Alternative titles; symbols
HGNC Approved Gene Symbol: ANTXR2
SNOMEDCT: 1197494003;
Cytogenetic location: 4q21.21 Genomic coordinates (GRCh38): 4:79,901,146-80,073,472 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 4q21.21 | Hyaline fibromatosis syndrome | 228600 | Autosomal recessive | 3 |
The ANTXR2 gene encodes a transmembrane protein in which the von Willebrand A (vWA) domain binds to both laminin (see, e.g., LMNA, 150330) and collagen IV (see, e.g., COL4A1, 120130), suggesting that this protein plays a role in basement membrane matrix assembly and endothelial cell morphogenesis. It also functions as a receptor for the anthrax toxin (summary by Denadai et al., 2012).
Using differential display and library screening to identify genes upregulated during capillary morphogenesis, Bell et al. (2001) cloned CMG2 from an umbilical vein endothelial cell cDNA library. The deduced 386-amino acid protein has a calculated molecular mass of 45 kD. CMG2 contains a potential N-terminal signal sequence, followed by a von Willebrand factor (613160) type A (VWFA) domain and a central transmembrane domain. RT-PCR of several adult and fetal tissues detected expression only in placenta. Infection of fluorescence-tagged CMG2 with an adenovirus vector revealed targeting of CMG2 to the endoplasmic reticulum. CMG2 was also present within intracellular vesicles in some cells.
Using an RT-PCR-based approach, Scobie et al. (2003) cloned full-length CMG2 from placenta mRNA. The deduced protein contains 489 amino acids. The VWFA domain of CMG2 shares 60% amino acid identity with the VWFA domain of TEM8 (ANTXR1; 606410), and both proteins have a metal ion-dependent adhesion site (MIDAS) within their VWFA domain. Scobie et al. (2003) determined that several isoforms of CMG2 are generated by alternative splicing. A 488-amino acid isoform differs from the 489-amino acid form only in the final 12 C-terminal amino acids. The 489-amino acid CMG2 protein was expressed at the plasma membrane of transfected Chinese hamster ovary cells. Northern blot analysis detected transcripts of about 3.4, 3.9, and 5.1 kb. Expression of at least 1 CMG2 transcript was detected in heart, lung, liver, skeletal muscle, peripheral blood leukocytes, placenta, small intestine, kidney, colon, and spleen. No expression was detected in brain and thymus.
Bell et al. (2001) determined that CMG2 was 1 of several transcripts upregulated by umbilical vein endothelial cells during capillary morphogenesis in 3-dimensional collagen matrices. A bacterially expressed recombinant VWFA domain of CMG2 bound collagen type IV (see 120130) and laminin (see 150320), but not other extracellular matrix proteins.
Scobie et al. (2003) determined that the 489-amino acid CMG2 isoform, like TEM8, functions as an anthrax toxin receptor. Following expression in receptor-deficient Chinese hamster ovary cells, CMG2 bound the protective antigen (PA) subunit of anthrax toxin and mediated toxin internalization. Binding between the VWFA domain of CMG2 and PA was direct and depended on divalent cations, with highest preference for Ca(2+), followed by Mn(2+), Mg(2+), and Zn(2+). A soluble version of the CMG2 VWFA domain inhibited intoxication of cells expressing endogenous toxin receptors.
Rainey et al. (2005) found that the pH threshold for conversion of the anthrax PA toxin prepore to pore and translocation of toxin from the endosome to the cytosol differed by a pH unit depending on which receptor was used. PA associated with the relatively low-affinity ANTXR1 receptor could proceed through these events at near neutral pH and showed low sensitivity to ammonium chloride. In contrast, PA associated with the high-affinity ANTXR2 receptor required more acidic conditions to proceed through these events and could be inhibited by ammonium chloride. Rainey et al. (2005) also found that PA dissociated from ANTXR1 or ANTXR2 upon pore formation. They proposed that toxin can form pores at different points in the endocytic pathway depending on which receptor is used for entry.
Carette et al. (2009) used insertional mutagenesis to develop a screening method to generate null alleles in a human cell line haploid for all chromosomes except chromosome 8. Using this approach, they identified genes encoding important elements of the biosynthetic pathway of diphthamide, which are required for the cytotoxic effects of diphtheria toxin and exotoxin A. Mutants in the known anthrax toxin receptor ANTXR2 were recovered, as well as mutants in HB-EGF (126150), the known diphtheria toxin receptor.
By genomic sequence analysis, Bell et al. (2001) mapped the CMG2 gene to chromosome 4q. The mapping of juvenile hyaline fibromatosis and infantile systemic hyalinosis (hyaline fibromatosis syndrome; see 228600) to 4q21 and the demonstration of mutations in CMG2 in both of these disorders (Hanks et al., 2003) indicated that the CMG2 gene is located at 4q21.
Crystal Structure
Santelli et al. (2004) reported the crystal structure of the anthrax protective antigen bound to CMG2 at 2.5-angstrom resolution. The structure reveals an extensive receptor-pathogen interaction surface mimicking the nonpathogenic recognition of the extracellular matrix by integrins. The binding surface is closely conserved in the 2 receptors across species, but is quite different in the integrin domains, explaining the specificity of the interaction. CMG2 engages 2 domains of the anthrax protective antigen. Modeling of the receptor-bound protective antigen(63) heptamer suggested that the receptor acts as a pH-sensitive brace to ensure accurate and timely membrane insertion.
In patients with variable age at onset of hyaline fibromatosis syndrome (HFS; 228600), Hanks et al. (2003) identified homozygous or compound heterozygous mutations in the ANTXR2 gene (608041.0001-608041.0002, 608041.0006-608041.0007). Preliminary genotype-phenotype analyses suggested that abrogation of binding by the VWFA domain resulted in a more severe disease, whereas in-frame mutations affecting a novel, highly conserved cytoplasmic domain result in a milder phenotype. CMG2 is a transmembrane protein that is induced during capillary morphogenesis and that binds laminin (156225) and collagen IV via a VWFA domain. The findings implicated perturbation of basement membrane matrix assembly as the cause of the characteristic perivascular hyaline deposition seen in this disorder.
Using the 4q21 location for the gene mutant in HFS as a guide for candidate gene identification, Dowling et al. (2003) identified and characterized mutations in the CMG2 gene causing the disorder (see 608041.0003-608041.0005).
Deuquet et al. (2009) analyzed the cellular consequences of several disease-associated mutations in the CMG2 gene, including mutations affecting the von Willebrand factor ectodomain (G105D; 608041.0003 and I189T; 608041.0006) and the transmembrane region (L329R; 608041.0004). All these mutant proteins were retained intracellularly, with labeling at the nuclear envelope and especially in the endoplasmic reticulum, in contrast to the wildtype protein, which showed mainly plasma membrane staining. Further studies showed decreased surface expression of these mutant proteins (less than 20% to about 30% of normal). Results of ligand-binding experiments with anthrax toxin showed that the mutants were able to bind ligand effectively, but there was a partial to complete loss of function in the cellular context due to varying degrees of retention of the mutant proteins in the endoplasmic reticulum. Deuquet et al. (2009) suggested that treatments based on chemical chaperones could be beneficial.
In 2 sibs and 2 unrelated patients, all of Brazilian origin, with HFS, Denadai et al. (2012) identified a truncating mutation in the ANTXR2 gene (1074delT; 608041.0008). All patients carried this mutation in compound heterozygosity with another pathogenic ANTXR2 mutation (see, e.g., 1073insC; 608041.0007). The 1074delT mutation had previously been reported by El-Kamah et al. (2010) in the homozygous state in 3 Egyptian sibs, born of consanguineous parents, who had a severe form of HFS resulting in death in childhood in all patients.
In 2 seemingly unrelated families in India, Hanks et al. (2003) found that juvenile-onset hyaline fibromatosis syndrome (HFS; 228600) was related to homozygosity for a 1707G-A transition in the CMG2 gene, a synonymous substitution that altered a consensus splice junction base, resulting in an in-frame deletion of exon 14; 4q21 haplotype data were consistent with this being a founder mutation in these 2 Indian families.
Denadai et al. (2012) noted that Hanks et al. (2003) did not number their mutations using the A of the ATG start codon of their ANTXR2 sequence (GenBank AK091721) as nucleotide 1. The correct numbering of this mutation, using the A of the ATG start codon of the ANTXR2 reference sequence (GenBank NM_058172.5) as nucleotide 1, is 1179G-A.
In 2 members of a Moroccan family with juvenile-onset hyaline fibromatosis syndrome (228600), Hanks et al. (2003) found that the disorder was associated with a 1670A-G transition in exon 14 of the CMG2 gene, resulting in a tyr381-to-cys (Y381C) substitution.
Denadai et al. (2012) noted that Hanks et al. (2003) did not number their mutations using the A of the ATG start codon of their ANTXR2 sequence (GenBank AK091721) as nucleotide 1. The correct numbering of this mutation, using the A of the ATG start codon of the ANTXR2 reference sequence (GenBank NM_058172.5) as nucleotide 1, is 1142A-G.
In a Turkish patient with juvenile-onset hyaline fibromatosis syndrome (228600) born to consanguineous parents, Dowling et al. (2003) identified a homoallelic gly105-to-asp (G105D) mutation in the CMG2 gene, which destabilized a von Willebrand factor A extracellular domain alpha helix.
In an African American patient with juvenile-onset hyaline fibromatosis syndrome (228600) from a consanguineous family, Dowling et al. (2003) identified homozygosity for a leu329-to-arg (L329R) mutation in the transmembrane domain of CMG2.
In a Turkish patient with infantile-onset hyaline fibromatosis syndrome (228600) born to consanguineous parents, Dowling et al. (2003) identified a truncating mutation in the CMG2 gene, glu220 to ter (E220X).
In 2 sibs of Swiss origin, Hanks et al. (2003) found that infantile-onset hyaline fibromatosis syndrome (228600) was related to compound heterozygosity for a 1094T-C transition in exon 7 of the CMG2 gene, resulting in an ile189-to-thr (I189T) mutation, and a frameshift 1-bp insertion in the poly(C) tract in exon 13 (1601insC; 608041.0007).
Denadai et al. (2012) noted that Hanks et al. (2003) did not number their mutations using the A of the ATG start codon of their ANTXR2 sequence (GenBank AK091721) as nucleotide 1. The correct numbering of this mutation, using the A of the ATG start codon of the ANTXR2 reference sequence (GenBank NM_058172.5) as nucleotide 1, is 566T-C.
In a Hispanic individual living in the United States, Hanks et al. (2003) found that infantile-onset hyaline fibromatosis syndrome (228600) was related to homozygosity for insertion of a cytosine in the poly(C) tract in exon 13 of the CMG2 gene. In 2 other families, each with 1 affected individual (1 of Puerto Rican/African American origin and 1 of Chinese origin), Hanks et al. (2003) identified the 1601insC frameshift mutation in heterozygous state; the other allele was not characterized in these cases. The mutation appeared to have arisen independently in these 3 families, because they carried different 4q21 haplotypes and CMG2 polymorphisms. Moreover, 2 further families had different mutations involving the poly(C) tract, which appears to be a mutation hotspot, presumably owing to the repetitive sequence.
Denadai et al. (2012) noted that Hanks et al. (2003) did not number their mutations using the A of the ATG start codon of their ANTXR2 sequence (GenBank AK091721) as nucleotide 1. The correct numbering of this mutation, using the A of the ATG start codon of the ANTXR2 reference sequence (GenBank NM_058172.5) as nucleotide 1, is 1073insC.
In 2 sibs and 2 unrelated patients, all of Brazilian origin, with hyaline fibromatosis syndrome (228600), Denadai et al. (2012) identified a 1-bp deletion (1074delT) in exon 13 of the ANTXR2 gene, resulting in a frameshift and premature termination (Ala359HisfsTer50). All patients carried this mutation in compound heterozygosity with another pathogenic ANTXR2 mutation (see, e.g., 1073insC; 608041.0007). The mutation had previously been reported by El-Kamah et al. (2010) in homozygous state in 3 Egyptian sibs, born of consanguineous parents, who had a severe form of hyaline fibromatosis syndrome resulting in death in childhood in all patients.
Bell, S. E., Mavila, A., Salazar, R., Bayless, K. J., Kanagala, S., Maxwell, S. A., Davis, G. E. Differential gene expression during capillary morphogenesis in 3D collagen matrices: regulated expression of genes involved in basement membrane matrix assembly, cell cycle progression, cellular differentiation and G-protein signaling. J. Cell Sci. 114: 2755-2773, 2001. [PubMed: 11683410] [Full Text: https://doi.org/10.1242/jcs.114.15.2755]
Carette, J. E., Guimaraes, C. P., Varadarajan, M., Park, A. S., Wuethrich, I., Godarova, A., Kotecki, M., Cochran, B. H., Spooner, E., Ploegh, H. L., Brummelkamp, T. R. Haploid genetic screens in human cells identify host factors used by pathogens. Science 326: 1231-1235, 2009. [PubMed: 19965467] [Full Text: https://doi.org/10.1126/science.1178955]
Denadai, R., Raposo-Amaral, C. E., Bertola, D., Kim, C., Alonso, N., Hart, T., Han, S., Stelini, R. F., Buzzo, C. L., Raposo-Amaral, C. A., Hart, P. S. Identification of 2 novel ANTXR2 mutations in patients with hyaline fibromatosis syndrome and proposal of a modified grading system. Am. J. Med. Genet. 158A: 732-742, 2012. [PubMed: 22383261] [Full Text: https://doi.org/10.1002/ajmg.a.35228]
Deuquet, J., Abrami, L., Difeo, A., Ramirez, M. C. M., Martignetti, J. A., van der Goot, F. G. Systemic hyalinosis mutations in the CMG2 ectodomain leading to loss of function through retention in the endoplasmic reticulum. Hum. Mutat. 30: 583-589, 2009. [PubMed: 19191226] [Full Text: https://doi.org/10.1002/humu.20872]
Dowling, O., Difeo, A., Ramirez, M. C., Tukel, T., Narla, G., Bonafe, L., Kayserili, H., Yuksel-Apak, M., Paller, A. S., Norton, K., Teebi, A. S., Grum-Tokars, V., Martin, G. S., Davis, G. E., Glucksman, M. J., Martignetti, J. A. Mutations in capillary morphogenesis gene-2 result in the allelic disorders juvenile hyaline fibromatosis and infantile systemic hyalinosis. Am. J. Hum. Genet. 73: 957-966, 2003. [PubMed: 12973667] [Full Text: https://doi.org/10.1086/378781]
El-Kamah, G. Y., Fong, K., El-Ruby, M., Afifi, H. H., Clements, S. E., Lai-Cheong, J. E., Amr, K., El-Darouti, M., McGrath, J. A. Spectrum of mutations in the ANTXR2 (CMG2) gene in infantile systemic hyalinosis and juvenile hyaline fibromatosis. (Letter) Brit. J. Derm. 163: 208-234, 2010. [PubMed: 20353455] [Full Text: https://doi.org/10.1111/j.1365-2133.2010.09784.x]
Hanks, S., Adams, S., Douglas, J., Arbour, L., Atherton, D. J., Balci, S., Bode, H., Campbell, M. E., Feingold, M., Keser, G., Kleijer, W., Mancini, G., and 9 others. Mutations in the gene encoding capillary morphogenesis protein 2 cause juvenile hyaline fibromatosis and infantile systemic hyalinosis. Am. J. Hum. Genet. 73: 791-800, 2003. [PubMed: 14508707] [Full Text: https://doi.org/10.1086/378418]
Rainey, G. J. A., Wigelsworth, D. J., Ryan, P. L., Scobie, H. M., Collier, R. J., Young, J. A. T. Receptor-specific requirements for anthrax toxin delivery into cells. Proc. Nat. Acad. Sci. 102: 13278-13283, 2005. [PubMed: 16141341] [Full Text: https://doi.org/10.1073/pnas.0505865102]
Santelli, E., Bankston, L. A., Leppla, S. H., Liddington, R. C. Crystal structure of a complex between anthrax toxin and its host cell receptor. Nature 430: 905-908, 2004. [PubMed: 15243628] [Full Text: https://doi.org/10.1038/nature02763]
Scobie, H. M., Rainey, G. J. A., Bradley, K. A., Young, J. A. T. Human capillary morphogenesis protein 2 functions as an anthrax toxin receptor. Proc. Nat. Acad. Sci. 100: 5170-5174, 2003. [PubMed: 12700348] [Full Text: https://doi.org/10.1073/pnas.0431098100]