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Severe Chilblain Lupus Is Associated with Heterozygous Missense Mutations of Catalytic Amino Acids or their Adjacent Mutations in the Exonuclease Domains of 3′-Repair Exonuclease 1

2012; Elsevier BV; Volume: 132; Issue: 12 Linguagem: Inglês

10.1038/jid.2012.210

1523-1747

Kazumitsu Sugiura, Takuya Takeichi, Michihiro Kono, Yasuki Ito, Yasushi Ogawa, Yoshinao Muro, Masashi Akiyama,

Viral Infections and Immunology Research

Aicardi–Goutières syndrome chilblain lupus double-stranded DNA familial chilblain lupus systemic lupus erythematosus single-stranded DNA 3′-repair DNA exonuclease 1 Chilblain lupus (CL) is a subtype of chronic cutaneous lupus erythematosus. Familial CL (FCL), inherited via an autosomal dominant trait, has been described in two families segregating distinct mutations in the 3′-repair DNA exonuclease 1 (TREX1) (Lee-Kirsch et al., 2007aLee-Kirsch M.A. Chowdhury D. Harvey S. et al.A mutation in TREX1 that impairs susceptibility to granzyme A-mediated cell death underlies familial chilblain lupus.J Mol Med. 2007; 85: 531-537Crossref PubMed Scopus (169) Google Scholar; Rice et al., 2007Rice G. Newman W.G. Dean J. et al.Heterozygous mutations in TREX1 cause familial chilblain lupus and dominant Aicardi-Goutieres syndrome.Am J Hum Genet. 2007; 80: 811-815Abstract Full Text Full Text PDF PubMed Scopus (299) Google Scholar). TREX1 is a potent 3′–5′ exonuclease that degrades single- and double-stranded DNA (ssDNA and dsDNA) in mammalian cells. TREX1 belongs to the exonuclease DEDDh family, whose members display low levels of sequence homology while possessing a common fold and identical active site organization termed the “DEDDh motif”(Brucet et al., 2007Brucet M. Querol-Audí J. Serra M. et al.Structure of the dimeric exonuclease TREX1 in complex with DNA displays a proline-rich binding site for WW domains.J Biol Chem. 2007; 282: 14547-14557Crossref PubMed Scopus (38) Google Scholar). Here we describe a Japanese case of FCL with the novel missense mutation p.Pro132Ala in TREX1. We demonstrate that the mutant TREX1 shows slightly reduced ssDNA cleavage function by in vitro exonuclease assays using recombinant mutant TREX1 proteins. A review of clinical features in patients with heterozygous missense mutations that are catalytic residues of or adjacent to the DEDDh motif in the three exonuclease domains of TREX1, including our case, revealed that all the patients had severe CL. The patient was a 62-year-old Japanese woman with painful bluish-red infiltrates with atrophic branching and ulcers on the fingers, hands, toes, cheeks, lips, and nose, which persisted in all seasons (Figure 1a and b). The eruptions occurred from 1 year of age. Five of her relatives from three generations had similar skin symptoms from early childhood (Figure 1d). Apart from the skin findings, physical examination was unremarkable. She never had any neurological symptoms. Histological examination of lesional skin from the left hand showed typical features of lupus erythematosus (Figure 1c). Laboratory investigations revealed the presence of antinuclear antibodies showing a homogeneous pattern with a titer of 1:80. Circulating autoantibodies against dsDNA and ssDNA were undetectable. Serum IgA and IgG were slightly elevated. There was no serological evidence for viral or bacterial infections. All other laboratory values, including complete blood cell count with differential coagulation, circulating complement factors, and liver function tests, as well as urine analysis, were within normal ranges. On the basis of the clinical, serological, and histological findings, as well as family history, FCL was suspected. The ethics committee of Nagoya University approved the studies described below. The study was conducted according to the Declaration of Helsinki Principles. The participants gave written informed consent. The coding region of TREX1 was amplified from genomic DNA from blood by PCR. Direct sequencing of the patient's PCR products revealed that the patient carried the heterozygous missense mutation p.Pro132Ala (c.394 C>G) in TREX1 (Figure 1e), which was not detected in the 100 control individuals (data not shown). The proline residue mutated by p.Pro132Ala is adjacent to the second aspartic acid residue of the DEDDh motif, an active catalytic site in the exonuclease domain of TREX 1 (Figure 2a). This proline residue was confirmed to be highly conserved in mammalians (Figure 2b). Thereafter, the ssDNA exonuclease activities were measured. Compared with the exonuclease activities of wild-type TREX1, those of TREX1 (P132A) were slightly reduced (Supplemental Figure S1 online). Download .pdf (.19 MB) Help with pdf files Supplementary Information TREX1 mutations are known to underlie four genetic disorders with distinctive phenotypes: Aicardi–Goutières syndrome (AGS), retinal vasculopathy with cerebral leukodystrophy, systemic lupus erythmatosus (SLE), and FCL (Crow et al., 2006Crow Y.J. Hayward B.E. Parmar R. et al.Mutations in the gene encoding the 3′-5′ DNA exonuclease TREX1 cause Aicardi-Goutières syndrome at the AGS1 locus.Nat Genet. 2006; 38: 917-920Crossref PubMed Scopus (655) Google Scholar; Lee-Kirsch et al., 2007bLee-Kirsch M.A. Gong M. Chowdhury D. et al.Mutations in the gene encoding the 3′-5′ DNA exonuclease TREX1 are associated with systemic lupus erythematosus.Nat Genet. 2007; 39: 1065-1067Crossref PubMed Scopus (518) Google Scholar; Richards et al., 2007Richards A. van den Maagdenberg A.M. Jen J.C. et al.C-terminal truncations in human 3′-5′ DNA exonuclease TREX1 cause autosomal dominant retinal vasculopathy with cerebral leukodystrophy.Nat Genet. 2007; 39: 1068-1070Crossref PubMed Scopus (314) Google Scholar). The majority of TREX1 mutations causing autosomal recessive AGS are predicted to be complete loss-of-function mutations. Only three AGS cases caused by heterozygous TREX1 mutations have been reported, and the causative TREX1 mutations were p.Asp18Asn, p.Asp200Asn, and p.Asp200His. It is noteworthy that all three patients had early-onset CL (Rice et al., 2007Rice G. Newman W.G. Dean J. et al.Heterozygous mutations in TREX1 cause familial chilblain lupus and dominant Aicardi-Goutieres syndrome.Am J Hum Genet. 2007; 80: 811-815Abstract Full Text Full Text PDF PubMed Scopus (299) Google Scholar; Haaxma et al., 2010Haaxma C.A. Crow Y.J. van Steensel M.A. et al.A de novo p.Asp18Asn mutation in TREX1 in a patient with Aicardi-Goutières syndrome.Am J Med Genet A. 2010; 152A: 2612-2617Crossref PubMed Scopus (33) Google Scholar; Ramantani et al., 2010Ramantani G. Kohlhase J. Hertzberg C. et al.Expanding the phenotypic spectrum of lupus erythematosus in Aicardi-Goutières syndrome.Arthritis Rheum. 2010; 62: 1469-1477Crossref PubMed Scopus (153) Google Scholar). The mutations in TREX1 in SLE patients were not reported in the exonuclease domains, except for the p.Arg128Asp mutation found in an SLE patient. The patient was suffering from neuropsychiatric lupus with digital gangrene (de Vries et al., 2010de Vries B. Steup-Beekman G.M. Haan J. et al.TREX1 gene variant in neuropsychiatric systemic lupus erythematosus.Ann Rheum Dis. 2010; 69: 1886-1887Crossref PubMed Scopus (42) Google Scholar). With regard to FCL, only two TREX1 mutations in two families have been reported. Rice et al., 2007Rice G. Newman W.G. Dean J. et al.Heterozygous mutations in TREX1 cause familial chilblain lupus and dominant Aicardi-Goutieres syndrome.Am J Hum Genet. 2007; 80: 811-815Abstract Full Text Full Text PDF PubMed Scopus (299) Google Scholar reported the TREX1 mutation c.375dupT in an FCL family with 67% (2 of 3) symptomatic penetrance. The mutation produced p.Asp125fs, which causes defects in key catalytic domains in the exonuclease domains II and III. It is noteworthy that one member of a family with FCL with c.375dupT had no CL or other symptoms even with this mutation. Therefore, the c.375dupT mutation of TREX1 does not always cause CL. Lee-Kirsch et al., 2006Lee-Kirsch M.A. Gong M. Schulz H. et al.Familial chilblain lupus, a monogenic form of cutaneous lupus erythematosus, maps to chromosome 3p.Am J Hum Genet. 2006; 79: 731-737Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar, Lee-Kirsch et al., 2007aLee-Kirsch M.A. Chowdhury D. Harvey S. et al.A mutation in TREX1 that impairs susceptibility to granzyme A-mediated cell death underlies familial chilblain lupus.J Mol Med. 2007; 85: 531-537Crossref PubMed Scopus (169) Google Scholar) reported another heterozygous missense mutation, p.Asp18Asn, in TREX1 in 13 patients in one large family with FCL. It is intriguing that p.Asp18Asn was also detected in an AGS patient showing CL (Haaxma et al., 2010Haaxma C.A. Crow Y.J. van Steensel M.A. et al.A de novo p.Asp18Asn mutation in TREX1 in a patient with Aicardi-Goutières syndrome.Am J Med Genet A. 2010; 152A: 2612-2617Crossref PubMed Scopus (33) Google Scholar). In summary, of all cases having heterozygous missense mutations in the three exonuclease domains of TREX1, we found 18 patients available for clinical information, including the present case, with a total of five missense mutations, and all the cases had severe early-onset CL or finger gangrene (Figure 2c). Of the five, three were heterozygous missense mutations, p.Asp18Asn, p.Asp200Asn, and p.Asp200His, which involve key catalytic residues of DEDDh motif, asparatic acids at codon No. 18 and No. 200 directly. The three missense mutations possess significantly reduced exonuclease activity against ssDNA and, in addition, to inhibit wild-type protein activity in vitro (Lee-Kirsch et al., 2007aLee-Kirsch M.A. Chowdhury D. Harvey S. et al.A mutation in TREX1 that impairs susceptibility to granzyme A-mediated cell death underlies familial chilblain lupus.J Mol Med. 2007; 85: 531-537Crossref PubMed Scopus (169) Google Scholar; Lehtinen et al., 2008Lehtinen D.A. Harvey S. Mulcahy M.J. et al.The TREX1 double-stranded DNA degradation activity is defective in dominant mutations associated with autoimmune disease.J Biol Chem. 2008; 283: 31649-31656Crossref PubMed Scopus (91) Google Scholar). The other two mutations, p.Arg128His and p.Pro132Ala, are missense mutations at conserved amino acids adjacent to the DEDDh motif. In addition, we speculate that these mutations have slightly reduced TREX1 exonuclease activity, but inhibit wild-type protein activity by forming dimers of wild-type and mutant. We also reviewed all heterozygous missense mutations of TREX1 that are outside of the exonuclease domains. A total of 20 SLE cases with 10 types of heterozygous missense mutations were described, but none of these had CL (Lee-Kirsch et al., 2007bLee-Kirsch M.A. Gong M. Chowdhury D. et al.Mutations in the gene encoding the 3′-5′ DNA exonuclease TREX1 are associated with systemic lupus erythematosus.Nat Genet. 2007; 39: 1065-1067Crossref PubMed Scopus (518) Google Scholar; Namjou et al., 2011Namjou B. Kothari P.H. Kelly J.A. et al.Evaluation of the TREX1 gene in a large multi-ancestral lupus cohort.Genes Immun. 2011; 12: 270-279Crossref PubMed Scopus (207) Google Scholar). In conclusion, it is noteworthy that heterozygous missense mutations of DEDDh motif or their adjacent in the exonuclease catalytic domain of TREX1 always lead to severe CL, without exception. Further studies are needed to elucidate the exact mechanisms of how the defective TREX1 activity results in the specific CL phenotype. This study was supported in part by a Grant-in-Aid for Scientific Research, (C) 23591617 (K.S.) from the Ministry of Education, Culture, Sports, Science and Technology of Japan and by a Grant-in-Aid for Scientific Research, (A) 23249058 (M.A.) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Supplementary material is linked to the online version of the paper at http://www.nature.com/jid