{"title":"Characterization of the N-terminal region of Crtac1B/LOTUS, an endogenous Nogo receptor-1 antagonist, required for secretion and soluble function","authors":"Yutaka Kawakami , Haruna Tezuka , Hirokazu Takaya , Junpei Matsubayashi , Kohtaro Takei","doi":"10.1016/j.neulet.2025.138284","DOIUrl":null,"url":null,"abstract":"<div><div>Lateral olfactory tract usher substance (LOTUS), also known as cartilage acidic protein-1B (Crtac1B), is a potent endogenous antagonist of Nogo receptor type-1 (NgR1). LOTUS exists in both membrane-bound (m-LOTUS) and soluble (s-LOTUS) forms. m-LOTUS inhibits NgR1 by binding to its C-terminal domain (UA-EC domain), thereby blocking ligand interactions, whereas s-LOTUS disrupts NgR1 signaling by interfering with its interaction with the p75 co-receptor. However, the molecular characteristics of s-LOTUS, including the functional domains required for secretion and NgR1 binding, remain unclear.</div><div>In this study, we identified the N-terminal 35Met-532Pro region as essential for s-LOTUS secretion. While N-type glycosylation patterns remained unchanged, differences in intracellular localization with the Golgi apparatus were observed between secretory and non-secretory forms. The non-secretory form exhibited higher aggregation and ubiquitination levels. Functionally, the soluble 35Met-532Pro fragment bound to both NgR1 and p75, disrupting the NgR1-p75 complex. In contrast, the UA-EC domain, corresponding to the functional domain of m-LOTUS, bound only to NgR1 and did not interfere with p75 interaction.</div><div>A growth cone collapse assay using cultured olfactory bulb neurons from <em>lotus</em>-deficient embryonic mice demonstrated that exogenous 35Met-532Pro, but not UA-EC, inhibited Nogo66-induced growth cone collapse. These findings indicate that the N-terminal 35Met-532Pro region of s-LOTUS functions as its active domain, antagonizing NgR1 signaling through dual binding to NgR1 and p75. In contrast, the UA-EC domain lacks this antagonistic property, highlighting the distinct functional domains and mechanisms of action between s-LOTUS and m-LOTUS.</div></div>","PeriodicalId":19290,"journal":{"name":"Neuroscience Letters","volume":"862 ","pages":"Article 138284"},"PeriodicalIF":2.5000,"publicationDate":"2025-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Neuroscience Letters","FirstCategoryId":"3","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0304394025001727","RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"NEUROSCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
Lateral olfactory tract usher substance (LOTUS), also known as cartilage acidic protein-1B (Crtac1B), is a potent endogenous antagonist of Nogo receptor type-1 (NgR1). LOTUS exists in both membrane-bound (m-LOTUS) and soluble (s-LOTUS) forms. m-LOTUS inhibits NgR1 by binding to its C-terminal domain (UA-EC domain), thereby blocking ligand interactions, whereas s-LOTUS disrupts NgR1 signaling by interfering with its interaction with the p75 co-receptor. However, the molecular characteristics of s-LOTUS, including the functional domains required for secretion and NgR1 binding, remain unclear.
In this study, we identified the N-terminal 35Met-532Pro region as essential for s-LOTUS secretion. While N-type glycosylation patterns remained unchanged, differences in intracellular localization with the Golgi apparatus were observed between secretory and non-secretory forms. The non-secretory form exhibited higher aggregation and ubiquitination levels. Functionally, the soluble 35Met-532Pro fragment bound to both NgR1 and p75, disrupting the NgR1-p75 complex. In contrast, the UA-EC domain, corresponding to the functional domain of m-LOTUS, bound only to NgR1 and did not interfere with p75 interaction.
A growth cone collapse assay using cultured olfactory bulb neurons from lotus-deficient embryonic mice demonstrated that exogenous 35Met-532Pro, but not UA-EC, inhibited Nogo66-induced growth cone collapse. These findings indicate that the N-terminal 35Met-532Pro region of s-LOTUS functions as its active domain, antagonizing NgR1 signaling through dual binding to NgR1 and p75. In contrast, the UA-EC domain lacks this antagonistic property, highlighting the distinct functional domains and mechanisms of action between s-LOTUS and m-LOTUS.
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