RasGRP1 Expression Research Articles

Abnormal RasGRP1 Expression in the Post-Mortem Brain and Blood Serum of Schizophrenia Patients.

Schizophrenia (SCZ) is a polygenic severe mental illness. Genome-wide association studies (GWAS) have detected genomic variants associated with this psychiatric disorder and pathway analyses have indicated immune system and dopamine signaling as core components of risk in dorsolateral-prefrontal cortex (DLPFC) and hippocampus, but the mechanistic links remain unknown. The RasGRP1 gene, encoding for a guanine nucleotide exchange factor, is implicated in dopamine signaling and immune response. RasGRP1 has been identified as a candidate risk gene for SCZ and autoimmune disease, therefore representing a possible point of convergence between mechanisms involving the nervous and the immune system. Here, we investigated RasGRP1 mRNA and protein expression in post-mortem DLPFC and hippocampus of SCZ patients and healthy controls, along with RasGRP1 protein content in the serum of an independent cohort of SCZ patients and control subjects. Differences in RasGRP1 expression between SCZ patients and controls were detected both in DLPFC and peripheral blood of samples analyzed. Our results indicate RasGRP1 may mediate risk for SCZ by involving DLPFC and peripheral blood, thus encouraging further studies to explore its possible role as a biomarker of the disease and/or a target for new medication.

NrasQ61R/+ and Kras−/− cooperate to downregulate Rasgrp1 and promote lympho-myeloid leukemia in early T-cell precursors

Early T-cell precursor acute lymphoblastic leukemia (ETP-ALL) is an aggressive subtype of T-cell ALL. Although genetic mutations hyperactivating cytokine receptor/Ras signaling are prevalent in ETP-ALL, it remains unknown how activated Ras signaling contributes to ETP-ALL. Here, we find that in addition to the frequent oncogenic RAS mutations, wild-type (WT) KRAS transcript level was significantly downregulated in human ETP-ALL cells. Similarly, loss of WT Kras in NrasQ61R/+ mice promoted hyperactivation of extracellular signal-regulated kinase (ERK) signaling, thymocyte hyperproliferation, and expansion of the ETP compartment. Kras−/−; NrasQ61R/+ mice developed early onset of T-cell malignancy that recapitulates many biological and molecular features of human ETP-ALL. Mechanistically, RNA-sequencing analysis and quantitative proteomics study identified that Rasgrp1, a Ras guanine nucleotide exchange factor, was greatly downregulated in mouse and human ETP-ALL. Unexpectedly, hyperactivated Nras/ERK signaling suppressed Rasgrp1 expression and reduced Rasgrp1 level led to increased ERK signaling, thereby establishing a positive feedback loop to augment Nras/ERK signaling and promote cell proliferation. Corroborating our cell line data, Rasgrp1 haploinsufficiency induced Rasgrp1 downregulation and increased phosphorylated ERK level and ETP expansion in NrasQ61R/+ mice. Our study identifies Rasgrp1 as a negative regulator of Ras/ERK signaling in oncogenic Nras-driven ETP-like leukemia.

Profiles of immune infiltration in abdominal aortic aneurysm and their associated marker genes: a gene expression-based study.

Immune-mediated inflammation plays a key role in the pathology of abdominal aortic aneurysm (AAA). We aimed to use a computational approach to profile the immune infiltration patterns and related core genes in AAA samples based on the overexpression of gene signatures. The microarray datasets of AAA and normal abdominal tissues were acquired from gene expression omnibus (GEO) database. We evaluated the composition of immune infiltrates through microenvironment cell populations (MCP)-counter. Weighted gene correlation network analysis (WGCNA) was employed to construct the co-expression network and extract gene information in the most relevant module. Functional and pathway enrichment analysis was performed and immune infiltration related core genes were screened. AAA tissues had a higher level of infiltration by cytotoxic lymphocytes, NK cells, T cells, fibroblasts, myeloid dendritic cells, and neutrophils than normal aorta. The red module was strongly correlated with the infiltrating levels of T cells and cytotoxic lymphocytes. Gene ontology (GO) and pathway analyses revealed that genes in the most relevant module were mainly enriched in T cell activation, regulation of lymphocyte activation, cytokine-cytokine receptor interaction, and chemokine signaling pathway, etc. The expression of GZMK, CCL5, GZMA, CD2, and EOMES showed significant correlations with cytotoxic lymphocytes, while CD247, CD2, CD6, RASGRP1, and CD48 expression were positively associated with T cell infiltration. In conclusion, we comprehensively analyzed profiles of infiltrated immune cells in AAA tissues and their associated marker genes. Our data may provide a novel clue to indicate the underlying molecular mechanisms of AAA formation in terms of immune infiltration.

Dysregulated RASGRP1 expression through RUNX1 mediated transcription promotes autoimmunity.

RasGRP1 is a Ras guanine nucleotide exchange factor, and an essential regulator of lymphocyte receptor signaling. In mice, Rasgrp1 deletion results in defective T lymphocyte development. RASGRP1‐deficient patients suffer from immune deficiency, and the RASGRP1 gene has been linked to autoimmunity. However, how RasGRP1 levels are regulated, and if RasGRP1 dosage alterations contribute to autoimmunity remains unknown. We demonstrate that diminished Rasgrp1 expression caused defective T lymphocyte selection in C57BL/6 mice, and that the severity of inflammatory disease inversely correlates with Rasgrp1 expression levels. In patients with autoimmunity, active inflammation correlated with decreased RASGRP1 levels in CD4+ T cells. By analyzing H3K27 acetylation profiles in human T cells, we identified a RASGRP1 enhancer that harbors autoimmunity‐associated SNPs. CRISPR‐Cas9 disruption of this enhancer caused lower RasGRP1 expression, and decreased binding of RUNX1 and CBFB transcription factors. Analyzing patients with autoimmunity, we detected reduced RUNX1 expression in CD4+ T cells. Lastly, we mechanistically link RUNX1 to transcriptional regulation of RASGRP1 to reveal a key circuit regulating RasGRP1 expression, which is vital to prevent inflammatory disease.

RasGRP1 induces autophagy and transformation-associated changes in primary human keratinocytes

Ras mutations are present in only a subset of sporadic human cutaneous squamous cell carcinomas (cSCC) even though Ras is activated in most. This suggests that other mechanisms of Ras activation play a role in the disease. The aberrant expression of RasGRP1, a guanyl nucleotide exchange factor for Ras, is critical for mouse cSCC development through its ability to increase Ras activity. However, the role of RasGRP1 in human keratinocyte carcinogenesis remains unknown. Here we report that RasGRP1 is significantly elevated in human cSCC and that high RasGRP1 expression in human primary keratinocytes triggered activation of endogenous Ras and significant morphological changes including cytoplasmic vacuole formation and growth arrest. Moreover, RasGRP1-expressing cells were autophagic as indicated by LC3-II increase and the formation of LC3 punctae. In an in vitro organotypic skin model, wild type keratinocytes generated a well-stratified epithelium, while RasGRP1-expressing cells failed to do so. Finally, RasGRP1 induced transformation-like changes in skin cells from Li-Fraumeni patients with inactivating p53 mutations, demonstrating the oncogenic potential of this protein. These results support a role for RasGRP1 in human epidermal keratinocyte carcinogenesis and might serve as an important new therapeutic target.

Increased baseline RASGRP1 signals enhance stem cell fitness during native hematopoiesis.

Oncogenic mutations in RAS genes, like KRASG12D or NRASG12D, trap Ras in the active state and cause myeloproliferative disorder and T cell leukemia (T-ALL) when induced in the bone marrow via Mx1CRE. The RAS exchange factor RASGRP1 is frequently overexpressed in T-ALL patients. In T-ALL cell lines overexpression of RASGRP1 increases flux through the RASGTP/RasGDP cycle. Here we expanded RASGRP1 expression surveys in pediatric T-ALL and generated a RoLoRiG mouse model crossed to Mx1CRE to determine the consequences of induced RASGRP1 overexpression in primary hematopoietic cells. RASGRP1-overexpressing, GFP-positive cells outcompeted wild type cells and dominated the peripheral blood compartment over time. RASGRP1 overexpression bestows gain-of-function colony formation properties to bone marrow progenitors in medium containing limited growth factors. RASGRP1 overexpression enhances baseline mTOR-S6 signaling in the bone marrow, but not in vitro cytokine-induced signals. In agreement with these mechanistic findings, hRASGRP1-ires-EGFP enhances fitness of stem- and progenitor- cells, but only in the context of native hematopoiesis. RASGRP1 overexpression is distinct from KRASG12D or NRASG12D, does not cause acute leukemia on its own, and leukemia virus insertion frequencies predict that RASGRP1 overexpression can effectively cooperate with lesions in many other genes to cause acute T cell leukemia.

Nurr1 performs its anti-inflammatory function by regulating RasGRP1 expression in neuro-inflammation

Nurr1, a transcription factor belonging to the orphan nuclear receptor, has an essential role in the generation and maintenance of dopaminergic neurons and is important in the pathogenesis of Parkinson’ disease (PD). In addition, Nurr1 has a non-neuronal function, and it is especially well known that Nurr1 has an anti-inflammatory function in the Parkinson’s disease model. However, the molecular mechanisms of Nurr1 have not been elucidated. In this study, we describe a novel mechanism of Nurr1 function. To provide new insights into the molecular mechanisms of Nurr1 in the inflammatory response, we performed Chromatin immunoprecipitation sequencing (ChIP-Seq) on LPS-induced inflammation in BV2 cells and finally identified the RasGRP1 gene as a novel target of Nurr1. Here, we show that Nurr1 directly binds to the RasGRP1 intron to regulate its expression. Moreover, we also identified that RasGRP1 regulates the Ras-Raf-MEK-ERK signaling cascade in LPS-induced inflammation signaling. Finally, we conclude that RasGRP1 is a novel regulator of Nurr1’s mediated inflammation signaling.

High-throughput transcriptome analysis reveals that the loss of Pten activates a novel NKX6-1/RASGRP1 regulatory module to rescue microphthalmia caused by Fgfr2-deficient lenses.

FGFR signaling is critical to development and disease pathogenesis, initiating phosphorylation-driven signaling cascades, notably the RAS-RAF-MEK-ERK and PI3K-AKT cascades. PTEN antagonizes FGFR signaling by reducing AKT and ERK activation. Mouse lenses lacking FGFR2 exhibit microphakia and reduced ERK and AKT phosphorylation, widespread apoptosis, and defective lens fiber cell differentiation. In contrast, simultaneous deletion of both Fgfr2 and Pten restores ERK and AKT activation levels as well as lens size, cell survival and aspects of fiber cell differentiation; however, the molecular basis of this "rescue" remains undefined. We performed transcriptomic analysis by RNA sequencing of mouse lenses with conditional deletion of Fgfr2, Pten or both Fgfr2 and Pten, which reveal new molecular mechanisms that uncover how FGFR2 and PTEN signaling interact during development. The FGFR2-deficient lens transcriptome demonstrates overall loss of fiber cell identity with deregulated expression of 1448 genes. We find that ~ 60% of deregulated genes return to normal expression levels in lenses lacking both Fgfr2 and Pten. Further, application of customized filtering parameters to these RNA-seq data sets identified 68 high-priority candidate genes. Bioinformatics analyses showed that the cis-binding motif of a high-priority homeodomain transcription factor, NKX6-1, was present in the putative promoters of ~ 78% of these candidates. Finally, biochemical reporter assays demonstrate that NKX6-1 activated the expression of the high-priority candidate Rasgrp1, a RAS-activating protein. Together, these data define a novel regulatory module in which NKX6-1 directly activates Rasgrp1 expression to restore the balance of ERK and AKT activation, thus providing new insights into alternate regulation of FGFR downstream events.

Impairment of PD-L2 positive B1a cells enhances susceptibility to sepsis in RasGRP1-deficient mice

RasGRP1 is a key molecule that mediates antigen-initiated signaling for activation of the RAS-MAPK pathway in lymphocytes. Patients with aberrant RasGRP1 expression experience lymphocyte dysfunction and are afflicted with recurrent microbial infections. Yet, the underlying mechanism that accounts for microbial infection remains unknown. We previously reported that B1a cells are heterogeneous with respect to PD-L2 expression and that RasGRP1 deficiency preferentially impairs PD-L2+ B1a cell development. In the present study, we show that PD-L2+ B1a cells exhibit increased capacity for differentiation to CD138+ plasma cells that secrete natural IgM antibody, as well as IL-10 and GM-CSF, in response to TLR stimulation. In keeping with this, we show here that RasGRP1-deficent mice are much more susceptible to septic infection triggered by cecalligation and puncture than wild type mice, and that reconstitution of RasGRP1-deficient mice with wild type PD-L2+ B1a cells greatly rescues RasGRP1-deficient mice from sepsis. Thus, this study indicates a mechanism for the association of RasGRP1 deficiency with predispostion to infection in the loss of a particular B1a subpopulation.

Nurr1 performs the anti-inflammatory function by regulating RasGRP1 expression in neuro-inflammation

Nurr1 performs the anti-inflammatory function by regulating RasGRP1 expression in neuro-inflammation

RasGRP1 is a potential biomarker to stratify anti-EGFR therapy response in colorectal cancer.

Colorectal cancer (CRC) is the third most frequent neoplastic disorder and is a main cause of tumor-related mortality as many patients progress to stage IV metastatic CRC. Standard care consists of combination chemotherapy (FOLFIRI or FOLFOX). Patients with WT KRAS typing are eligible to receive anti-EGFR therapy combined with chemotherapy. Unfortunately, predicting efficacy of CRC anti-EGFR therapy has remained challenging. Here we uncover that the EGFR-pathway component RasGRP1 acts as CRC tumor suppressor in the context of aberrant Wnt signaling. We find that RasGRP1 suppresses EGF-driven proliferation of colonic epithelial organoids. Having established that RasGRP1 dosage levels impacts biology, we focused on CRC patients next. Mining five different data platforms, we establish that RasGRP1 expression levels decrease with CRC progression and predict poor clinical outcome of patients. Lastly, deletion of one or two Rasgrp1 alleles makes CRC spheroids more susceptible to EGFR inhibition. Retrospective analysis of the CALGB80203 clinical trial shows that addition of anti-EGFR therapy to chemotherapy significantly improves outcome for CRC patients when tumors express low RasGRP1 suppressor levels. In sum, RasGRP1 is a unique biomarker positioned in the EGFR pathway and of potential relevance to anti-EGFR therapy for CRC patients.

Mechanistic Characterization of RASGRP1 Variants Identifies an hnRNP-K-Regulated Transcriptional Enhancer Contributing to SLE Susceptibility.

Systemic lupus erythematosus (SLE) is an autoimmune disease with a strong genetic component. We recently identified a novel SLE susceptibility locus near RASGRP1, which governs the ERK/MAPK kinase cascade and B-/T-cell differentiation and development. However, precise causal RASGRP1 functional variant(s) and their mechanisms of action in SLE pathogenesis remain undefined. Our goal was to fine-map this locus, prioritize genetic variants likely to be functional, experimentally validate their biochemical mechanisms, and determine the contribution of these SNPs to SLE risk. We performed a meta-analysis across six Asian and European cohorts (9,529 cases; 22,462 controls), followed by in silico bioinformatic and epigenetic analyses to prioritize potentially functional SNPs. We experimentally validated the functional significance and mechanism of action of three SNPs in cultured T-cells. Meta-analysis identified 18 genome-wide significant (p < 5 × 10−8) SNPs, mostly concentrated in two haplotype blocks, one intronic and the other intergenic. Epigenetic fine-mapping, allelic, eQTL, and imbalance analyses predicted three transcriptional regulatory regions with four SNPs (rs7170151, rs11631591-rs7173565, and rs9920715) prioritized for functional validation. Luciferase reporter assays indicated significant allele-specific enhancer activity for intronic rs7170151 and rs11631591-rs7173565 in T-lymphoid (Jurkat) cells, but not in HEK293 cells. Following up with EMSA, mass spectrometry, and ChIP-qPCR, we detected allele-dependent interactions between heterogeneous nuclear ribonucleoprotein K (hnRNP-K) and rs11631591. Furthermore, inhibition of hnRNP-K in Jurkat and primary T-cells downregulated RASGRP1 and ERK/MAPK signaling. Comprehensive association, bioinformatics, and epigenetic analyses yielded putative functional variants of RASGRP1, which were experimentally validated. Notably, intronic variant (rs11631591) is located in a cell type-specific enhancer sequence, where its risk allele binds to the hnRNP-K protein and modulates RASGRP1 expression in Jurkat and primary T-cells. As risk allele dosage of rs11631591 correlates with increased RASGRP1 expression and ERK activity, we suggest that this SNP may underlie SLE risk at this locus.

Decreased Expression of Serine/Arginine-Rich Splicing Factor 1 in T Cells From Patients With Active Systemic Lupus Erythematosus Accounts for Reduced Expression of RasGRP1 and DNA Methyltransferase 1.

T cells from systemic lupus erythematosus (SLE) patients have reduced protein levels of RasGRP1, a guanine nucleotide exchange factor for Ras, and increased transcript of alternatively spliced (AS) forms lacking exon 11. Serine/arginine-rich splicing factor 1 (SRSF1) binds pre-messenger RNA (pre-mRNA) to regulate AS forms of several genes, including CD3ζ in SLE T cells. This study was undertaken to assess whether SRSF1 controls the expression of RasGRP1 in T cells from patients with SLE. We studied T cells from 45 SLE patients and 18 healthy subjects. Expression levels of SRSF1, wild-type (WT) RasGRP1, and DNA methyltransferase 1(DNMT1) were assessed by quantitative polymerase chain reaction. Direct binding of SRSF1 to exon 11 of RasGRP1 mRNA was evaluated with an oligonucleotide-protein pulldown assay. Healthy T cells and SLE T cells were treated with SRSF1-specific small interfering RNA or SRSF1 expression vector, respectively, and then evaluated for mRNA/protein expression. SRSF1 expression levels were significantly lower in T cells from SLE patients compared to those from healthy subjects, and correlated inversely with disease activity and positively with levels of RasGRP1-WT and DNMT1. SRSF1 bound directly to exon 11 of RasGRP1 mRNA. Silencing of SRSF1 in human T cells led to increased ratios of RasGRP1-AS to RasGRP1-WT and decreased levels of RasGRP1 protein, whereas overexpression of SRSF1 in SLE T cells caused recovery of RasGRP1, which in turn induced DNMT1/interleukin-2 expression. SRSF1 controls the alternative splicing of RasGRP1 and subsequent protein expression. Our findings extend evidence that alternative splicing plays a central role in the aberrant T cell function in patients with SLE by controlling the expression of multiple genes.

Loss of RASGRP1 in humans impairs T‐cell expansion leading to Epstein‐Barr virus susceptibility

Inherited CTPS1, CD27, and CD70 deficiencies in humans have revealed key factors of T‐lymphocyte expansion, a critical prerequisite for an efficient immunity to Epstein–Barr virus (EBV) infection. RASGRP1 is a T‐lymphocyte‐specific nucleotide exchange factor known to activate the pathway of MAP kinases (MAPK). A deleterious homozygous mutation in RASGRP1 leading to the loss RASGRP1 expression was identified in two siblings who both developed a persistent EBV infection leading to Hodgkin lymphoma. RASGRP1‐deficient T cells exhibited defective MAPK activation and impaired proliferation that was restored by expression of wild‐type RASGRP1. Similar defects were observed in T cells from healthy individuals when RASGRP1 was downregulated. RASGRP1‐deficient T cells also exhibited decreased CD27‐dependent proliferation toward CD70‐expressing EBV‐transformed B cells, a crucial pathway required for expansion of antigen‐specific T cells during anti‐EBV immunity. Furthermore, RASGRP1‐deficient T cells failed to upregulate CTPS1, an important enzyme involved in DNA synthesis. These results show that RASGRP1 deficiency leads to susceptibility to EBV infection and demonstrate the key role of RASGRP1 at the crossroad of pathways required for the expansion of activated T lymphocytes.

Suppressive signals in colorectal cancer: RasGRP1 a new marker for anti-EGFR therapy?

625 Background: Treatment of metastatic colorectal cancer (mCRC) is largely palliative, making potentially curative therapy via molecular inhibition of specific cellular targets in CRC is a highly sought-after goal. One target of considerable focus in both basic and clinical investigation in CRC is the Epidermal Growth Factor Receptor (EGFR). Despite widespread EGFR expression in CRC, clinical trials have shown modest benefit from the use of anti-EGFR blocking antibodies and tumors with activating mutations in KRAS (KRASMUT) do not benefit from EGFR blockade. Given the ubiquitous expression of EGFR in CRC, why does such a large subset of patients fail to benefit from anti-EGFR antibodies? Methods: We combine the analysis of genetic mouse models, CRC cell line, and CRC patient database information and tumor samples. Results: We recently reported that two structurally distinct types of RasGEFs, SOS1 and RasGRP1, are co-expressed in both normal intestinal epithelial cells and in CRC cells. We observed that EGFR signals in CRC cells with KRASMUT result in even more RAS activation, arguing that RasGEFs load more RAS molecules with GTP following EGF stimulation. Indeed, we found that both SOS1 and RasGRP1 are activated downstream of the EGFR. Quite surprisingly, SOS1 and RasGRP1 have opposing functions here. Biochemically, RasGRP1 limits the amount of EGFR-SOS1-RAS signals. Biologically, knockdown of RasGRP1 expression in KRASMUT CRC cells leads to increased tumor growth in a xenograft mouse model. Conclusions: We hypothesize that anti-EGFR therapy may lead to unwanted inhibition of the inhibitory EGFR signals when CRC tumor express significant levels of RasGRP1 protein. We will discuss our current research that focuses on RasGRP1 as a prognostic marker of CRC outcome but also as a diagnostic indicator for EGFR therapy.

RasGRP1 opposes proliferative EGFR-SOS1-Ras signals and restricts intestinal epithelial cell growth.

The character of EGFR signals can influence cell fate but mechanistic insights into intestinal EGFR-Ras signalling are limited. Here we show that two distinct Ras nucleotide exchange factors, RasGRP1 and SOS1, lie downstream of EGFR but act in functional opposition. RasGRP1 is expressed in intestinal crypts where it restricts epithelial growth. High RasGRP1 expression in colorectal cancer (CRC) patient samples correlates with a better clinical outcome. Biochemically, we find that RasGRP1 creates a negative feedback loop that limits proliferative EGFR-SOS1-Ras signals in CRC cells. Genetic Rasgrp1 depletion from mice with either an activating mutation in KRas or with aberrant Wnt signalling due to a mutation in Apc resulted in both cases in exacerbated Ras-ERK signalling and cell proliferation. The unexpected opposing cell biological effects of EGFR-RasGRP1 and EGFR-SOS1 signals in the same cell shed light on the intricacy of EGFR-Ras signalling in normal epithelium and carcinoma.

Abstract LB-306: The Ras exchange factor RasGRP1 opposes proliferative EGFR-SOS1 Ras signals and restricts intestinal epithelial cell growth

Abstract The character of EGFR signals can influence cell fate. Anti-EGFR treatment has been successful as cancer therapy but not in colorectal cancer (CRC) where activating somatic KRAS mutations (KRASMUT) are prevalent. While relevant to CRC, intestinal EGFR signaling is poorly understood, particularly in the context of KRASMUT. Here we show that two distinct Ras nucleotide exchange factors, RasGRP1 and SOS1, lie downstream of the EGFR but act in functional opposition to one another in the context of KRASMUT. RasGRP1 creates a negative feedback loop that limits EGFR-SOS1-Ras signals and restricts CRC growth. Genetic Rasgrp1 depletion from KRasMUT mice exacerbates intestinal epithelial cell growth and dysplasia, leading to a highly serrated colonic epithelium. Furthermore, low RasGRP1 expression in CRC patient specimens correlates with poor clinical outcome. The unexpected inhibitory role of EGFR-RasGRP1 signals in KRASMUT gastrointestinal malignancies reveals an intricacy of EGFR signaling that should be considered for future molecular therapeutics. Citation Format: Philippe Depeille, Linda M. Henricks, Robert van de Ven, Ed Lemmens, Mary Matli, Kevin M. Haigis, David Donner, Robert Warren, Jeroen P. Roose. The Ras exchange factor RasGRP1 opposes proliferative EGFR-SOS1 Ras signals and restricts intestinal epithelial cell growth. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-306. doi:10.1158/1538-7445.AM2014-LB-306

AB0052 Tnfa influences rasgrp1 and rasgrp3 expression levels in pbmc, b and t cells.

BackgroundRheumatoid arthritis (RA) is the most common inflammatory arthritis. B and T lymphocytes play a central role in the pathophysiology of RA. RasGRP is a member of the CDC25 family...

The RAS Guanyl Nucleotide-releasing Protein RasGRP1 Is Involved in Lymphatic Development in Zebrafish

The molecular basis of the lymphatic development remains largely unknown. Using zebrafish as a model, we discovered a novel role for the Ras guanine-releasing protein 1 (RasGRP1), a protein involved in Ras activation in lymphangiogenesis. Secondary lymphatic sprouts from the posterior cardinal vein give rise to thoracic duct which is the first lymphatic vessel in zebrafish. Knockdown of rasgrp1 by injecting morpholino in zebrafish embryos impaired formation of thoracic duct accompanied by pericardial and truck edema, whereas blood vessel development of the embryos was largely unaffected. In rasgrp1-knockdown embryos, the number of sprouts producing the string of parachordal lymphangioblast cells was reduced. Meanwhile the total number of the secondary sprouts was not changed. As a result, the number of venous intersegmental vessels was increased, whereas the number of lymphatic vessel was reduced at a later stage. The lymphatic developmental defects caused by rasgrp1 knockdown could be rescued by ectopic expression of a constitutively active HRas. Further analysis revealed that RasGRP1 knockdown could synergize with flt4/vegfr3 knockdown to induce defects in lymphangiogenesis. Taken together, this finding demonstrates a critical role for RasGRP1 in lymphatic development in zebrafish.

RasGRP1 and RasGRP3 expression in lymphocytes of rheumatoid arthritis patients

IntroductionRasGRP is a member of the CDC25 family of Ras guanyl nucleotide exchange factors. RasGRP1 is expressed in T and B cells whereas RasGRP3 is only expressed in B cells....