Identification of SOX9-related prognostic DEGs and a prediction model for hepatitis C-induced early-stage fibrosis

BACKGROUND

Hepatitis C virus (HCV) infection induces liver inflammation, activating hepatic stellate cells (HSC) and advancing fibrosis. Studies have indicated that SOX9 overexpression is closely linked to HSC activation. The study aims to identify genes associated with SOX9 and search for potential targets for detecting and treating liver fibrosis.

METHOD

The dataset GSE15654, containing 216 biopsy samples from HCV-induced early-stage cirrhosis patients, was obtained from the GEO database. Prognostic genes were identified through differential gene analysis, LASSO, and Cox regression analyses. CIBERSORT analysis quantified infiltration levels across 22 immune cell types. Constructing a prognostic prediction model using screened genes and conducting preliminary validation using qRT PCR and RNA sequencing techniques.

RESULTS

Elevated SOX9 expression correlates with unfavorable outcomes in patients with early-stage liver fibrosis induced by HCV. We identified nine SOX9-related prognostic DEGs in our study. ADAMTS2, ARHGEF5, CCT8, ERG, LBH, FRMD6, INMT, and RASGRF2 were considered risk factors in the disease progression, while DHRS4 was considered a protective factor. SOX9 expression showed a positive correlation with mast cell infiltration, whereas ARHGEF5 and FRMD6 expressions were positively associated with M0 macrophage infiltration. Our combined model surpasses the commonly used APRI and FIB4 indicators in predicting patient prognosis. The testing of clinical samples also preliminarily validated our research results.

CONCLUSION

The prognostic model based on nine SOX9-related DEGs provides an effective tool for forecasting the progression and outcomes of liver fibrosis. This study introduces a new strategy for advancing liver fibrosis prediction and treatment.

Identification and functional analysis of genes mediating osteoclast-driven progression of osteoporosis

OBJECTIVE

The pathological mechanism of osteoporosis (OP) involves increased bone resorption mediated by osteoclasts and decreased bone formation mediated by osteoblasts, leading to an imbalance in bone homeostasis. Identifying key molecules in osteoclast-mediated OP progression is crucial for the prevention and treatment of OP.

METHODS

Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were performed on the OP patient datasets from the GEO database. The results were intersected with the differential expression results from the osteoclast differentiation dataset to identify key genes. These key genes were then subjected to disease relevance analysis, and consensus clustering was performed on OP patient samples based on their expression profiles. The subgroups were analyzed for differences, followed by GO, KEGG, GSEA, and GSVA analyses, and immune infiltration. Finally, osteoclast differentiation model was constructed. After validating the success of the model using TRAP and F-actin staining, the differential expression of key genes was validated in vitro via Western blot.

RESULTS

CTRL, ARHGEF5, PPAP2C, VSIG2, and PBLD were identified as key genes. These genes exhibited strong disease relevance (AUC > 0.9). Functional enrichment results also indicated their close association with OP and osteoclast differentiation. In vitro differential expression validation showed that during osteoclast differentiation, CTRL was downregulated, while ARHGEF5, PPAP2C, VSIG2, and PBLD were upregulated, with all differences being statistically significant (P < 0.05).

DISCUSSION

Currently, there are no studies on the effects of these five genes on osteoclast differentiation. Therefore, it is meaningful to design in vivo and in vitro perturbation experiments to observe the impact of each gene on osteoclast differentiation and OP progression.

CONCLUSION

CTRL, ARHGEF5, PPAP2C, VSIG2, and PBLD show high potential as molecular targets for basic and clinical research in osteoclast-mediated OP.

High expression of ARHGEF5 predicts unfavorable prognosis in acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly heterogeneous hematological neoplasm, highlighting the need for new molecular markers to improve prognosis prediction and therapeutic strategies. While Rho guanine nucleotide exchange factor 5 (ARHGEF5) is known to be overexpressed in various cancers, its role in AML is not well understood. This study investigates the correlation between ARHGEF5 expression and AML using data from the Cancer Genome Atlas (TCGA). ARHGEF5 expression levels in AML patients and normal samples were compared using the Wilcoxon rank-sum test. The Kaplan-Meier method and Cox regression analysis (CRA) assessed the association between ARHGEF5 expression and patient survival. A prognostic nomogram was constructed using CRA, incorporating patient age and cytogenetic risk.Our findings indicate significant overexpression of ARHGEF5 in AML compared to normal samples. Elevated ARHGEF5 levels were associated with poor prognosis, particularly in patients ≤ 60 years, those with NPM1 mutations, FLT3 mutation-positive, and wild-type RAS (P < 0.05). CRA confirmed that high ARHGEF5 expression independently predicts poor prognosis. Additionally, 412 differentially expressed genes (DEGs) were identified between high and low ARHGEF5 expression groups, with 216 genes upregulated and 196 downregulated. Pathway enrichment analyses using GO and KEGG, along with protein-protein interaction network and single sample gene set enrichment analyses, revealed key pathways and immune cell associations linked to ARHGEF5. These findings suggest that ARHGEF5 overexpression could serve as a biomarker for unfavorable outcomes in AML, providing insights into the underlying mechanisms of AML onset and progression.

ARHGEF5 binds Drebrin and affects α-tubulin acetylation to direct neuronal morphogenesis and migration during mouse brain development

Rho guanine nucleotide exchange factors (Rho GEFs) activate Rho GTPases, which act as molecular switches regulating various essential cellular functions. This study investigated the role of ARHGEF5, a Rho GEF known for its involvement in cell migration and invasion processes, in the context of brain development. We found that ARHGEF5 is essential for dendrite development during the early stages of neuronal growth. We also discovered that ARHGEF5 binds to Drebrin E, which is vital for coordinating actin and microtubule dynamics, and facilitates the interaction between Drebrin E and Cyclin-dependent kinase 5, which phosphorylates Drebrin E. Notably, ARHGEF5 deficiency resulted in a decrease in acetylated α-tubulin levels, and the expression of an α-tubulin acetylation mimetic mutant (K40Q) rescued the defects in dendrite development and neuronal migration, suggesting ARHGEF5's role in modulating microtubule stability. Additionally, ARHGEF5 was shown to influence Golgi positioning in the leading processes of migrating cortical neurons during brain development. Our study suggests that ARHGEF5 plays a crucial role in integrating cytoskeletal dynamics with neuronal morphogenesis and migration processes during brain development.

Ephexin3/ARHGEF5 Together with Cell Migration Signaling Partners within the Tumor Microenvironment Define Prognostic Transcriptional Signatures in Multiple Cancer Types

Cancer cell migration involves a repertoire of signaling proteins that lead cytoskeleton reorganization as a critical step in metastatic dissemination. RhoGEFs are multidomain effectors that integrate signaling inputs to activate the molecular switches that orchestrate actin cytoskeleton reorganization. Ephexins, a group of five RhoGEFs, play oncogenic roles in invasive and metastatic cancer, leading to a mechanistic hypothesis about their function as signaling nodes assembling functional complexes that guide cancer cell migration. To identify clinically significant Ephexin signaling partners, we applied three systematic data mining strategies, based on the screening of essential Ephexins in multiple cancer cell lines and the identification of coexpressed signaling partners in the TCGA cancer patient datasets. Based on the domain architecture of encoded proteins and gene ontology criteria, we selected Ephexin signaling partners with a role in cytoskeletal reorganization and cell migration. We focused on Ephexin3/ARHGEF5, identified as an essential gene in multiple cancer cell types. Based on significant coexpression data and coessentiality, the signaling repertoire that accompanies Ephexin3 corresponded to three groups: pan-cancer, cancer-specific and coessential. To further select the Ephexin3 signaling partners likely to be relevant in clinical settings, we first identified those whose high expression was statistical linked to shorter patient survival. The resulting Ephexin3 transcriptional signatures represent significant accumulated risk, predictive of shorter survival, in 17 cancer types, including PAAD, LUAD, LGG, OSC, AML, KIRC, THYM, BLCA, LIHC and UCEC. The signaling landscape that accompanies Ephexin3 in various cancer types included the tyrosine kinase receptor MET and the tyrosine phosphatase receptor PTPRF, the serine/threonine kinases MARK2 and PAK6, the Rho GTPases RHOD, RHOF and RAC1, and the cytoskeletal regulator DIAHP1. Our findings set the basis to further explore the role of Ephexin3/ARHGEF5 as an essential effector and signaling hub in cancer cell migration.

A TGF-β-responsive enhancer regulates SRC expression and epithelial-mesenchymal transition-associated cell migration

The non-receptor tyrosine kinase SRC is overexpressed and/or hyperactivated in various human cancers, and facilitates cancer progression by promoting invasion and metastasis. However, the mechanisms underlying SRC upregulation are poorly understood. In this study, we demonstrate that transforming growth factor-β (TGF-β) induces SRC expression at the transcriptional level by activating an intragenic the SRC enhancer. In the human breast epithelial cell line MCF10A, TGF-β1 stimulation upregulated one of the SRC promotors, the 1A promoter, resulting in increased SRC mRNA and protein levels. Chromatin immunoprecipitation (ChIP)-sequencing analysis revealed that the SMAD complex is recruited to three enhancer regions ∼15 kb upstream and downstream of the SRC promoter, and one of them is capable of activating the SRC promoter in response to TGF-β. JUN, a member of the activator protein (AP)-1 family, localises to the enhancer and regulates TGF-β-induced SRC expression. Furthermore, TGF-β-induced SRC upregulation plays a crucial role in epithelial-mesenchymal transition (EMT)-associated cell migration by activating the SRC-focal adhesion kinase (FAK) circuit. Overall, these results suggest that TGF-β-induced SRC upregulation promotes cancer cell invasion and metastasis in a subset of human malignancies.

CSK-mediated signalling by integrins in cancer

Cancer progression and metastasis are processes heavily controlled by the integrin receptor family. Integrins are cell adhesion molecules that constitute the central components of mechanosensing complexes called focal adhesions, which connect the extracellular environment with the cell interior. Focal adhesions act as key players in cancer progression by regulating biological processes, such as cell migration, invasion, proliferation, and survival. Src family kinases (SFKs) can interplay with integrins and their downstream effectors. SFKs also integrate extracellular cues sensed by integrins and growth factor receptors (GFR), transducing them to coordinate metastasis and cell survival in cancer. The non-receptor tyrosine kinase CSK is a well-known SFK member that suppresses SFK activity by phosphorylating its specific negative regulatory loop (C-terminal Y⁵²⁷ residue). Consequently, CSK may play a pivotal role in tumour progression and suppression by inhibiting SFK oncogenic effects in several cancer types. Remarkably, CSK can localise near focal adhesions when SFKs are activated and even interact with focal adhesion components, such as phosphorylated FAK and Paxillin, among others, suggesting that CSK may regulate focal adhesion dynamics and structure. Even though SFK oncogenic signalling has been extensively described before, the specific role of CSK and its crosstalk with integrins in cancer progression, for example, in mechanosensing, remain veiled. Here, we review how CSK, by regulating SFKs, can regulate integrin signalling, and focus on recent discoveries of mechanotransduction. We additionally examine the cross talk of integrins and GFR as well as the membrane availability of these receptors in cancer. We also explore new pharmaceutical approaches to these signalling pathways and analyse them as future therapeutic targets.

Src stimulates Abl-dependent phosphorylation of the guanine exchange factor Net1A to promote its cytosolic localization and cell motility

The neuroepithelial cell transforming gene 1 (Net1) is a guanine nucleotide exchange factor for the small GTPase RhoA that promotes cancer cell motility and metastasis. Two isoforms of Net1 exist, Net1 and Net1A, both of which are sequestered in the nucleus in quiescent cells to prevent aberrant RhoA activation. Many cell motility stimuli drive cytosolic relocalization of Net1A, but mechanisms controlling this event are not fully understood. Here, we demonstrate that epithelial growth factor stimulates protein kinase Src- and Abl1-dependent phosphorylation of Net1A to promote its cytosolic localization. We show that Abl1 efficiently phosphorylates Net1A on Y373, and that phenylalanine substitution of Y373 prevents Net1A cytosolic localization. Furthermore, we found that Abl1-driven cytosolic localization of Net1A does not require S52, which is a phosphorylation site of a different kinase, c-Jun N-terminal kinase, that inhibits nuclear import of Net1A. However, we did find that MKK7-stimulated cytosolic localization of Net1A does require Y373. We also demonstrate that aspartate substitution at Y373 is sufficient to promote Net1A cytosolic accumulation, and expression of Net1A Y373D potentiates epithelial growth factor-stimulated RhoA activation, downstream myosin light chain 2 phosphorylation, and F-actin accumulation. Moreover, we show that expression of Net1A Y373D in breast cancer cells also significantly increases cell motility and Matrigel invasion. Finally, we show that Net1A is required for Abl1-stimulated cell motility, which is rescued by expression of Net1A Y373D, but not Net1A Y373F. Taken together, this work demonstrates a novel mechanism controlling Net1A subcellular localization to regulate RhoA-dependent cell motility and invasion.

Guanine nucleotide exchange factors for Rho GTPases (RhoGEFs) as oncogenic effectors and strategic therapeutic targets in metastatic cancer

Metastatic cancer cells dynamically adjust their shape to adhere, invade, migrate, and expand to generate secondary tumors. Inherent to these processes is the constant assembly and disassembly of cytoskeletal supramolecular structures. The subcellular places where cytoskeletal polymers are built and reorganized are defined by the activation of Rho GTPases. These molecular switches directly respond to signaling cascades integrated by Rho guanine nucleotide exchange factors (RhoGEFs), which are sophisticated multidomain proteins that control morphological behavior of cancer and stromal cells in response to cell-cell interactions, tumor-secreted factors and actions of oncogenic proteins within the tumor microenvironment. Stromal cells, including fibroblasts, immune and endothelial cells, and even projections of neuronal cells, adjust their shapes and move into growing tumoral masses, building tumor-induced structures that eventually serve as metastatic routes. Here we review the role of RhoGEFs in metastatic cancer. They are highly diverse proteins with common catalytic modules that select among a variety of homologous Rho GTPases enabling them to load GTP, acquiring an active conformation that stimulates effectors controlling actin cytoskeleton remodeling. Therefore, due to their strategic position in oncogenic signaling cascades, and their structural diversity flanking common catalytic modules, RhoGEFs possess unique characteristics that make them conceptual targets of antimetastatic precision therapies. Preclinical proof of concept, demonstrating the antimetastatic effect of inhibiting either expression or activity of βPix (ARHGEF7), P-Rex1, Vav1, ARHGEF17, and Dock1, among others, is emerging.

Proteolytic and mechanical remodeling of the extracellular matrix by invadopodia in cancer

Cancer invasion and metastasis require remodeling of the adjacent extracellular matrix (ECM). In this mini review, we will cover the mechanisms of proteolytic degradation and the mechanical remodeling of the ECM by cancer cells, with a focus on invadopodia. Invadopodia are membrane protrusions unique to cancer cells, characterized by an actin core and by the focal degradation of ECM via matrix metalloproteases (MMPs). While ECM can also be remodeled, at lower levels, by focal adhesions, or internal collagen digestion, invadopodia are now recognized as the major mechanism for MMP-dependent pericellular ECM degradation by cancer cells. Recent evidence suggests that the completion of epithelial-mesenchymal transition may be dispensable for invadopodia and metastasis, and that invadopodia are required not only for mesenchymal, single cell invasion, but also for collective invasion. During collective invasion, invadopodia was then shown to be located in leader cells, allowing follower cells to move via cooperation. Collectively, this suggests that invadopodia function may be a requirement not only for later steps of metastasis, but also for early invasion of epithelial cells into the stromal tissue. Over the last decade, invadopodia studies have transitioned into in 3D andin vivosettings, leading to the confirmation of their essential role in metastasis in preclinical animal models. In summary, invadopodia may hold a great potential for individual risk assessment as a prognostic marker for metastasis, as well as a therapeutic target.

Maturation of a postsynaptic domain: Role of small Rho GTPases in organising nicotinic acetylcholine receptor aggregates at the vertebrate neuromuscular junction

The neuromuscular junction (NMJ) is the peripheral synapse formed between a motor axon and a skeletal muscle fibre that allows muscle contraction and the coordinated movement in many species. A main hallmark of the mature NMJ is the assembly of nicotinic acetylcholine receptor (nAChR) aggregates in the muscle postsynaptic domain, that distributes in perfect apposition to presynaptic motor terminals. To assemble its unique functional architecture, initial embryonic NMJs undergo an early postnatal maturation process characterised by the transformation of homogenous nAChR-containing plaques to elaborate and branched pretzel-like structures. In spite of a detailed morphological characterisation, the molecular mechanisms controlling the intracellular scaffolding that organises a postsynaptic domain at the mature NMJ have not been fully elucidated. In this review, we integrate evidence of key processes and molecules that have shed light on our current understanding of the NMJ maturation process. On the one hand, we consider in vitro studies revealing the potential role of podosome-like structures to define discrete low nAChR-containing regions to consolidate a plaque-to-pretzel transition at the NMJ. On the other hand, we focus on in vitro and in vivo evidence demonstrating that members of the Ras homologous (Rho) protein family of small GTPases (small Rho GTPases) play indispensable roles on NMJ maturation by regulating the stability of nAChR aggregates. We combine this evidence to propose that small Rho GTPases are key players in the assembly of podosome-like structures that drive the postsynaptic maturation of vertebrate NMJs.

Src activation in lipid rafts confers epithelial cells with invasive potential to escape from apical extrusion during cell competition

Abnormal/cancerous cells within healthy epithelial tissues undergo apical extrusion to protect against carcinogenesis, although they acquire invasive capacity once carcinogenesis progresses. However, the molecular mechanisms by which cancer cells escape from apical extrusion and invade surrounding tissues remain elusive. In this study, we demonstrate a molecular mechanism for cell fate switching during epithelial cell competition. We found that during competition within epithelial cell layers, Src transformation promotes maturation of focal adhesions and degradation of extracellular matrix. Src-transformed cells underwent basal delamination by Src activation within sphingolipid/cholesterol-enriched membrane microdomains/lipid rafts, whereas they were apically extruded when Src was outside of lipid rafts. A comparative analysis of contrasting phenotypes revealed that activation of the Src-STAT3-MMP axis through lipid rafts was required for basal delamination. CUB-domain-containing protein 1 (CDCP1) was identified as an Src-activating scaffold and as a Met regulator in lipid rafts, and its overexpression induced basal delamination. In renal cancer models, CDCP1 promoted epithelial-mesenchymal transition-mediated invasive behavior by activating the Src-STAT3-MMP axis through Met activation. Overall, these results suggest that spatial activation of Src signaling in lipid rafts confers resistance to apical extrusion and invasive potential on epithelial cells to promote carcinogenesis.

A Three-Genes Signature Predicting Colorectal Cancer Relapse Reveals LEMD1 Promoting CRC Cells Migration by RhoA/ROCK1 Signaling Pathway

Objective

Colorectal cancer (CRC) patients that experience early relapse consistently exhibit poor survival. However, no effective approach has been developed for the diagnosis and prognosis prediction of postoperative relapsed CRC.

Methods

Multiple datasets from the GEO database and TCGA database were utilized for bioinformatics analysis. WGCNA analyses and RRA analysis were performed to identify key genes. The COX/Lasso regression model was used to construct the recurrence model. Subsequent in vitro experiments further validated the potential role of the hub genes in CRC.

Results

A comprehensive analysis was performed on multiple CRC datasets and a CRC recurrence model was constructed containing LEMD1, SERPINE1, and SIAE. After further validation in two independent databases, we selected LEMD1 for in vitro experiments and found that LEMD1 could regulate CRC cell proliferation, migration, invasion, and promote EMT transition. The Rho-GTPase pulldown experiments further indicated that LEMD1 could affect RhoA activity and regulate cytoskeletal dynamics. Finally, we demonstrated that LEMD1 promoted CRC cell migration through the RhoA/ROCK1 signaling pathway.

Conclusions

In this study, a CRC relapse model consisting of LEMD1, SERPINE1, and SIAE was constructed by comprehensive analysis of multiple CRC datasets. LEMD1 could promote CRC cell migration through the RhoA/ROCK signaling pathway.

The circle of life: Phases of podosome formation, turnover and reemergence

Podosomes are highly dynamic actin-rich structures in a variety of cell types, especially monocytic cells. They fulfill multiple functions such as adhesion, mechanosensing, or extracellular matrix degradation, thus allowing cells to detect and respond to a changing environment. These abilities are based on an intricate architecture that enables podosomes to sense mechanical properties of their substratum and to transduce them intracellularly in order to generate an appropriate cellular response. These processes are enabled through the tightly orchestrated interplay of more than 300 different components that are dynamically recruited during podosome formation and turnover. In this review, we discuss the different phases of the podosome life cycle and the current knowledge on regulatory factors that impact on the genesis, activity, dissolution and reemergence of podosomes. We also highlight mechanoregulatory processes that become important during these different stages, on the level of individual podosomes, and also at podosome sub- and superstructures.

Identifying Key Genes and Functionally Enriched Pathways of Diverse Adipose Tissue Types in Cattle

Background: Fat is a tissue that not just stores energy and plays a protective role; it is also a vital endocrine organ that generates and integrates signals to influence metabolism. Meanwhile, the excessive accumulation of lipids in adipose tissue can lead to metabolic disturbance and diseases. To date, the complicated molecular mechanisms of bovine adipose tissue are still unknown. This study aimed to identify key genes and functionally enriched pathways in various adipose tissue types.

Results: The RNAseq data of 264 samples were downloaded from Gene Expression Omnibus (GEO) and analyzed by weighted gene co-expression network analysis (WGCNA). We identified 19 modules that significantly associated with at least one adipose tissue type. The brown module from GSE39618 was most closely associated with intramuscular fat tissue, which contained 550 genes. These genes were significantly enriched in pathways that related to inflammation and disease, such as TNF signaling pathway, IL-17 signaling pathway, and NF-kappa B signaling pathway. The pink module (GSE39618) that contained 58 genes was most closely associated with omental fat tissue. The turquoise (GSE39618), blue (GSE116775), and yellow (GSE65125) module were most closely associated with subcutaneous fat tissue. Genes in these modules were significantly enriched in pathways related to fat metabolism, such as the PPAR signaling pathway, fatty acid metabolism and PI3K-Akt signaling pathway. At last, key genes for intramuscular fat (PTGS2 and IL6), omental fat (ARHGEF5 and WT1), and subcutaneous fat (KIT, QR6Q1, PKD2L1, etc.) were obtained and verified. In addition, it was found that IL10 and VCAM1 might be potential genes to distinguish adipose and muscle.

Conclusion: The study applied WGCNA to generate a landscape of adipose tissue and provide a basis for identifying potential pathways and hub genes of different adipose tissue types.

Rho GTPase signalling networks in cancer cell transendothelial migration

Rho GTPases are small signalling G-proteins that are central regulators of cytoskeleton dynamics, and thereby regulate many cellular processes, including the shape, adhesion and migration of cells. As such, Rho GTPases are also essential for the invasive behaviour of cancer cells, and thus involved in several steps of the metastatic cascade, including the extravasation of cancer cells. Extravasation, the process by which cancer cells leave the circulation by transmigrating through the endothelium that lines capillary walls, is an essential step for metastasis towards distant organs. During extravasation, Rho GTPase signalling networks not only regulate the transmigration of cancer cells but also regulate the interactions between cancer and endothelial cells and are involved in the disruption of the endothelial barrier function, ultimately allowing cancer cells to extravasate into the underlying tissue and potentially form metastases. Thus, targeting Rho GTPase signalling networks in cancer may be an effective approach to inhibit extravasation and metastasis. In this review, the complex process of cancer cell extravasation will be discussed in detail. Additionally, the roles and regulation of Rho GTPase signalling networks during cancer cell extravasation will be discussed, both from a cancer cell and endothelial cell point of view.

CDCP1 promotes compensatory renal growth by integrating Src and Met signaling

CDCP1 promotes HGF-induced compensatory renal growth by focally and temporally integrating Src and Met-STAT3 signaling in lipid rafts.

Compensatory growth of organs after loss of their mass and/or function is controlled by hepatocyte growth factor (HGF), but the underlying regulatory mechanisms remain elusive. Here, we show that CUB domain-containing protein 1 (CDCP1) promotes HGF-induced compensatory renal growth. Using canine kidney cells as a model of renal tubules, we found that HGF-induced temporal up-regulation of Src activity and its scaffold protein, CDCP1, and that the ablation of CDCP1 robustly abrogated HGF-induced phenotypic changes, such as morphological changes and cell growth/proliferation. Mechanistic analyses revealed that up-regulated CDCP1 recruits Src into lipid rafts to activate STAT3 associated with the HGF receptor Met, and activated STAT3 induces the expression of matrix metalloproteinases and mitogenic factors. After unilateral nephrectomy in mice, the Met-STAT3 signaling is transiently up-regulated in the renal tubules of the remaining kidney, whereas CDCP1 ablation attenuates regenerative signaling and significantly suppresses compensatory growth. These findings demonstrate that CDCP1 plays a crucial role in controlling compensatory renal growth by focally and temporally integrating Src and Met signaling.

Control of SRC molecular dynamics encodes distinct cytoskeletal responses by specifying signaling pathway usage

Upon activation by different transmembrane receptors, the same signaling protein can induce distinct cellular responses. A way to decipher the mechanisms of such pleiotropic signaling activity is to directly manipulate the decision-making activity that supports the selection between distinct cellular responses. We developed an optogenetic probe (optoSRC) to control SRC signaling, an example of a pleiotropic signaling node, and we demonstrated its ability to generate different acto-adhesive structures (lamellipodia or invadosomes) upon distinct spatio-temporal control of SRC kinase activity. The occurrence of each acto-adhesive structure was simply dictated by the dynamics of optoSRC nanoclusters in adhesive sites, which were dependent on the SH3 and Unique domains of the protein. The different decision-making events regulated by optoSRC dynamics induced distinct downstream signaling pathways, which we characterized using time-resolved proteomic and network analyses. Collectively, by manipulating the molecular mobility of SRC kinase activity, these experiments reveal the pleiotropy-encoding mechanism of SRC signaling.

Potential involvement of Streptococcus mutans possessing collagen binding protein Cnm in infective endocarditis

Streptococcus mutans, a significant contributor to dental caries, is occasionally isolated from the blood of patients with infective endocarditis. We previously showed that S. mutans strains expressing collagen-binding protein (Cnm) are present in the oral cavity of approximately 10-20% of humans and that they can effectively invade human umbilical vein endothelial cells (HUVECs). Here, we investigated the potential molecular mechanisms of HUVEC invasion by Cnm-positive S. mutans. The ability of Cnm-positive S. mutans to invade HUVECs was significantly increased by the presence of serum, purified type IV collagen, and fibrinogen (p < 0.001). Microarray analyses of HUVECs infected by Cnm-positive or -negative S. mutans strains identified several transcripts that were differentially upregulated during invasion, including those encoding the small G protein regulatory proteins ARHGEF38 and ARHGAP9. Upregulation of these proteins occurred during invasion only in the presence of serum. Knockdown of ARHGEF38 strongly reduced HUVEC invasion by Cnm-positive S. mutans. In a rat model of infective endocarditis, cardiac endothelial cell damage was more prominent following infection with a Cnm-positive strain compared with a Cnm-negative strain. These results suggest that the type IV collagen-Cnm-ARHGEF38 pathway may play a crucial role in the pathogenesis of infective endocarditis.

Collateral Sprouting of Peripheral Sensory Neurons Exhibits a Unique Transcriptomic Profile

Peripheral nerve injuries result in motor and sensory dysfunction which can be recovered by compensatory or regenerative processes. In situations where axonal regeneration of injured neurons is hampered, compensation by collateral sprouting from uninjured neurons contributes to target reinnervation and functional recovery. Interestingly, this process of collateral sprouting from uninjured neurons has been associated with the activation of growth-associated programs triggered by Wallerian degeneration. Nevertheless, the molecular alterations at the transcriptomic level associated with these compensatory growth mechanisms remain to be fully elucidated. We generated a surgical model of partial sciatic nerve injury in mice to mechanistically study degeneration-induced collateral sprouting from spared fibers in the peripheral nervous system. Using next-generation sequencing and Ingenuity Pathway Analysis, we described the sprouting-associated transcriptome of uninjured sensory neurons and compare it with the activated by regenerating neurons. In vitro approaches were used to functionally assess sprouting gene candidates in the mechanisms of axonal growth. Using a novel animal model, we provide the first description of the sprouting transcriptome observed in uninjured sensory neurons after nerve injury. This collateral sprouting-associated transcriptome differs from that seen in regenerating neurons, suggesting a molecular program distinct from axonal growth. We further demonstrate that genetic upregulation of novel sprouting-associated genes activates a specific growth program in vitro, leading to increased neuronal branching. These results contribute to our understanding of the molecular mechanisms associated with collateral sprouting in vivo. The data provided here will therefore be instrumental in developing therapeutic strategies aimed at promoting functional recovery after injury to the nervous system.

Approaches to Manipulate Ephrin-A:EphA Forward Signaling Pathway

Erythropoietin-producing hepatocellular carcinoma A (EphA) receptors and their ephrin-A ligands are key players of developmental events shaping the mature organism. Their expression is mostly restricted to stem cell niches in adults but is reactivated in pathological conditions including lesions in the heart, lung, or nervous system. They are also often misregulated in tumors. A wide range of molecular tools enabling the manipulation of the ephrin-A:EphA system are available, ranging from small molecules to peptides and genetically-encoded strategies. Their mechanism is either direct, targeting EphA receptors, or indirect through the modification of intracellular downstream pathways. Approaches enabling manipulation of ephrin-A:EphA forward signaling for the dissection of its signaling cascade, the investigation of its physiological roles or the development of therapeutic strategies are summarized here.

Arhgef5 Binds α-Dystrobrevin 1 and Regulates Neuromuscular Junction Integrity

The neuromuscular junctions (NMJs) connect muscle fibers with motor neurons and enable the coordinated contraction of skeletal muscles. The dystrophin-associated glycoprotein complex (DGC) is an essential component of the postsynaptic machinery of the NMJ and is important for the maintenance of NMJ structural integrity. To identify novel proteins that are important for NMJ organization, we performed a mass spectrometry-based screen for interactors of α-dystrobrevin 1 (aDB1), one of the components of the DGC. The guanidine nucleotide exchange factor (GEF) Arhgef5 was found to be one of the aDB1 binding partners that is recruited to Tyr-713 in a phospho-dependent manner. We show here that Arhgef5 localizes to the NMJ and that its genetic depletion in the muscle causes the fragmentation of the synapses in conditional knockout mice. Arhgef5 loss in vivo is associated with a reduction in the levels of active GTP-bound RhoA and Cdc42 GTPases, highlighting the importance of actin dynamics regulation for the maintenance of NMJ integrity.

Ubiquitination of Src promotes its secretion via small extracellular vesicles

Upregulation of the Src tyrosine kinase is implicated in the progression of cancer. The oncogenic potential of Src is suppressed via several negative regulation systems including degradation via the ubiquitin-proteasome pathway. Here, we show that ubiquitination of Src promotes its secretion via small extracellular vesicles (sEVs) to suppress its oncogenic potential. In MDCK cells expressing a modified Src that can be activated by hydroxytamoxifen, activated Src was transported to late endosomes/lysosomes and secreted via sEVs. The secretion of Src was suppressed by ablation of Cbl E3-ligase, suggesting the contribution of ubiquitination to this process. Activated Src was ubiquitinated at multiple sites, and Lys429 was identified as a critical site for sEV-mediated secretion. Mutation of Src at Lys429 (R429) caused resistance to ubiquitination and decreased its secretion via sEVs. The activated R429 mutant was also transported to late endosomes/lysosomes, whereas its incorporation into intraluminal vesicles was reduced. Activation of the R429 mutant induced a greater FAK activation than that of wild-type Src, thereby potentiating Src-induced invasive phenotypes, such as invadopodia formation and invasive activity. These findings demonstrate that ubiquitination of activated Src at Lys429 promotes its secretion via sEVs, suggesting a potential strategy to suppress the oncogenic function of upregulated Src.

DLC3 suppresses MT1-MMP-dependent matrix degradation by controlling RhoB and actin remodeling at endosomal membranes

Cancer cells degrade the extracellular matrix through actin-rich protrusions termed invadopodia. The formation of functional invadopodia requires polarized membrane trafficking driven by Rho GTPase-mediated cytoskeletal remodeling. We identify the Rho GTPase-activating protein deleted in liver cancer 3 (DLC3; also known as STARD8) as an integral component of the endosomal transport and sorting machinery. We provide evidence for the direct regulation of RhoB by DLC3 at endosomal membranes to which DLC3 is recruited by interacting with the sorting nexin SNX27. In TGF-β-treated MCF10A breast epithelial cells, DLC3 knockdown enhanced metalloproteinase-dependent matrix degradation, which was partially rescued by RhoB co-depletion. This was recapitulated in MDA-MB-231 breast cancer cells in which early endosomes demonstrated aberrantly enriched F-actin and accumulated the metalloproteinase MT1-MMP (also known as MMP14) upon DLC3 knockdown. Remarkably, Rab4 (herein referring to Rab4A) downregulation fully rescued the enhanced matrix degradation of TGF-β-treated MCF10A and MDA-MB-231 cells. In summary, our findings establish a novel role for DLC3 in the suppression of MT1-MMP-dependent matrix degradation by inactivating RhoB signaling at endosomal membranes. We propose that DLC3 function is required to limit endosomal actin polymerization, Rab4-dependent recycling of MT1-MMP and, consequently, matrix degradation mediated by invadopodial activity.

Emerging Roles of Ephexins in Physiology and Disease

Dbl (B-cell lymphoma)-related guanine nucleotide exchange factors (GEFs), the largest family of GEFs, are directly responsible for the activation of Rho family GTPases and essential for a number of cellular events such as proliferation, differentiation and movement. The members of the Ephexin (Eph-interacting exchange protein) family, a subgroup of Dbl GEFs, initially were named for their interaction with Eph receptors and sequence homology with Ephexin1. Although the first Ephexin was identified about two decades ago, their functions in physiological and pathological contexts and regulatory mechanisms remained elusive until recently. Ephexins are now considered as GEFs that can activate Rho GTPases such as RhoA, Rac, Cdc42, and RhoG. Moreover, Ephexins have been shown to have pivotal roles in neural development, tumorigenesis, and efferocytosis. In this review, we discuss the known and proposed functions of Ephexins in physiological and pathological contexts, as well as their regulatory mechanisms.

AMPA receptors modulate the reorganization of F-actin in Bergmann glia cells through the activation of RhoA

Alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid glutamate receptors have been shown to modulate the morphology of the lamelar processes of Bergmann glia cells in the molecular layer of the cerebellum. Here we suggest that reorganization of F-actin may underlay the changes in the morphology of the lamelar processes. Using the fluorescent staining of F-actin with Phalloidin and the quantification of RhoA activation through immunoprecipitation or pull-down assays, we show that RhoA is activated after stimulation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors and leads to the reorganization of the actin cytoskeleton of Bergmann fibers. This reorganization of the actin cytoskeleton is reflected in the form of an increase in the intensity of the F-actin staining as well as in the loss of the number of Bergmann fibers stained with Phalloidin. Moreover, using a pharmacological approach, we show that activation of RhoA and the change in the intensity of the F-actin staining depends on the activation of PI3-K, focal adhesion kinase, and protein kinase C, whereas changes in the number of Bergmann fibers depend on external calcium in a RhoA independent manner. Our findings show that glutamate may induce a form of structural plasticity in Bergmann glia cells through the reorganization of the actin cytoskeleton. This may have implications in the way the synaptic transmission is processed in the cerebellum.

Hematopoietic stem cells under pressure

PURPOSE OF REVIEW

Hematopoietic stem cells (HSCs) and progenitors are tasked with maintaining hematopoietic homeostasis in the face of numerous insults and challenges, including infection, inflammation, and exsanguination. HSCs possess the remarkable ability to reconstitute the entire hematopoietic system of an organism whose own hematopoietic system has been ablated. This ability is exploited routinely in the clinic via HSC transplantation (HSCT). Here, we focus on the physiological and molecular bottlenecks overcome by HSCs during transplantation.

RECENT FINDINGS

During transplantation, HSCs encounter a damaged bone marrow niche, characterized molecularly by increases in oxygen concentrations and an altered cytokine milieu. New mechanisms and pathways have been recently implicated during HSCT, including transplanted HSC-dependent secretion of conditioning molecules that facilitate engraftment and pathways that protect HSCs from perturbed organelle homeostasis.

SUMMARY

Better understanding the molecular processes HSCs employ to withstand the stress of transplant will illuminate novel targets for further improving conditioning regimens and engraftment during HSCT.

Paving the Rho in cancer metastasis: Rho GTPases and beyond

Malignant carcinomas are often characterized by metastasis, the movement of carcinoma cells from a primary site to colonize distant organs. For metastasis to occur, carcinoma cells first must adopt a pro-migratory phenotype and move through the surrounding stroma towards a blood or lymphatic vessel. Currently, there are very limited possibilities to target these processes therapeutically. The family of Rho GTPases is an ubiquitously expressed division of GTP-binding proteins involved in the regulation of cytoskeletal dynamics and intracellular signaling. The best characterized members of the Rho family GTPases are RhoA, Rac1 and Cdc42. Abnormalities in Rho GTPase function have major consequences for cancer progression. Rho GTPase activation is driven by cell surface receptors that activate GTP exchange factors (GEFs) and GTPase-activating proteins (GAPs). In this review, we summarize our current knowledge on Rho GTPase function in the regulation of metastasis. We will focus on key discoveries in the regulation of epithelial-mesenchymal-transition (EMT), cell-cell junctions, formation of membrane protrusions, plasticity of cell migration and adaptation to a hypoxic environment. In addition, we will emphasize on crosstalk between Rho GTPase family members and other important oncogenic pathways, such as cyclic AMP-mediated signaling, canonical Wnt/β-catenin, Yes-associated protein (YAP) and hypoxia inducible factor 1α (Hif1α) and provide an overview of the advancements and challenges in developing pharmacological tools to target Rho GTPase and the aforementioned crosstalk in the context of cancer therapeutics.

Proteomic Characteristics of Blood Serum in Rats with Different Behavioral Parameters after Acute Stress

We studied proteome profile of blood serum of Wistar rats with different behavioral activity immediately and in 1 and 3 days after acute stress on the model of 12-h immobilization during the nighttime. Comparative analysis of 2D-electrophoretograms revealed differences in the expression of serum proteins in non-stressed (control) and stressed (experimental) rats. We found 22 protein spots that characterized the proteomic features of blood serum in rats with different prognostic resistance to stress. Mass-spectrometry of isolated spots identified 6 functional proteins. Persistent proteome changes in the blood of animals at different stages after acute stress were determined. The specificity of proteomic characteristics of blood serum was shown in behaviorally passive and active rats during the post-stress period. These data extend the concept on specific protein markers for the formation of a negative emotional state and adaptive-and-compensatory processes in mammals with different sensitivity to stressogenic factors.

The Rho guanine nucleotide exchange factor ARHGEF5 promotes tumor malignancy via epithelial-mesenchymal transition

Epithelial tumor cells often acquire malignant properties, such as invasion/metastasis and uncontrolled cell growth, by undergoing epithelial–mesenchymal transition (EMT). However, the mechanisms by which EMT contributes to malignant progression remain elusive. Here we show that the Rho guanine nucleotide exchange factor (GEF) ARHGEF5 promotes tumor malignancy in a manner dependent on EMT status. We previously identified ARHGEF5, a member of the Dbl family of GEFs, as a multifunctional mediator of Src-induced cell invasion and tumor growth. In the present study, ARHGEF5 was upregulated during tumor growth factor-β-induced EMT in human epithelial MCF10A cells, and promoted cell migration by activating the Rho-ROCK pathway. ARHGEF5 was necessary for the invasive and in vivo metastatic activity of human colorectal cancer HCT116 cells. These findings underscore the crucial role of ARHGEF5 in cell migration and invasion/metastasis. An in vivo tumorigenesis assay revealed that ARHGEF5 had the potential to promote tumor growth via the phosphatidylinositol 3-kinase (PI3K) pathway. However, ARHGEF5 was not required for tumor growth in epithelial-like human colorectal cancer HCT116 and HT29 cells, whereas the growth of mesenchymal-like SW480 and SW620 cells depended on ARHGEF5. Induction of EMT by tumor necrosis factor-α or Slug in HCT116 cells resulted in the dependence of tumor growth on ARHGEF5. In these mesenchymal-like cells, Akt was activated via ARHGEF5 and its activity was required for tumor growth. Analysis of a transcriptome data set revealed that the combination of ARHGEF5 upregulation and E-cadherin downregulation or Snail upregulation was significantly correlated with poor prognosis in patients with colorectal cancers. Taken together, our findings suggest that EMT-induced ARHGEF5 activation contributes to the progression of tumor malignancy. ARHGEF5 may serve as a potential therapeutic target in a subset of malignant tumors that have undergone EMT.

Tyrosine Phosphorylation of SGEF Regulates RhoG Activity and Cell Migration

SGEF and Ephexin4 are members of the Ephexin subfamily of RhoGEFs that specifically activate the small GTPase RhoG. It is reported that Ephexin1 and Ephexin5, two well-characterized Ephexin subfamily RhoGEFs, are tyrosine-phosphorylated by Src, and that their phosphorylation affect their activities and functions. In this study, we show that SGEF, but not Ephexin4, is tyrosine-phosphorylated by Src. Tyrosine phosphorylation of SGEF suppresses its interaction with RhoG, the elevation of RhoG activity, and SGEF-mediated promotion of cell migration. We identified tyrosine 530 (Y530), which is located within the Dbl homology domain, as a major phosphorylation site of SGEF by Src, and Y530F mutation blocked the inhibitory effect of Src on SGEF. Taken together, these results suggest that the activity of SGEF is negatively regulated by tyrosine phosphorylation of the DH domain.

Significance of kinase activity in the dynamic invadosome

Invadosomes are actin rich protrusive structures that facilitate invasive migration in multiple cell types. Comprised of invadopodia and podosomes, these highly dynamic structures adhere to and degrade the extracellular matrix, and are also thought to play a role in mechanosensing. Many extracellular signals have been implicated in invadosome stimulation, activating complex signalling cascades to drive the formation, activity and turnover of invadosomes. While the structural components of invadosomes have been well studied, the regulation of invadosome dynamics is still poorly understood. Protein kinases are essential to this regulation, affecting all stages of invadosome dynamics and allowing tight spatiotemporal control of their activity. Invadosome organisation and function have been linked to pathophysiological states such as cancer invasion and metastasis; therapeutic targeting of invadosome regulatory components is thus warranted. In this review, we discuss the involvement of kinase signalling in every stage of the invadosome life cycle and evaluate its significance.

Functional screen identifies regulators of murine hematopoietic stem cell repopulation

Holmfeldt et al. perform a transplant-based screen to identify regulators of HSPC engraftment and report that Foxa3 is critical for optimal HSC function after transplant.

Understanding the molecular regulation of hematopoietic stem and progenitor cell (HSPC) engraftment is paramount to improving transplant outcomes. To discover novel regulators of HSPC repopulation, we transplanted >1,300 mice with shRNA-transduced HSPCs within 24 h of isolation and transduction to focus on detecting genes regulating repopulation. We identified 17 regulators of HSPC repopulation: Arhgef5, Armcx1, Cadps2, Crispld1, Emcn, Foxa3, Fstl1, Glis2, Gprasp2, Gpr56, Myct1, Nbea, P2ry14, Smarca2, Sox4, Stat4, and Zfp521. Knockdown of each of these genes yielded a loss of function, except in the cases of Armcx1 and Gprasp2, whose loss enhanced hematopoietic stem cell (HSC) repopulation. The discovery of multiple genes regulating vesicular trafficking, cell surface receptor turnover, and secretion of extracellular matrix components suggests active cross talk between HSCs and the niche and that HSCs may actively condition the niche to promote engraftment. We validated that Foxa3 is required for HSC repopulating activity, as Foxa3^−/− HSC fails to repopulate ablated hosts efficiently, implicating for the first time Foxa genes as regulators of HSPCs. We further show that Foxa3 likely regulates the HSC response to hematologic stress. Each gene discovered here offers a window into the novel processes that regulate stable HSPC engraftment into an ablated host.

Α-Dystrobrevin-1 recruits Grb2 and α-catulin to organize neurotransmitter receptors at the neuromuscular junction

Neuromuscular junctions (NMJs), the synapses made by motor neurons on muscle fibers, form during embryonic development but undergo substantial remodeling postnatally. Several lines of evidence suggest that α-dystrobrevin, a component of the dystrophin-associated glycoprotein complex (DGC), is a crucial regulator of the remodeling process and that tyrosine phosphorylation of one isoform, α-dystrobrevin-1, is required for its function at synapses. We identified a functionally important phosphorylation site on α-dystrobrevin-1, generated phosphorylation-specific antibodies to it and used them to demonstrate dramatic increases in phosphorylation during the remodeling period, as well as in nerve-dependent regulation in adults. We then identified proteins that bind to this site in a phosphorylation-dependent manner and others that bind to α-dystrobrevin-1 in a phosphorylation-independent manner. They include multiple members of the DGC, as well as α-catulin, liprin-α1, Usp9x, PI3K, Arhgef5 and Grb2. Finally, we show that two interactors, α-catulin (phosphorylation independent) and Grb2 (phosphorylation dependent) are localized to NMJs in vivo, and that they are required for proper organization of neurotransmitter receptors on myotubes.

Bioinformatical analysis and preliminary study of the role of lipase in lipid metabolism in Mucor circinelloides

The filamentous fungusMucor circinelloideshas been widely used as a model organism to investigate the mechanisms of lipid accumulation.

Cdc42 and Tks5: a minimal and universal molecular signature for functional invadosomes

Invadosomes are actin-based structures involved in extracellular-matrix degradation. Invadosomes, either known as podosomes or invadopodia, are found in an increasing number of cell types. Moreover, their overall organization and molecular composition may vary from one cell type to the other. Some are constitutive such as podosomes in hematopoietic cells whereas others are inducible. However, they share the same feature, their ability to interact and to degrade the extracellular matrix. Based on the literature and our own experiments, the aim of this study was to establish a minimal molecular definition of active invadosomes. We first highlighted that Cdc42 is the key RhoGTPase involved in invadosome formation in all described models. Using different cellular models, such as NIH-3T3, HeLa, and endothelial cells, we demonstrated that overexpression of an active form of Cdc42 is sufficient to form invadosome actin cores. Therefore, active Cdc42 must be considered not only as an inducer of filopodia, but also as an inducer of invadosomes. Depending on the expression level of Tks5, these Cdc42-dependent actin cores were endowed or not with a proteolytic activity. In fact, Tks5 overexpression rescued this activity in Tks5 low expressing cells. We thus described the adaptor protein Tks5 as a major actor of the invadosome degradation function. Surprisingly, we found that Src kinases are not always required for invadosome formation and function. These data suggest that even if Src family members are the principal kinases involved in the majority of invadosomes, it cannot be considered as a common element for all invadosome structures. We thus define a minimal and universal molecular signature of invadosome that includes Cdc42 activity and Tks5 presence in order to drive the actin machinery and the proteolytic activity of these invasive structures.

Importance of RhoGTPases in formation, characteristics, and functions of invadosomes

Podosomes and invadopodia (collectively known as invadosomes) are specialized plasma-membrane actin-based microdomains that combine adhesive properties with matrix degrading and/or mechanosensor activities. These organelles have been extensively studied in vitro and current concerted efforts aim at establishing their physiological relevance and subsequent association with human diseases. Proper functioning of the bone, immune, and vascular systems is likely to depend on these structures while their occurrence in cancer cells appears to be linked to tumor metastasis. The elucidation of the mechanisms driving invadosome assembly is a prerequisite to understanding their role in vivo and ultimately to controlling their functions. Adhesive and soluble ligands act via transmembrane receptors that propagate signals to the cytoskeleton via small G proteins of the Rho family, assisted by tyrosine kinases and scaffold proteins to induce invadosome formation and rearrangements. Oncogene expression and cell-cell interactions may also trigger their assembly. Manipulation of the signals that regulate invadosome formation and dynamics could therefore be a strategy to interfere with their functions in a multitude of pathological settings, such as excessive bone breakdown, infections, vascular remodeling, transendothelial diapedesis, and metastasis.

YES, a Src family kinase, is a proximal glucose-specific activator of cell division cycle control protein 42 (Cdc42) in pancreatic islet β cells

Second-phase insulin secretion sustains insulin release in the face of hyperglycemia associated with insulin resistance, requiring the continued mobilization of insulin secretory granules to the plasma membrane. Cdc42, the small Rho family GTPase recognized as the proximal glucose-specific trigger to elicit second-phase insulin secretion, signals downstream to activate the p21-activated kinase (PAK1), which then signals to Raf-1/MEK/ERK to induce filamentous actin (F-actin) remodeling, to ultimately mobilize insulin granules to the plasma membrane. However, the steps required to initiate Cdc42 activation in a glucose-specific manner in β cells have remained elusive. Toward this, we identified the involvement of the Src family kinases (SFKs), based upon the ability of SFK inhibitors to block glucose-stimulated Cdc42 and PAK1 activation events as well as the amplifying pathway of glucose-stimulated insulin release, in MIN6 β cells. Indeed, subsequent studies performed in human islets revealed that SFK phosphorylation was induced only by glucose and within 1 min of stimulation before the activation of Cdc42 at 3 min. Furthermore, pervanadate treatment validated the phosphorylation event to be tyrosine-specific. Although RT-PCR showed β cells to express five different SFK proteins, only two of these, YES and Fyn kinases, were found localized to the plasma membrane, and of these two, only YES kinase underwent glucose-stimulated tyrosine phosphorylation. Immunodetection and RNAi analyses further established YES kinase as a proximal glucose-specific signal in the Cdc42-signaling cascade. Identification of YES kinase provides new insight into the mechanisms underlying the sustainment of insulin secretion via granule mobilization/replenishment and F-actin remodeling.

c-Src-induced activation of ceramide metabolism impairs membrane microdomains and promotes malignant progression by facilitating the translocation of c-Src to focal adhesions

We found that c-Src up-regulation perturbs sphingolipid/cholesterol-enriched membrane microdomains by activating ceramide synthesis, which contributes to malignant progression by promoting the translocation of c-Src from microdomains to focal adhesions/podosomes.

Integrin-matrix clusters form podosome-like adhesions in the absence of traction forces

Matrix-activated integrins can form different adhesion structures. We report that nontransformed fibroblasts develop podosome-like adhesions when spread on fluid Arg-Gly-Asp peptide (RGD)-lipid surfaces, whereas they habitually form focal adhesions on rigid RGD glass surfaces. Similar to classic macrophage podosomes, the podosome-like adhesions are protrusive and characterized by doughnut-shaped RGD rings that surround characteristic core components including F-actin, N-WASP, and Arp2/Arp3. Furthermore, there are 18 podosome markers in these adhesions, though they lack matrix metalloproteinases that characterize invadopodia and podosomes of Src-transformed cells. When nontransformed cells develop force on integrin-RGD clusters by pulling RGD lipids to prefabricated rigid barriers (metal lines spaced by 1–2 μm), these podosomes fail to form and instead form focal adhesions. The formation of podosomes on fluid surfaces is mediated by local activation of phosphoinositide 3-kinase (PI3K) and the production of phosphatidylinositol-(3,4,5)-triphosphate (PIP3) in a FAK/PYK2-dependent manner. Enrichment of PIP3 precedes N-WASP activation and the recruitment of RhoA-GAP ARAP3. We propose that adhesion structures can be modulated by traction force development and that production of PIP3 stimulates podosome formation and subsequent RhoA downregulation in the absence of traction force.

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Nontransformed fibroblasts on RGD membranes form podosome-like protrusions

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Nanopatterned RGD membranes enable traction force, suppressing protrusion formation

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Local activation of PI3K transforms prepodosomal-like RGD clusters

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PIP3-bound RhoA GAP ARAP3 is recruited at the protrusion and downregulates RhoA-GTP

Co-expression of Rho guanine nucleotide exchange factor 5 and Src associates with poor prognosis of patients with resected non-small cell lung cancer

Specific and sensitive enough molecular biomarkers are lacking to accurately predict the survival of non-small cell lung cancer (NSCLC) patients. ARHGEF5 and Src have been shown to play an important role in tumorigenesis. However, the involvement of ARHGEF5 and Src in NSCLC remains unknown. Therefore, we evaluated the expression of ARHGEF5 and Src in resected NSCLC tissues and the correlation of co-expression of ARHGEF5 and Src and the prognosis of patients with resected NSCLC. Positive expression of ARHGEF5 was detected in 133 cases of 193 patients (68.91%). A total of 193 NSCLC patients (male: 145; female: 48; average age: 61.84 years; age range: 31-84) were enrolled in this study, of which 99 cases were squamous cell carcinomas (SCCs) (51.30%) and 94 cases were adenocarcinomas (ADCs) (48.70%). The expression of ARHGEF5 was mainly located in the cytoplasm of tumor cells, but not in the corresponding adjacent lung tissues. The levels of ARHGEF5 were significantly associated with age, differentiation and tumor stage. ARHGEF5 protein expression was associated with Src protein expression in NSCLC (χ(2) = 11.874, P<0.01) and in ADC (χ(2) = 12.194, P<0.01), but not in SCC. Co-immunoprecipitation revealed that there was a physical interaction between Src and ARHGEF5 in lung cancer cells. The patients with ARHGEF5(+)/Src(+) had a shorter survival time compared with the other patients (29.37 months versus 39.90 months, P = 0.029). In conclusion, ARHGEF5/Src can be considered as a prognostic biomarker and a therapeutic target for patients with resected NSCLC.

Podosomes in adhesion, migration, mechanosensing and matrix remodeling

Cells use various actin-based motile structures to allow them to move across and through matrix of varying density and composition. Podosomes are actin cytoskeletal structures that form in motile cells and that mediate adhesion to substrate, migration, and other specialized functions such as transmigration through cell and matrix barriers. The podosome is a unique and interesting entity, which appears in the light microscope as an individual punctum, but is linked to other podosomes like a node on a network of the underlying cytoskeleton. Here, we discuss the signals that control podosome assembly and dynamics in different cell types and the actin organising proteins that regulate both the inner actin core and integrin-rich surrounding ring structures. We review the structure and composition of podosomes and also their functions in various cell types of both myeloid and endothelial lineage. We also discuss the emerging idea that podosomes can sense matrix stiffness and enable cells to respond to their environment.

Temporal regulation of EGF signalling networks by the scaffold protein Shc1

Cell-surface receptors frequently employ scaffold proteins to recruit cytoplasmic targets, but the rationale for this is uncertain. Activated receptor tyrosine kinases, for example, engage scaffolds such as Shc1 that contain phosphotyrosine (pTyr) binding (PTB) domains. Using quantitative mass spectrometry, we find that Shc1 responds to epidermal growth factor (EGF) stimulation through multiple waves of distinct phosphorylation events and protein interactions. Following stimulation, Shc1 rapidly binds a group of proteins that activate pro-mitogenic/survival pathways dependent on recruitment of the Grb2 adaptor to Shc1 pTyr sites. Akt-mediated feedback phosphorylation of Shc1 Ser29 then recruits the Ptpn12 tyrosine phosphatase. This is followed by a sub-network of proteins involved in cytoskeletal reorganization, trafficking and signal termination that binds Shc1 with delayed kinetics, largely through the SgK269 pseudokinase/adaptor protein. Ptpn12 acts as a switch to convert Shc1 from pTyr/Grb2-based signaling to SgK269-mediated pathways that regulate cell invasion and morphogenesis. The Shc1 scaffold therefore directs the temporal flow of signaling information following EGF stimulation.

Palladin promotes invasion of pancreatic cancer cells by enhancing invadopodia formation in cancer-associated fibroblasts

The stromal compartment surrounding epithelial-derived pancreatic tumors is thought to have a key role in the aggressive phenotype of this malignancy. Emerging evidence suggests that cancer-associated fibroblasts (CAFs), the most abundant cells in the stroma of pancreatic tumors, contribute to the tumor's invasion, metastasis and resistance to therapy, but the precise molecular mechanisms that regulate CAFs behavior are poorly understood. In this study, we utilized immortalized human pancreatic CAFs to investigate molecular pathways that control the matrix-remodeling and invasion-promoting activity of CAFs. We showed previously that palladin, an actin-associated protein, is expressed at high levels in CAFs of pancreatic tumors and other solid tumors, and also in an immortalized line of human CAFs. In this study, we found that short-term exposure of CAFs to phorbol esters reduced the number of stress fibers and triggered the appearance of individual invadopodia and invadopodial rosettes in CAFs. Molecular analysis of invadopodia revealed that their composition resembled that of similar structures (that is, invadopodia and podosomes) described in other cell types. Pharmacological inhibition and small interfering RNA knockdown experiments demonstrated that protein kinase C, the small GTPase Cdc42 and palladin were necessary for the efficient assembly of invadopodia by CAFs. In addition, GTPase activity assays showed that palladin contributes to the activation of Cdc42. In mouse xenograft experiments using a mixture of CAFs and tumor cells, palladin expression in CAFs promoted the rapid growth and metastasis of human pancreatic tumor cells. Overall, these results indicate that high levels of palladin expression in CAFs enhance their ability to remodel the extracellular matrix by regulating the activity of Cdc42, which in turn promotes the assembly of matrix-degrading invadopodia in CAFs and tumor cell invasion. Together, these results identify a novel molecular signaling pathway that may provide new molecular targets for the inhibition of pancreatic cancer metastasis.

Regulation of the SRC family kinases by Csk

The non-receptor tyrosine kinase Csk serves as an indispensable negative regulator of the Src family tyrosine kinases (SFKs) by specifically phosphorylating the negative regulatory site of SFKs, thereby suppressing their oncogenic potential. Csk is primarily regulated through its SH2 domain, which is required for membrane translocation of Csk via binding to scaffold proteins such as Cbp/PAG1. The binding of scaffolds to the SH2 domain can also upregulate Csk kinase activity. These regulatory features have been elucidated by analyses of Csk structure at the atomic levels. Although Csk itself may not be mutated in human cancers, perturbation of the regulatory system consisting of Csk, Cbp/PAG1, or other scaffolds, and certain tyrosine phosphatases may explain the upregulation of SFKs frequently observed in human cancers. This review focuses on the molecular bases for the function, structure, and regulation of Csk as a unique regulatory tyrosine kinase for SFKs.

Spatiotemporal regulation of Src and its substrates at invadosomes

In the past decade, substantial progress has been made in understanding how Src family kinases regulate the formation and function of invadosomes. Invadosomes are organized actin-rich structures that contain an F-actin core surrounded by an adhesive ring and mediate invasive migration. Src kinases orchestrate, either directly or indirectly, each phase of the invadosome life cycle including invadosome assembly, maturation and matrix degradation and disassembly. Complex arrays of Src effector proteins are involved at different stages of invadosome maturation and their spatiotemporal activity must be tightly regulated to achieve effective invasive migration. In this review, we highlight some recent progress and the challenges of understanding how Src is regulated temporally and spatially to orchestrate the dynamics of invadosomes and mediate cell invasion.