RIAM, an Ena/VASP and Profilin ligand, interacts with Rap1-GTP and mediates Rap1-induced adhesion

PI3Kγ in Tumour Inflammation: Bridging Immune Response and Cancer Progression-A Mini-Review

Phosphatidylinositol 3-kinase gamma (PI3Kγ), a class I PI3K family member, plays a critical role in modulating inflammation and immune responses within the tumour microenvironment. Emerging evidence suggests that PI3Kγ promotes myeloid cell trafficking and transcription, leading to tumour progression and metastasis. This review explores the multifaceted roles of PI3Kγ in tumour-associated inflammation, highlighting its involvement in immune cell polarisation, cytokine production, and the dynamic interaction between tumour cells and the surrounding stromal environment. We also discuss the potential therapeutic implications of targeting PI3Kγ to modulate inflammation and inhibit tumour growth. Given its pivotal role in immune response and tumour progression, PI3Kγ represents a promising target for future cancer therapies to reduce inflammation-driven tumorigenesis.

Phosphorylation of USP32 by CDK5 regulates Rap1 stability and therapeutic resistance in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal human cancer. Gemcitabine-based chemotherapy remains the cornerstone for advanced PDAC. However, resistance to chemotherapy greatly limits its clinical therapeutic efficacy. Accordingly, the identification of novel therapeutic targets to overcome chemoresistance and improve prognosis is urgently needed. Screening of deubiquitinase family members, tandem affinity purification, mass spectrometry, and RNA sequencing (RNA-Seq) analysis were performed to predict the interactions and function of the CDK5-USP32-Rap1 axis in PDAC. In vitro and in vivo experiments were performed to elucidate the regulatory mechanism and biological roles of this axis in glycolytic reprogramming and chemoresistance in PDAC. Finally, TCGA database analysis and immunohistochemistry were performed to determine the expression and clinical significance of CDK5, USP32, and Rap1 in PDAC tissues. USP32 was identified as a bona fide deubiquitinase of Rap1. USP32 deubiquitinates and stabilizes Rap1, thereby promoting glycolytic reprogramming and chemoresistance in PDAC cells. Moreover, we unexpectedly found that CDK5-mediated phosphorylation of USP32 is required for its deubiquitinase activity toward Rap1 and drives malignant phenotypes of PDAC. Additionally, these functions can be significantly inhibited by pharmacological inhibition (roscovitine) or genetic ablation of CDK5. Importantly, combining a CDK5 inhibitor with gemcitabine has a synergetic anticancer effect. Indeed, the effectiveness of targeting CDK5 to sensitize PDAC cells to gemcitabine was confirmed in a patient-derived xenograft (PDX) model. CDK5 and USP32 expression is markedly elevated in PDAC samples and positively associated with Rap1 expression. Increased expression of CDK5, USP32, and Rap1 is significantly associated with poorer prognosis in PDAC. We identified the previously unrecognized oncogenic function and clinical importance of the CDK5-USP32-Rap1 axis, providing preclinical evidence for potential new combination strategies for PDAC therapy.

The PTTG1/VASP axis promotes oral squamous cell carcinoma metastasis by modulating focal adhesion and actin filaments

The dynamics of focal adhesions (FAs) are essential physiological processes involved in cell spreading, metastasis, and regulation of the actin cytoskeleton. FAs are complex structures comprising proteins, such as paxillin and zyxin, which interact with extracellular membranes and influence cell motility and morphology. Although related studies have been reported in various cancers, the function and molecular mechanisms of oral squamous cell carcinoma (OSCC) remain unknown. We investigated the coordination between the actin cytoskeleton and FA proteins, specifically introducing pituitary tumor-transforming gene 1 (PTTG1; also known as PTTG1 regulator of sister chromatid separation, securin) into OSCC. Furthermore, we explored the co-localization of several FAs and PTTG1 through small interfering RNA (siRNA) control or siRNA-vasodilator-stimulated phosphoprotein (VASP) and -PTTG1, examining the mechanisms mediated by the induced changes in OSCC both in vitro and in vivo. The knockdown of VASP and PTTG1 regulates the dynamic actin cytoskeleton, restricting cell protrusion and motility from the front to the rear of OSCC cells. Our findings may provide new insights into how cells interact with each other on the surface of FAs in OSCC, influencing metastatic properties.

The autophagy component LC3 regulates lymphocyte adhesion via LFA1 transport in response to outside-in signaling

The leukocyte integrin LFA1 is indispensable for immune responses, orchestrating lymphocyte trafficking and adhesion. While LFA1 activation induces LFA1 clustering at the cell contact surface via outside-in signaling, the regulatory mechanisms remain unclear. Here, we uncovered a previously hidden function of the autophagosome component LC3 beyond its role in autophagy by bridging two seemingly unrelated pathways: LFA1 transport and autophagosome transport. LFA1 clusters co-trafficked with LC3, facilitating LFA1 accumulation at the contact surface. LC3b knockout decreased lymphocyte adhesiveness. LFA1 activation did not induce autophagy, whereas it increased mTOR and AMPK activity. LFA1-dependent AMPK activation enhances LFA1 and LC3 clustering and adhesion. Inhibiting Mst1 kinase-mediated LC3 phosphorylation promoted LC3-mediated LFA1 recruitment to the contact surface through direct interaction with RAPL, uncovering an unprecedented integrin recruitment route. These findings uncover a function of LC3 and expand our understanding of lymphocyte regulation via LFA1.

Liquid-like condensates that bind actin promote assembly and bundling of actin filaments

Biomolecular condensates perform diverse physiological functions. Previous work showed that VASP, a processive actin polymerase, forms condensates that assemble and bundle actin. Here, we show that this behavior does not require proteins with specific polymerase activity. Specifically, condensates composed of Lamellipodin, a protein that binds actin but is not an actin polymerase, were also capable of assembling actin filaments. To probe the minimum requirements for condensate-mediated actin bundling, we developed an agent-based computational model. Guided by its predictions, we hypothesized that any condensate-forming protein that binds filamentous actin could bundle filaments through multivalent crosslinking. To test this, we added a filamentous-actin-binding motif to Eps15, a condensate-forming protein that does not normally bind actin. The resulting chimera formed condensates that facilitated efficient assembly and bundling of actin filaments. Collectively, these findings broaden the family of proteins that could organize cytoskeletal filaments to include any filamentous-actin-binding protein that participates in protein condensation.

RAP1 is essential for PRRSV replication and the synthesis of the viral genome

Since its emergence, porcine reproductive and respiratory syndrome (PRRS) has caused enormous economic losses to the global swine industry. The pathogenesis of PRRS remains under investigation. The porcine reproductive and respiratory syndrome virus (PRRSV) causes reproductive disorders in pigs and respiratory in piglets, which is a 15 kb RNA virus that encodes 16 viral proteins, most of which exhibit multiple functions during the virus lifecycle. RAP1 (Ras-proximate-1), a small GTPase, is known to regulates cell adhesion across different cell types and is one of the most conserved telomere proteins. Thus, this study explored the effect of RAP1 after PRRSV infection. In this study, RAP1 did not participate in the adsorption and internalization process of PRRSV, however, it promoted viral RNA synthesis and enhanced PRRSV replication. Additionally, we discovered that RAP1 interacted with Nsp10 and the N protein. Specifically, the Myb domain of RAP1 primarily bound to the viral genome interacted with the N-terminal structural domain of the N protein, which contains an RNA-binding domain. Additionally, the C-terminal region of RAP1 interacted with the N-terminal domain of Nsp10. These results suggested that RAP1 is a critical factor in the PRRSV infection process, particularly in the context of viral RNA synthesis. RAP1 could be a potential target for the prevention and control of PRRSV.

PairK: Pairwise k-mer alignment for quantifying protein motif conservation in disordered regions

Protein-protein interactions are often mediated by a modular peptide recognition domain binding to a short linear motif (SLiM) in the disordered region of another protein. To understand the features of SLiMs that are important for binding and to identify motif instances that are important for biological function, it is useful to examine the evolutionary conservation of motifs across homologous proteins. However, the intrinsically disordered regions (IDRs) in which SLiMs reside evolve rapidly. Consequently, multiple sequence alignment (MSA) of IDRs often misaligns SLiMs and underestimates their conservation. We present PairK (pairwise k-mer alignment), an MSA-free method to align and quantify the relative local conservation of subsequences within an IDR. Lacking a ground truth for conservation, we tested PairK on the task of distinguishing biologically important motif instances from background motifs, under the assumption that biologically important motifs are more conserved. The method outperforms both standard MSA-based conservation scores and a modern LLM-based conservation score predictor. PairK can quantify conservation over wider phylogenetic distances than MSAs, indicating that some SLiMs are more conserved than MSA-based metrics imply. PairK is available as an open-source python package at https://github.com/jacksonh1/pairk. It is designed to be easily adapted for use with other SLiM tools and for diverse applications.

IL-13 and IL-17A activate β1 integrin through an NF-kB/Rho kinase/PIP5K1γ pathway to enhance force transmission in airway smooth muscle

Integrin activation resulting in enhanced adhesion to the extracellular matrix plays a key role in fundamental cellular processes. Although integrin activation has been extensively studied in circulating cells such as leukocytes and platelets, much less is known about the regulation and functional impact of integrin activation in adherent cells such as smooth muscle. Here, we show that two different asthmagenic cytokines, IL-13 and IL-17A, activate type I and IL-17 cytokine receptor families, respectively, to enhance adhesion of airway smooth muscle. These cytokines also induce activation of β1 integrins detected by the conformation-specific antibody HUTS-4. Moreover, HUTS-4 binding is increased in the smooth muscle of patients with asthma compared to nonsmokers without lung disease, suggesting a disease-relevant role for integrin activation in smooth muscle. Indeed, integrin activation induced by the β1-activating antibody TS2/16, the divalent cation manganese, or the synthetic peptide β1-CHAMP that forces an extended-open integrin conformation dramatically enhances force transmission in smooth muscle cells and airway rings even in the absence of cytokines. We demonstrate that cytokine-induced activation of β1 integrins is regulated by a common pathway of NF-κB-mediated induction of RhoA and its effector Rho kinase, which in turn stimulates PIP5K1γ-mediated synthesis of PIP2 at focal adhesions, resulting in β1 integrin activation. Taken together, these data identify a pathway by which type I and IL-17 cytokine receptor family stimulation induces functionally relevant β1 integrin activation in adherent smooth muscle and help to explain the exaggerated force transmission that characterizes chronic airway diseases such as asthma.

Differential Lipid Binding Specificities of RAP1A and RAP1B are Encoded by the Amino Acid Sequence of the Membrane Anchors

RAP1 proteins belong to the RAS family of small GTPases that operate as molecular switches by cycling between GDP-bound inactive and GTP-bound active states. The C-terminal anchors of RAP1 proteins are known to direct membrane localization, but how these anchors organize RAP1 on the plasma membrane (PM) has not been investigated. Using high-resolution imaging, we show that RAP1A and RAP1B form spatially segregated nanoclusters on the inner leaflet of the PM, with further lateral segregation between GDP-bound and GTP-bound proteins. The C-terminal polybasic anchors of RAP1A and RAP1B differ in their amino acid sequences and exhibit different lipid binding specificities, which can be modified by single-point mutations in the respective polybasic domains (PBD). Molecular dynamics simulations reveal that single PBD mutations substantially reduce the interactions of the membrane anchors with the PM lipid phosphatidylserine. In summary, we show that aggregate lipid binding specificity encoded within the C-terminal anchor determines PM association and nanoclustering of RAP1A and RAP1B. Taken together with previous observations on RAC1 and KRAS, the study reveals that the PBD sequences of small GTPase membrane anchors can encode distinct lipid binding specificities that govern PM interactions.

PairK: Pairwise k-mer alignment for quantifying protein motif conservation in disordered regions

Protein-protein interactions are often mediated by a modular peptide recognition domain binding to a short linear motif (SLiM) in the disordered region of another protein. The ability to predict domain-SLiM interactions would allow researchers to map protein interaction networks, predict the effects of perturbations to those networks, and develop biologically meaningful hypotheses. Unfortunately, sequence database searches for SLiMs generally yield mostly biologically irrelevant motif matches or false positives. To improve the prediction of novel SLiM interactions, researchers employ filters to discriminate between biologically relevant and improbable motif matches. One promising criterion for identifying biologically relevant SLiMs is the sequence conservation of the motif, exploiting the fact that functional motifs are more likely to be conserved than spurious motif matches. However, the difficulty of aligning disordered regions has significantly hampered the utility of this approach. We present PairK (pairwise k-mer alignment), an MSA-free method to quantify motif conservation in disordered regions. PairK outperforms both standard MSA-based conservation scores and a modern LLM-based conservation score predictor on the task of identifying biologically important motif instances. PairK can quantify conservation over wider phylogenetic distances than MSAs, indicating that SLiMs may be more conserved than is implied by MSA-based metrics. PairK is available as open-source code at https://github.com/jacksonh1/pairk.

Liquid-like condensates that bind actin drive filament polymerization and bundling

Liquid-like protein condensates perform diverse physiological functions. Previous work showed that VASP, a processive actin polymerase, forms condensates that polymerize and bundle actin. To minimize their curvature, filaments accumulated at the inner condensate surface, ultimately deforming the condensate into a rod-like shape, filled with a bundle of parallel filaments. Here we show that this behavior does not require proteins with specific polymerase activity. Specifically, we found that condensates composed of Lamellipodin, a protein that binds actin but is not an actin polymerase, were also capable of polymerizing and bundling actin filaments. To probe the minimum requirements for condensate-mediated actin bundling, we developed an agent-based computational model. Guided by its predictions, we hypothesized that any condensate-forming protein that binds actin could bundle filaments through multivalent crosslinking. To test this idea, we added an actin-binding motif to Eps15, a condensate-forming protein that does not normally bind actin. The resulting chimera formed condensates that drove efficient actin polymerization and bundling. Collectively, these findings broaden the family of proteins that could organize cytoskeletal filaments to include any actin-binding protein that participates in protein condensation.

IL-13 and IL-17A Activate β1 Integrin through an NF-kB/Rho kinase/PIP5K1γ pathway to Enhance Force Transmission in Airway Smooth Muscle

Integrin activation resulting in enhanced adhesion to the extracellular matrix plays a key role in fundamental cellular processes. Although G-protein coupled receptor-mediated integrin activation has been extensively studied in non-adherent migratory cells such as leukocytes and platelets, much less is known about the regulation and functional impact of integrin activation in adherent stationary cells such as airway smooth muscle. Here we show that two different asthmagenic cytokines, IL-13 and IL-17A, activate type I and IL-17 cytokine receptor families respectively, to enhance adhesion of muscle to the matrix. These cytokines also induce activation of β1 integrins as detected by the conformation-specific antibody HUTS-4. Moreover, HUTS-4 binding is significantly increased in the smooth muscle of patients with asthma compared to healthy controls, suggesting a disease-relevant role for aberrant integrin activation. Indeed, we find integrin activation induced by a β1 activating antibody, the divalent cation manganese, or the synthetic peptide β1-CHAMP, dramatically enhances force transmission in collagen gels, mouse tracheal rings, and human bronchial rings even in the absence of cytokines. We further demonstrate that cytokine-induced activation of β1 integrins is regulated by a common pathway of NF-κB-mediated induction of RhoA and its effector Rho kinase, which in turn stimulates PIP5K1γ-mediated synthesis of PIP2 resulting in β1 integrin activation. Taken together, these data identify a previously unknown pathway by which type I and IL-17 cytokine receptor family stimulation induces functionally relevant β1 integrin activation in adherent smooth muscle and help explain the exaggerated force transmission that characterizes chronic airways diseases such as asthma.

MET receptor serves as a promising target in melanoma brain metastases

The development of brain metastases hallmarks disease progression in 20-40% of melanoma patients and is a serious obstacle to therapy. Understanding the processes involved in the development and maintenance of melanoma brain metastases (MBM) is critical for the discovery of novel therapeutic strategies. Here, we generated transcriptome and methylome profiles of MBM showing high or low abundance of infiltrated Iba1high tumor-associated microglia and macrophages (TAMs). Our survey identified potential prognostic markers of favorable disease course and response to immune checkpoint inhibitor (ICi) therapy, among them APBB1IP and the interferon-responsive gene ITGB7. In MBM with high ITGB7/APBB1IP levels, the accumulation of TAMs correlated significantly with the immune score. Signature-based deconvolution of MBM via single sample GSEA revealed enrichment of interferon-response and immune signatures and revealed inflammation, stress and MET receptor signaling. MET receptor phosphorylation/activation maybe elicited by inflammatory processes in brain metastatic melanoma cells via stroma cell-released HGF. We found phospho-METY1234/1235 in a subset of MBM and observed a marked response of brain metastasis-derived cell lines (BMCs) that lacked druggable BRAF mutations or developed resistance to BRAF inhibitors (BRAFi) in vivo to MET inhibitors PHA-665752 and ARQ197 (tivantinib). In summary, the activation of MET receptor in brain colonizing melanoma cells by stromal cell-released HGF may promote tumor self-maintenance and expansion and might counteract ICi therapy. Therefore, therapeutic targeting of MET possibly serves as a promising strategy to control intracranial progressive disease and improve patient survival.

Integrated proteome and malonylome analyses reveal the potential meaning of TLN1 and ACTB in end-stage renal disease

BACKGROUND

End-stage renal disease (ESRD) is a condition that is characterized by the loss of kidney function. ESRD patients suffer from various endothelial dysfunctions, inflammation, and immune system defects. Lysine malonylation (Kmal) is a recently discovered post-translational modification (PTM). Although Kmal has the ability to regulate a wide range of biological processes in various organisms, its specific role in ESRD is limited.

METHODS

In this study, the affinity enrichment and liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques have been used to create the first global proteome and malonyl proteome (malonylome) profiles of peripheral blood mononuclear cells (PBMCs) from twenty patients with ESRD and eighty-one controls.

RESULTS

On analysis, 793 differentially expressed proteins (DEPs) and 12 differentially malonylated proteins (DMPs) with 16 Kmal sites were identified. The Rap1 signaling pathway and platelet activation pathway were found to be important in the development of chronic kidney disease (CKD), as were DMPs TLN1 and ACTB, as well as one malonylated site. One conserved Kmal motif was also discovered.

CONCLUSIONS

These findings provided the first report on the Kmal profile in ESRD, which could be useful in understanding the potential role of lysine malonylation modification in the development of ESRD.

GSK3 and lamellipodin balance lamellipodial protrusions and focal adhesion maturation in mouse neural crest migration

Neural crest cells are multipotent cells that delaminate from the neuroepithelium, migrating throughout the embryo. Aberrant migration causes developmental defects. Animal models are improving our understanding of neural crest anomalies, but in vivo migration behaviors are poorly understood. Here, we demonstrate that murine neural crest cells display actin-based lamellipodia and filopodia in vivo. Using neural crest-specific knockouts or inhibitors, we show that the serine-threonine kinase glycogen synthase kinase-3 (GSK3) and the cytoskeletal regulator lamellipodin (Lpd) are required for lamellipodia formation while preventing focal adhesion maturation. Lpd is a substrate of GSK3, and phosphorylation of Lpd favors interactions with the Scar/WAVE complex (lamellipodia formation) at the expense of VASP and Mena interactions (adhesion maturation and filopodia formation). This improved understanding of cytoskeletal regulation in mammalian neural crest migration has general implications for neural crest anomalies and cancer.

Rap1 regulates lumen continuity via Afadin in renal epithelia

The continuity of a lumen within an epithelial tubule is critical for its function. We previously found that the F-actin binding protein Afadin is required for timely lumen formation and continuity in renal tubules formed from the nephrogenic mesenchyme in mice. Afadin is a known effector and interactor of the small GTPase Rap1, and in the current study, we examine the role of Rap1 in nephron tubulogenesis. Here, we demonstrate that Rap1 is required for nascent lumen formation and continuity in cultured 3D epithelial spheroids and in vivo in murine renal epithelial tubules derived from the nephrogenic mesenchyme, where its absence ultimately leads to severe morphogenetic defects in the tubules. By contrast, Rap1 is not required for lumen continuity or morphogenesis in renal tubules derived from the ureteric epithelium, which differ in that they form by extension from a pre-existing tubule. We further demonstrate that Rap1 is required for correct localization of Afadin to adherens junctions both in vitro and in vivo. Together, these results suggest a model in which Rap1 localizes Afadin to junctional complexes, which in turn regulates nascent lumen formation and positioning to ensure continuous tubulogenesis.

Rap1 organizes lymphocyte front-back polarity via RhoA signaling and talin1

Lymphocyte trafficking requires fine-tuning of chemokine-mediated cell migration. This process depends on cytoskeletal dynamics and polarity, but its regulation remains elusive. We quantitatively measured cell polarity and revealed critical roles performed by integrin activator Rap1 in this process, independent of substrate adhesion. Rap1-deficient naive T cells exhibited impaired abilities to reorganize the actin cytoskeleton into pseudopods and actomyosin-rich uropods. Rap1-GTPase activating proteins (GAPs), Rasa3 and Sipa1, maintained an unpolarized shape; deletion of these GAPs spontaneously induced cell polarization, indicative of the polarizing effect of Rap1. Rap1 activation required F-actin scaffolds, and stimulated RhoA activation and actomyosin contractility at the rear. Furthermore, talin1 acted on Rap1 downstream effectors to promote actomyosin contractility in the uropod, which occurred independently of substrate adhesion and talin1 binding to integrins. These findings indicate that Rap1 signaling to RhoA and talin1 regulates chemokine-stimulated lymphocyte polarization and chemotaxis in a manner independent of adhesion.

Monocyte-endothelial cell interactions in vascular and tissue remodeling

Monocytes are circulating leukocytes of innate immunity derived from the bone marrow that interact with endothelial cells under physiological or pathophysiological conditions to orchestrate inflammation, angiogenesis, or tissue remodeling. Monocytes are attracted by chemokines and specific receptors to precise areas in vessels or tissues and transdifferentiate into macrophages with tissue damage or infection. Adherent monocytes and infiltrated monocyte-derived macrophages locally release a myriad of cytokines, vasoactive agents, matrix metalloproteinases, and growth factors to induce vascular and tissue remodeling or for propagation of inflammatory responses. Infiltrated macrophages cooperate with tissue-resident macrophages during all the phases of tissue injury, repair, and regeneration. Substances released by infiltrated and resident macrophages serve not only to coordinate vessel and tissue growth but cellular interactions as well by attracting more circulating monocytes (e.g. MCP-1) and stimulating nearby endothelial cells (e.g. TNF-α) to expose monocyte adhesion molecules. Prolonged tissue accumulation and activation of infiltrated monocytes may result in alterations in extracellular matrix turnover, tissue functions, and vascular leakage. In this review, we highlight the link between interactions of infiltrating monocytes and endothelial cells to regulate vascular and tissue remodeling with a special focus on how these interactions contribute to pathophysiological conditions such as cardiovascular and chronic liver diseases.

Cardiovascular Functions of Ena/VASP Proteins: Past, Present and Beyond

Actin binding proteins are of crucial importance for the spatiotemporal regulation of actin cytoskeletal dynamics, thereby mediating a tremendous range of cellular processes. Since their initial discovery more than 30 years ago, the enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) family has evolved as one of the most fascinating and versatile family of actin regulating proteins. The proteins directly enhance actin filament assembly, but they also organize higher order actin networks and link kinase signaling pathways to actin filament assembly. Thereby, Ena/VASP proteins regulate dynamic cellular processes ranging from membrane protrusions and trafficking, and cell-cell and cell-matrix adhesions, to the generation of mechanical tension and contractile force. Important insights have been gained into the physiological functions of Ena/VASP proteins in platelets, leukocytes, endothelial cells, smooth muscle cells and cardiomyocytes. In this review, we summarize the unique and redundant functions of Ena/VASP proteins in cardiovascular cells and discuss the underlying molecular mechanisms.

Dynamic subcellular localization of DydA in Dictyostelium cells

DydA plays an important role in chemotaxis, development, and cell growth as an adaptor protein that connects Ras signaling and cytoskeletal rearrangement. DydA is a downstream effector of RasG and is involved in controlling cell polarity and pseudopodia formation during chemoattractant-directed cell migration. To understand the mechanism by which DydA functions on the cell migration, we investigated the dynamic subcellular localization of DydA in response to chemoattractant stimulation and found that DydA rapidly and transiently translocated to the cell cortex through the RA domain and the PRM region in DydA in response to chemoattractant stimulation. The PRM region appears to play a primary role in the translocation of DydA to the cell cortex and in its localization to the actin foci at the bottom of cells. Colocalization experiments of GFP-PRM with RFP-coronin indicated that GFP-PRM preceded GFP-coronin by 2-3 s in response to chemoattractant stimulation. These results suggest that the PRM region plays an indispensable role in relaying upstream regulators, such as RasG, to downstream effectors by mediating the localization of DydA to the cell cortex upon chemoattractant stimulation.

Myosin-X recruits lamellipodin to filopodia tips

Myosin-X (MYO10), a molecular motor localizing to filopodia, is thought to transport various cargo to filopodia tips, modulating filopodia function. However, only a few MYO10 cargoes have been described. Here, using GFP-Trap and BioID approaches combined with mass spectrometry, we identified lamellipodin (RAPH1) as a novel MYO10 cargo. We report that the FERM domain of MYO10 is required for RAPH1 localization and accumulation at filopodia tips. Previous studies have mapped the RAPH1 interaction domain for adhesome components to its talin-binding and Ras-association domains. Surprisingly, we find that the RAPH1 MYO10-binding site is not within these domains. Instead, it comprises a conserved helix located just after the RAPH1 pleckstrin homology domain with previously unknown functions. Functionally, RAPH1 supports MYO10 filopodia formation and stability but is not required to activate integrins at filopodia tips. Taken together, our data indicate a feed-forward mechanism whereby MYO10 filopodia are positively regulated by MYO10-mediated transport of RAPH1 to the filopodium tip.

PtdIns(3,4)P2, Lamellipodin, and VASP coordinate actin dynamics during phagocytosis in macrophages

Phosphoinositides are pivotal regulators of vesicular traffic and signaling during phagocytosis. Phagosome formation, the initial step of the process, is characterized by local membrane remodeling and reorganization of the actin cytoskeleton that leads to formation of the pseudopods that drive particle engulfment. Using genetically encoded fluorescent probes, we found that upon particle engagement a localized pool of PtdIns(3,4)P2 is generated by the sequential activities of class I phosphoinositide 3-kinases and phosphoinositide 5-phosphatases. Depletion of this locally generated pool of PtdIns(3,4)P2 blocks pseudopod progression and ultimately phagocytosis. We show that the PtdIns(3,4)P2 effector Lamellipodin (Lpd) is recruited to nascent phagosomes by PtdIns(3,4)P2. Furthermore, we show that silencing of Lpd inhibits phagocytosis and produces aberrant pseudopodia with disorganized actin filaments. Finally, vasodilator-stimulated phosphoprotein (VASP) was identified as a key actin-regulatory protein mediating phagosome formation downstream of Lpd. Mechanistically, our findings imply that a pathway involving PtdIns(3,4)P2, Lpd, and VASP mediates phagocytosis at the stage of particle engulfment.

Expression of the phagocytic receptors αMβ2 and αXβ2 is controlled by RIAM, VASP and Vinculin in neutrophil-differentiated HL-60 cells

Activation of the integrin phagocytic receptors CR3 (α_Mβ₂, CD11b/CD18) and CR4 (α_Xβ₂, CD11c/CD18) requires Rap1 activation and RIAM function. RIAM controls integrin activation by recruiting Talin to β₂ subunits, enabling the Talin-Vinculin interaction, which in term bridges integrins to the actin-cytoskeleton. RIAM also recruits VASP to phagocytic cups and facilitates VASP phosphorylation and function promoting particle internalization. Using a CRISPR-Cas9 knockout approach, we have analyzed the requirement for RIAM, VASP and Vinculin expression in neutrophilic-HL-60 cells. All knockout cells displayed abolished phagocytosis that was accompanied by a significant and specific reduction in ITGAM (α_M), ITGAX (α_X) and ITGB2 (β₂) mRNA, as revealed by RT-qPCR. RIAM, VASP and Vinculin KOs presented reduced cellular F-actin content that correlated with αM expression, as treatment with the actin filament polymerizing and stabilizing drug jasplakinolide, partially restored α_M expression. In general, the expression of α_X was less responsive to jasplakinolide treatment than α_M, indicating that regulatory mechanisms independent of F-actin content may be involved. The Serum Response Factor (SRF) was investigated as the potential transcription factor controlling α_Mβ₂ expression, since its coactivator MRTF-A requires actin polymerization to induce transcription. Immunofluorescent MRTF-A localization in parental cells was primarily nuclear, while in knockouts it exhibited a diffuse cytoplasmic pattern. Localization of FHL-2 (SRF corepressor) was mainly sub-membranous in parental HL-60 cells, but in knockouts the localization was disperse in the cytoplasm and the nucleus, suggesting RIAM, VASP and Vinculin are required to maintain FHL-2 close to cytoplasmic membranes, reducing its nuclear localization and inhibiting its corepressor activity. Finally, reexpression of VASP in the VASP knockout resulted in a complete reversion of the phenotype, as knock-ins restored α_M expression. Taken together, our results suggest that RIAM, VASP and Vinculin, are necessary for the correct expression of α_Mβ₂ and α_Xβ₂ during neutrophilic differentiation in the human promyelocytic HL-60 cell line, and strongly point to an involvement of these proteins in the acquisition of a phagocytic phenotype.

Hepatocyte Rap1a contributes to obesity- and statin-associated hyperglycemia

Excessive hepatic glucose production contributes to the development of hyperglycemia and is a key feature of type 2 diabetes. Here, we report that activation of hepatocyte Rap1a suppresses gluconeogenic gene expression and glucose production, whereas Rap1a silencing stimulates them. Rap1a activation is suppressed in obese mouse liver, and restoring its activity improves glucose intolerance. As Rap1a′s membrane localization and activation depends on its geranylgeranylation, which is inhibited by statins, we show that statin-treated hepatocytes and the human liver have lower active-Rap1a levels. Similar to Rap1a inhibition, statins stimulate hepatic gluconeogenesis and increase fasting blood glucose in obese mice. Geranylgeraniol treatment, which acts as the precursor for geranylgeranyl isoprenoids, restores Rap1a activity and improves statin-mediated glucose intolerance. Mechanistically, Rap1a activation induces actin polymerization, which suppresses gluconeogenesis by Akt-mediated FoxO1 inhibition. Thus, Rap1a regulates hepatic glucose homeostasis, and blocking its activity, via lowering geranylgeranyl isoprenoids, contributes to statin-induced glucose intolerance.

Wang et al. show that activation of hepatic Rap1a suppresses gluconeogenic gene expression and improves glucose intolerance via Akt-mediated FoxO1 inhibition. Statins lower intracellular isoprenoid levels and inhibit Rap1a activation, which contributes to their hyperglycemic effect. These findings identify a role of hepatic Rap1a in obesity- and statin-associated glucose homeostasis.

The complex role of tumor-infiltrating macrophages

Long recognized as an evolutionarily ancient cell type involved in tissue homeostasis and immune defense against pathogens, macrophages are being re-discovered as regulators of several diseases, including cancer. Tumor-associated macrophages (TAMs) represent the most abundant innate immune population in the tumor microenvironment (TME). Macrophages are professional phagocytic cells of the hematopoietic system specializing in the detection, phagocytosis and destruction of bacteria and other harmful micro-organisms, apoptotic cells and metabolic byproducts. In contrast to these healthy macrophage functions, TAMs support cancer cell growth and metastasis and mediate immunosuppressive effects on the adaptive immune cells of the TME. Cancer is one of the most potent insults on macrophage physiology, inducing changes that are intimately linked with disease progression. In this Review, we outline hallmarks of TAMs and discuss the emerging mechanisms that contribute to their pathophysiological adaptations and the vulnerabilities that provide attractive targets for therapeutic exploitation in cancer.

Adiposity associated DNA methylation signatures in adolescents are related to leptin and perinatal factors

Epigenetics links perinatal influences with later obesity. We identifed differentially methylated CpG (dmCpG) loci measured at 17 years associated with concurrent adiposity measures and examined whether these were associated with hsCRP, adipokines, and early life environmental factors. Genome-wide DNA methylation from 1192 Raine Study participants at 17 years, identified 29 dmCpGs (Bonferroni corrected p < 1.06E-07) associated with body mass index (BMI), 10 with waist circumference (WC) and 9 with subcutaneous fat thickness. DmCpGs within Ras Association (RalGDS/AF-6), Pleckstrin Homology Domains 1 (RAPH1), Musashi RNA-Binding Protein 2 (MSI2), and solute carrier family 25 member 10 (SLC25A10) are associated with both BMI and WC. Validation by pyrosequencing confirmed these associations and showed that MSI2 , SLC25A10 , and RAPH1 methylation was positively associated with serum leptin. These were  also associated with the early environment; MSI2 methylation (β = 0.81, p = 0.0004) was associated with pregnancy maternal smoking, SLC25A10 (CpG2 β = 0.12, p = 0.002) with pre- and early pregnancy BMI, and RAPH1 (β = -1.49, p = 0.036) with gestational weight gain. Adjusting for perinatal factors, methylation of the dmCpGs within MSI2, RAPH1, and SLC25A10 independently predicted BMI, accounting for 24% of variance. MSI2 methylation was additionally associated with BMI over time (17 years old β = 0.026, p = 0.0025; 20 years old β = 0.027, p = 0.0029) and between generations (mother β = 0.044, p = 7.5e-04). Overall findings suggest that DNA methylation in MSI2, RAPH1, and SLC25A10 in blood may be robust markers, mediating through early life factors.

Fine-tuning cell organelle dynamics during mitosis by small GTPases

During mitosis, the allocation of genetic material concurs with organelle transformation and distribution. The coordination of genetic material inheritance with organelle dynamics directs accurate mitotic progression, cell fate determination, and organismal homeostasis. Small GTPases belonging to the Ras superfamily regulate various cell organelles during division. Being the key regulators of membrane dynamics, the dysregulation of small GTPases is widely associated with cell organelle disruption in neoplastic and non-neoplastic diseases, such as cancer and Alzheimer's disease. Recent discoveries shed light on the molecular properties of small GTPases as sophisticated modulators of a remarkably complex and perfect adaptors for rapid structure reformation. This review collects current knowledge on small GTPases in the regulation of cell organelles during mitosis and highlights the mediator role of small GTPase in transducing cell cycle signaling to organelle dynamics during mitosis.

The Connection Between Rap1 and Talin1 in the Activation of Integrins in Blood Cells

Integrins regulate the adhesion and migration of blood cells to ensure the proper positioning of these cells in the environment. Integrins detect physical and chemical stimuli in the extracellular matrix and regulate signaling pathways in blood cells that mediate their functions. Integrins are usually in a resting state in blood cells until agonist stimulation results in a high-affinity conformation ("integrin activation"), which is central to integrins' contribution to blood cells' trafficking and functions. In this review, we summarize the mechanisms of integrin activation in blood cells with a focus on recent advances understanding of mechanisms whereby Rap1 regulates talin1-integrin interaction to trigger integrin activation in lymphocytes, platelets, and neutrophils.

LFA1 Activation: Insights from a Single-Molecule Approach

Integrin LFA1 is a cell adhesion receptor expressed exclusively in leukocytes, and plays crucial roles in lymphocyte trafficking, antigen recognition, and effector functions. Since the discovery that the adhesiveness of LFA1 can be dynamically changed upon stimulation, one challenge has been understanding how integrins are regulated by inside-out signaling coupled with macromolecular conformational changes, as well as ligand bindings that transduce signals from the extracellular domain to the cytoplasm in outside-in signaling. The small GTPase Rap1 and integrin adaptor proteins talin1 and kindlin-3 have been recognized as critical molecules for integrin activation. However, their cooperative regulation of integrin adhesiveness in lymphocytes requires further research. Recent advances in single-molecule imaging techniques have revealed dynamic molecular processes in real-time and provided insight into integrin activation in cellular environments. This review summarizes integrin regulation and discusses new findings regarding the bidirectionality of LFA1 activation and signaling processes in lymphocytes.

DNA Methylation in Noncancerous Liver Tissues as Biomarker for Multicentric Occurrence of Hepatitis C Virus-Related Hepatocellular Carcinoma

Background and Aims

Hepatitis C virus (HCV)-related hepatocellular carcinoma (HCC) progresses with a highly multicentric occurrence (MO) even after radical hepatectomy. Despite several efforts to clarify the pathogenesis of MO, the underlying molecular mechanism remains elusive. The aim of this study was to evaluate alterations in DNA methylation in noncancerous liver tissues in the MO of HCC.

Methods

A total of 203 patients with HCV-related HCC who underwent radical hepatectomy at our hospital between January 2008 and January 2012 were recruited. We defined a group of nonearly recurrence of HCC (NR) for ≥3 years after radical hepatectomy and a group of early recurrence of HCC (ER) with MO within 2 years after radical hepatectomy.

Results

Three patients each were selected in the NR and ER groups in the first set, and 13 patients in the NR group and 17 patients in the ER group were selected in the second set. Genome-wide DNA methylation profiles were obtained from noncancerous liver tissues using a Human Methylation 450 BeadChip, and the differences between the groups were analyzed for each set. After excluding single nucleotide polymorphism-associated methylation sites and low-call sites, 401,282 sites were assessed using a generalized linear model without any adjustments. Nine gene regions, APBB1P, CLSTN3, DLG5, IRX5, OAS1, SOX12, SNX19, TENM2, and TRIM54, exhibiting a significant difference (P < .001) in DNA methylation levels were identified in the common direction between the 2 analysis sets.

Conclusion

Alterations in DNA methylation of 9 genes in noncancerous liver tissues appear to be involved in MO after radical hepatectomy for HCV-related HCC.

Application of piconewton forces to individual filopodia reveals mechanosensory role of L-type Ca2+ channels

Filopodia are ubiquitous membrane projections that play crucial role in guiding cell migration on rigid substrates and through extracellular matrix by utilizing yet unknown mechanosensing molecular pathways. As recent studies show that Ca²⁺ channels localized to filopodia play an important role in regulation of their formation and since some Ca²⁺ channels are known to be mechanosensitive, force-dependent activity of filopodial Ca²⁺ channels might be linked to filopodia's mechanosensing function. We tested this hypothesis by monitoring changes in the intra-filopodial Ca²⁺ level in response to application of stretching force to individual filopodia of several cell types using optical tweezers. Results show that stretching forces of tens of pN strongly promote Ca²⁺ influx into filopodia, causing persistent Ca²⁺ oscillations that last for minutes even after the force is released. Several known mechanosensitive Ca²⁺ channels, such as Piezo 1, Piezo 2 and TRPV4, were found to be dispensable for the observed force-dependent Ca²⁺ influx, while L-type Ca²⁺ channels appear to be a key player in the discovered phenomenon. As previous studies have shown that intra-filopodial transient Ca²⁺ signals play an important role in guidance of cell migration, our results suggest that the force-dependent activation of L-type Ca²⁺ channels may contribute to this process. Overall, our study reveals an intricate interplay between mechanical forces and Ca²⁺ signaling in filopodia, providing novel mechanistic insights for the force-dependent filopodia functions in guidance of cell migration.

Direct Binding of Rap1 to Talin1 and to MRL Proteins Promotes Integrin Activation in CD4+ T Cells

Agonist-induced Rap1 GTP loading results in integrin activation involved in T cell trafficking and functions. MRL proteins Rap1-interacting adapter molecule (RIAM) and lamellipodin (LPD) are Rap1 effectors that can recruit talin1 to integrins, resulting in integrin activation. Recent work also implicates direct Rap1-talin1 interaction in integrin activation. Here, we analyze in mice the connections between Rap1 and talin1 that support integrin activation in conventional CD4+ T (Tconv) and CD25HiFoxp3+CD4+ regulatory T (Treg) cells. Talin1(R35E, R118E) mutation that disrupts both Rap1 binding sites results in a partial defect in αLβ2, α4β1, and α4β7 integrin activation in both Tconv and Treg cells with resulting defects in T cell homing. Talin1(R35E,R118E) Tconv manifested reduced capacity to induce colitis in an adoptive transfer mouse model. Loss of RIAM exacerbates the defects in Treg cell function caused by the talin1(R35E,R118E) mutation, and deleting both MRL proteins in combination with talin1(R35E,R118E) phenocopy the complete lack of integrin activation observed in Rap1a/b-null Treg cells. In sum, these data reveal the functionally significant connections between Rap1 and talin1 that enable αLβ2, α4β1, and α4β7 integrin activation in CD4+ T cells.

Ena/VASP proteins in cell edge protrusion, migration and adhesion

The tightly coordinated, spatiotemporal control of actin filament remodeling provides the basis of fundamental cellular processes, such as cell migration and adhesion. Specific protein assemblies, composed of various actin-binding proteins, are thought to operate in these processes to nucleate and elongate new filaments, arrange them into complex three-dimensional (3D) arrays and recycle them to replenish the actin monomer pool. Actin filament assembly is not only necessary to generate pushing forces against the leading edge membrane or to propel pathogens through the cytoplasm, but also coincides with the generation of stress fibers (SFs) and focal adhesions (FAs) that generate, transmit and sense mechanical tension. The only protein families known to date that directly enhance the elongation of actin filaments are formins and the family of Ena/VASP proteins. Their mechanisms of action, however, in enhancing processive filament elongation are distinct. The aim of this Review is to summarize our current knowledge on the molecular mechanisms of Ena/VASP-mediated actin filament assembly, and to discuss recent insights into the cell biological functions of Ena/VASP proteins in cell edge protrusion, migration and adhesion.

Avian Hepatitis E Virus ORF2 Protein Interacts with Rap1b to Induce Cytoskeleton Rearrangement That Facilitates Virus Internalization

Avian hepatitis E virus (HEV) causes liver diseases and multiple extrahepatic disorders in chickens. However, the mechanisms involved in avian HEV entry remain elusive. Herein, we identified the RAS-related protein 1b (Rap1b) as a potential HEV-ORF2 protein interacting candidate. Experimental infection of chickens and cells with an avian HEV isolate from China (CaHEV) led to upregulated expression and activation of Rap1b both in vivo and in vitro. By using CaHEV capsid as mimic of virion to treat cell in vitro, it appears that the interaction between the viral capsid and Rap1b promoted cell membrane recruitment of the downstream effector Rap1-interacting molecule (RIAM). In turn, RIAM further enhanced Talin-1 membrane recruitment and retention, which led to the activation of integrin α5/β1, as well as integrin-associated membrane protein kinases, including focal adhesion kinase (FAK). Meanwhile, FAK activation triggered activation of downstream signaling molecules, such as Ras-related C3 botulinum toxin substrate 1 RAC1 cell division cycle 42 (CDC42), p21-activated kinase 1 (PAK1), and LIM domain kinase 1 (LIMK1). Finally, F-actin rearrangement induced by Cofilin led to the formation of lamellipodia, filopodia, and stress fibers, contributes to plasma membrane remodeling, and might enhance CaHEV virion internalization. In conclusion, our data suggested that Rap1b activation was triggered during CaHEV infection and appeared to require interaction between CaHEV-ORF2 and Rap1b, thereby further inducing membrane recruitment of Talin-1. Membrane-bound Talin-1 then activates key Integrin-FAK-Cofilin cascades involved in modulation of actin kinetics, and finally leads to F-actin rearrangement and membrane remodeling to potentially facilitate internalization of CaHEV virions into permissive cells. IMPORTANCE Rap1b is a multifunctional protein that is responsible for cell adhesion, growth, and differentiation. The inactive form of Rap1b is phosphorylated and distributed in the cytoplasm, while active Rap1b is prenylated and loaded with GTP to the cell membrane. In this study, the activation of Rap1b was induced during the early stage of avian HEV infection under the regulation of PKA and SmgGDS. Continuously activated Rap1b recruited its effector RIAM to the membrane, thereby inducing the membrane recruitment of Talin-1 that led to the activation of membrane α5/β1 integrins. The triggering of the signaling pathway-associated Integrin α5/β1-FAK-CDC42&RAC1-PAK1-LIMK1-Cofilin culminated in F-actin polymerization and membrane remodeling that might promote avian HEV virion internalization. These findings suggested a novel mechanism that is potentially utilized by avian HEV to invade susceptible cells.

Transcription factor regulation of eQTL activity across individuals and tissues

Tens of thousands of genetic variants associated with gene expression (cis-eQTLs) have been discovered in the human population. These eQTLs are active in various tissues and contexts, but the molecular mechanisms of eQTL variability are poorly understood, hindering our understanding of genetic regulation across biological contexts. Since many eQTLs are believed to act by altering transcription factor (TF) binding affinity, we hypothesized that analyzing eQTL effect size as a function of TF level may allow discovery of mechanisms of eQTL variability. Using GTEx Consortium eQTL data from 49 tissues, we analyzed the interaction between eQTL effect size and TF level across tissues and across individuals within specific tissues and generated a list of 10,098 TF-eQTL interactions across 2,136 genes that are supported by at least two lines of evidence. These TF-eQTLs were enriched for various TF binding measures, supporting with orthogonal evidence that these eQTLs are regulated by the implicated TFs. We also found that our TF-eQTLs tend to overlap genes with gene-by-environment regulatory effects and to colocalize with GWAS loci, implying that our approach can help to elucidate mechanisms of context-specificity and trait associations. Finally, we highlight an interesting example of IKZF1 TF regulation of an APBB1IP gene eQTL that colocalizes with a GWAS signal for blood cell traits. Together, our findings provide candidate TF mechanisms for a large number of eQTLs and offer a generalizable approach for researchers to discover TF regulators of genetic variant effects in additional QTL datasets.

Proteomic Landscape of Adeno-Associated Virus (AAV)-Producing HEK293 Cells

Adeno-associated viral (AAV) vectors are widely used for gene therapy, providing treatment for diseases caused by absent or defective genes. Despite the success of gene therapy, AAV manufacturing is still challenging, with production yields being limited. With increased patient demand, improvements in host cell productivity through various engineering strategies will be necessary. Here, we study the host cell proteome of AAV5-producing HEK293 cells using reversed phase nano-liquid chromatography and tandem mass spectrometry (RPLC-MS/MS). Relative label-free quantitation (LFQ) was performed, allowing a comparison of transfected vs. untransfected cells. Gene ontology enrichment and pathway analysis revealed differential expression of proteins involved in fundamental cellular processes such as metabolism, proliferation, and cell death. Furthermore, changes in expression of proteins involved in endocytosis and lysosomal degradation were observed. Our data provides highly valuable insights into cellular mechanisms involved during recombinant AAV production by HEK293 cells, thus potentially enabling further improvements of gene therapy product manufacturing.

Structural, biochemical, and functional properties of the Rap1-Interacting Adaptor Molecule (RIAM)

Leukocytes, the leading players of immune system, are involved in innate and adaptive immune responses. Leukocyte adhesion to endothelial cells during transmigration or to antigen presenting cells during T cell activation, requires integrin activation through a process termed inside-out integrin signaling. In hematopoietic cells, Rap1 and its downstream effector RIAM (Rap1-interacting adaptor molecule) form a cornerstone for inside-out integrin activation. The Rap1/RIAM pathway is involved in signal integration for activation, actin remodeling and cytoskeletal reorganization in T cells, as well as in myeloid cell differentiation and function. RIAM is instrumental for phagocytosis, a process requiring particle recognition, cytoskeletal remodeling and membrane protrusion for engulfment and digestion. In the present review, we discuss the structural and molecular properties of RIAM and the recent discoveries regarding the functional role of the Rap1/RIAM module in hematopoietic cells.

PI3K in T Cell Adhesion and Trafficking

PI3K signalling is required for activation, differentiation, and trafficking of T cells. PI3Kδ, the dominant PI3K isoform in T cells, has been extensively characterised using PI3Kδ mutant mouse models and PI3K inhibitors. Furthermore, characterisation of patients with Activated PI3K Delta Syndrome (APDS) and mouse models with hyperactive PI3Kδ have shed light on how increased PI3Kδ activity affects T cell functions. An important function of PI3Kδ is that it acts downstream of TCR stimulation to activate the major T cell integrin, LFA-1, which controls transendothelial migration of T cells as well as their interaction with antigen-presenting cells. PI3Kδ also suppresses the cell surface expression of CD62L and CCR7 which controls the migration of T cells across high endothelial venules in the lymph nodes and S1PR1 which controls lymph node egress. Therefore, PI3Kδ can control both entry and exit of T cells from lymph nodes as well as the recruitment to and retention of T cells within inflamed tissues. This review will focus on the regulation of adhesion receptors by PI3Kδ and how this contributes to T cell trafficking and localisation. These findings are relevant for our understanding of how PI3Kδ inhibitors may affect T cell redistribution and function.

Binding of Rap1 and Riam to Talin1 Fine-Tune β2 Integrin Activity During Leukocyte Trafficking

β2 integrins mediate key processes during leukocyte trafficking. Upon leukocyte activation, the structurally bent β2 integrins change their conformation towards an extended, intermediate and eventually high affinity conformation, which mediate slow leukocyte rolling and firm arrest, respectively. Translocation of talin1 to integrin adhesion sites by interactions with the small GTPase Rap1 and the Rap1 effector Riam precede these processes. Using Rap1 binding mutant talin1 and Riam deficient mice we show a strong Riam-dependent T cell homing process to lymph nodes in adoptive transfer experiments and by intravital microscopy. Moreover, neutrophils from compound mutant mice exhibit strongly increased rolling velocities to inflamed cremaster muscle venules compared to single mutants. Using Hoxb8 cell derived neutrophils generated from the mutant mouse strains, we show that both pathways regulate leukocyte rolling and adhesion synergistically by inducing conformational changes of the β2 integrin ectodomain. Importantly, a simultaneous loss of both pathways results in a rolling phenotype similar to talin1 deficient neutrophils suggesting that β2 integrin regulation primarily occurs via these two pathways.

The Multiple Roles of the Cytosolic Adapter Proteins ADAP, SKAP1 and SKAP2 for TCR/CD3 -Mediated Signaling Events

T cells are the key players of the adaptive immune response. They coordinate the activation of other immune cells and kill malignant and virus-infected cells. For full activation T cells require at least two signals. Signal 1 is induced after recognition of MHC/peptide complexes presented on antigen presenting cells (APCs) by the clonotypic TCR (T-cell receptor)/CD3 complex whereas Signal 2 is mediated via the co-stimulatory receptor CD28, which binds to CD80/CD86 molecules that are present on APCs. These signaling events control the activation, proliferation and differentiation of T cells. In addition, triggering of the TCR/CD3 complex induces the activation of the integrin LFA-1 (leukocyte function associated antigen 1) leading to increased ligand binding (affinity regulation) and LFA-1 clustering (avidity regulation). This process is termed "inside-out signaling". Subsequently, ligand bound LFA-1 transmits a signal into the T cells ("outside-in signaling") which enhances T-cell interaction with APCs (adhesion), T-cell activation and T-cell proliferation. After triggering of signal transducing receptors, adapter proteins organize the proper processing of membrane proximal and intracellular signals as well as the activation of downstream effector molecules. Adapter proteins are molecules that lack enzymatic or transcriptional activity and are composed of protein-protein and protein-lipid interacting domains/motifs. They organize and assemble macromolecular complexes (signalosomes) in space and time. Here, we review recent findings regarding three cytosolic adapter proteins, ADAP (Adhesion and Degranulation-promoting Adapter Protein), SKAP1 and SKAP2 (Src Kinase Associated Protein 1 and 2) with respect to their role in TCR/CD3-mediated activation, proliferation and integrin regulation.

Mechanosensitive expression of lamellipodin promotes intracellular stiffness, cyclin expression and cell proliferation

Cell cycle control is a key aspect of numerous physiological and pathological processes. The contribution of biophysical cues, such as stiffness or elasticity of the underlying extracellular matrix (ECM), is critically important in regulating cell cycle progression and proliferation. Indeed, increased ECM stiffness causes aberrant cell cycle progression and proliferation. However, the molecular mechanisms that control these stiffness-mediated cellular responses remain unclear. Here, we address this gap and show good evidence that lamellipodin (symbol RAPH1), previously known as a critical regulator of cell migration, stimulates ECM stiffness-mediated cyclin expression and intracellular stiffening in mouse embryonic fibroblasts. We observed that increased ECM stiffness upregulates lamellipodin expression. This is mediated by an integrin-dependent FAK-Cas-Rac signaling module and supports stiffness-mediated lamellipodin induction. Mechanistically, we find that lamellipodin overexpression increased, and lamellipodin knockdown reduced, stiffness-induced cell cyclin expression and cell proliferation, and intracellular stiffness. Overall, these results suggest that lamellipodin levels may be critical for regulating cell proliferation. This article has an associated First Person interview with the first author of the paper.

Src-mediated phosphorylation of RIAM promotes integrin activation

In this issue of Structure, Cho et al. (2020) identified an intermolecular interaction between two RIAM pleckstrin homology (PH) domains that masks the phosphoinositide-binding site, and that phosphorylation by Src unmasks the PH domain. This provides an explanation of how RIAM plasma membrane translocation is regulated to promote integrin activation.

PLEK2 promotes osteosarcoma tumorigenesis and metastasis by activating the PI3K/AKT signaling pathway

Increasing evidence suggest that pleckstrin-2 (PLEK2) acts as an oncogene in several malignancies. The present study aimed to investigate the effects of PLEK2 on osteosarcoma (OS) tumorigenesis and metastasis. PLEK2 expression in OS was analyzed via bioinformatics, reverse transcription-quantitative PCR, western blot and immunohistochemistry analyses. The Cell Counting Kit-8 (CCK-8), colony formation and EdU assays were performed to assess the role of PLEK2 in OS cell proliferation. The pro-metastatic effects of PLEK2 were assessed via the Transwell and wound healing assays. In addition, the PLEK2 downstream pathway was analyzed via bioinformatics analysis and verified via western blot analysis. The results demonstrated that PLEK2 expression was upregulated in both OS cell lines and specimens. The results of the CCK-8, colony formation and EdU assays demonstrated that PLEK2 promoted OS cell proliferation in vitro. The in vivo experiments further demonstrated that PLEK2 knockdown significantly suppressed OS growth. In addition, the Transwell and wound healing assays indicated that PLEK2 promoted OS invasiveness in vitro, which was induced by the activation of the epithelial-to-mesenchymal transition process. Bioinformatics analysis revealed that PLEK2 can activate the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mechanistic target of rapamycin (mTOR) pathway, which was verified via western blot analysis. Taken together, the results of the present study suggest that PLEK2 may play a tumor-promoting role in OS via the PI3K/AKT signaling pathway.

The role of profilin-1 in cardiovascular diseases

Dynamic remodeling of the actin cytoskeleton is an essential feature for virtually all actin-dependent cellular processes, including cell migration, cell cycle progression, chromatin remodeling and gene expression, and even the DNA damage response. An altered actin cytoskeleton is a structural hallmark associated with numerous pathologies ranging from cardiovascular diseases to immune disorders, neurological diseases and cancer. The actin cytoskeleton in cells is regulated through the orchestrated actions of a myriad of actin-binding proteins. In this Review, we provide a brief overview of the structure and functions of the actin-monomer-binding protein profilin-1 (Pfn1) and then discuss how dysregulated expression of Pfn1 contributes to diseases associated with the cardiovascular system.

Functional Mapping of Adhesiveness on Live Cells Reveals How Guidance Phenotypes Can Emerge From Complex Spatiotemporal Integrin Regulation

Immune cells have the ubiquitous capability to migrate disregarding the adhesion properties of the environment, which requires a versatile adaptation of their adhesiveness mediated by integrins, a family of specialized adhesion proteins. Each subtype of integrins has several ligands and several affinity states controlled by internal and external stimuli. However, probing cell adhesion properties on live cells without perturbing cell motility is highly challenging, especially in vivo. Here, we developed a novel in vitro method using micron-size beads pulled by flow to functionally probe the local surface adhesiveness of live and motile cells. This method allowed a functional mapping of the adhesiveness mediated by VLA-4 and LFA-1 integrins on the trailing and leading edges of live human T lymphocytes. We show that cell polarization processes enhance integrin-mediated adhesiveness toward cell rear for VLA-4 and cell front for LFA-1. Furthermore, an inhibiting crosstalk of LFA-1 toward VLA-4 and an activating crosstalk of VLA-4 toward LFA-1 were found to modulate cell adhesiveness with a long-distance effect across the cell. These combined signaling processes directly support the bistable model that explains the emergence of the versatile guidance of lymphocyte under flow. Molecularly, Sharpin, an LFA-1 inhibitor in lymphocyte uropod, was found involved in the LFA-1 deadhesion of lymphocytes; however, both Sharpin and Myosin inhibition had a rather modest impact on adhesiveness. Quantitative 3D immunostaining identified high-affinity LFA-1 and VLA-4 densities at around 50 and 100 molecules/μm² in basal adherent zones, respectively. Interestingly, a latent adhesiveness of dorsal zones was not grasped by immunostaining but assessed by direct functional assays with beads. The combination of live functional assays, molecular imaging, and genome editing is instrumental to characterizing the spatiotemporal regulation of integrin-mediated adhesiveness at molecular and cell scales, which opens a new perspective to decipher sophisticated phenotypes of motility and guidance.

The Activation and Regulation of β2 Integrins in Phagocytes and Phagocytosis

Phagocytes, which include neutrophils, monocytes, macrophages, and dendritic cells, protect the body by removing foreign particles, bacteria, and dead or dying cells. Phagocytic integrins are greatly involved in the recognition of and adhesion to specific antigens on cells and pathogens during phagocytosis as well as the recruitment of immune cells. β2 integrins, including αLβ2, αMβ2, αXβ2, and αDβ2, are the major integrins presented on the phagocyte surface. The activation of β2 integrins is essential to the recruitment and phagocytic function of these phagocytes and is critical for the regulation of inflammation and immune defense. However, aberrant activation of β2 integrins aggravates auto-immune diseases, such as psoriasis, arthritis, and multiple sclerosis, and facilitates tumor metastasis, making them double-edged swords as candidates for therapeutic intervention. Therefore, precise regulation of phagocyte activities by targeting β2 integrins should promote their host defense functions with minimal side effects on other cells. Here, we reviewed advances in the regulatory mechanisms underlying β2 integrin inside-out signaling, as well as the roles of β2 integrin activation in phagocyte functions.

Role of FAT1 in health and disease

FAT atypical cadherin 1 (FAT1), which encodes a protocadherin, is one of the most frequently mutated genes in human cancer. Over the past 20 years, the role of FAT1 in tissue growth and in the development of diseases has been extensively studied. There is definitive evidence that FAT1 serves a substantial role in the maintenance of organs and development, and its expression appears to be tissue-specific. FAT1 activates a variety of signaling pathways through protein-protein interactions, including the Wnt/β-catenin, Hippo and MAPK/ERK signaling pathways, which affect cell proliferation, migration and invasion. Abnormal FAT1 expression may lead to the development of tumors and may affect prognosis. Therefore, FAT1 may have potential in tumor therapy. The structural and functional changes mediated by FAT1, its tissue distribution and changes in FAT1 expression in human diseases are described in the present review, which provides further insight for understanding the role of FAT1 in development and disease.

Identification of prognostic biomarkers associated with metastasis and immune infiltration in osteosarcoma

Osteosarcoma is the most common primary malignancy of the bones, and is associated with a high rate of metastasis and a poor prognosis. A tight association between the tumor microenvironment (TME) and osteosarcoma metastasis has been established. In the present study, the Estimation of STromal and Immune cells in MAlignant Tumor tissues using Expression data (ESTIMATE) algorithm was applied to calculate the immune and stromal scores of patients with osteosarcoma based on data from The Cancer Genome Atlas database. A metagene approach and deconvolution method were used to reveal distinct TME landscapes in patients with osteosarcoma. Bioinformatics analysis was used to identify differentially expressed genes (DEGs) associated with metastasis and immune infiltration in osteosarcoma, and a risk model was constructed using the DEGs with potential prognostic significance. Subsequently, gene set enrichment and Spearman's correlation analyses were used to delineate the biological processes associated with these prognostic biomarkers. Finally, immunohistochemical (IHC) analysis was performed to evaluate the expression levels of immune infiltrates and prognostic biomarkers in clinical osteosarcoma tissues. The results of the ESTIMATE demonstrated that patients with non-metastatic osteosarcoma presented with higher immune/stromal scores and a more favorable prognosis compared with those with metastatic osteosarcoma. The TME landscapes in patients with osteosarcoma suggested that high levels of tumor-infiltrating immune cells (TIICs) may suppress metastasis. Increased numbers of CD56bright natural killer cells, immature B cells, M1 macrophages and neutrophils, and lower levels of M2 macrophages were observed in the non-metastatic tissues compared with those in the metastatic tissues. A total of 69 DEGs were identified to be associated with metastasis and immune infiltration in osteosarcoma. Of these, GATA3, LPAR5, EVI2B, RIAM and CFH exhibited prognostic potential and were highly expressed in non-metastatic osteosarcoma tissues based on the IHC analysis results. These biomarkers were involved in various immune-related biological processes and were positively associated with multiple TIICs and immune signatures. The risk model constructed using these prognostic biomarkers demonstrated high predictive accuracy for the prognosis of osteosarcoma. In conclusion, the present study proposed a five-biomarker prognostic signature for the prediction of metastasis and immune infiltration in patients with osteosarcoma.

Molecular Response in Intestinal and Immune Tissues to in Ovo Administration of Inulin and the Combination of Inulin and Lactobacillus lactis Subsp. cremoris

Intestinal microbiota are a key factor in maintaining good health and production results in chickens. They play an important role in the stimulation of immune responses, as well as in metabolic processes and nutrient digestion. Bioactive substances such as prebiotics, probiotics, or a combination of the two (synbiotic) can effectively stimulate intestinal microbiota and therefore replace antibiotic growth promoters. Intestinal microbiota might be stimulated at the early stage of embryo development in ovo. The aim of the study was to analyze the expression of genes related to energy metabolism and immune response after the administration of inulin and a synbiotic, in which lactic acid bacteria were combined with inulin in the intestines and immune tissues of chicken broilers. The experiment was performed on male broiler chickens. Eggs were incubated for 21 days in a commercial hatchery. On day 12 of egg incubation, inulin as a prebiotic and inulin with Lactobacillus lactis subsp. cremoris as a synbiotic were delivered to the egg chamber. The control group was injected with physiological saline. On day 35 post-hatching, birds from each group were randomly selected and sacrificed. Tissues (spleen, cecal tonsils, and large intestine) were collected and intended for RNA isolation. The gene panel (ABCG8, HNF4A, ACOX2, APBB1IP, BRSK2, APOA1, and IRS2) was selected based on the microarray dataset and biological functions of genes related to the energy metabolism and immune responses. Isolated RNA was analyzed using the RT-qPCR method, and the relative gene expression was calculated. In our experiment, distinct effects of prebiotics and synbiotics following in ovo delivery were manifested in all analyzed tissues, with the lowest number of genes with altered expression shown in the large intestines of broilers. The results demonstrated that prebiotics or synbiotics provide a potent stimulation of gene expression in the spleen and cecal tonsils of broiler chickens. The overall number of gene expression levels and the magnitude of their changes in the spleen and cecal tonsils were higher in the group of synbiotic chickens compared to the prebiotic group.

Immunological Role and Prognostic Value of APBB1IP in Pan-Cancer Analysis

Objective: APBB1IP is a Rap1-binding protein that mainly acts as a regulator of leukocyte recruitment and pathogen clearance through complement-mediated phagocytosis. However, the role of APBB1IP in tumor immunity remains unclear. This study was carried out to evaluate the prognostic landscape of APBB1IP in pan-cancer analysis and investigate the relationship between APBB1IP expression and immune infiltration. Methods: We explored the expression pattern and prognostic value of APBB1IP in pan-cancer analysis through Kaplan-Meier Plotter and multiple databases, including TCGA, Oncomine. We then assessed the correlation between APBB1IP expression and immune cell infiltration using the TIMER database. Furthermore, we identified the proteins that interact with APBB1IP and performed epigenetic and transcriptional analyses. Multivariate Cox regression analyses were applied to construct a prognostic model, which consisted of APBB1IP and its interacting proteins, based on the lung cancer cohorts from the Gene Expression Omnibus (GEO) database. Results: The expression of APBB1IP was correlated with the prognosis of several types of cancer. APBB1IP upregulation was found to be associated with increased immune cell infiltration, especially for CD8+ T cells, natural killer (NK) cells, and immune regulators. A link was found between APBB1IP and immune-related proteins including RAP1A/B, TLN1/2 and VCL in the interaction network. Conclusion: APBB1IP can serve as a prognostic biomarker in pan-cancer analysis. APBB1IP upregulation was correlated with increased immune-cell infiltration, and the expression APBB1IP in different tumors might be related to the tumor immune microenvironment.