Abstract
Aims: Histidine triad nucleotide-binding protein 1 (HINT1) exhibits proapoptotic and tumor-suppressive activity. HINT1 binds to transcription factors such as teneurin1 and to the regulator of G protein signaling 17 (RGS) (Z2) protein, which incorporates the small ubiquitin-like modifier (SUMO), and is implicated in several types of cancer. HINT1 interacts with proteins such as PKCγ and Raf-1 through zinc ions provided by the cysteine-rich domain of RGSZ2 and the coupled neural nitric oxide synthase (nNOS). Recently, a series of HINT1 mutants have been reported to cause human autosomal recessive axonal neuropathy with neuromyotonia (ARAN-NM). However, the specific alteration in the function of HINT1 induced by these mutants remains to be elucidated. Because sumoylation modifies protein association and transcriptional regulation, we investigated whether HINT1 exhibits zinc- and redox-regulated sumoylase activity, which may be altered in those mutants.Results: HINT1 exhibits cysteine protease activity to remove SUMO from a variety of signaling proteins. HINT1 sumoylase activity is blocked by zinc, and it is released by nitric oxide or calcium-activated calmodulin (CaM). HINT1 contains a SUMO-interacting motif (110–116 HIHLHVL) and the catalytic triad Cys84-Asp87-His114 in the C-terminal region. Thus, zinc probably provided by the RGSZ2–nNOS complex may bind to Cys84 to block HINT1 isopeptidase activity.Innovation: To date, HINT1 is the only sumoylase that is regulated by two alternate pathways, redox- and calcium-activated CaM.Conclusion: The 15 human HINT1 mutants reported to cause ARAN-NM exhibited altered sumoylase activity, which may contribute to the onset of this human motor disease.
Highlights
The histidine triad nucleotide-binding protein 1 (HINT1) is a zinc-binding protein of *14 kDa that is highly conserved in phylogeny
As Histidine triad nucleotide-binding protein 1 (HINT1) interactions with signaling proteins and nucleotide hydrolase activity can be regulated by zinc [43, 53], we studied whether HINT1 might regulate small ubiquitin-like modifier (SUMO) posttranslational modification of interacting proteins by zinc and redox mechanisms and whether such a novel function was found to be altered in the autosomal recessive axonal neuropathy with neuromyotonia (ARAN-NM)-related mutants
Our study shows that HINT1 cleaves sumoylated substrates, such as regulator of G protein signaling 17 (RGS)-Rz proteins, intracellular domain (ICD) teneurin1, and Ran GTPase activating protein 1 (RanGAP1), and that this activity is inhibited by zinc and promoted by nitric oxide (NO) or calciumactivated calmodulin (CaM)
Summary
The histidine triad nucleotide-binding protein 1 (HINT1) is a zinc-binding protein of *14 kDa that is highly conserved in phylogeny. HINT1 is widely expressed in the central nervous system (CNS) and other tissues [27, 32], and at the cellular level, this protein is present in the plasma membrane, nucleus, and cytoplasm. HINT1 was initially described as a protein kinase C (PKC)-inhibiting protein [39], and, conventional PKCc and PKCa establish nitric oxide (NO) and zinc-dependent inhibitory associations with HINT1 [43, 44]. Crystallization studies indicated that HINT1 exists as a homodimer with the protomers interacting through their Cterminal sequences [26, 35], and its amino acid sequence revealed that it belongs to the histidine triad (HIT) family with HINT2 and HINT3 as its closest paralogs.
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