Rac GTPase Activating Protein ARHGAP25 Regulates Leukocyte Transendothelial Migration in Mice

Neutrophil-specific interactome of ARHGAP25 reveals novel partners and regulatory insights

ARHGAP25, a crucial molecule in immunological processes, serves as a Rac-specific GTPase-activating protein. Its role in cell migration and phagocyte functions, affecting the outcome of complex immunological diseases such as rheumatoid arthritis, renders it a promising target for drug research. Despite its importance, our knowledge of its intracellular interactions is still limited. This study employed proteomic analysis of glutathione S-transferase (GST)-tag pulldowns and co-immunoprecipitation from neutrophilic granulocyte cell lysate, revealing 76 candidates for potential physical interactions that complement ARHGAP25's known profile. Notably, four small GTPases (RAC2, RHOG, ARF4, and RAB27A) exhibited high affinity for ARHGAP25. The ARHGAP25-RAC2 and ARHGAP25-RHOG interactions appeared to be affected by the activation state of the small GTPases, suggesting a GTP-GDP cycle-dependent interaction. In silico dimer prediction pinpointed ARHGAP25's GAP domain as a credible binding interface, suggesting its suitability for GTP hydrolysis. Additionally, a list of Fc receptor-related kinases, phosphatases, and three of the 14-3-3 members were identified as potential partners, with in silico predictions highlighting eight binding sites, presenting novel insight on a potential regulatory mechanism for ARHGAP25.

The expression and clinical significance of ARHGAP25 in osteosarcoma based on bioinformatics analysis

ARHGAP25, a member of the ARHGAP family, encodes a negative regulator of Rho-GTPase that is important for actin remodeling, cell polarity, and cell migration. ARHGAP25 is down-regulated in a variety of solid tumors and promotes cancer cell growth, migration, and invasion. However, nothing is understood about ARHGAP25's biological function in osteosarcoma. This work used qPCR and WB to confirm the expression of ARHGAP25 in osteosarcoma following the initial analysis of its expression in pan-cancer. For GO and KEGG analysis, we have chosen 300 genes from the TARGET osteosarcoma data that had the strongest positive correlation with ARHGAP25, and we created nomogram and calibration charts. We simultaneously overexpressed ARHGAP25 in osteosarcoma cells to examine its impact on apoptosis and proliferation. By using MSP, we determined their methylation status in osteosarcoma cells and normal bone cells. We observed that ARHGAP25 was significantly downregulated in a range of malignancies, including osteosarcoma, and was associated with poor patient outcomes. The decrease of ARHGAP25 expression in osteosarcoma is related to DNA methylation. Overexpression of ARHGAP25 induced apoptosis and inhibited the proliferation of osteosarcoma cells in vitro. In addition, ARHGAP25 is also associated with immune-related pathways in osteosarcoma. These findings suggest that ARHGAP25 is a valuable prognostic biomarker in osteosarcoma patients.

Multi-omic integration reveals alterations in nasal mucosal biology that mediate air pollutant effects on allergic rhinitis

BACKGROUND

Allergic rhinitis is a common inflammatory condition of the nasal mucosa that imposes a considerable health burden. Air pollution has been observed to increase the risk of developing allergic rhinitis. We addressed the hypotheses that early life exposure to air toxics is associated with developing allergic rhinitis, and that these effects are mediated by DNA methylation and gene expression in the nasal mucosa.

METHODS

In a case-control cohort of 505 participants, we geocoded participants' early life exposure to air toxics using data from the US Environmental Protection Agency, assessed physician diagnosis of allergic rhinitis by questionnaire, and collected nasal brushings for whole-genome DNA methylation and transcriptome profiling. We then performed a series of analyses including differential expression, Mendelian randomization, and causal mediation analyses to characterize relationships between early life air toxics, nasal DNA methylation, nasal gene expression, and allergic rhinitis.

RESULTS

Among the 505 participants, 275 had allergic rhinitis. The mean age of the participants was 16.4 years (standard deviation = 9.5 years). Early life exposure to air toxics such as acrylic acid, phosphine, antimony compounds, and benzyl chloride was associated with developing allergic rhinitis. These air toxics exerted their effects by altering the nasal DNA methylation and nasal gene expression levels of genes involved in respiratory ciliary function, mast cell activation, pro-inflammatory TGF-β1 signaling, and the regulation of myeloid immune cell function.

CONCLUSIONS

Our results expand the range of air pollutants implicated in allergic rhinitis and shed light on their underlying biological mechanisms in nasal mucosa.

Lacking ARHGAP25 mitigates the symptoms of autoantibody-induced arthritis in mice

Objective

Despite intensive research on rheumatoid arthritis, the pathomechanism of the disease is still not fully understood and the treatment has not been completely resolved. Previously we demonstrated that the GTPase-activating protein, ARHGAP25 has a crucial role in the regulation of basic phagocyte functions. Here we investigate the role of ARHGAP25 in the complex inflammatory process of autoantibody-induced arthritis.

Methods

Wild-type and ARHGAP25 deficient (KO) mice on a C57BL/6 background, as well as bone marrow chimeric mice, were treated i.p. with the K/BxN arthritogenic or control serum, and the severity of inflammation and pain-related behavior was measured. Histology was prepared, leukocyte infiltration, cytokine production, myeloperoxidase activity, and superoxide production were determined, and comprehensive western blot analysis was conducted.

Results

In the absence of ARHGAP25, the severity of inflammation, joint destruction, and mechanical hyperalgesia significantly decreased, similarly to phagocyte infiltration, IL-1β, and MIP-2 levels in the tibiotarsal joint, whereas superoxide production or myeloperoxidase activity was unchanged. We observed a significantly mitigated phenotype in KO bone marrow chimeras as well. In addition, fibroblast-like synoviocytes showed comparable expression of ARHGAP25 to neutrophils. Significantly reduced ERK1/2, MAPK, and I-κB protein signals were detected in the arthritic KO mouse ankles.

Conclusion

Our findings suggest that ARHGAP25 has a key role in the pathomechanism of autoantibody-induced arthritis in which it regulates inflammation via the I-κB/NF-κB/IL-1β axis with the involvement of both immune cells and fibroblast-like synoviocytes.

A novel BRET-Based GAP assay reveals phosphorylation-dependent regulation of the RAC-specific GTPase activating protein ARHGAP25

ARHGAP25, a RAC-specific GTPase activating protein (GAP), is an essential regulator of phagocyte effector functions such as phagocytosis, superoxide production, and transendothelial migration. Furthermore, its complex role in tumor behavior has recently been recognized. We previously demonstrated that phosphorylation of serine 363 in ARHGAP25 regulates hematopoietic stem cells and progenitor cells in mouse bone marrow. However, the significance of other potential phosphorylation sites of ARHGAP25 remained unknown. Now, we developed a novel, real-time bioluminescence resonance energy transfer (BRET) assay to monitor the GAP activity of ARHGAP25 in vitro. Using this approach, we revealed that phosphorylation of S363 and S488, but not that of S379-380, controls ARHGAP25's RACGAP activity. On the other hand, we found in granulocyte-differentiated human PLB-985 cells that superoxide production and actin depolymerization are regulated by residues S363 and S379-380. The present data demonstrate the value of our BRET-GAP assay and show that different phosphorylation patterns regulate ARHGAP25's GAP activity and its effect on superoxide production and phagocytosis.

Identification of novel genes influencing eosinophil-specific protein levels in asthma families

BACKGROUND

Eosinophils play a key role in the asthma allergic response by releasing cytotoxic molecules such as eosinophil cationic protein (ECP) and eosinophil-derived neurotoxin (EDN) that generate epithelium damages.

OBJECTIVE

To identify genetic variants influencing ECP and EDN levels in asthma-ascertained families.

METHODS

We performed univariate and bivariate genome-wide association analyses of ECP and EDN levels in 1,018 subjects from EGEA study with follow-up in 153 subjects from SLSJ study and combined the results of these two studies through meta-analysis. We then conducted Bayesian statistical fine-mapping together with quantitative trait locus and functional annotation analyses to identify the most likely functional genetic variants and candidate genes.

RESULTS

We identified five genome-wide significant loci (P<5x10^-8) including seven distinct signals associated with ECP and/or EDN levels. The genes targeted by our fine-mapping and functional search include RNASE2 and RNASE3 (14q11) which encode EDN and ECP respectively and four other genes which regulate ECP/EDN levels. These four genes were the following: JAK1 (1p31) a transcription factor with a key role in the immune response and a potential therapeutic target for eosinophilic asthma, ARHGAP25 (2p13) involved in leukocyte recruitment to inflammatory sites, NDUFA4 (7p21) encoding a component of the mitochondrial respiratory chain and involved in cellular response to stress and CTSL (9q22) involved in immune response, extra-cellular remodeling and allergic inflammation.

CONCLUSION

This study demonstrates that the analysis of specific phenotypes produced by eosinophils allows identifying genes with a major role in allergic response and inflammation and offering potential therapeutic targets for asthma.

ARHGAP25 expression in colorectal cancer as a biomarker associated with favorable prognosis

Although progress has been made in the early diagnosis of colorectal cancer (CRC) and in the systemic therapy of patients with CRC, the prognosis for advanced CRC remains poor. Our previous study demonstrated that ARHGAP25 overexpression significantly inhibits CRC cell growth, invasion and migration. However, it was not possible to evaluate and analyze the overall survival (OS) rate of patients with CRC. Thus, the discovery of relevant factors and their expression on the basis of existing research is necessary to predict the OS rate of patients with advanced CRC. Therefore, the aim of the present study was to define the value of Rho GTPase-activating protein 25 (ARHGAP25) expression in predicting the OS rate in patients with CRC. The clinical data of 153 patients with CRC who underwent colorectal resection were retrospectively analyzed. In order to explore the expression of ARHGAP25, immunohistochemical analysis of the tumor tissues of these patients, was performed. Univariate Cox regression analysis was used to assess the prognostic value of ARHGAP25 expression for OS. Multivariate analysis was used to evaluate the effect of ARHGAP25 expression in the presence of other variables. Confounding factors and interaction were assessed by a stratified analysis using ARHGAP25 expression and other variables associated with survival. The univariate analysis revealed that, ARHGAP25 expression was associated with an improved OS in patients with CRC (P<0.05). The multivariate analysis revealed that ARHGAP25 expression was still correlated with an improved OS after adjusting for sex, age, invasion degree, lymph node metastasis, distant metastasis, TNM stage, tumor location, histological type, histological grade, tumor deposits, and postoperative treatment (P<0.05). The stratified analysis demonstrated that the predictive value of ARHGAP25 for the OS of patients with CRC was stronger in males, elderly patients (>70 years old), patients with T3 stage tumor, lymph node metastasis, TNM stage III, right hemicolon location and patients with a poorly differentiated tumor (P<0.05). Overall, our results demonstrated that ARHGAP25 may have an important potential value for improving the prognosis of patients with CRC.

Understanding the regulation of β-catenin expression and activity in colorectal cancer carcinogenesis: beyond destruction complex

Aberrant Wnt/β-catenin signaling is central to colorectal cancer carcinogenesis. The well-known potential of targeting the canonical Wnt signaling pathway for the treatment of CRC is largely attributed to the ability of this pathway to regulate various cellular processes such as cell proliferation, metastasis, drug resistance, immune response, apoptosis, and cellular metabolism. However, with the current approach of targeting this pathway, none of the Wnt-targeted agents have been successfully implicated in clinical practice. Instead of using classical approaches to target this pathway, there is a growing need to find new and modified approaches to achieve the same. For this, a better understanding of the regulation of β-catenin, a major effector of the canonical Wnt pathway is a must. The present review addresses the importance of understanding the regulation of β-catenin beyond the destruction complex. Few recently discovered β-catenin regulators such as ZNF281, TTPAL, AGR2, ARHGAP25, TREM2, and TIPE1 showed significant potential in regulating the development of CRC through modulation of the Wnt/β-catenin signaling pathway in both in vitro and in vivo studies. Although the expression and activity of β-catenin is influenced by many protein regulators, the abovementioned proteins not only influence its expression and activation but are also directly involved in the development of CRC and various other solid tumors. Therefore, we hypothesise that focusing the current research on finding the detailed mechanism of action of these regulators may assist in providing with a better treatment approach or improve the current therapeutic regimens.

The role of ARHGAP9: clinical implication and potential function in acute myeloid leukemia

Background

Rho GTPase activating protein 9 (ARHGAP9) is expressed in various types of cancers and can inactivate Rho GTPases that mainly regulate cytoskeletal dynamics. However, the exact role of ARHGAP9 in acute myeloid leukemia (AML) has yet to be clarified.

Methods

We compared the transcriptional expression, prognosis, differentially expressed genes, functional enrichment, and hub genes in AML patients on the basis of the data published in the following databases: UALCAN, GEPIA, Gene Expression Omnibus, the Human Protein Atlas, Cancer Cell Line Encyclopedia, LinkedOmics, Metascape, and String. Data from the Cancer Genome Atlas database was used to evaluate the correlations between ARHGAP9 expression and various clinicopathological parameters, as well as the significantly different genes associated with ARHGAP9 expression.

Results

We found that ARHGAP9 expression was higher in the tissues and cell lines extracted from patients with AML than corresponding control tissues and other cancer types. ARHGAP9 overexpression was associated with decreased overall survival (OS) in AML. Compared with the ARHGAP9^low group, the ARHGAP9^high group, which received only chemotherapy, showed significantly worse OS and event-free survival (EFS); however, no significant difference was observed after treatment with autologous or allogeneic hematopoietic stem cell transplantation (auto/allo-HSCT). The ARHGAP9^high patients undergoing auto/allo-HSCT also had a significantly better prognosis with respect to OS and EFS than those receiving only chemotherapy. Most overlapping genes of the significantly different genes and co-expression genes exhibited enriched immune functions, suggesting the immune regulation potential of ARHGAP9 in AML. A total of 32 hub genes were identified from the differentially expressed genes, within which the KIF20A had a significant prognostic value for AML.

Conclusions

ARHGAP9 overexpression was associated with poor OS in AML patients and can be used as a prognostic biomarker. AML patients with ARHGAP9 overexpression can benefit from auto/allo-HSCT rather than chemotherapy.

ArhGAP15, a RacGAP, Acts as a Temporal Signaling Regulator of Mac-1 Affinity in Sterile Inflammation

During inflammation, leukocyte recruitment has to be tightly controlled to prevent overwhelming leukocyte infiltration, activation, and, consequently, organ damage. A central regulator of leukocyte recruitment is Rac1. In this study, we analyzed the effects of the RacGAP ArhGAP15 on leukocyte recruitment. Using ArhGAP15-deficient mice, reduced neutrophil adhesion and transmigration in the TNF-α-inflamed cremaster muscle and a prolongation of chemokine-dependent leukocyte adhesion could be observed. In a murine model of sterile kidney injury, reduced neutrophil infiltration, and serum creatinine levels were apparent. Further in vitro and in vivo analyses revealed a defective intravascular crawling capacity, resulting from increased affinity of the β₂-integrin Mac-1 after prolonged chemokine stimulation of neutrophils. LFA-1 activity regulation was not affected. Summarizing, ArhGAP15 specifically regulates Mac-1, but not LFA-1, and affects leukocyte recruitment by controlling postadhesion strengthening and intravascular crawling in a Mac-1-dependent manner. In conclusion, ArhGAP15 is involved in the time-dependent regulation of leukocyte postadhesion in sterile inflammation.

Arhgap25 Deficiency Leads to Decreased Numbers of Peripheral Blood B Cells and Defective Germinal Center Reactions

Rho family GTPases are critical for normal B cell development and function, and their activity is regulated by a large and complex network of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). However, the role of GAPs in B cell development is poorly understood. In this study, we show that the novel Rac-GAP ARHGAP25 is important for B cell development in mice in a CXCR4-dependent manner. We show that Arhgap25 deficiency in mice leads to a significant decrease in peripheral blood B cell numbers as well as defects in mature B cell differentiation. Arhgap25^-/- B cells respond to Ag stimulation in vitro and in vivo but have impaired germinal center formation and decreased IgG1 class switching. Additionally, Arhgap25^-/- B cells show evidence of increased baseline motility and augmented chemotaxis to CXCL12. Taken together, these studies demonstrate an important role for Arhgap25 in peripheral B cell development and Ag response.

The neglected terminators: Rho family GAPs in neutrophils

BACKGROUND

GTPase-activating proteins (GAPs) accelerate the rate of hydrolysis of GTP bound to small GTPases, thereby limiting the prevalence and concentration of the active, GTP-bound form of these proteins. The large number of potential GAPs acting on members of the Rho family of small GTPases raises the question of specificity or redundancy.

RESULTS

In this review, we summarize experimental data obtained on the role of Rho family GAPs in neutrophils, highlight cases where more than one GAP is involved in a physiological function and show examples that GAPs can be involved not only in termination but also in initiation of cellular processes. We demonstrate that the expression-level regulation of GAPs may also occur in short-living cells such as neutrophils. Finally, we provide insight into the existence and structure of molecular complexes in which Rho family GAPs are involved.

CONCLUSION

GAPs play more complex and varied roles than being simple terminators of cellular processes.

ActivinA: a new leukemia-promoting factor conferring migratory advantage to B-cell precursor-acute lymphoblastic leukemic cells

B-cell precursor-acute lymphoblastic leukemia modulates the bone marrow (BM) niche to become leukemia-supporting and chemo-protective by reprogramming the stromal microenvironment. New therapies targeting the interplay between leukemia and stroma can help improve disease outcome. We identified ActivinA, a TGF-β family member with a well-described role in promoting several solid malignancies, as a factor favoring leukemia that could represent a new potential target for therapy. ActivinA resulted over-expressed in the leukemic BM and its production was strongly induced in mesenchymal stromal cells after culture with leukemic cells. Moreover, MSCs isolated from BM of leukemic patients showed an intrinsic ability to secrete higher amounts of ActivinA compared to their normal counterparts. The pro-inflammatory leukemic BM microenvironment synergized with leukemic cells to induce stromal-derived ActivinA. Gene expression analysis of ActivinA-treated leukemic cells showed that this protein was able to significantly influence motility-associated pathways. Interestingly, ActivinA promoted random motility and CXCL12-driven migration of leukemic cells, even at suboptimal chemokine concentrations, characterizing the leukemic niche. Conversely, ActivinA severely impaired CXCL12-induced migration of healthy CD34⁺ cells. This opposite effect can be explained by the ability of ActivinA to increase intracellular calcium only in leukemic cells, boosting cytoskeleton dynamics through a higher rate of actin polymerization. Moreover, by stimulating the invasiveness of the leukemic cells, ActivinA was found to be a leukemia-promoting factor. Importantly, the ability of ActivinA to enhance BM engraftment and the metastatic potential of leukemic cells was confirmed in a xenograft mouse model of the disease. Overall, ActivinA was seen to be a key factor in conferring a migratory advantage to leukemic cells over healthy hematopoiesis within the leukemic niche.

Role of negative regulation of immune signaling pathways in neutrophil function

Polymorphonuclear neutrophils (PMNs) play a critical role in host defense against infection and in the resolution of inflammation. However, immune responses mediated by PMN must be tightly regulated to facilitate elimination of invading pathogens without inducing detrimental inflammation and host tissue damage. Specific engagement of cell surface immunoreceptors by a diverse range of extracellular signals regulates PMN effector functions through differential activation of intracellular signaling cascades. Although mechanisms of PMN activation mediated via cell signaling pathways have been well described, less is known about negative regulation of PMN function by immune signaling cascades. Here, we provide an overview of immunoreceptor-mediated negative regulation of key PMN effector functions including maturation, migration, phagocytosis, reactive oxygen species release, degranulation, apoptosis, and NET formation. Increased understanding of mechanisms of suppression of PMN effector functions may point to possible future therapeutic targets for the amelioration of PMN-mediated autoimmune and inflammatory diseases.

Cross-talk between Rho GTPases and PI3K in the neutrophil

Neutrophils are short-lived, abundant peripheral blood leukocytes that provide a first line of defense against bacterial and fungal infections while also being a key part of the inflammatory response. Chemokines induce neutrophil recruitment to inflammatory sites, where neutrophils perform several diverse functions that are aimed at fighting infections. Neutrophil effector functions are tightly regulated processes that are governed by an array of intracellular signaling pathways and initiated by receptor-ligand binding events. Dysregulated neutrophil activation can result in excessive inflammation and host damage, as is evident in several autoimmune diseases. Rho family small GTPases and agonist-activated phosphoinositide 3-kinases (PI3Ks) represent 2 classes of key regulators of the highly specialized neutrophil. Here we review cross-talk between these important signaling intermediates in the context of neutrophil functions. We include PI3K-dependent activation of Rho family small GTPases and of their guanine nucleotide exchange factors and GTPase activating proteins, as well as Rho GTPase-dependent regulation of PI3K.