ALADIN ^I482S causes selective failure of nuclear protein import and hypersensitivity to oxidative stress in triple A syndrome

Abstract

Triple A syndrome is an autosomal recessive neuroendocrinological disease caused by mutations in a gene that encodes 546 amino acid residues. The encoded protein is the nucleoporin ALADIN, a component of nuclear pore complex (NPC). We identified a mutant ALADIN I482S that fails to target NPC and investigated the consequences of mistargeting using cultured fibroblasts (I482Sf) from a patient with triple A syndrome. ALADIN I482S affected a karyopherin-␣͞␤-mediated import pathway and decreased nuclear accumulations of aprataxin (APTX), a repair protein for DNA singlestrand breaks (SSBs), and of DNA ligase I in I482Sf. This decrease was restored by wild-type ALADIN. ALADIN I482S had no effect on imports of M9͞kap-␤2, BIB͞kap-␤3, histone H1͞importin 7, the ubiquitin conjugating enzyme UbcM2͞importin 11, or the spliceosome protein U1A, indicating that ALADIN I482S selectively impaired transport of discrete import complexes through NPC. Cell survival assay showed hypersensitivity of I482Sf to L-buthionine-(S,R)-sulfoximine (BSO), a glutathione-depleting agent. BSO decreased nuclear APTX and ligase I levels in I482Sf and normal control fibroblasts, but increased SSBs only in I482Sf. These observations implied that I482Sf are hypersensitive to BSO and no longer sufficiently repair SSBs. Consistent with this notion, I482Sf transfected with both APTX and ligase I had increased resistance to BSO, whereas I482Sf transfected with LacZ vector remained hypersensitive to BSO. We propose that oxidative stress aggravates nuclear import failure, which is already compromised in patient cells. Consequent DNA damage, beyond the limited capacity of DNA repair proteins, i.e., APTX and ligase I, may participate in triggering cell death.aprataxin ͉ DNA ligase I ͉ nuclear pore complex

Achalasia: will genetic studies provide insights?

“…Furthermore, mutant ALADIN appears to result in the impaired nuclear import of DNA repair proteins such as DNA ligase I and aprataxin, which leads to increased DNA damage and cell death (Hirano et al 2006). Interestingly, mutations in the aprataxin gene (APTX) cause hereditary cerebellar ataxia (MIM 208920), a disease which has been reported in one patient with sporadic achalasia (see supplementary table 1) (Murphy et al 1989).…”

Adult or late-onset triple A syndrome

“…Sudden death due to an acute crisis of hypoglycemia frequently occurs in childhood when the disease is not yet recognized. Recently, several reports have described adult or late-onset patients whose clinical presentations are milder than the classic phenotype [2][3][4][5][6][7][8].…”

Neuroprotection resulting from insufficiency of RANBP2 is associated with the modulation of protein and lipid homeostasis of functionally diverse but linked pathways in response to oxidative stress

“…A variety of stressors, including age-induced oxidative stress, are known to induce alterations in the nucleocytoplasmic gradient of the GTPase Ras-related nuclear protein (RAN) and to impair nucleocytoplasmic transport, a process thought to constitute an intrinsic signal for apoptosis, and to contribute to aging manifestations and pathogenesis of human diseases (Casanova et al, 2008;Crampton et al, 2009;D' Angelo et al, 2009;Hirano et al, 2006;Kodiha et al, 2004;Wong et al, 2009;Yasuda et al, 2006). At least two key partners of RANBP2 -RAN GTPase and the ubiquitin-conjugating enzyme UBC9 -have been found to mediate novel oxidative stress and apoptotic signaling events (Bossis and Melchior, 2006;Heo, 2008;Kodiha et al, 2004;Yasuda et al, 2006).…”