Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.bbrc.2022.12.090

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Language：English   Publishing type：Research paper (scientific journal)  

The peripheral protein quality control (periQC) system eliminates the conformationally defective cystic fibrosis transmembrane conductance regulator (CFTR), including ∆F508-CFTR, from the plasma membrane (PM) and limits the efficacy of pharmacological therapy for cystic fibrosis (CF). The ubiquitin (Ub) ligase RFFL is responsible for the chaperone-independent ubiquitination and lysosomal degradation of CFTR in the periQC. Here, we report that the Ub ligase RNF34 participates in the CFTR periQC in parallel to RFFL. An in vitro study reveals that RNF34 directly recognizes the CFTR NBD1 and selectively promotes the ubiquitination of unfolded proteins. RNF34 was localized in the cytoplasm and endosomes, where RFFL was equally colocalized. RNF34 ablation increased the PM density as well as the mature form of ∆F508-CFTR rescued at low temperatures. RFFL ablation, with the exception of RNF34 ablation, increased the functional PM expression of ∆F508-CFTR upon a triple combination of CFTR modulators (Trikafta) treatment by inhibiting the K63-linked polyubiquitination. Interestingly, simultaneous ablation of RNF34 and RFFL dramatically increased the functional PM ∆F508-CFTR by inhibiting the ubiquitination in the post-Golgi compartments. The CFTR-NLuc assay demonstrates that simultaneous ablation of RNF34 and RFFL dramatically inhibits the degradation of mature ∆F508-CFTR after Trikafta treatment. Therefore, these results suggest that RNF34 plays a crucial role in the CFTR periQC, especially when there is insufficient RFFL. We propose that simultaneous inhibition of RFFL and RNF34 may improve the efficacy of CFTR modulators.

DOI： 10.3389/fmolb.2022.840649

PubMed

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Language：English   Publishing type：Research paper (scientific journal)  

RNautophagy and DNautophagy (RDA) are unconventional autophagic pathways where nucleic acids are directly transported through the lysosomal membrane, then degraded inside lysosomes. We have previously shown that bitopic protein LAMP2C and putative RNA transporter SIDT2, both lysosomal membrane proteins, mediate the direct transport of nucleic acids into lysosomes and that LAMP2C interacts with the nucleic acids and functions as a receptor during RDA. Because SIDT2-mediated RDA occurs in isolated lysosomes that lack LAMP2C, in this study, we tested the hypothesis that SIDT2 itself could also interact with the nucleic acids. Our results show that SIDT2 directly binds RNA and DNA through an arginine-rich motif (ARM) located within its main cytosolic domain, and disruption of this motif dramatically impairs SIDT2-mediated RNautophagic activity. We also found that SIDT2 interacts with exon 1 of HTT (huntingtin) transcript through the ARM in a CAG-dependent manner. Moreover, overexpression of SIDT2 promoted degradation of HTT mRNA and reduced the levels of polyglutamine-expanded HTT aggregates, hallmarks of Huntington disease. In addition, a comparative analysis of LAMP2C and SIDT2 functions at the cellular level revealed that the two proteins exert a synergistic effect on RNautophagic activity and that the ARMs which mediate the interactions of SIDT2 and LAMP2C with RNA are essential for the synergy. Together, our results point out the importance of nucleic acid-binding capacity of SIDT2 for its function in translocating nucleic acids through the lipid bilayer and suggests a potential application of RNautophagy activation to reduce the expression levels of disease-causing toxic proteins. Abbreviations: ACTB/β-actin: actin beta; ARM: arginine-rich motif; CBB: Coomassie Brilliant Blue; CD: cytosolic domain; COX4I1/COX4: cytochrome c oxidase subunit 4I1; E. coli: Escherichia coli; EGFP: enhanced green fluorescent protein; EtBr: ethidium bromide; FITC: fluorescein isothiocyanate; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GOLGA2/GM130: golgin A2; GST: glutathione S-transferase; HRP: horseradish peroxidase; HSPA5/GRP78: heat shock protein family A (Hsp70) member 5; HTT: huntingtin; HTTex1: exon 1 of the HTT gene; LAMP2: lysosomal associated membrane protein 2; LMNA: lamin A/C; PAGE: polyacrylamide gel electrophoresis; PBS: phosphate-buffered saline; PEI: polyethyleneimine; polyQ: polyglutamine; qPCR: quantitative PCR; RAB5A: RAB5A, member RAS oncogene family; RDA: RNautophagy and DNautophagy; SCARB2/LIMP2: scavenger receptor class B member 2; SDS: sodium dodecyl sulfate; SID-1: systemic RNA interference deficient-1; SIDT2: SID1 transmembrane family member 2; WT: wild type.

DOI： 10.1080/15548627.2020.1712109

PubMed

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Publisher：Cold Spring Harbor Laboratory  

Regulated degradation of cellular components plays an essential role in homeostasis. Accumulating evidence indicates the importance of lysosomal degradation of cellular proteins¹: Dysfunctions in multiple pathways to deliver cytosolic substrates into lysosomes are related to various diseases, including cancers, neurodegenerative diseases, and myopathies². However, much of the effort at understanding such pathways has been devoted to studies on macroautophagy, which entails vast and dynamic rearrangement of membrane structure, and knowledge on other delivery systems and functions of lysosomes <italic>per se</italic> remains scant. Here, we show that cytosolic proteins are directly imported into lysosomes by a mechanism distinct from any known pathways and degraded. We find that a lysosomal membrane protein, SIDT2, which was previously reported as a putative nucleic acid transporter, is involved in the translocation of substrate proteins in this system. Gain- and loss-of-function analyses reveal that SIDT2 contributes conspicuously to the lysosomal degradation of a wide range of cytosolic proteins in cells at the constitutive level. Furthermore, a dominant-negative type of mutation in <italic>SIDT2</italic> causes familial rimmed vacuolar myopathy in humans. <italic>Sidt2</italic> knockout mice recapitulated typical features of rimmed vacuolar myopathy, including atrophy and accumulation of cytoplasmic inclusions in skeletal muscles. These results reveal a previously unknown pathway of proteolysis in lysosomes and highlight the importance of noncanonical types of autophagy in human physiology and pathophysiology.

DOI： 10.1101/2020.08.11.245688

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Language：English   Publisher：Cold Spring Harbor Laboratory  

Regulated degradation of cellular components plays an essential role in homeostasis. Accumulating evidence indicates the importance of lysosomal degradation of cellular proteins¹: Dysfunctions in multiple pathways to deliver cytosolic substrates into lysosomes are related to various diseases, including cancers, neurodegenerative diseases, and myopathies². However, much of the effort at understanding such pathways has been devoted to studies on macroautophagy, which entails vast and dynamic rearrangement of membrane structure, and knowledge on other delivery systems and functions of lysosomes <italic>per se</italic> remains scant. Here, we show that cytosolic proteins are directly imported into lysosomes by a mechanism distinct from any known pathways and degraded. We find that a lysosomal membrane protein, SIDT2, which was previously reported as a putative nucleic acid transporter, is involved in the translocation of substrate proteins in this system. Gain- and loss-of-function analyses reveal that SIDT2 contributes conspicuously to the lysosomal degradation of a wide range of cytosolic proteins in cells at the constitutive level. Furthermore, a dominant-negative type of mutation in <italic>SIDT2</italic> causes familial rimmed vacuolar myopathy in humans. <italic>Sidt2</italic> knockout mice recapitulated typical features of rimmed vacuolar myopathy, including atrophy and accumulation of cytoplasmic inclusions in skeletal muscles. These results reveal a previously unknown pathway of proteolysis in lysosomes and highlight the importance of noncanonical types of autophagy in human physiology and pathophysiology.

DOI： 10.1101/2020.08.11.245688

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Language：Japanese   Publisher：(公社)日本生化学会  

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Language：Japanese   Publisher：(公社)日本生化学会  

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Language：Japanese   Publisher：生命科学系学会合同年次大会運営事務局  

J-GLOBAL

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Language：Japanese   Publisher：(公社)日本生化学会  

J-GLOBAL

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