Alternative titles; symbols
HGNC Approved Gene Symbol: RAC2
SNOMEDCT: 723443003;
Cytogenetic location: 22q13.1 Genomic coordinates (GRCh38): 22:37,225,270-37,244,269 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 22q13.1 | ?Immunodeficiency 73C with defective neutrophil chemotaxis and hypogammaglobulinemia | 618987 | Autosomal recessive | 3 |
| Immunodeficiency 73A with defective neutrophil chemotaxix and leukocytosis | 608203 | Autosomal dominant | 3 | |
| Immunodeficiency 73B with defective neutrophil chemotaxis and lymphopenia | 618986 | Autosomal dominant | 3 |
The RAC2 gene encodes a member of the RHO family of GTPases, which are a group of cellular signaling molecules that bind downstream effectors to activate a variety of cellular signaling pathways, including actin polymerization, cell migration, and formation of the phagocytic NADPH oxidase complex. RAC2 expression is limited to the hematopoietic system (summary by Lougaris et al., 2020).
Didsbury et al. (1989) identified 2 human cDNAs, which they called RAC1 (602048) and RAC2, that are 92% identical and share 58% and 26 to 30% amino acid identity with human RHOS and RAS, respectively. The 2 genes encode the C-terminal consensus sequence (CXXX-COOH), which localizes RAS to the inner plasma membrane, and the residues gly12 and ala59, at which sites mutations elicit transforming potential to RAS. RAC2 mRNA displayed relative myeloid tissue selectivity and showed an increase upon differentiation of HL-60 and U937 cells to neutrophil-like and monocyte-like morphology, respectively. Using transfection experiments, Didsbury et al. (1989) showed that RAC1 and RAC2 are substrates for ADP-ribosylation by the C3 component of botulinum toxin. See also RAC3 (602050).
Using a cDNA subtraction method, representational display analysis, Li et al. (2000) showed that Rac2 is selectively expressed in mouse type 1 helper T lymphocytes (Th1). Rac2 induces the interferon-gamma (147570) promoter through cooperative interaction of the NF-kappa-B (164011) and p38 MAP kinase (600289) pathways.
Diebold and Bokoch (2001) showed that RAC2 is required for the transfer of electrons from NADPH to cytochrome b-associated FAD, then to cytochrome b heme, and finally to oxygen. Using site-specific mutants, they showed that RAC2 acts independently of p67-phox (233710) to regulate the initial transfer of electrons from NADPH to FAD and that RAC2 binding to p67-phox is necessary to complete electron transfer to molecular oxygen to form superoxide anion.
Gu et al. (2002) found that the expression of 38 known genes was significantly altered in Rac2 -/- mouse mast cells after cytokine stimulation compared with those of wildtype cells. Of these, Mcp7 (TPSAB1; 191080) transcription in wildtype cells was increased 4-fold after stimulation with stem cell factor (SCF) (KITLG; 184745); however, in spite of a compensatory Rac1 increase in Rac2-deficient cells, SCF-induced Mcp7 transcription did not occur in these cells. Gu et al. (2002) concluded that in Rac2 -/- mast cells loss of Mcp7 induction was due to reduced Jnk (see MAPK8; 601158) activity but not due to reduced NFKB (see 164011) activity.
By studying host responses to E. coli cytotoxic necrotizing factor-1 (CNF1) in Drosophila and human cells, Boyer et al. (2011) showed that the host indirectly sensed the pathogen via its modification and activation of RAC2. After CNF1 modified RAC2, RAC2 interacted with the innate immune adaptors Imd and RIPK1 (603453)-RIPK2 (603455) in flies and human cells, respectively. Induction of the immune response in flies required CNF1 enzymatic activity, which, in mammals, catalyzes deamidation of a glutamine to glutamic acid in RAC2, abolishing GTPase activity and locking the enzyme into an active form. Modified RAC2 interacted with RIPK1 and RIPK2 to induce immune activation via NFKB and IL8 (146930) expression in human cells. Boyer et al. (2011) concluded that virulence factors such as CNF1 induce an immune response through this mechanism, whereas avirulent microbes fail to provoke host responses.
Courjal et al. (1997) determined that RAC2 contains at least 7 exons, spanning over 18 kb of DNA.
By fluorescence in situ hybridization, Courjal et al. (1997) mapped the RAC2 gene to 22q12.3-q13.2.
Immunodeficiency 73A with Defective Neutrophil Chemotaxis and Leukocytosis
In a boy with immunodeficiency-73A with defective neutrophil chemotaxis and leukocytosis (IMD73A; 608203), Ambruso et al. (2000) identified a de novo heterozygous missense mutation in the RAC2 gene (D57N; 602049.0001). The mutant D57N RAC2 bound GDP, but not GTP, and inhibited oxidase activation and superoxide anion production in vitro. Thus it was an inhibitory mutation for RAC2 activity. Williams et al. (2000) reported functional studies demonstrating that the D57N mutant behaves in a dominant-negative fashion at the cellular level.
In a boy with IMD73A, Accetta et al. (2011) identified de novo heterozygosity for the D57N mutation in the RAC2 gene. In vitro studies of patient neutrophils showed abnormally enhanced adhesion to fibronectin associated with disorganized actin formation compared to controls.
Immunodeficiency 73B with Defective Neutrophil Chemotaxis and Lymphopenia
In 3 unrelated patients with immunodeficiency-73B with defective neutrophil chemotaxis and lymphopenia (IMD73B; 618986), Hsu et al. (2019) identified a de novo heterozygous missense mutation in the RAC2 gene (E62K; 602049.0002). The mutation, which was found by exome sequencing or targeted sequencing of a gene panel, was confirmed by Sanger sequencing in all cases. Patient neutrophils and cells transfected with the mutation had increased production of reactive oxygen species (ROS) both at a basal rate and in response to fMLF. Additional abnormalities included impaired fMLF-induced chemotaxis, increased ruffling, abnormal actin cycling, and large vesicle formation in neutrophils. Further studies suggested that E62K favors the active GTP-bound state and causes impaired GTP hydrolysis compared to wildtype, resulting in prolonged activation of downstream effectors. The mutation resulted in a dominant gain-of-function effect.
In 3 members of a 3-generation family with IMD73B, Smits et al. (2020) identified a heterozygous E62K mutation in the RAC2 gene. In vitro studies of patient neutrophils showed defective migration and reduced bacterial killing. However, there was an increase of GTP-bound RAC2 after fMLF stimulation compared to controls, consistent with a gain-of-function activating effect. T-cell subsets showed increased effector T cells and decreased recent thymic emigrant cells, suggesting disturbances in RAC2 signal-mediated chemotactic function of T cells. The authors suggested that increased GTP-bound RAC2 may impede physiologic actin polymerization.
In a 10-year-old Ukrainian girl with IMD73B, Sharapova et al. (2019) identified a heterozygous missense mutation in the RAC2 gene (N92T; 602049.0004). The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not present in the mother; DNA from the father was not available. The mutation was not found in public databases, including gnomAD. Cell lines transfected with the N92T mutation showed characteristics of active GTP-bound RAC2, including enhanced NADHPH oxidase activity both at rest and in response to PMA. The findings suggested that the N92T mutation confers a gain-of-function activating effect resulting in defects in both the lymphoid and myeloid lineages.
Immunodeficiency 73C with Defective Neutrophil Chemotaxis and Hypogammaglobulinemia
In 2 sibs, born of consanguineous Iranian parents, with immunodeficiency-73C with defective neutrophil chemotaxis and hypogammaglobulinemia (IMD73C; 618987), Alkhairy et al. (2015) identified a homozygous nonsense mutation in the RAC2 gene (W56X; 602049.0005). The mutation was found by whole-exome sequencing and confirmed by Sanger sequencing. It was found in heterozygous state in the mother but a sample from the father was not available. Western blot analysis of fibroblasts transfected with the mutation showed absent RAC2 expression, consistent with a loss of function. The patients had hypogammaglobulinemia; all known causative gene defects responsible for common variable immunodeficiency (CVID) were excluded.
Gu et al. (2003) generated mice with a conditional deficiency in Rac1 in order to avoid the embryonic lethality observed in homozygous Rac1-deficient mice. Rac1-deficient hematopoietic stem cells (HSCs), but not Rac2-deficient HSCs, failed to engraft in the marrow of irradiated recipient mice. Deletion of both Rac1 and Rac2 resulted in a massive egress of HSCs into the peripheral blood circulation. Rac2, but not Rac1, regulated superoxide production and directed migration in neutrophils. Gu et al. (2003) concluded that the 2 GTPases play distinct roles in actin organization, cell survival, and proliferation in neutrophils and HSCs, possibly due to the subcellular localization of each protein.
Walmsley et al. (2003) generated mice with a conditional Rac1 deficiency specifically in the B-cell lineage. In the absence of both Rac1 and Rac2, B-cell development was almost completely blocked. Both GTPases were required to transduce B-cell receptor (BCR) signals leading to proliferation, survival, and the upregulation of Baffr (TNFRSF13C; 606269), the B-cell-activating receptor for BAFF (TNFSF13B; 603969), which is required for B-cell development and maintenance.
Using 2-photon video microscopy and lymph node cells from Rac1- and Rac2-deficient mice, Benvenuti et al. (2004) showed that dendrites of mature dendritic cells, under the control of Rac1 and Rac2, but not Rho (165390) itself, contact and then entrap naive T cells.
In an adaptation of loss-of-function screening to mouse models of cancer, Meacham et al. (2009) introduced a library of shRNAs into individual mice using transplantable E-mu-myc lymphoma cells. This approach allowed them to screen nearly 1,000 genetic alterations in the context of a single tumor-bearing mouse. Their experiments identified a central role for regulators of actin dynamics and cell motility in lymphoma cell homeostasis in vivo. Validation experiments confirmed that these proteins represent bona fide lymphoma drug targets. Additionally, suppression of 2 of these targets, Rac2 and twinfilin (610932), potentiated the action of the front-line chemotherapeutic vincristine, suggesting a critical relationship between cell motility and tumor relapse in hematopoietic malignancies.
Hsu et al. (2019) found that mice heterozygous for the E62K Rac2 mutation (602049.0002) developed lymphopenia, increased neutrophil F-actin, and excessive superoxide production, similar to that observed in patients with IMD73B.
In a male infant, born to nonconsanguineous parents, with immunodeficiency-73A with defective neutrophil chemotaxis and leukocytosis (IMD73A; 608203), Ambruso et al. (2000) and Williams et al. (2000) identified a de novo heterozygous c.169G-A transition in exon 3 of the RAC2 gene, resulting in an asp57-to-asn (D57N) substitution at a highly conserved residue in a GTP-binding domain. The unaffected parents and a healthy sib did not carry the mutation. The mutant D57N RAC2 bound GDP but not GTP and inhibited oxidase activation and superoxide anion production in vitro. Thus it was an inhibitory mutation. Williams et al. (2000) reported functional studies demonstrating that the D57N mutant behaves in a dominant-negative fashion at the cellular level.
In a boy with IMD73A, Accetta et al. (2011) identified a de novo heterozygous D57N mutation in the RAC2 gene. In vitro studies of patient neutrophils showed abnormally enhanced adhesion to fibronectin associated with disorganized actin formation compared to controls. Accetta et al. (2011) concluded that the mutation resulted in defective T-cell development in the thymus due to defects in migration, adhesion, and proper T-cell activation and selection.
In 3 unrelated patients with immunodeficiency-73B with defective neutrophil chemotaxis and lymphopenia (IMD73B; 618986), Hsu et al. (2019) identified a de novo heterozygous c.184G-A transition in exon 3 of the RAC2 gene, resulting in a glu62-to-lys (E62K) substitution in the highly conserved Switch II domain. The mutation, which was found by exome sequencing or targeted sequencing of a gene panel, was confirmed by Sanger sequencing in all cases. Patient neutrophils and cells transfected with the mutation had increased production of reactive oxygen species (ROS), both at a basal rate and in response to fMLF. Additional abnormalities included impaired fMLF-induced chemotaxis, increased ruffling, abnormal actin cycling, and large vesicle formation in neutrophils. Further studies suggested that E62K favors the active GTP-bound state and causes impaired GTP hydrolysis compared to wildtype, resulting in prolonged activation of downstream effectors. The mutation resulted in a dominant gain-of-function effect.
In 3 members of a 3-generation family with IMD73B, Smits et al. (2020) identified a heterozygous E62K mutation in the RAC2 gene. In vitro studies of patient neutrophils showed defective migration and reduced bacterial killing. However, there was an increase of GTP-bound RAC2 after fMLF stimulation compared to controls, consistent with a gain-of-function activating effect. T-cell subsets showed increased effector T cells and decreased recent thymic emigrant cells, suggesting disturbances in RAC2 signal-mediated chemotactic function of T cells. The authors suggested that increased GTP-bound RAC2 may impede physiologic actin polymerization.
In a father and his 2 daughters with immunodeficiency-73B with defective neutrophil chemotaxis and lymphopenia (IMD73B; 618986), Lougaris et al. (2019) identified a heterozygous c.101C-A transversion (c.101C-A, NM_002872) in the RAC2 gene, resulting in a pro34-to-his (P34H) substitution within the highly conserved Switch I domain, which is important for interactions with GEFs and downstream effectors. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. Patient cells showed normal levels of the RAC2 protein, but in vitro cellular functional studies showed that the mutant RAC2 protein had increased binding to the PAK effector protein compared to wildtype, consistent with a gain-of-function effect. Patient neutrophils showed increased filamentous actin content and an increased oxidative respiratory burst after stimulation of fMLP compared to controls. Response to PMA was normal. The patients also had lymphopenia, increased lymphocyte apoptosis, and reduced numbers of NK cells.
In a 10-year-old Ukrainian girl with immunodeficiency-73B with defective neutrophil chemotaxis and lymphopenia (IMD73B; 618986), Sharapova et al. (2019) identified a heterozygous c.275A-C transversion in the RAC2 gene, resulting in an asn92-to-thr (N92T) substitution. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not present in the mother; DNA from the father was not available. The mutation was not found in public databases, including gnomAD. Cell lines transfected with the N92T mutation showed characteristics of active GTP-bound RAC2, including enhanced NADHPH oxidase activity both at rest and in response to PMA. The findings suggested that the N92T mutation confers a gain-of-function activating effect resulting in defects in both the lymphoid and myeloid lineages.
In 2 sibs, born of consanguineous Iranian parents, with immunodeficiency-73C with defective neutrophil chemotaxis and hypogammaglobulinemia (IMD73C; 618987), Alkhairy et al. (2015) identified a homozygous mutation in the RAC2 gene, resulting in a trp56-to-ter (W56X) substitution. The mutation was found by whole-exome sequencing and confirmed by Sanger sequencing. The mutation was present in heterozygous state in the mother but DNA from the father was not available. Western blot analysis of fibroblasts transfected with the mutation showed absent RAC2 expression, consistent with a loss of function. The patients had hypogammaglobulinemia; all known causative gene defects responsible for common variable immunodeficiency (CVID) were excluded.
Accetta, D., Syverson, G., Bonacci, B., Reddy, S., Bengtson, C., Surfus, J., Harbeck, R., Huttenlocher, A., Grossman, W., Routes, J., Verbsky, J. Human phagocyte defect caused by a Rac2 mutation detected by means of neonatal screening for T-cell lymphopenia. (Letter) J. Allergy Clin. Immun. 127: 535-538, 2011. [PubMed: 21167572] [Full Text: https://doi.org/10.1016/j.jaci.2010.10.013]
Alkhairy, O. K., Rezaei, N., Graham, R. R., Abolhassani, H., Borte, S., Hultenby, K., Wu, C., Aghamohammadi, A., Williams, D. A., Behrens, T. W., Hammarstrom, L., Pan-Hammarstrom, Q. RAC2 loss-of-function mutation in 2 siblings with characteristics of common variable immunodeficiency. (Letter) J. Allergy Clin. Immun. 135: 1380-1384, 2015. [PubMed: 25512081] [Full Text: https://doi.org/10.1016/j.jaci.2014.10.039]
Ambruso, D. R., Knall, C., Abell, A. N., Panepinto, J., Kurkchubasche, A., Thurman, G., Gonzalez-Aller, C., Hiester, A., deBoer, M., Harbeck, R. J., Oyer, R., Johnson, G. L., Roos, D. Human neutrophil immunodeficiency syndrome is associated with an inhibitory Rac2 mutation. Proc. Nat. Acad. Sci. 97: 4654-4659, 2000. [PubMed: 10758162] [Full Text: https://doi.org/10.1073/pnas.080074897]
Benvenuti, F., Hugues, S., Walmsley, M., Ruf, S., Fetler, L., Popoff, M., Tybulewicz, V. L. J., Amigorena, S. Requirement of Rac1 and Rac2 expression by mature dendritic cells for T cell priming. Science 305: 1150-1153, 2004. [PubMed: 15326354] [Full Text: https://doi.org/10.1126/science.1099159]
Boyer, L., Magoc, L., Dejardin, S., Cappillino, M., Paquette, N., Hinault, C., Charriere, G. M., Ip, W. K. E., Fracchia, S., Hennessy, E., Erturk-Hasdemir, D., Reichhart, J.-M., Silverman, N., Lacy-Hulbert, A., Stuart, L. M. Pathogen-derived effectors trigger protective immunity via activation of the Rac2 enzyme and the IMD or Rip kinase signaling pathway. Immunity 35: 536-549, 2011. [PubMed: 22018470] [Full Text: https://doi.org/10.1016/j.immuni.2011.08.015]
Courjal, F., Chuchana, P., Theillet, C., Fort, P. Structure and chromosomal assignment to 22q12 and 17qter of the ras-related Rac2 and Rac3 human genes. Genomics 44: 242-246, 1997. [PubMed: 9299243] [Full Text: https://doi.org/10.1006/geno.1997.4871]
Didsbury, J., Weber, R. F., Bokoch, G. M., Evans, T., Snyderman, R. rac, a novel ras-related family of proteins that are botulinum toxin substrates. J. Biol. Chem. 264: 16378-16382, 1989. [PubMed: 2674130]
Diebold, B. A., Bokoch, G. M. Molecular basis for Rac2 regulation of phagocyte NADPH oxidase. Nature Immun. 2: 211-215, 2001. [PubMed: 11224519] [Full Text: https://doi.org/10.1038/85259]
Gu, Y., Byrne, M. C., Paranavitana, N. C., Aronow, B., Siefring, J. E., D'Souza, M., Horton, H. F., Quilliam, L. A., Williams, D. A. Rac2, a hematopoiesis-specific Rho GTPase, specifically regulates mast cell protease gene expression in bone marrow-derived mast cells. Molec. Cell. Biol. 22: 7645-7657, 2002. [PubMed: 12370311] [Full Text: https://doi.org/10.1128/MCB.22.21.7645-7657.2002]
Gu, Y., Filippi, M.-D., Cancelas, J. A., Siefring, J. E., Williams, E. P., Jasti, A. C., Harris, C. E., Lee, A. W., Prabhakar, R., Atkinson, S. J., Kwiatkowski, D. J., Williams, D. A. Hematopoietic cell regulation by Rac1 and Rac2 guanosine triphosphatases. Science 302: 445-449, 2003. [PubMed: 14564009] [Full Text: https://doi.org/10.1126/science.1088485]
Hsu, A. P., Donko, A., Arrington, M. E., Swamydas, M., Fink, D., Das, A., Escobedo, O., Bonagura, V., Szabolcs, P., Steinberg, H. N., Bergerson, J., Skoskiewicz, A., and 12 others. Dominant activating RAC2 mutation with lymphopenia, immunodeficiency, and cytoskeletal defects. Blood 133: 1977-1988, 2019. [PubMed: 30723080] [Full Text: https://doi.org/10.1182/blood-2018-11-886028]
Li, B., Yu, H., Zheng, W., Voll, R., Na, S., Roberts, A. W., Williams, D. A., Davis, R. J., Ghosh, S., Flavell, R. A. Role of the guanosine triphosphatase Rac2 in T helper 1 cell differentiation. Science 288: 2219-2222, 2000. [PubMed: 10864872] [Full Text: https://doi.org/10.1126/science.288.5474.2219]
Lougaris, V., Baronio, M., Gazzurelli, L., Benvenuto, A., Plebani, A. RAC2 and primary human immune deficiencies. J. Leukoc. Biol. 108: 687-696, 2020. [PubMed: 32542921] [Full Text: https://doi.org/10.1002/JLB.5MR0520-194RR]
Lougaris, V., Chou, J., Beano, A., Wallace, J. G., Baronio, M., Gazzurelli, L., Lorenzini, T., Moratto, D., Tabellini, G., Parolini, S., Seleman, M., Stafstrom, K., Xu, H., Harris, C., Geha, R. S., Plebani, A. A monoallelic activating mutation in RAC2 resulting in a combined immunodeficiency. (Letter) J. Allergy Clin. Immun. 143: 1649-1653, 2019. [PubMed: 30654050] [Full Text: https://doi.org/10.1016/j.jaci.2019.01.001]
Meacham, C. E., Ho, E. E., Dubrovsky, E., Gertler, F. B., Hemann, M. T. In vivo RNAi screening identifies regulators of actin dynamics as key determinants of lymphoma progression. Nature Genet. 41: 1133-1137, 2009. [PubMed: 19783987] [Full Text: https://doi.org/10.1038/ng.451]
Sharapova, S. O., Haapaniemi, E., Sakovich, I. S., Kostyuchenko, L. V., Donko, A., Dulau-Florea, A., Malko, O., Bondarenko, A. V., Stegantseva, M. V., Leto, T. L., Uygun, V., Karasu, G. T., Holland, S. M., Hsu, A. P., Aleinikova, O. V. Heterozygous activating mutation in RAC2 causes infantile-onset combined immunodeficiency with susceptibility to viral infections. Clin. Immun. 205: 1-5, 2019. [PubMed: 31071452] [Full Text: https://doi.org/10.1016/j.clim.2019.05.003]
Smits, B. M., Lelieveld, P. H. C., Ververs, F. A., Turkenburg, M., de Koning, C., van Dijk, M., Leavis, H. L., Boelens, J. J., Lindemans, C. A., Bloem, A. C., van de Corput, L., van Montfrans, J., Nierkens, S., van Gijn, M. E., Geerke, D. P., Waterham, H. R., Koenderman, L., Boes, M. A dominant activating RAC2 variant associated with immunodeficiency and pulmonary disease. (Letter) Clin. Immun. 212: 108248, 2020. Note: Electronic Article. [PubMed: 31382036] [Full Text: https://doi.org/10.1016/j.clim.2019.108248]
Walmsley, M. J., Ooi, S. K. T., Reynolds, L. F., Smith, S. H., Ruf, S., Mathiot, A., Vanes, L., Williams, D. A., Cancro, M. P., Tybulewicz, V. L. J. Critical roles for Rac1 and Rac2 GTPases in B cell development and signaling. Science 302: 459-462, 2003. [PubMed: 14564011] [Full Text: https://doi.org/10.1126/science.1089709]
Williams, D. A., Tao, W., Yang, F., Kim, C., Gu, Y., Mansfield, P., Levine, J. E., Petryniak, B., Derrow, C. W., Harris, C., Jia, B., Zheng, Y., Ambruso, D. R., Lowe, J. B., Atkinson, S. J., Dinauer, M. C., Boxer, L. Dominant negative mutation of the hematopoietic-specific Rho GTPase, Rac 2, is associated with a human phagocyte immunodeficiency. Blood 96: 1646-1654, 2000. [PubMed: 10961859]