Characterization, expression and chromosomal localization of a human gene homologous to the mouse Lsc oncogene, with strongest expression in hematopoetic tissues

Integrative multiomics and in silico analysis revealed the role of ARHGEF1 and its screened antagonist in mild and severe COVID-19 patients

COVID‐19 is a sneaking deadly disease caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). The rapid increase in the number of infected patients worldwide enhances the exigency for medicines. However, precise therapeutic drugs are not available for COVID‐19; thus, exhaustive research is critically required to unscramble the pathogenic tools and probable therapeutic targets for the development of effective therapy. This study utilizes a chemogenomics strategy, including computational tools for the identification of viral‐associated differentially expressed genes (DEGs), and molecular docking of potential chemical compounds available in antiviral, anticancer, and natural product‐based libraries against these DEGs. We scrutinized the messenger RNA expression profile of SARS‐CoV‐2 patients, publicly available on the National Center for Biotechnology Information–Gene Expression Omnibus database, stratified them into different groups based on the severity of infection, superseded by identification of overlapping mild and severe infectious (MSI)‐DEGs. The profoundly expressed MSI‐DEGs were then subjected to trait‐linked weighted co‐expression network construction and hub module detection. The hub module MSI‐DEGs were then exposed to enrichment (gene ontology + pathway) and protein–protein interaction network analyses where Rho guanine nucleotide exchange factor 1 (ARHGEF1) gene conjectured in all groups and could be a probable target of therapy. Finally, we used the molecular docking and molecular dynamics method to identify inherent hits against the ARHGEF1 gene from antiviral, anticancer, and natural product‐based libraries. Although the study has an identified significant association of the ARHGEF1 gene in COVID19; and probable compounds targeting it, using in silico methods, these targets need to be validated by both in vitro and in vivo methods to effectively determine their therapeutic efficacy against the devastating virus.

Loss of ARHGEF1 causes a human primary antibody deficiency

ARHGEF1 is a RhoA-specific guanine nucleotide exchange factor expressed in hematopoietic cells. We used whole-exome sequencing to identify compound heterozygous mutations in ARHGEF1, resulting in the loss of ARHGEF1 protein expression in 2 primary antibody-deficient siblings presenting with recurrent severe respiratory tract infections and bronchiectasis. Both ARHGEF1-deficient patients showed an abnormal B cell immunophenotype, with a deficiency in marginal zone and memory B cells and an increased frequency of transitional B cells. Furthermore, the patients' blood contained immature myeloid cells. Analysis of a mediastinal lymph node from one patient highlighted the small size of the germinal centers and an abnormally high plasma cell content. On the molecular level, T and B lymphocytes from both patients displayed low RhoA activity and low steady-state actin polymerization (even after stimulation of lysophospholipid receptors). As a consequence of disturbed regulation of the RhoA downstream target Rho-associated kinase I/II (ROCK), the patients' lymphocytes failed to efficiently restrain AKT phosphorylation. Enforced ARHGEF1 expression or drug-induced activation of RhoA in the patients' cells corrected the impaired actin polymerization and AKT regulation. Our results indicate that ARHGEF1 activity in human lymphocytes is involved in controlling actin cytoskeleton dynamics, restraining PI3K/AKT signaling, and confining B lymphocytes and myelocytes within their dedicated functional environment.

Expression of p114RhoGEF predicts lymph node metastasis and poor survival of squamous-cell lung carcinoma patients

The Rho-specific guanine nucleotide exchanging factor p114RhoGEF is involved in RhoA activation and cell motility. Previous studies suggest that altered expression of p114RhoGEF could contribute to cancer progression. We investigated an association of p114RhoGEF expression with progression and prognosis of non-small cell lung cancer (NSCLC). Immunohistochemistry was performed to detect p114RhoGEF expression in 105 NSCLC (34 adenocarcinoma and 71 squamous-cell carcinoma) and 32 normal lung tissues. We found that p114RhoGEF expression was upregulated in squamous-cell lung carcinoma and that p114RhoGEF expression was significantly higher in squamous-cell carcinoma than in adenocarcinoma or normal tissues (P<0.05, both). Expression of p114RhoGEF protein was significantly associated with lymph node metastasis of lung cancer (P<0.05), but not with patients' age, gender, tumor size, differentiation, or stage. Expression of p114RhoGEF protein was also associated with poor overall and event-free survival of squamous-cell lung carcinoma patients (P<0.05). Taken together, p114RhoGEF expression may be useful in predicting progression and survival of squamous-cell lung carcinoma patients. A future study will investigate whether p114RhoGEF can serve as a novel therapeutic target in squamous-cell lung cancer.

Loss of Lsc/p115 protein leads to neuronal hypoplasia in the esophagus and an achalasia-like phenotype in mice

BACKGROUND & AIMS

Lsc/p115 originally was described as hematopoietic Ras homologous protein guanine exchange factor (Rho-GEF) regulating leukocyte migration, adhesion, and marginal zone B-cell homeostasis. Here we investigate the expression pattern of lsc/p115 in the gastrointestinal tract and the consequences of lsc/p115 deficiency in lsc/p115-knockout mice.

METHODS

The phenotype of lsc/p115-deficient mice was analyzed in vivo with small-animal computed tomography scans and esophageal manometry. The morphology and myenteric plexus were evaluated with immunohistochemistry, morphometry, Western blot analyses, and quantitative reverse-transcription polymerase chain reaction.

RESULTS

lsc/p115 is expressed in the gastrointestinal tract, sparing the segment of the small intestine. Immunohistochemical staining detects lsc/p115 in the muscle layer and the glial fibrillary acidic protein-positive glia in the esophagus. Esophageal manometry uncovers a severe motor dysfunction in lsc/p115-deficient mice. This achalasia-like phenotype is characterized by disturbed peristalsis, hypertension of the lower esophageal sphincter, and impaired relaxation of the lower esophageal sphincter. Lsc/p115-deficient mice develop a progressive dilatation of the esophagus and decrease of the muscle layer. The muscle cell differentiation is not altered in lsc/p115-deficient mice. However, the density of inhibitory and excitatory neurons and glia cells in the myenteric plexus and the muscle layer are reduced in morphometric analyses. This reduced number of glia cells is accompanied by reduced expression of the neurotrophic nerve growth factor.

CONCLUSIONS

lsc/p115 deficiency results in impaired neuronal innervation and in motor dysfunction recapitulating several aspects of esophageal achalasia. Reduced expression of nerve growth factor and a reduced number of glia cells most likely contribute to this phenotype.

The effect of membrane domains on the G protein-phospholipase Cbeta signaling pathway

The plasma membrane serves as a barrier to limit the exit and entry of components into and out of the cell, offering protection from the external environment. Communication between the cell and the external environment is mediated by multiple signaling pathways. While the plasma membrane was historically viewed as a lipid bilayer with freely diffusing proteins, the last decade has shown that the lipids and proteins in the plasma membrane are organized in a non-random manner, and that this organization can direct and modify various signaling pathways in the cell. In this review, we qualitatively discuss the ways that membrane domains can affect cell signaling. We then focus on how membrane domains can affect a specific signaling pathway--the G protein-phospholipase Cbeta pathway and show how membrane domains can play an active role in directing or redirecting G protein signals.

Arhgef1 regulates alpha5beta1 integrin-mediated matrix metalloproteinase expression and is required for homeostatic lung immunity

Pulmonary immunity depends on the ability of leukocytes to neutralize potentially harmful and frequent insults to the lung, and appropriate regulation of leukocyte migration and adhesion is integral to this process. Arhgef1 is a hematopoietic-restricted signaling molecule that regulates leukocyte migration and integrin-mediated adhesion. To explore a possible regulatory role for Arhgef1 in pulmonary immunity we examined the lung and its leukocytes in wild-type and Arhgef1-deficient animals. Here we report that the lungs of Arhgef1-/- mice harbored significantly more leukocytes, increased expression and activity of matrix metalloproteinases (MMPs), airspace enlargement, and decreased lung elastance compared with wild-type lungs. Transfer of Arhgef1-/- lung leukocytes to wild-type mice led to airspace enlargement and impaired lung function, indicating that loss of Arhgef1 in leukocytes was sufficient to induce pulmonary pathology. Furthermore, we showed that Arhgef1-deficient peritoneal macrophages when either injected into the lungs of wild-type mice or cultured on fibronectin significantly increased expression and activity of MMPs relative to control macrophages, and the in vitro fibronectin induction was dependent on the alpha5beta1 integrin pair. Together these data demonstrate that Arhgef1 regulates alpha5beta1-mediated MMP expression by macrophages and that loss of Arhgef1 by leukocytes leads to pulmonary pathology.

Regulation and physiological functions of G12/13-mediated signaling pathways

Accumulating data indicate that G12 subfamily (Galpha12/13)-mediated signaling pathways play pivotal roles in a variety of physiological processes, while aberrant regulation of this pathway has been identified in various human diseases. It has been demonstrated that Galpha12/13-mediated signals form networks with other signaling proteins at various levels, from cell surface receptors to transcription factors, to regulate cellular responses. Galpha12/13 have slow rates of nucleotide exchange and GTP hydrolysis, and specifically target RhoGEFs containing an amino-terminal RGS homology domain (RH-RhoGEFs), which uniquely function both as a GAP and an effector for Galpha12/13. In this review, we will focus on the mechanisms regulating the Galpha12/13 signaling system, particularly the Galpha12/13-RH-RhoGEF-Rho pathway, which can regulate a wide variety of cellular functions from migration to transformation.

Reversible translocation of p115-RhoGEF by G(12/13)-coupled receptors

G protein-coupled receptors (GPCRs) are important targets for medicinal agents. Four different G protein families, G(s), G(i), G(q), and G(12), engage in their linkage to activation of receptor-specific signal transduction pathways. G(12) proteins were more recently studied, and upon activation by GPCRs they mediate activation of RhoGTPase guanine nucleotide exchange factors (RhoGEFs), which in turn activate the small GTPase RhoA. RhoA is involved in many cellular and physiological aspects, and a dysfunction of the G(12/13)-Rho pathway can lead to hypertension, cardiovascular diseases, stroke, impaired wound healing and immune cell functions, cancer progression and metastasis, or asthma. In this study, regulator of G protein signaling (RGS) domain-containing RhoGEFs were tagged with enhanced green fluorescent protein (EGFP) to detect their subcellular localization and translocation upon receptor activation. Constitutively active Galpha(12) and Galpha(13) mutants induced redistribution of these RhoGEFs from the cytosol to the plasma membrane. Furthermore, a pronounced and rapid translocation of p115-RhoGEF from the cytosol to the plasma membrane was observed upon activation of several G(12/13)-coupled GPCRs in a cell type-independent fashion. Plasma membrane translocation of p115-RhoGEF stimulated by a GPCR agonist could be completely and rapidly reversed by subsequent application of an antagonist for the respective GPCR, that is, p115-RhoGEF relocated back to the cytosol. The translocation of RhoGEF by G(12/13)-linked GPCRs can be quantified and therefore used for pharmacological studies of the pathway, and to discover active compounds in a G(12/13)-related disease context.

Lsc activity is controlled by oligomerization and regulates integrin adhesion

Lsc is a hematopoietic-restricted protein that functions as an effector of G alpha(12/13)-associated G-protein coupled receptors that activates RhoA. In the absence of Lsc leukocytes exhibit impaired migration and B lymphocytes inefficiently resolve integrin-mediated adhesion. Here, we demonstrate that Lsc exists physiologically in primary B lymphocytes as a large molecular weight complex resembling a homo-tetramer. Interfering with the assembly of this large molecular weight Lsc oligomer results in the activation of both Lsc functional activities and leads to cell rounding and inhibition of integrin-mediated adhesion. During cell migration on integrin ligands we find Lsc localizes predominantly toward the rear of migrating cells where we suggest it activates RhoA to resolve integin-mediated adhesion. Together these data demonstrate that Lsc regulates integrin-mediated adhesive events at the trailing edge of migrating cells.

Arhgef1 is required by T cells for the development of airway hyperreactivity and inflammation

RATIONALE

Arhgef1 is an intracellular protein, expressed by hematopoietic cells, that regulates signaling by both G protein-coupled receptors and RhoA, and, consequently, is required for appropriate migration and adhesion of diverse leukocyte populations.

OBJECTIVES

To evaluate a possible contribution for Arhgef1 in the development of airway inflammation and airway hyperreactivity.

METHODS

Arhgef1-deficient (Arhgef1-/-) and wild-type (WT) mice were sensitized and airway challenged, followed by measurement of airway responsiveness to inhaled methacholine. Inflammation was assessed by several parameters that included flow cytometric analysis and histology. Arhgef1-deficient recipients were reconstituted with WT T lymphocytes before sensitization and challenge, and again measured for airway responsiveness and inflammation. Cytokine production in response to specific antigen was measured in cultures of isolated leukocytes from lung and spleen and compared with the levels generated in lung and spleen explant cultures.

MEASUREMENTS AND MAIN RESULTS

Arhgef1-/- mice display significantly reduced airway hyperreactivity, Th2 cytokine production, and lung inflammation, despite intact systemic immunity. After airway challenge of Arhgef1-/- mice, antigen-specific T cells were present in mutant lungs, but were found to interact with CD11c+ cells at a significantly reduced frequency. Adoptive transfer of WT T cells into Arhgef1-/- mice restored airway hyperreactivity and inflammation.

CONCLUSIONS

These data demonstrate that T cells depend on Arhgef1 to promote lung inflammation. Moreover, a deficiency in Arhgef1 results in reduced T cell-CD11c+ antigen-presenting cell interaction, and likely underscores the inability of Arhgef1-/- mice to mount an adaptive immune response to airway challenge.

Lsc regulates marginal-zone B cell migration and adhesion and is required for the IgM T-dependent antibody response

The humoral immune response to protein antigens is composed of a rapid low-affinity IgM antibody response followed by an IgG response exhibiting higher affinity. Here, we demonstrate that Lsc, a protein that regulates G protein-coupled-receptor signaling and RhoA activation, is required by B lymphocytes for the antigen-specific IgM antibody response to a protein antigen. We further show that in lsc(-/-) mice, MZB cells are selectively affected such that naive and in vivo-activated MZB cells migrate toward sphingosine-1-phosphate at increased proportions but release inefficiently from integrin ligands. Consequently, lsc(-/-) MZB cells do not traffick appropriately in an immune response and do not contribute to the TD antibody response. These data demonstrate that Lsc regulates the migration and adhesion of MZB cells, and this regulation appears to be required for these cells to contribute to the antibody response to TD antigens.

Differential gene expression of human stem progenitor cells derived from early stages of in utero human hematopoiesis

Hematopoietic stem progenitor cells (HSPCs) are highly enriched in a rare subset of Lin-CD34+CD38- cells. Independent of stage of human development, HSPC function segregates to the subset of Lin-CD34+CD38- cells. However, fetal-derived HSPCs demonstrate distinct self-renewal and differentiation capacities compared with their adult counterparts. Here, to characterize the molecular nature of fetal HSPCs, suppressive subtractive hybridization was used to compare gene expression of HSPCs isolated from fetal blood (FB-HSPCs) versus adult mobilized peripheral blood (MPB-HSPCs). We identified 97 differentially expressed genes that could be annotated into distinct groups that include transcription factors, cell cycle regulators, and genes involved in signal transduction. Candidate regulators, such as Lim only domain-2 (LMO2), nuclear factor–kappa B (NF-κB), tripartite motif 28 (Trim28), and N-myc protooncogene (MYCN), and a novel homeobox gene product were among transcripts that were found to be differentially expressed and could be associated with specific proliferation and differentiation properties unique to FB-HSPCs. Interestingly, the majority of genes associated with signal transduction belong to Ras pathway, highlighting the significance of Ras signaling in FB-HSPCs. Genes differentially expressed in FB-HSPCs versus adult MPB-HSPCs were verified using quantitative real-time polymerase chain reaction (Q-PCR). This approach also resulted in the identification of a transcript that is highly expressed in FB-HSPCs but not detectable in more differentiated Lin-CD34+CD38+ FB progenitors. Our investigation represents the first study to compare phenotypically similar, but functionally distinct, HSPC populations and to provide a gene profile of unique human HSPCs with higher proliferative capacity derived from early in utero human blood development.

Receptor-dependent RhoA activation in G12/G13-deficient cells: genetic evidence for an involvement of Gq/G11

The small GTPase RhoA is involved in the regulation of various cellular functions like the remodeling of the actin cytoskeleton and the induction of transcriptional activity. G-protein-coupled receptors (GPCRs), which are able to activate Gq/G11 and G12/G13 are major upstream regulators of RhoA activity, and G12/G13 have been shown to couple GPCRs to the activation of Rho by regulating the activity of a subfamily of RhoGEF proteins. However, the possible contribution of Gq/G11 to the regulation of RhoA activity via GPCRs is controversial. We have used a genetic approach to study the role of heterotrimeric G-proteins in the activation of RhoA via endogenous GPCRs. In pertussis toxin-treated Galpha12/Galpha13-deficient as well as in Galphaq/Galpha11-deficient mouse embryonic fibroblasts (MEFs), in which coupling of receptors is restricted to Gq/G11 and G12/G13, respectively, receptor activation results in Rho activation. Rho activation induced by receptor agonists via Gq/G11 occurs with lower potency than Rho activation via G12/G13. Activation of RhoA via Gq/G11 is not affected by the phospholipase-C blocker U73122 or the Ca2+-chelator BAPTA, but can be blocked by a dominant-negative mutant of the RhoGEF protein LARG. Our data clearly show that G12/G13 as well as Gq/G11 alone can couple GPCRs to the rapid activation of RhoA. Gq/G11-mediated RhoA activation occurs independently of phospholipase C-beta and appears to involve LARG.

Lsc is required for marginal zone B cells, regulation of lymphocyte motility and immune responses

Lsc (the murine homolog of human p115 Rho GEF) is a member of the Dbl-homology family of GTP exchange factors and is a specific activator of Rho. Lsc is activated by the G alpha(13) subunit of heterotrimeric G proteins and contains a regulator of G protein signaling domain that downmodulates G alpha(12) and G alpha(13). Lsc is expressed primarily in the hematopoietic system and links the activation of G alpha(12) and G alpha(13)-coupled receptors to actin polymerization in B and T cells. Lsc is essential for marginal zone B (MZB) cell homeostasis and for the generation of immune responses. Although Lsc-deficient lymphocytes show reduced basal motility, MZB cells show enhanced migration after serum activation. Thus, Lsc is a critical regulator of MZB cells and immune functions.

Modulation of HIV-1 replication by a novel RhoA effector activity

The RhoA GTPase is involved in regulating actin cytoskeletal organization, gene expression, cell proliferation, and survival. We report here that p115-RhoGEF, a specific guanine nucleotide exchange factor (GEF) and activator of RhoA, modulates HIV-1 replication. Ectopic expression of p115-RhoGEF or Galpha13, which activates p115-RhoGEF activity, leads to inhibition of HIV-1 replication. RhoA activation is required and the inhibition affects HIV-1 gene expression. The RhoA effector activity in inhibiting HIV-1 replication is genetically separable from its activities in transformation of NIH3T3 cells, activation of serum response factor, and actin stress fiber formation. These findings reveal that the RhoA signal transduction pathway regulates HIV-1 replication and suggest that RhoA inhibits HIV-1 replication via a novel effector activity.