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Background Cerebral ischemia/reperfusion injury (CIRI), a common, universal clinical problem that costs a large proportion of the economic and disease burden. Identifying the key regulators of cerebral I/R injury could provide potential strategies for clinically improving the prognosis of stroke. Ring finger protein 13 (RNF13) has been proven to be involved in the inflammatory response. Here, we aimed to identify the role of RNF13 in cerebral I/R injury and further reveal its immanent mechanisms. Methods The CRISPR/Cas9 based knockout mice, RNA sequencing, mass spectrometry, co-immunoprecipitation, GST-pull down, immunofluorescent staining, western blot, RT-PCR were used to investigate biodistribution, function and mechanism of RNF13 during cerebral I/R injury. Results In the present study, we found that RNF13 was significantly up-regulated in patients, mice and primary neurons after I/R injury. Deficiency of RNF13 aggravated I/R-induced neurological impairment, inflammatory response and apoptosis while overexpression of RNF13 inhibited I/R injury. Mechanistically, this inhibitory effect of RNF13 during I/R injury was confirmed to be dependent on the blocking of TRIM21-mediated autophagy-dependent degradation of p62 and the stabilization of the p62-mediated Nrf2/HO-1 signaling pathway. Conclusion RNF13 is a crucial regulator of cerebral I/R injury that plays its role in inhibiting cell apoptosis and inflammatory response by preventing the autophagy-medicated degradation of the p62/Nrf2/HO-1 signaling pathway via blocking the interaction of TRIM21-p62 complex. Therefore, RNF13 represents a potential pharmacological target in acute ischemia stroke therapy.

The objective of this study was to understand if RNF13 can affect Parkinson’s disease (PD) model mice by modulating the endoplasmic reticulum stress (ERS)-mediated IRE1α-TRAF2-ASK1-JNK pathway. C57BL/6 mice injected with MPTP to establish PD mice models were divided into Control, MPTP, MPTP + sh-RNF13, and MPTP + sh-NC groups. Rotarod, balance beam, and open-field tests were used to assess the behavioral changes of experimental mice. Immunofluorescence assay was used to determine TH-positive expression in substantia nigra, TUNEL staining to detect apoptosis, and Western blotting to measure the expression of IRE1α-TRAF2-ASK1-JNK pathway. Besides, SH-SY5Y cells treated with MPP+ were assigned into Control, MPP+, MPP+ + sh-RNF13, and MPP+ + sh-NC groups in vitro to detect cell viability, apoptosis and Ca2+ level. When compared with those Control mice, MPTP mice showed decreased retention time spent on rotarod performance and prolonged time on balance beam test, as well as evident reductions in floor plane (FP) movements, moving time, moving distance, and mean velocity in open-field test, which had an obvious increase of TUNEL-positive cells, significant decrease of TH-positive cells, and remarkable up-regulations of RNF13, p-IRE1α/IRE1α, TRAF2, ASK1, and p-JNK/JNK. Meanwhile, MPTP mice treated with sh-RNF13 were improved in all above indexes. In vitro, MPP+ treated SH-SY5Y cells had decreased cell viability and increased cell apoptosis, as well as the upregulated IRE1α-TRAF2-ASK1-JNK pathway proteins and Ca2+ level. RNF13 knockdown improved all above indexes in SH-SY5Y cells treated with MPP+. Silencing RNF13 can alleviate motor dysfunction and dopamine neuronal damage in PD mice by inhibiting ERS-mediated IRE1α-TRAF2-ASK1-JNK pathway.

As a highly organized system, endo‐lysosomes play a crucial role in maintaining immune homeostasis. However, the mechanisms involved in regulating endo‐lysosome progression and subsequent inflammatory responses are not fully understood. By screening 103 E3 ubiquitin ligases in regulating endo‐lysosomal acidification, it is discovered that lysosomal RNF13 inhibits lysosome maturation and promotes inflammatory responses mediated by endosomal Toll‐like receptors (TLRs) in macrophages. Mechanistically, RNF13 mediates K48‐linked polyubiquitination of LAMP‐1 at residue K128 for proteasomal degradation. Upon TLRs activation, LAMP‐1 promotes lysosomes maturation, which accelerates lysosomal degradation of TLRs and reduces TLR signaling in macrophages. Furthermore, peripheral blood mononuclear cells (PBMCs) from patients with rheumatoid arthritis (RA) show increased RNF13 levels and decreased LAMP‐1 expression. Accordingly, the immunosuppressive agent hydroxychloroquine (HCQ) can increase the polyubiquitination of RNF13. Taken together, the study establishes a linkage between proteasomal and lysosomal degradation mechanisms for the induction of appropriate innate immune response, and offers a promising approach for the treatment of inflammatory diseases by targeting intracellular TLRs. Liu et al. identify lysosomal E3 ubiquitin ligase RNF13 as a positive regulator of the TLR‐triggered innate response through high‐content screening. They provide mechanistic insights into the interplay between lysosomal progression, inflammation and ubiquitylation, and highlight the important role of E3 ubiquitin ligases in the regulation of inflammatory responses and related autoimmune diseases.

The ubiquitin–proteasome system is of fundamental importance in all fields of biology due to its impact on proteostasis and in regulating cellular processes. Ubiquitination, a type of protein post-translational modification, involves complex enzymatic machinery, such as E3 ubiquitin ligases. The E3 ligases regulate the covalent attachment of ubiquitin to a target protein and are involved in various cellular mechanisms, including the cell cycle, cell division, endoplasmic reticulum stress, and neurotransmission. Because the E3 ligases regulate so many physiological events, they are also associated with pathologic conditions, such as cancer, neurological disorders, and immune-related diseases. This review focuses specifically on the protease-associated transmembrane-containing the Really Interesting New Gene (RING) subset of E3 ligases. We describe the structure, partners, and physiological functions of the Drosophila Godzilla E3 ligase and its human homologues, RNF13, RNF167, and ZNRF4. Also, we summarize the information that has emerged during the last decade regarding the association of these E3 ligases with pathophysiological conditions, such as cancer, asthma, and rare genetic disorders. We conclude by highlighting the limitations of the current knowledge and pinpointing the unresolved questions relevant to RNF13, RNF167, and ZNRF4 ubiquitin ligases.

Developmental and epileptic encephalopathies (DEE) are rare and serious neurological disorders characterized by severe epilepsy with refractory seizures and a significant developmental delay. Recently, DEE73 was linked to genetic alterations of the RNF13 gene, which convert positions 311 or 312 in the RNF13 protein from leucine to serine or proline, respectively (L311S and L312P). Using a fluorescence microscopy approach to investigate the molecular and cellular mechanisms affected by RNF13 protein variants, the current study shows that wild-type RNF13 localizes extensively with endosomes and lysosomes, while L311S and L312P do not extensively colocalize with the lysosomal marker Lamp1. Our results show that RNF13 L311S and L312P proteins affect the size of endosomal vesicles along with the temporal and spatial progression of fluorescently labeled epidermal growth factor, but not transferrin, in the endolysosomal system. Furthermore, GST-pulldown and co-immunoprecipitation show that RNF13 variants disrupt association with AP-3 complex. Knockdown of AP-3 complex subunit AP3D1 alters the lysosomal localization of wild-type RNF13 and similarly affects the size of endosomal vesicles. Importantly, our study provides a first step toward understanding the cellular and molecular mechanism altered by DEE73-associated genetic variations of RNF13.

Changes in the structure and number of synapses modulate learning, memory and cognitive disorders. Ubiquitin-mediated protein modification is a key mechanism for regulating synaptic activity, though the precise control of this process remains poorly understood. RING finger protein 13 (RNF13) is a recently identified E3 ubiquitin ligase, and its in vivo function remains completely unknown. We show here that genetic deletion of RNF13 in mice leads to a significant deficit in spatial learning as determined by the Morris water maze test and Y-maze learning test. At the ultrastructral level, the synaptic vesicle density was decreased and the area of the active zone was increased at hippocampal synapses of RNF13-null mice compared with those of wild-type littermates. We found no change in the levels of SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) complex proteins in the hippocampus of RNF13-null mice, but impaired SNARE complex assembly. RNF13 directly interacted with snapin, a SNAP-25-interacting protein. Interestingly, snapin was ubiquitinated by RNF13 via the lysine-29 conjugated polyubiquitin chain, which in turn promoted the association of snapin with SNAP-25. Consistently, we found an attenuated interaction between snapin and SNAP-25 in the RNF13-null mice. Therefore, these results suggest that RNF13 is involved in the regulation of the SNARE complex, which thereby controls synaptic function.

RING finger protein 13 (RNF13) is a newly identified E3 ligase reported to be functionally significant in the regulation of cancer development, muscle cell growth, and neuronal development. In this study, the function of RNF13 in cardiotoxin-induced skeletal muscle regeneration was investigated using RNF13-knockout mice. RNF13 -/- mice exhibited enhanced muscle regeneration —characterized by accelerated satellite cell proliferation —compared with wild-type mice. The expression of RNF13 was remarkably induced in macrophages rather than in the satellite cells of wild-type mice at the very early stage of muscle damage. This result indicated that inflammatory cells are important in RNF13-mediated satellite cell functions. The cytokine levels in skeletal muscles were further analyzed and showed that RNF13 -/- mice produced greater amounts of various cytokines than wild-type mice. Among these, IL-4 and IL-6 levels significantly increased in RNF13 -/- mice. The accelerated muscle regeneration phenotype was abrogated by inhibiting IL-4/IL-6 action in RNF13 -/- mice with blocking antibodies. These results indicate that RNF13 deficiency promotes skeletal muscle regeneration via the effects on satellite cell niche mediated by IL-4 and IL-6.

RING finger protein 13 (RNF13) is a novel E3 ubiquitin ligase whose expression is associated with cancer development. However, its specific role in cancer progression and metastasis remains unclear. Here, a B16F10/LLC experimental pulmonary metastatic model was developed to examine the formation of metastatic foci in the lung. A greater number of tumor colonies were observed in the lungs of RNF13-knockout (KO) mice than in their wild-type (WT) littermates, whereas no significant differences in tumor size were observed between the two groups. In short-term experiments, the number of fluorescently-labeled B16F10 cells increased remarkably in RNF13-KO lungs at early time points, whereas clearance of tumor cells from the blood was not affected. These results indicated that RNF13 may inhibit the colonization of B16F10 cells in the lung. Assessment of the concentration of various cytokines in tumor bearing lungs and blood did not detect significant differences between the blood of RNF13-KO and WT mice; however the levels of GM-CSF were significantly reduced in RNF13-KO tumor bearing lungs, which may have guided more B16F10 cells to migrate to the lungs. This was confirmed by lower GM-CSF concentrations in conditioned media from the culture of RNF13-KO lung slices. Collectively, our results suggest that host RNF13 affects the concentration of GM-CSF in tumor-bearing lungs, leading to a reduction in the colonization of metastatic tumor cells in the lung.