embryos display dysfunctional short cilia and hallmarks of ciliopathies, including left-right asymmetry defects. Thus, MiniBAR is a dual Rac and Rab effector that controls both actin cytoskeleton and membrane trafficking for ciliogenesis.

TPPP3 promote epithelial-mesenchymal transition via Snail1 in glioblastoma

Tubulin polymerization promoting protein 3 (TPPP3), a member of the tubulin polymerization family, participates in cell progressions in several human cancers, its biological function and the underlying mechanisms in glioblastoma multiforme (GBM) remain unclear. Here, we investigated the role and application value of TPPP3 in gliomas and found that the expression of TPPP3 in glioma was higher than that in normal brain tissue (NBT), and increased with the grade of glioma. Up-regulation of TPPP3 expression in glioblastoma cells confer stronger ability of migration, invasion, proliferation and lower apoptosis in vitro. Inhibition of TPPP3 expression in GBM could reduce the migration, invasion, proliferation and induce the apoptosis of glioblastoma cells. TPPP3 affected the process of EMT by regulating the expression of Snail 1 protein. In clinical data analysis, we found a positive correlation between TPPP3 and Snail1 protein expression levels in glioblastomas. Low TPPP3 expression leads to better survival expectations in glioblastomas patients. The content of this study paves the way for further in-depth exploration of the role of TPPP3 in glioblastoma in the future, and provides new treatment and research directions.

VAV3 in human cancers: Mechanism and clinical implication

Guanine nucleotide exchange factors (GEFs) are primarily involved in signal transmission between cell membrane receptors and intracellular mediators. Upon replacing GDP with GTP, GEFs can alter their conformation, resulting in their binding to downstream effectors, such as GTPases like Ras homologous (Rho). VAV GEF family are versatile proteins working as an adaptor mediator and GEF for Rho GTPase. They act as a phosphorylation-dependent molecular switcher, fluctuating between active (tyrosine phosphorylated) and inactive (non-phosphorylated) conformation in cell signaling. Accumulating data showed that VAV3 is implicated in cancer progression. The higher levels of VAV3 in human cancers proposed that it may have an oncogenic role in cancer progression. Available studies demonstrated that VAV3 promoted cell proliferation, epithelial-mesenchymal transition (EMT), colony formation, cell cycle, survival, migration and invasion, and suppressed cell apoptosis. In addition, other studies indicated that VAV3 may have a prognostic value in cancer as well as it may act as a mediator in cancer chemoresistance. Here, we aimed to investigate the underlying molecular mechanism of VAV3 in cancer progression as well as to review its value as a prognostic biomarker and chemoresistance mediator in human cancers.

Computational study of biomechanical drivers of renal cystogenesis

Renal cystogenesis is the pathological hallmark of autosomal dominant polycystic kidney disease, caused by PKD1 and PKD2 mutations. The formation of renal cysts is a common manifestation in ciliopathies, a group of syndromic disorders caused by mutation of proteins involved in the assembly and function of the primary cilium. Cystogenesis is caused by the derailment of the renal tubular architecture and tissue deformation that eventually leads to the impairment of kidney function. However, the biomechanical imbalance of cytoskeletal forces that are altered in cells with Pkd1 mutations has never been investigated, and its nature and extent remain unknown. In this computational study, we explored the feasibility of various biomechanical drivers of renal cystogenesis by examining several hypothetical mechanisms that may promote morphogenetic markers of cystogenesis. Our objective was to provide physics-based guidance for our formulation of hypotheses and our design of experimental studies investigating the role of biomechanical disequilibrium in cystogenesis. We employed the finite element method to explore the role of (1) wild-type versus mutant cell elastic modulus; (2) contractile stress magnitude in mutant cells; (3) localization and orientation of contractile stress in mutant cells; and (4) sequence of cell contraction and cell proliferation. Our objective was to identify the factors that produce the characteristic tubular cystic growth. Results showed that cystogenesis occurred only when mutant cells contracted along the apical-basal axis, followed or accompanied by cell proliferation, as long as mutant cells had comparable or lower elastic modulus than wild-type cells, with their contractile stresses being significantly greater than their modulus. Results of these simulations allow us to focus future in vitro and in vivo experimental studies on these factors, helping us formulate physics-based hypotheses for renal tubule cystogenesis.

Mechanosensitive stem cell fate choice is instructed by dynamic fluctuations in activation of Rho GTPases

During the intricate process by which cells give rise to tissues, embryonic and adult stem cells are exposed to diverse mechanical signals from the extracellular matrix (ECM) that influence their fate. Cells can sense these cues in part through dynamic generation of protrusions, modulated and controlled by cyclic activation of Rho GTPases. However, it remains unclear how extracellular mechanical signals regulate Rho GTPase activation dynamics and how such rapid, transient activation dynamics are integrated to yield long-term, irreversible cell fate decisions. Here, we report that ECM stiffness cues alter not only the magnitude but also the temporal frequency of RhoA and Cdc42 activation in adult neural stem cells (NSCs). Using optogenetics to control the frequency of RhoA and Cdc42 activation, we further demonstrate that these dynamics are functionally significant, where high- vs. low-frequency activation of RhoA and Cdc42 drives astrocytic vs. neuronal differentiation, respectively. In addition, high-frequency Rho GTPase activation induces sustained phosphorylation of the TGFβ pathway effector SMAD1, which in turn drives the astrocytic differentiation. By contrast, under low-frequency Rho GTPase stimulation, cells fail to accumulate SMAD1 phosphorylation and instead undergo neurogenesis. Our findings reveal the temporal patterning of Rho GTPase signaling and the resulting accumulation of an SMAD1 signal as a critical mechanism through which ECM stiffness cues regulate NSC fate.

Small GTPase control of pituitary hormone secretion: Evidence from studies in the goldfish (Carassius auratus) neuroendocrine model

The secretion of vertebrate pituitary hormones is regulated by multiple hypothalamic factors, which, while generally activating unique receptor systems, ultimately propagate signals through interacting intracellular regulatory elements to modulate hormone exocytosis. One important family of intracellular regulators is the monomeric small GTPases, a subset of which (Arf1/6, Rac, RhoA, and Ras) is highly conserved across vertebrates and regulates secretory vesicle exocytosis in many cell types. In this study, we investigated the roles of these small GTPases in basal and agonist-dependent hormone release from dispersed goldfish (Carassius auratus) pituitary cells in perifusion experiments. Inhibition of these small GTPases elevated basal LH and GH secretion, except for Ras inhibition which only increased basal LH release. However, variable responses were observed with regard to LH and GH responses to the two goldfish native gonadotropin-releasing hormones (GnRH2 and GnRH3). GnRH-dependent LH release, but not GH secretion, was mediated by Arf1/6 GTPases. In contrast, inhibition of Rac and RhoA GTPases selectively enhanced GnRH3- and GnRH2-dependent GH release, respectively, while Ras inhibition only enhanced GnRH3-evoked LH secretion. Together, our results reveal novel divergent cell-type- and ligand-specific roles for small GTPases in the control of goldfish pituitary hormone exocytosis in unstimulated and GnRH-evoked release.

Golgi screen identifies the RhoGEF Solo as a novel regulator of RhoB and endocytic transport

The control of intracellular membrane trafficking by Rho GTPases is central to cellular homeostasis. How specific guanine nucleotide exchange factors and GTPase-activating proteins locally balance GTPase activation in this process is nevertheless largely unclear. By performing a microscopy-based RNAi screen, we here identify the RhoGEF protein Solo as a functional counterplayer of DLC3, a RhoGAP protein with established roles in membrane trafficking. Biochemical, imaging and optogenetics assays further uncover Solo as a novel regulator of endosomal RhoB. Remarkably, we find that Solo and DLC3 control not only the activity, but also total protein levels of RhoB in an antagonistic manner. Together, the results of our study uncover the first functionally connected RhoGAP-RhoGEF pair at endomembranes, placing Solo and DLC3 at the core of endocytic trafficking.

Muscle stem cells get a new look: Dynamic cellular projections as sensors of the stem cell niche

Cellular mechanisms whereby quiescent stem cells sense tissue injury and transition to an activated state are largely unknown. Quiescent skeletal muscle stem cells (MuSCs, also called satellite cells) have elaborate, heterogeneous projections that rapidly retract in response to muscle injury. They may therefore act as direct sensors of their niche environment. Retraction is driven by a Rac-to-Rho GTPase activity switch that promotes downstream MuSC activation events. These and other observations lead to several hypotheses: (1) projections are morphologically dynamic at quiescence, providing a surveillance function for muscle damage; (2) quiescent projection dynamics are regulated by the relative balance of Rac and Rho activities promoted by niche-derived cues; (3) projections, particularly their associated filopodia, sense tissue damage via changes to the biomechanical properties of the niche and/or detection of signaling cues released by damaged myofibers; and (4) the dynamic nature of projections result in a population of MuSCs with heterogeneous functional properties. These concepts may extend to other types of quiescent stem cells, as well as prove useful in translational research settings.

YULINK regulates vascular formation in zebrafish and HUVECs

BACKGROUND

The distinct arterial and venous cell fates are dictated by a combination of various genetic factors which form diverse types of blood vessels such as arteries, veins, and capillaries. We report here that YULINK protein is involved in vasculogenesis, especially venous formation.

METHODS

In this manuscript, we employed gene knockdown, yeast two-hybrid, FLIM-FRET, immunoprecipitation, and various imaging technologies to investigate the role of YULINK gene in zebrafish and human umbilical vein endothelial cells (HUVECs).

RESULTS

Knockdown of YULINK during the arterial-venous developmental stage of zebrafish embryos led to the defective venous formation and abnormal vascular plexus formation. Knockdown of YULINK in HUVECs impaired their ability to undergo cell migration and differentiation into a capillary-like tube formation. In addition, the phosphorylated EPHB4 was decreased in YULINK knockdown HUVECs. Yeast two-hybrid, FLIM-FRET, immunoprecipitation, as well as imaging technologies showed that YULINK colocalized with endosome related proteins (EPS15, RAB33B or TICAM2) and markers (Clathrin and RHOB). VEGF-induced VEGFR2 internalization was also compromised in YULINK knockdown HUVECs, demonstrating to the involvement of YULINK.

CONCLUSION

This study suggests that YULINK regulates vasculogenesis, possibly through endocytosis in zebrafish and HUVECs.

Lipopolysaccharide Primes Human Macrophages for Noncanonical Inflammasome-Induced Extracellular Vesicle Secretion

Human macrophages secrete extracellular vesicles (EVs) loaded with numerous immunoregulatory proteins. Vesicle-mediated protein secretion in macrophages is regulated by poorly characterized mechanisms; however, it is now known that inflammatory conditions significantly alter both the quantities and protein composition of secreted vesicles. In this study, we employed high-throughput quantitative proteomics to characterize the modulation of EV-mediated protein secretion during noncanonical caspase-4/5 inflammasome activation via LPS transfection. We show that human macrophages activate robust caspase-4-dependent EV secretion upon transfection of LPS, and this process is also partially dependent on NLRP3 and caspase-5. A similar effect occurs with delivery of the LPS with Escherichia coli-derived outer membrane vesicles. Moreover, sensitization of the macrophages through TLR4 by LPS priming prior to LPS transfection dramatically augments the EV-mediated protein secretion. Our data demonstrate that this process differs significantly from canonical inflammasome activator ATP-induced vesiculation, and it is dependent on the autocrine IFN signal associated with TLR4 activation. LPS priming preceding the noncanonical inflammasome activation significantly enhances vesicle-mediated secretion of inflammasome components caspase-1, ASC, and lytic cell death effectors GSDMD, MLKL, and NINJ1, suggesting that inflammatory EV transfer may exert paracrine effects in recipient cells. Moreover, using bioinformatics methods, we identify 15-deoxy-Δ12,14-PGJ2 and parthenolide as inhibitors of caspase-4-mediated inflammation and vesicle secretion, indicating new therapeutic potential of these anti-inflammatory drugs.

Extracellular matrix stiffness-The central cue for skin fibrosis

Skin fibrosis is a physiopathological process featuring the excessive deposition of extracellular matrix (ECM), which is the main architecture that provides structural support and constitutes the microenvironment for various cellular behaviors. Recently, increasing interest has been drawn to the relationship between the mechanical properties of the ECM and the initiation and modulation of skin fibrosis, with the engagement of a complex network of signaling pathways, the activation of mechanosensitive proteins, and changes in immunoregulation and metabolism. Simultaneous with the progression of skin fibrosis, the stiffness of ECM increases, which in turn perturbs mechanical and humoral homeostasis to drive cell fate toward an outcome that maintains and enhances the fibrosis process, thus forming a pro-fibrotic "positive feedback loop". In this review, we highlighted the central role of the ECM and its dynamic changes at both the molecular and cellular levels in skin fibrosis. We paid special attention to signaling pathways regulated by mechanical cues in ECM remodeling. We also systematically summarized antifibrotic interventions targeting the ECM, hopefully enlightening new strategies for fibrotic diseases.

Arf GTPase activates the WAVE regulatory complex through a distinct binding site

Cross-talk between Rho- and Arf-family guanosine triphosphatases (GTPases) plays an important role in linking the actin cytoskeleton to membrane protrusions, organelle morphology, and vesicle trafficking. The central actin regulator, WAVE regulatory complex (WRC), integrates Rac1 (a Rho-family GTPase) and Arf signaling to promote Arp2/3-mediated actin polymerization in many processes, but how WRC senses Arf signaling is unknown. Here, we have reconstituted a direct interaction between Arf and WRC. This interaction is greatly enhanced by Rac1 binding to the D site of WRC. Arf1 binds to a previously unidentified, conserved surface on the Sra1 subunit of WRC, which, in turn, drives WRC activation using a mechanism distinct from that of Rac1. Mutating the Arf binding site abolishes Arf1-WRC interaction, disrupts Arf1-mediated WRC activation, and impairs lamellipodia formation and cell migration. This work uncovers a new mechanism underlying WRC activation and provides a mechanistic foundation for studying how WRC-mediated actin polymerization links Arf and Rac signaling in cells.

Axonal Regeneration: Underlying Molecular Mechanisms and Potential Therapeutic Targets

Axons in the peripheral nervous system have the ability to repair themselves after damage, whereas axons in the central nervous system are unable to do so. A common and important characteristic of damage to the spinal cord, brain, and peripheral nerves is the disruption of axonal regrowth. Interestingly, intrinsic growth factors play a significant role in the axonal regeneration of injured nerves. Various factors such as proteomic profile, microtubule stability, ribosomal location, and signalling pathways mark a line between the central and peripheral axons' capacity for self-renewal. Unfortunately, glial scar development, myelin-associated inhibitor molecules, lack of neurotrophic factors, and inflammatory reactions are among the factors that restrict axonal regeneration. Molecular pathways such as cAMP, MAPK, JAK/STAT, ATF3/CREB, BMP/SMAD, AKT/mTORC1/p70S6K, PI3K/AKT, GSK-3β/CLASP, BDNF/Trk, Ras/ERK, integrin/FAK, RhoA/ROCK/LIMK, and POSTN/integrin are activated after nerve injury and are considered significant players in axonal regeneration. In addition to the aforementioned pathways, growth factors, microRNAs, and astrocytes are also commendable participants in regeneration. In this review, we discuss the detailed mechanism of each pathway along with key players that can be potentially valuable targets to help achieve quick axonal healing. We also identify the prospective targets that could help close knowledge gaps in the molecular pathways underlying regeneration and shed light on the creation of more powerful strategies to encourage axonal regeneration after nervous system injury.

OVOL2 impairs RHO GTPase signaling to restrain mitosis and aggressiveness of Anaplastic Thyroid Cancer

Background

Anaplastic Thyroid Cancer (ATC) is an undifferentiated and aggressive tumor that often originates from well-Differentiated Thyroid Carcinoma (DTC) through a trans-differentiation process. Epithelial-to-Mesenchymal Transition (EMT) is recognized as one of the major players of this process. OVOL2 is a transcription factor (TF) that promotes epithelial differentiation and restrains EMT during embryonic development. OVOL2 loss in some types of cancers is linked to aggressiveness and poor prognosis. Here, we aim to clarify the unexplored role of OVOL2 in ATC.

Methods

Gene expression analysis in thyroid cancer patients and cell lines showed that OVOL2 is mainly associated with epithelial features and its expression is deeply impaired in ATC. To assess OVOL2 function, we established an OVOL2-overexpression model in ATC cell lines and evaluated its effects by analyzing gene expression, proliferation, invasion and migration abilities, cell cycle, specific protein localization through immunofluorescence staining. RNA-seq profiling showed that OVOL2 controls a complex network of genes converging on cell cycle and mitosis regulation and Chromatin Immunoprecipitation identified new OVOL2 target genes.

Results

Coherently with its reported function, OVOL2 re-expression restrained EMT and aggressiveness in ATC cells. Unexpectedly, we observed that it caused G2/M block, a consequent reduction in cell proliferation and an increase in cell death. This phenotype was associated to generalized abnormalities in the mitotic spindle structure and cytoskeletal organization. By RNA-seq experiments, we showed that many pathways related to cytoskeleton and migration, cell cycle and mitosis are profoundly affected by OVOL2 expression, in particular the RHO-GTPase pathway resulted as the most interesting. We demonstrated that RHO GTPase pathway is the central hub of OVOL2-mediated program in ATC and that OVOL2 transcriptionally inhibits RhoU and RhoJ. Silencing of RhoU recapitulated the OVOL2-driven phenotype pointing to this protein as a crucial target of OVOL2 in ATC.

Conclusions

Collectively, these data describe the role of OVOL2 in ATC and uncover a novel function of this TF in inhibiting the RHO GTPase pathway interlacing its effects on EMT, cytoskeleton dynamics and mitosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02316-2.

Increasing cancer permeability by photodynamic priming: from microenvironment to mechanotransduction signaling

The dense cancer microenvironment is a significant barrier that limits the penetration of anticancer agents, thereby restraining the efficacy of molecular and nanoscale cancer therapeutics. Developing new strategies to enhance the permeability of cancer tissues is of major interest to overcome treatment resistance. Nonetheless, early strategies based on small molecule inhibitors or matrix-degrading enzymes have led to disappointing clinical outcomes by causing increased chemotherapy toxicity and promoting disease progression. In recent years, photodynamic therapy (PDT) has emerged as a novel approach to increase the permeability of cancer tissues. By producing excessive amounts of reactive oxygen species selectively in the cancer microenvironment, PDT increases the accumulation, penetration depth, and efficacy of chemotherapeutics. Importantly, the increased cancer permeability has not been associated to increased metastasis formation. In this review, we provide novel insights into the mechanisms by which this effect, called photodynamic priming, can increase cancer permeability without promoting cell migration and dissemination. This review demonstrates that PDT oxidizes and degrades extracellular matrix proteins, reduces the capacity of cancer cells to adhere to the altered matrix, and interferes with mechanotransduction pathways that promote cancer cell migration and differentiation. Significant knowledge gaps are identified regarding the involvement of critical signaling pathways, and to which extent these events are influenced by the complicated PDT dosimetry. Addressing these knowledge gaps will be vital to further develop PDT as an adjuvant approach to improve cancer permeability, demonstrate the safety and efficacy of this priming approach, and render more cancer patients eligible to receive life-extending treatments.

RhoB Promotes Endometrial Stromal Cells Decidualization Via Semaphorin3A/PlexinA4 Signaling in Early Pregnancy

Endometrial decidualization refers to a series of morphological changes and functional remodeling of the uterine endometrium to accept the embryo under the effect of estrogen and progesterone secreted by ovaries after ovulation. During decidualization, endometrial stromal cells (ESCs) proliferate and differentiate into decidual stromal cells, undergoing cytoskeletal rearrangement-mediated morphological changes and expressing decidualization markers, such as insulin-like growth factor-binding protein-1 and prolactin. Ras homology (Rho) proteins, a family of small G proteins, are well known as regulators of cellular morphology and involved in multiple other cellular processes. In this study, we found ras homolog family member B (RHOB) was the most significantly upregulated gene in the Rho protein family after the in vitro decidualization of human primary ESCs. RhoB expression was induced mainly by 3',5'-cyclic adenosine 5'-monophosphate (cAMP) / protein kinase A (PKA) / cyclic adenosine monophosphate-response element binding protein signaling and partly by progesterone signaling. Knockdown of RhoB in ESCs greatly inhibited actin cytoskeletal rearrangement, cell morphological transformation, and upregulation of insulin-like growth factor-binding protein-1, suggesting an indispensable role of RhoB in decidualization. Mechanistically, the downstream target of RhoB was semaphorin3A (Sema3A), which mediated its signaling via interacting with the receptor, plexinA4. More importantly, decreased expression of RhoB, Sema3A, and plexinA4 were detected in deciduas from patients with unexplained spontaneous miscarriage. Collectively, our results indicate that RhoB/Sema3A/plexinA4 signaling plays a positive role in endometrial decidualization and relates to unexplained spontaneous miscarriage, which is worthy of further exploration so as to provide new insights into therapeutic strategies for pregnancy diseases associated with poor decidualization.

Mechanical strain stimulates COPII-dependent secretory trafficking via Rac1

Cells are constantly exposed to various chemical and physical stimuli. While much has been learned about the biochemical factors that regulate secretory trafficking from the endoplasmic reticulum (ER), much less is known about whether and how this trafficking is subject to regulation by mechanical signals. Here, we show that subjecting cells to mechanical strain both induces the formation of ER exit sites (ERES) and accelerates ER-to-Golgi trafficking. We found that cells with impaired ERES function were less capable of expanding their surface area when placed under mechanical stress and were more prone to develop plasma membrane defects when subjected to stretching. Thus, coupling of ERES function to mechanotransduction appears to confer resistance of cells to mechanical stress. Furthermore, we show that the coupling of mechanotransduction to ERES formation was mediated via a previously unappreciated ER-localized pool of the small GTPase Rac1. Mechanistically, we show that Rac1 interacts with the small GTPase Sar1 to drive budding of COPII carriers and stimulates ER-to-Golgi transport. This interaction therefore represents an unprecedented link between mechanical strain and export from the ER.

Pinocytotic engulfment of lipoproteins by macrophages

Atherosclerosis is a major cause of acute coronary syndrome and stroke. Foam cell formation in macrophages is involved in controlling plaque stability and the pathogenesis of atherosclerosis. Accordingly, many studies have examined the processes of lipid incorporation, such as scavenger receptor-mediated uptake of oxidized low-density lipoprotein, in cells. In addition to receptor-mediated machinery, growing evidence has suggested that pinocytosis, which is a receptor-independent endocytic pathway, is associated with foam cell formation when a sufficient number of lipoproteins is accumulated around cells. Pinocytotic engulfment of nanoparticles is initiated by plasma membrane ruffling in a phosphatidylinositol-3 kinase-dependent manner. Subsequent to pinosome closure, the majority of pinosomes are internalized through endocytic processes, and they can be recycled into the plasma membrane. These pinocytotic processes are modulated by small GTPases and their cytoskeletal rearrangement. Moreover, pinocytotic abilities may vary between immunological subsets in cells. Accordingly, macrophages may show diverse pinocytotic abilities depending on the surrounding microenvironment. This review summarizes the current understanding of pinocytotic engulfment of lipoprotein in macrophages, and discusses how this endocytic process is governed under hypercholesterolemic conditions.

PUFA-Derived N-Acylethanolamide Probes Identify Peroxiredoxins and Small GTPases as Molecular Targets in LPS-Stimulated RAW264.7 Macrophages

We studied the mechanistic and biological origins of anti-inflammatory poly-unsaturated fatty acid-derived N-acylethanolamines using synthetic bifunctional chemical probes of docosahexaenoyl ethanolamide (DHEA) and arachidonoyl ethanolamide (AEA) in RAW264.7 macrophages stimulated with 1.0 μg mL^-1 lipopolysaccharide. Using a photoreactive diazirine, probes were covalently attached to their target proteins, which were further studied by introducing a fluorescent probe or biotin-based affinity purification. Fluorescence confocal microscopy showed DHEA and AEA probes localized in cytosol, specifically in structures that point toward the endoplasmic reticulum and in membrane vesicles. Affinity purification followed by proteomic analysis revealed peroxiredoxin-1 (Prdx1) as the most significant binding interactor of both DHEA and AEA probes. In addition, Prdx4, endosomal related proteins, small GTPase signaling proteins, and prostaglandin synthase 2 (Ptgs2, also known as cyclooxygenase 2 or COX-2) were identified. Lastly, confocal fluorescence microscopy revealed the colocalization of Ptgs2 and Rac1 with DHEA and AEA probes. These data identified new molecular targets suggesting that DHEA and AEA may be involved in reactive oxidation species regulation, cell migration, cytoskeletal remodeling, and endosomal trafficking and support endocytosis as an uptake mechanism.

Rnd3 Expression is Necessary to Maintain Mitochondrial Homeostasis but Dispensable for Autophagy

Autophagy is a highly conserved process that mediates the targeting and degradation of intracellular components to lysosomes, contributing to the maintenance of cellular homeostasis and to obtaining energy, which ensures viability under stress conditions. Therefore, autophagy defects are common to different neurodegenerative disorders. Rnd3 belongs to the family of Rho GTPases, involved in the regulation of actin cytoskeleton dynamics and important in the modulation of cellular processes such as migration and proliferation. Murine models have shown that Rnd3 is relevant for the correct development and function of the Central Nervous System and lack of its expression produces several motor alterations and neural development impairment. However, little is known about the molecular events through which Rnd3 produces these phenotypes. Interestingly we have observed that Rnd3 deficiency correlates with the appearance of autophagy impairment profiles and irregular mitochondria. In this work, we have explored the impact of Rnd3 loss of expression in mitochondrial function and autophagy, using a Rnd3 KO CRISPR cell model. Rnd3 deficient cells show no alterations in autophagy and mitochondria turnover is not impaired. However, Rnd3 KO cells have an altered mitochondria oxidative metabolism, resembling the effect caused by oxidative stress. In fact, lack of Rnd3 expression makes these cells strictly dependent on glycolysis to obtain energy. Altogether, our results demonstrate that Rnd3 is relevant to maintain mitochondria function, suggesting a possible relationship with neurodegenerative diseases.

CARD9 Signaling, Inflammation, and Diseases

Caspase-recruitment domain 9 (CARD9) protein is expressed in many cells especially in immune cells, and is critically involved in the function of the innate and adaptive immune systems through extensive interactions between CARD9 and other signaling molecules including NF-κB and MAPK. CARD9-mediated signaling plays a central role in regulating inflammatory responses and oxidative stress through the productions of important cytokines and chemokines. Abnormalities of CARD9 and CARD9 signaling or CARD9 mutations or polymorphism are associated with a variety of pathological conditions including infections, inflammation, and autoimmune disorders. This review focuses on the function of CARD9 and CARD9-mediated signaling pathways, as well as interactions with other important signaling molecules in different cell types and the relations to specific disease conditions including inflammatory diseases, infections, tumorigenesis, and cardiovascular pathologies.

Local Anesthetic Ropivacaine Exhibits Therapeutic Effects in Cancers

Despite the significant progress in cancer treatment, new anticancer therapeutics drugs with new structures and/or mechanisms are still in urgent need to tackle many key challenges. Drug repurposing is a feasible strategy in discovering new drugs among the approved drugs by defining new indications. Recently, ropivacaine, a local anesthetic that has been applied in clinical practice for several decades, has been found to possess inhibitory activity and sensitizing effects when combined with conventional chemotherapeutics toward cancer cells. While its full applications and the exact targets remain to be revealed, it has been indicated that its anticancer potency was mediated by multiple mechanisms, such as modulating sodium channel, inducing mitochondria-associated apoptosis, cell cycle arrest, inhibiting autophagy, and/or regulating other key players in cancer cells, which can be termed as multi-targets/functions that require more in-depth studies. In this review, we attempted to summarize the research past decade of using ropivacaine in suppressing cancer growth and sensitizing anticancer drugs both in-vitro and in-vivo, and tried to interpret the underlying action modes. The information gained in these findings may inspire multidisciplinary efforts to develop/discover more novel anticancer agents via drug repurposing.

Rho GTPase gene expression and breast cancer risk: a Mendelian randomization analysis

The Rho GTPase family consists of 20 genes encoding intracellular signalling proteins that influence cytoskeletal dynamics, cell migration and cell cycle progression. They are implicated in breast cancer progression but their role in breast cancer aetiology is unknown. As aberrant Rho GTPase activity could be associated with breast cancer, we aimed to determine the potential for a causal role of Rho GTPase gene expression in breast cancer risk, using two-sample Mendelian randomization (MR). MR was undertaken in 122,977 breast cancer cases and 105,974 controls, including 69,501 estrogen receptor positive (ER+) cases and 105,974 controls, and 21,468 ER negative (ER-) cases and 105,974 controls. Single nucleotide polymorphisms (SNPs) underlying expression quantitative trait loci (eQTLs) obtained from normal breast tissue, breast cancer tissue and blood were used as genetic instruments for Rho GTPase expression. As a sensitivity analysis, we undertook co-localisation to examine whether findings reflected shared causal variants or genomic confounding. We identified genetic instruments for 14 of the 20 human Rho GTPases. Using eQTLs obtained from normal breast tissue and normal blood, we identified evidence of a causal role of RHOD in overall and ER+ breast cancers (overall breast cancer: odds ratio (OR) per standard deviation (SD) increase in expression level 1.06; (95% confidence interval (CI) 1.03, 1.09; P = 5.65 × 10-5) and OR 1.22 (95% CI 1.11, 1.35; P = 5.22 × 10-5) in normal breast tissue and blood respectively). There was a consistent direction of association for ER- breast cancer, although the effect-estimate was imprecisely estimated. Using eQTLs from breast cancer tissue and normal blood there was some evidence that CDC42 was negatively associated with overall and ER + breast cancer risk. The evidence from colocalization analyses strongly supported our MR results particularly for RHOD. Our study suggests a potential causal role of increased RHOD gene expression, and, although the evidence is weaker, a potential protective role for CDC42 gene expression, in overall and ER+ breast cancers. These finding warrant validation in independent samples and further biological investigation to assess whether they may be suitable targets for drug targeting.

Exosomes derived from human umbilical cord mesenchymal stem cells reduce tendon injuries via the miR-27b-3p/ARHGAP5/RhoA signaling pathway

Tendon injuries are common clinical issues resulted from tissue overuse and age-related degeneration. Previous sutdies have suggested that exosomes secreted by mesenchymal stem cells (MSCs) contribute to tissue injury repair. Here, we provide evidence for a critical role of human umbilical cord mesenchymal stem cell (hucMSC)-derived exosomes in reducing tendon injury by activating the RhoA signaling. Treatment of primary injured tenocytes with hucMSC exosomes increases cell proliferation and invasion, which correlates with increased RhoA activity. RhoA mediates the effects of hucMSC exosomes, as treatment of primary injured tenocytes with the RhoA inhibitor, CCG-1423, abolishes the effects of hucMSC exosomes on cell proliferation and invasion. Mechanistically, we observe that hucMSC exosomes induce the expression of a microRNA, miR-27b-3p, which targets and suppresses ARHGAP5, a negative regulator of RhoA. Consistent with this observation, ARHGAP5 overexpression suppresses the effects of hucMSC exosomes on cell proliferation and invasion, while knockdown of ARHGAP5 rescues these effects. Finally, we demonstrate the functional significance of our findings using an Achilles tendon injury model and show that treatment with exosomes reduces tendon injury in rats, which correlates with increased RhoA activity and reduced ARHGAP5 expression. Taken together, our findings highlight a critical role of hucMSC exosomes in reducing tendon injury via miR-27b-3p-mediated suppression of ARHGAP5, resulting in RhoA activation, and leading to increased cell proliferation and invasion of primary injured tenocytes.

Nutraceuticals and mitochondrial oxidative stress: bridging the gap in the management of bronchial asthma

Asthma is a chronic inflammatory disease primarily characterized by inflammation and reversible bronchoconstriction. It is currently one of the leading causes of morbidity and mortality in the world. Oxidative stress further complicates the pathology of the disease. The current treatment strategies for asthma mainly involve the use of anti-inflammatory agents and bronchodilators. However, long-term usage of such medications is associated with severe adverse effects and complications. Hence, there is an urgent need to develop newer, novel, and safe treatment modalities for the management of asthma. This has therefore prompted further investigations and detailed research to identify and develop novel therapeutic interventions from potent untapped resources. This review focuses on the significance of oxidative stressors that are primarily derived from both mitochondrial and non-mitochondrial sources in initiating the clinical features of asthma. The review also discusses the biological scavenging system of the body and factors that may lead to its malfunction which could result in altered states. Furthermore, the review provides a detailed insight into the therapeutic role of nutraceuticals as an effective strategy to attenuate the deleterious effects of oxidative stress and may be used in the mitigation of the cardinal features of bronchial asthma.

Integrated physiological and comparative proteomics analysis of contrasting genotypes of pearl millet reveals underlying salt-responsive mechanisms

Salinity stress poses a significant risk to plant development and agricultural yield. Therefore, elucidation of stress-response mechanisms has become essential to identify salt-tolerance genes in plants. In the present study, two genotypes of pearl millet (Pennisetum glaucum L.) with contrasting tolerance for salinity exhibited differential morpho-physiological and proteomic responses under 150 mM NaCl. The genotype IC 325825 was shown to withstand the stress better than IP 17224. The salt-tolerance potential of IC 325825 was associated with its ability to maintain intracellular osmotic, ionic, and redox homeostasis and membrane integrity under stress. The IC 325825 genotype exhibited a higher abundance of C4 photosynthesis enzymes, efficient enzymatic and non-enzymatic antioxidant system, and lower Na⁺ /K⁺ ratio compared with IP 17224. Comparative proteomics analysis revealed greater metabolic perturbation in IP 17224 under salinity, in contrast to IC 325825 that harbored pro-active stress-responsive machinery, allowing its survival and better adaptability under salt stress. The differentially abundant proteins were in silico characterized for their functions, subcellular-localization, associated pathways, and protein-protein interaction. These proteins were mainly involved in photosynthesis/response to light stimulus, carbohydrate and energy metabolism, and stress responses. Proteomics data were validated through expression profiling of the selected genes, revealing a poor correlation between protein abundance and their relative transcript levels. This study has provided novel insights into salt adaptive mechanisms in P. glaucum, demonstrating the power of proteomics-based approaches. The critical proteins identified in the present study could be further explored as potential objects for engineering stress tolerance in salt-sensitive major crops.

STEAP3 promotes cancer cell proliferation by facilitating nuclear trafficking of EGFR to enhance RAC1-ERK-STAT3 signaling in hepatocellular carcinoma

STEAP3 (Six-transmembrane epithelial antigen of the prostate 3, TSAP6, dudulin-2) has been reported to be involved in tumor progression in human malignancies. Nevertheless, how it participates in the progression of human cancers, especially HCC, is still unknown. In the present study, we found that STEAP3 was aberrantly overexpressed in the nuclei of HCC cells. In a large cohort of clinical HCC tissues, high expression level of nuclear STEAP3 was positively associated with tumor differentiation and poor prognosis (p < 0.001), and it was an independent prognostic factor for HCC patients. In HCC cell lines, nuclear expression of STEAP3 significantly promoted HCC cells proliferation by promoting stemness phenotype and cell cycle progression via RAC1-ERK-STAT3 and RAC1-JNK-STAT6 signaling axes. Through upregulating the expression and nuclear trafficking of EGFR, STEAP3 participated in regulating EGFR-mediated STAT3 transactivity in a manner of positive feedback. In summary, our findings support that nuclear expression of STEAP3 plays a critical oncogenic role in the progression of HCC via modulation on EGFR and intracellular signaling, and it could be a candidate for prognostic marker and therapeutic target in HCC.

Extracellular Matrix Signals as Drivers of Mitochondrial Bioenergetics and Metabolic Plasticity of Cancer Cells During Metastasis

The role of metabolism in tumor growth and chemoresistance has received considerable attention, however, the contribution of mitochondrial bioenergetics in migration, invasion, and metastasis is recently being understood. Migrating cancer cells adapt their energy needs to fluctuating changes in the microenvironment, exhibiting high metabolic plasticity. This occurs due to dynamic changes in the contributions of metabolic pathways to promote localized ATP production in lamellipodia and control signaling mediated by mitochondrial reactive oxygen species. Recent evidence has shown that metabolic shifts toward a mitochondrial metabolism based on the reductive carboxylation, glutaminolysis, and phosphocreatine-creatine kinase pathways promote resistance to anoikis, migration, and invasion in cancer cells. The PGC1a-driven metabolic adaptations with increased electron transport chain activity and superoxide levels are essential for metastasis in several cancer models. Notably, these metabolic changes can be determined by the composition and density of the extracellular matrix (ECM). ECM stiffness, integrins, and small Rho GTPases promote mitochondrial fragmentation, mitochondrial localization in focal adhesion complexes, and metabolic plasticity, supporting enhanced migration and metastasis. Here, we discuss the role of ECM in regulating mitochondrial metabolism during migration and metastasis, highlighting the therapeutic potential of compounds affecting mitochondrial function and selectively block cancer cell migration.

RHO GTPase-Related Long Noncoding RNAs in Human Cancers

RHO GTPases are critical signal transducers that regulate cell adhesion, polarity, and migration through multiple signaling pathways. While all these cellular processes are crucial for the maintenance of normal cell homeostasis, disturbances in RHO GTPase-associated signaling pathways contribute to different human diseases, including many malignancies. Several members of the RHO GTPase family are frequently upregulated in human tumors. Abnormal gene regulation confirms the pivotal role of lncRNAs as critical gene regulators, and thus, they could potentially act as oncogenes or tumor suppressors. lncRNAs most likely act as sponges for miRNAs, which are known to be dysregulated in various cancers. In this regard, the significant role of miRNAs targeting RHO GTPases supports the view that the aberrant expression of lncRNAs may reciprocally change the intensity of RHO GTPase-associated signaling pathways. In this review article, we summarize recent advances in lncRNA research, with a specific focus on their sponge effects on RHO GTPase-targeting miRNAs to crucially mediate gene expression in different cancer cell types and tissues. We will focus in particular on five members of the RHO GTPase family, including RHOA, RHOB, RHOC, RAC1, and CDC42, to illustrate the role of lncRNAs in cancer progression. A deeper understanding of the widespread dysregulation of lncRNAs is of fundamental importance for confirmation of their contribution to RHO GTPase-dependent carcinogenesis.

Paternal preconception phthalate exposure alters sperm methylome and embryonic programming

Preconception environmental conditions have been demonstrated to shape sperm epigenetics and subsequently offspring health and development. Our previous findings in humans showed that urinary anti-androgenic phthalate metabolites in males were associated with altered sperm methylation and blastocyst-stage embryo development. To corroborate this, we examined the effect of preconception exposure to di(2-ethylhexyl) phthalate (DEHP) on genome-wide DNA methylation and gene expression profiles in mice. Eight-week old C57BL/6J male mice were exposed to either a vehicle control, low, or high dose of DEHP (2.5 and 25 mg/kg/weight, respectively) for 67 days (~2 spermatogenic cycles) and were subsequently mated with unexposed females. Reduced representation bisulfite sequencing (RRBS) of epididymal sperm was performed and gastrulation stage embryos were collected for RRBS and transcriptome analyses in both embryonic and extra-embryonic lineages. Male preconception DEHP exposure resulted in 704 differentially methylated regions (DMRs; q-value < 0.05; ≥10% methylation change) in sperm, 1,716 DMRs in embryonic, and 3,181 DMRs in extra-embryonic tissue. Of these, 29 DMRs overlapped between sperm and F1 tissues, half of which showed concordant methylation changes between F0 and F1 generations. F1 transcriptomes at E7.5 were also altered by male preconception DEHP exposure including developmental gene families such as Hox, Gata, and Sox. Additionally, gene ontology analyses of DMRs and differentially expressed genes showed enrichment of multiple developmental processes including embryonic development, pattern specification and morphogenesis. These data indicate that spermatogenesis in adult may represent a sensitive window in which exposure to DEHP alters the sperm methylome as well as DNA methylation and gene expression in the developing embryo.

Lysophosphatidic Acid Regulates Rho Family of GTPases in Lungs

The bio-active lipid, lysophosphatidic acid (LPA) interacts with various lysophosphatidic acid receptors (LPARs) to affect a variety of cellular functions, including proliferation, differentiation, survival, migration, morphogenesis and others. The Rho family of small GTPases, is well-known downstream signaling pathways activated by LPA. Among the Rho GTPases, RhoA, Rac1, and Cdc42 are best characterized and LPA-induced activation of the GTPases RhoA, Rac1, and Cdc42 influences a wide range of cellular processes and functions such as cell differentiation, contractile movements, cellular migration, or infiltration. In this review, we will briefly discuss the interplay between LPA and each of these three Rho family proteins, summarizing the main interactions between them. Our discussion will focus mainly on their interplay within lung endothelial and epithelial cells, drawing attention to how these interactions may contribute to pro-inflammatory processes.

Post-Translational Modification and Subcellular Compartmentalization: Emerging Concepts on the Regulation and Physiopathological Relevance of RhoGTPases

Cells and tissues are continuously exposed to both chemical and physical stimuli and dynamically adapt and respond to this variety of external cues to ensure cellular homeostasis, regulated development and tissue-specific differentiation. Alterations of these pathways promote disease progression-a prominent example being cancer. Rho GTPases are key regulators of the remodeling of cytoskeleton and cell membranes and their coordination and integration with different biological processes, including cell polarization and motility, as well as other signaling networks such as growth signaling and proliferation. Apart from the control of GTP-GDP cycling, Rho GTPase activity is spatially and temporally regulated by post-translation modifications (PTMs) and their assembly onto specific protein complexes, which determine their controlled activity at distinct cellular compartments. Although Rho GTPases were traditionally conceived as targeted from the cytosol to the plasma membrane to exert their activity, recent research demonstrates that active pools of different Rho GTPases also localize to endomembranes and the nucleus. In this review, we discuss how PTM-driven modulation of Rho GTPases provides a versatile mechanism for their compartmentalization and functional regulation. Understanding how the subcellular sorting of active small GTPase pools occurs and what its functional significance is could reveal novel therapeutic opportunities.

Cdc42 and its BORG2 and BORG3 effectors control the subcellular localization of septins between actin stress fibers and microtubules

Cell resistance to taxanes involves several complementary mechanisms, among which septin relocalization from actin stress fibers to microtubules plays an early role. By investigating the molecular mechanism underlying this relocalization, we found that acute paclitaxel treatment triggers the release from stress fibers and subsequent proteasome-mediated degradation of binder of Rho GTPases 2 (BORG2)/Cdc42 effector protein 3 (Cdc42EP3) and to a lesser extent of BORG3/Cdc42EP5, two Cdc42 effectors that link septins to actin in interphase cells. BORG2 or BORG3 silencing not only caused septin detachment from stress fibers but also mimicked the effects of paclitaxel by triggering both septin relocalization to microtubules and significant drug resistance. Conversely, BORG2 or BORG3 overexpression retained septins on actin fibers even after paclitaxel treatment, without affecting paclitaxel sensitivity. We found that drug-induced inhibition of Cdc42 resulted in a drop in BORG2 level and in the relocalization of septins to microtubules. Accordingly, although septins relocalized when overexpressing an inactive mutant of Cdc42, the expression of a constitutively active mutant acted locally at actin stress fibers to prevent septin release, even after paclitaxel treatment. These findings reveal the role of Cdc42 upstream of BORG2 and BORG3 in controlling the interplay between septins, actin fibers, and microtubules in basal condition and in response to taxanes.

Regulation of the Actin Cytoskeleton via Rho GTPase Signalling in Dictyostelium and Mammalian Cells: A Parallel Slalom

Both Dictyostelium amoebae and mammalian cells are endowed with an elaborate actin cytoskeleton that enables them to perform a multitude of tasks essential for survival. Although these organisms diverged more than a billion years ago, their cells share the capability of chemotactic migration, large-scale endocytosis, binary division effected by actomyosin contraction, and various types of adhesions to other cells and to the extracellular environment. The composition and dynamics of the transient actin-based structures that are engaged in these processes are also astonishingly similar in these evolutionary distant organisms. The question arises whether this remarkable resemblance in the cellular motility hardware is accompanied by a similar correspondence in matching software, the signalling networks that govern the assembly of the actin cytoskeleton. Small GTPases from the Rho family play pivotal roles in the control of the actin cytoskeleton dynamics. Indicatively, Dictyostelium matches mammals in the number of these proteins. We give an overview of the Rho signalling pathways that regulate the actin dynamics in Dictyostelium and compare them with similar signalling networks in mammals. We also provide a phylogeny of Rho GTPases in Amoebozoa, which shows a variability of the Rho inventories across different clades found also in Metazoa.

Physical and mechanical cues affecting biomaterial-mediated plasmid DNA delivery: insights into non-viral delivery systems

BACKGROUND

Whilst traditional strategies to increase transfection efficiency of non-viral systems aimed at modifying the vector or the polyplexes/lipoplexes, biomaterial-mediated gene delivery has recently sparked increased interest. This review aims at discussing biomaterial properties and unravelling underlying mechanisms of action, for biomaterial-mediated gene delivery. DNA internalisation and cytoplasmic transport are initially discussed. DNA immobilisation, encapsulation and surface-mediated gene delivery (SMD), the role of extracellular matrix (ECM) and topographical cues, biomaterial stiffness and mechanical stimulation are finally outlined.

MAIN TEXT

Endocytic pathways and mechanisms to escape the lysosomal network are highly variable. They depend on cell and DNA complex types but can be diverted using appropriate biomaterials. 3D scaffolds are generally fabricated via DNA immobilisation or encapsulation. Degradation rate and interaction with the vector affect temporal patterns of DNA release and transgene expression. In SMD, DNA is instead coated on 2D surfaces. SMD allows the incorporation of topographical cues, which, by inducing cytoskeletal re-arrangements, modulate DNA endocytosis. Incorporation of ECM mimetics allows cell type-specific transfection, whereas in spite of discordances in terms of optimal loading regimens, it is recognised that mechanical loading facilitates gene transfection. Finally, stiffer 2D substrates enhance DNA internalisation, whereas in 3D scaffolds, the role of stiffness is still dubious.

CONCLUSION

Although it is recognised that biomaterials allow the creation of tailored non-viral gene delivery systems, there still are many outstanding questions. A better characterisation of endocytic pathways would allow the diversion of cell adhesion processes and cytoskeletal dynamics, in order to increase cellular transfection. Further research on optimal biomaterial mechanical properties, cell ligand density and loading regimens is limited by the fact that such parameters influence a plethora of other different processes (e.g. cellular adhesion, spreading, migration, infiltration, and proliferation, DNA diffusion and release) which may in turn modulate gene delivery. Only a better understanding of these processes may allow the creation of novel robust engineered systems, potentially opening up a whole new area of biomaterial-guided gene delivery for non-viral systems.

The Multiple Functions of Rho GTPases in Fission Yeasts

The Rho family of GTPases represents highly conserved molecular switches involved in a plethora of physiological processes. Fission yeast Schizosaccharomyces pombe has become a fundamental model organism to study the functions of Rho GTPases over the past few decades. In recent years, another fission yeast species, Schizosaccharomyces japonicus, has come into focus offering insight into evolutionary changes within the genus. Both fission yeasts contain only six Rho-type GTPases that are spatiotemporally controlled by multiple guanine-nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs), and whose intricate regulation in response to external cues is starting to be uncovered. In the present review, we will outline and discuss the current knowledge and recent advances on how the fission yeasts Rho family GTPases regulate essential physiological processes such as morphogenesis and polarity, cellular integrity, cytokinesis and cellular differentiation.