BACKGROUND & AIMS:Single-cell fixed RNA profiling (FLEX) is a novel technique that captures RNA expression in frozen tissues at a single-cell resolution. We applied FLEX to mouse model of liver fibrosis progression and regression to identify novel antifibrotic targets. METHODS:Mice were administered intraperitoneal thioacetamide for 10 weeks to induce fibrosis, regression was assessed 2 weeks after cessation. The livers were fixed, dissociated, and analysed using FLEX. Molecular validation included immunoblotting, immunohistochemistry, gene silencing/overexpression, cytokine/phosphokinase arrays, and human liver samples. RESULTS:Approximately 40,000 liver cells were profiled, integrated, and annotated into 10 major cell types using lineage-specific markers. Pericentral signature restoration in hepatocytes, scar-resolving genes (Mmp14 and Ctsl), fenestrae restoration in liver sinusoidal endothelial cells, anti-inflammatory Kupffer cells, reduced fibrogenic cholangiocytes, and recovery-associated immune cell subsets were observed. During fibrosis, monocyte-derived macrophages secrete semaphorin-4D (SEMA4D), which binds to Plexin B2 on hepatic stellate cells (HSCs). SEMA4D+ cells were upregulated in mouse fibrotic livers (n = 6, p <0.05). Recombinant SEMA4D induces type I collagen in HSCs, whereas humanised monoclonal IgG4 SEMA4D blockade (VX15/2503) attenuates fibrosis in vivo (n = 5, p <0.05). LIM and cysteine-rich domains 1 (LMCD1) was enriched in fibrotic HSCs and suppressed during regression. LMCD1 knockdown reduced the expression of fibrotic protein, while LMCD1 overexpression promoted the expression of fibrotic protein via AKT/mTOR signalling. LMCD1 and SEMA4D are localised in the fibrotic septa and are correlated with the fibrotic stage of MASLD (n = 34, p <0.05) and HCV (n = 76, p <0.05) in humans. CONCLUSIONS:This FLEX-based single-cell atlas revealed critical transcriptional programs and cell-cell interactions, identifying SEMA4D and LMCD1 as promising therapeutic targets for liver fibrosis. IMPACT AND IMPLICATIONS:In this study, we applied a novel technique, single-cell fixed RNA profiling, to profile 38,136 cells obtained from control, thioacetamide-induced liver fibrosis, and regression-phase mouse livers, generating a high-resolution atlas of liver fibrosis progression and regression. We identified the transcriptomic patterns of regressed cell subpopulations and uncovered two key therapeutic targets: the macrophage-derived factor semaphorin-4D (SEMA4D) and the hepatic stellate cell-specific transcription factor LIM and cysteine-rich domains 1 (LMCD1). Treatment with a humanised monoclonal IgG4 antibody against SEMA4D significantly alleviated liver fibrosis in the thioacetamide-induced mouse model. SEMA4D and LMCD1 expression correlated with the metabolic dysfunction-associated steatotic liver disease-related fibrosis stage, and the attenuation of SEMA4D and LMCD1 after HCV-sustained virologic response reduced the risk of progression to hepatocellular carcinoma.

Background & Aims Single-cell fixed RNA profiling (FLEX) is a novel technique that captures RNA expression in frozen tissues at a single-cell resolution. We applied FLEX to mouse model of liver fibrosis progression and regression to identify novel anti-fibrotic targets. Methods Mice were administered intraperitoneal thioacetamide (TAA) for 10 weeks to induce fibrosis, regression was assessed 2 weeks after cessation. The livers were fixed, dissociated, and analysed using FLEX. Molecular validation included immunoblotting, immunohistochemistry, gene silencing/overexpression, cytokine/phosphokinase arrays, and human liver samples. Results Approximately 40,000 liver cells were profiled, integrated, and annotated into 10 major cell types using lineage-specific markers. Pericentral signature restoration in hepatocytes, scar-resolving genes (Mmp14 and Ctsl), fenestrae restoration in liver sinusoidal endothelial cells, anti-inflammatory Kupffer cells, reduced fibrogenic cholangiocytes, and recovery-associated immune cell subsets were observed. During fibrosis, monocyte-derived macrophages secrete semaphorin-4D (SEMA4D), which binds to Plexin B2 on hepatic stellate cells (HSCs). SEMA4D+ cells were upregulated in mouse fibrotic livers (n = 6, p <0.05). Recombinant SEMA4D induces type I collagen in HSCs, whereas humanised monoclonal IgG4 SEMA4D blockade (VX15/2503) attenuates fibrosis in vivo (n = 5, p <0.05). LIM and cysteine-rich domains 1 (LMCD1) was enriched in fibrotic HSCs and suppressed during regression. LMCD1 knockdown reduced the expression of fibrotic protein, while LMCD1 overexpression promoted the expression of fibrotic protein via AKT/mTOR signalling. LMCD1 and SEMA4D are localised in the fibrotic septa and are correlated with the fibrotic stage of MASLD (n = 34, p <0.05) and HCV (n=76, p < 0.05) in humans. Conclusions This FLEX-based single-cell atlas revealed critical transcriptional programs and cell-cell interactions, identifying SEMA4D and LMCD1 as promising therapeutic targets for liver fibrosis. Impact and Implication In this study, we applied a novel technique, single-cell fixed RNA profiling (FLEX), to profile 38,136 cells obtained from control, thioacetamide-induced liver fibrosis, and regression-phase mouse livers, generating a high-resolution atlas of liver fibrosis progression and regression. We identified the transcriptomic patterns of regressed cell subpopulations and uncovered two key therapeutic targets: the macrophage-derived factor semaphorin-4D (SEMA4D) and the hepatic stellate cell-specific transcription factor LIM and cysteine-rich domains 1 (LMCD1). Treatment with a humanized monoclonal IgG4 antibody against SEMA4D significantly alleviated liver fibrosis in the TAA-induced mouse model. SEMA4D and LMCD1 expression correlated with the metabolic dysfunction-associated steatotic liver disease-related fibrosis stage, and the attenuation of SEMA4D and LMCD1 after hepatitis C virus-sustained virologic response reduced the risk of progression to hepatocellular carcinoma.

Lipopolysaccharide-responsive and beige-like anchor protein (LRBA) deficiency is a rare genetic disorder characterized by immune dysregulation. The immune checkpoint molecule cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) fails to perform proper membrane trafficking in the absence of LRBA. In addition to immune cells, LRBA localizes to intracellular vesicles in various epithelial cells; however, its physiological roles have not been accurately deciphered. It was observed in this study that LRBA facilitates water and sodium transport by promoting vesicular trafficking of aquaporin-2 (AQP2) and AQP4 in renal collecting duct cells and that of sterile 20/SPS1-related proline/alanine-rich kinase (SPAK) in distal convoluted tubule cells. Consequently, Lrba knockout mice exhibited vasopressin-resistant polyuria and hypotension under sodium-restricted conditions. This registry study revealed a polyuric phenotype in a subset of patients with LRBA deficiency, characterized by inappropriately low urine specific gravity despite the presence of chronic diarrhea. Notably, desmopressin treatment ameliorated impaired urinary concentration in a mouse model of human LRBA deficiency. LRBA functions as a central coordinator of fluid and sodium homeostasis by organizing segment-specific vesicular trafficking systems in renal epithelial cells.

Liver fibrosis progression and regression are dynamic processes involving diverse hepatic and immune cell populations. Here, we utilize single-cell fixed RNA profiling (FLEX) of a TAA-induced mouse liver cirrhosis model, with and without a recovery phase, to depict the cellular landscape and molecular mechanisms of fibrosis resolution. The regression phase was characterized by the emergence of pericentral hepatocytes enriched in detoxification and antioxidant genes (e.g., Cyp2e1, Txn1), which secreted Rarres2 to modulate hepatic stellate cell (HSC) function. This was accompanied by the upregulation of scar-resolving genes (Mmp14, Ctsl), restoration of fenestrae in liver sinusoidal endothelial cells, anti-inflammatory phenotypes of Kupffer cells, a decrease in fibrogenic cholangiocyte subsets, and recovery-associated signatures in NK/T cells, B cells, and neutrophils. In contrast, SEMA4D secreted by monocyte-derived macrophages during fibrosis progression activated Plxnb2⁺ HSCs, and its blockade attenuated fibrosis in vivo. Furthermore, LMCD1 was identified as a novel marker for HSC activation and regulation. This single-cell atlas reveals key transcriptional programs and intercellular signaling pathways dependent on the fibrotic condition, offering new therapeutic targets for liver cirrhosis. ### Competing Interest Statement The authors have declared no competing interest. L.T.T.T. received a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS Kaken C, 22K08083). N.K. received a Grant-in-Aid for Scientific Research from JSPS (J192640002), and a grant for a research program on hepatitis from the Japan Agency for Medical Research and Development (AMED-J202620103)

LPS-responsive beige -like anchor protein (LRBA) regulates vesicular trafficking and receptor recycling, and its deficiency results in immunodeficiency characterized by hypogammaglobulinemia and autoimmune syndrome. However, its role in liver pathophysiology remains unclear. Here, we reveal a previously unrecognized function of LRBA as a critical intracellular scaffold for mitogen-activated protein kinase (MAPK) activation that promotes liver injury. Lrba-/- mice exhibit reduced acetaminophen (APAP)-induced hepatic necrosis through the suppression of JNK activation. In a model of metabolic dysfunction-associated steatotic liver disease (MASLD) induced by a high-fat, high-cholesterol (HFHC) diet, Lrba deficiency reduces hepatic inflammation, fibrosis, and Kupffer cell activation. Mechanistically, LRBA homodimers directly interact with specific mitogen-activated protein kinase kinase kinases (MAP3Ks), including transforming growth factor-β-activated kinase 1 (TAK1) and mixed-lineage kinase 3 (MLK3), to facilitate their activation. LRBA, which is primarily expressed in hepatocytes under physiological conditions, is upregulated in non-parenchymal cells such as Kupffer cells and cholangiocytes in both HFHC diet-fed mice and patients with MASLD and cirrhosis, linking its scaffolding function to pathological inflammation. Thus, LRBA promotes liver disease progression by amplifying inflammatory signaling.

Although liver kinase B1 (LKB1) has been established as a tumor suppressor kinase, its mechanism of action is incompletely understood. Here we describe a novel nonenzymatic function of LKB1 in cell death induced by Fas/CD95. In BID knockout HeLa cells, inactivation of mitochondrial outer membrane permeabilization (MOMP) prevents Smac-induced inhibition of X-linked inhibitor of apoptosis (XIAP), causing resistance to Fas-induced apoptosis. However, reexpression of LKB1 in those cells naturally deficient for endogenous LKB1 restored apoptosis. Mechanistically, caspase-8 activated by Fas processed LKB1 to a truncated form, tLKB1. Both WT and kinase-inactive LKB1 antagonized XIAP to restore apoptosis, but somatic mutants of LKB1 found in Peutz-Jeghers syndrome (PJS) failed to do so. Thus, in addition to the known caspase-8 / tBid / Smac / XIAP pro-apoptotic axis, our results unveil a novel one, caspase-8 / tLKB1 / XIAP that potentially contributes to the antitumor functions of LKB1.

Age-related macular degeneration (AMD) is the leading sight-threatening disease in developed countries. On the other hand, recent studies indicated an ethnic variation in the phenotype of AMD. For example, several reports demonstrated that the incidence of drusen in AMD patients is less in Asians compared to Caucasians though the reason has not been clarified yet. In the last decades, several genome association studies have disclosed many susceptible genes of AMD and revealed that the association strength of some genes was different among races and AMD phenotypes. In this review article, the essential findings of the clinical studies and genome association studies for the most significant genes CFH and ARMS2/HTRA1 in AMD of different races are summarized, and theoretical hypotheses about the molecular mechanisms underlying the ethnic variation in the AMD manifestation mainly focused on those genes between Caucasians and Asians are discussed.

Protein ubiquitination, which is catalyzed by ubiquitin-activating enzymes, ubiquitin-conjugating enzymes, and ubiquitin ligases, is a crucial post-translational modification to regulate numerous cellular functions in a spatio–temporal-specific manner. The human genome encodes ~100 deubiquitinating enzymes (DUBs), which antagonistically regulate the ubiquitin system. OTUD1, an ovarian tumor protease (OTU) family DUB, has an N-terminal-disordered alanine-, proline-, glycine-rich region (APGR), a catalytic OTU domain, and a ubiquitin-interacting motif (UIM). OTUD1 preferentially hydrolyzes lysine-63-linked ubiquitin chains in vitro; however, recent studies indicate that OTUD1 cleaves various ubiquitin linkages, and is involved in the regulation of multiple cellular functions. Thus, OTUD1 predominantly functions as a tumor suppressor by targeting p53, SMAD7, PTEN, AKT, IREB2, YAP, MCL1, and AIF. Furthermore, OTUD1 regulates antiviral signaling, innate and acquired immune responses, and cell death pathways. Similar to Nrf2, OTUD1 contains a KEAP1-binding ETGE motif in its APGR and regulates the reactive oxygen species (ROS)-mediated oxidative stress response and cell death. Importantly, in addition to its association with various cancers, including multiple myeloma, OTUD1 is involved in acute graft-versus-host disease and autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and ulcerative colitis. Thus, OTUD1 is an important DUB as a therapeutic target for a variety of diseases.

Aquaporin-2 (AQP2) water channels are proteins that are recycled between intracellular vesicles and the apical plasma membrane in renal collecting ducts. Lipopolysaccharide-responsive beige-like anchor protein (LRBA) is a protein kinase A (PKA) anchoring protein that creates compartmentalized PKA signalling responsible for AQP2 phosphorylation. In response to increased plasma osmolality, vasopressin/cyclic adenosine monophosphate (cAMP)/PKA signalling phosphorylates AQP2, promoting AQP2 trafficking into the apical plasma membrane and increasing water reabsorption from urine. However, the molecular mechanisms by which LRBA mediates vasopressin-induced AQP2 phosphorylation remain unknown. To investigate AQP2 intracellular localization and phosphorylation status in vivo, a density gradient ultracentrifugation technique was combined with an in situ proximity ligation assay, super-resolution structured illumination microscopy and immunoelectron microscopy. Most of the AQP2 was localized on the recycling endosome in the presence of tolvaptan, a vasopressin type 2 receptor (V2R) antagonist. Desmopressin, a V2R agonist, phosphorylated AQP2, translocating it from the recycling endosome to the apical plasma membrane. In contrast, LRBA was constitutively localized at the recycling endosome. Therefore, LRBA and AQP2 were well colocalized in the absence of vasopressin stimulation. The loss of LRBA/PKA signalling by Lrba knockout impaired vasopressin-induced AQP2 phosphorylation, resulting in AQP2 retention at the recycling endosome. Defective AQP2 trafficking caused low urinary concentrating ability in Lrba-/- mice. The LRBA-PKA complex created compartmentalized PKA signalling at the recycling endosome, which facilitated AQP2 phosphorylation in response to vasopressin. image

In neurodegenerative diseases such as Alzheimer’s disease (AD) and amyotrophic lateral sclerosis (ALS), the progressive accumulation of ubiquitin-positive cytoplasmic inclusions leads to proteinopathy and neurodegeneration. Along with the seven types of Lys-linked ubiquitin chains, the linear ubiquitin chain assembly complex (LUBAC)-mediated Met1-linked linear ubiquitin chain, which activates the canonical NF-κB pathway, is also involved in cytoplasmic inclusions of tau in AD and TAR DNA-binding protein 43 in ALS. Post-translational modifications, including heterologous ubiquitination, affect proteasomal and autophagic degradation, inflammatory responses, and neurodegeneration. Single nucleotide polymorphisms (SNPs) in SHARPIN and RBCK1 (which encodes HOIL-1L), components of LUBAC, were recently identified as genetic risk factors of AD. A structural biological simulation suggested that most of the SHARPIN SNPs that cause an amino acid replacement affect the structure and function of SHARPIN. Thus, the aberrant LUBAC activity is related to AD. Protein ubiquitination and ubiquitin-binding proteins, such as ubiquilin 2 and NEMO, facilitate liquid-liquid phase separation (LLPS), and linear ubiquitination seems to promote efficient LLPS. Therefore, the development of therapeutic approaches that target ubiquitination, such as proteolysis-targeting chimeras (PROTACs) and inhibitors of ubiquitin ligases, including LUBAC, is expected to be an additional effective strategy to treat neurodegenerative diseases.

BackgroundOptineurin (OPTN) is associated with several human diseases, including amyotrophic lateral sclerosis (ALS), and is involved in various cellular processes, including autophagy. Optineurin regulates the expression of interferon beta (IFNβ), which plays a central role in the innate immune response to viral infection. However, the role of optineurin in response to viral infection has not been fully clarified. It is known that optineurin-deficient cells produce more IFNβ than wild-type cells following viral infection. In this study, we investigate the reasons for, and effects of, IFNβ overproduction during optineurin deficiency both in vitro and in vivo.MethodsTo investigate the mechanism of IFNβ overproduction, viral nucleic acids in infected cells were quantified by RT-qPCR and the autophagic activity of optineurin-deficient cells was determined to understand the basis for the intracellular accumulation of viral nucleic acids. Moreover, viral infection experiments using optineurin-disrupted (Optn-KO) animals were performed with several viruses.ResultsIFNβ overproduction following viral infection was observed not only in several types of optineurin-deficient cell lines but also in Optn-KO mice and human ALS patient cells carrying mutations in OPTN. IFNβ overproduction in Optn-KO cells was revealed to be caused by excessive accumulation of viral nucleic acids, which was a consequence of reduced autophagic activity caused by the loss of optineurin. Additionally, IFNβ overproduction in Optn-KO mice suppressed viral proliferation, resulting in increased mouse survival following viral challenge.ConclusionOur findings indicate that the combination of optineurin deficiency and viral infection leads to IFNβ overproduction in vitro and in vivo. The effects of optineurin deficiency are elicited by viral infection, therefore, viral infection may be implicated in the development of optineurin-related diseases.

Pancreatic cancer is a highly challenging malignancy with extremely poor prognosis. Cytoglobin (CYGB), a hemeprotein involved in liver fibrosis and cancer development, is expressed in pericytes of all organs. Here, we examined the role of CYGB in the development of pancreatic cancer. CYGB expression appeared predominately in the area surrounding adenocarcinoma and negatively correlated with tumor size in patients with pancreatic cancer. Directly injecting 7, 12-dimethylbenz[a]anthracene into the pancreatic tail in wild-type mice resulted in time-dependent induction of severe pancreatitis, fibrosis, and oxidative damage, which was rescued by Cygb overexpression in transgenic mice. Pancreatic cancer incidence was 93% in wild-type mice but only 55% in transgenic mice. Enhanced CYGB expression in human pancreatic stellate cells in vitro reduced cellular collagen synthesis, inhibited cell activation, increased expression of antioxidant-related genes, and increased CYGB secretion into the medium. Cygb -overexpressing or recombinant human CYGB (rhCYGB) -treated MIA PaCa-2 cancer cells exhibited dose-dependent cell cycle arrest at the G1 phase, diminished cell migration, and reduction in colony formation. RNA sequencing in rhCYGB-treated MIA PaCa-2 cells revealed downregulation of cell cycle and oxidative phosphorylation pathways. An increase in MIA PaCa-2 cell proliferation and reactive oxygen species production by H 2 O 2 challenge was blocked by rhCYGB treatment or Cygb overexpression. PANC-1, OCUP-A2, and BxPC-3 cancer cells showed similar responses to rhCYGB. Known antioxidants N-acetyl cysteine and glutathione also inhibited cancer cell growth. These results demonstrate that CYGB suppresses pancreatic stellate cell activation, pancreatic fibrosis, and tumor growth, suggesting its potential therapeutic application against pancreatic cancer.

Protein kinase A (PKA) directly phosphorylates aquaporin-2 (AQP2) water channels in renal collecting ducts to reabsorb water from urine for the maintenance of systemic water homeostasis. More than 50 functionally distinct PKA-anchoring proteins (AKAPs) respectively create compartmentalized PKA signaling to determine the substrate specificity of PKA. Identification of an AKAP responsible for AQP2 phosphorylation is an essential step toward elucidating the molecular mechanisms of urinary concentration. PKA activation by several compounds is a novel screening strategy to uncover PKA substrates whose phosphorylation levels were nearly perfectly correlated with that of AQP2. The leading candidate in this assay proved to be an AKAP termed lipopolysaccharide-responsive and beige-like anchor protein (LRBA). We found that LRBA colocalized with AQP2 in vivo, and Lrba knockout mice displayed a polyuric phenotype with severely impaired AQP2 phosphorylation. Most of the PKA substrates other than AQP2 were adequately phosphorylated by PKA in the absence of LRBA, demonstrating that LRBA-anchored PKA preferentially phosphorylated AQP2 in renal collecting ducts. Furthermore, the LRBA-PKA interaction, rather than other AKAP-PKA interactions, was robustly dissociated by PKA activation. AKAP-PKA interaction inhibitors have attracted attention for their ability to directly phosphorylate AQP2. Therefore, the LRBA-PKA interaction is a promising drug target for the development of anti-aquaretics.

Background & aimsHepatic stellate cells (HSCs) are the primary cell type in liver fibrosis, a significant global health care burden. Cytoglobin (CYGB), a globin family member expressed in HSCs, inhibits HSC activation and reduces collagen production. We studied the antifibrotic properties of globin family members hemoglobin (HB), myoglobin (MB), and neuroglobin (NGB) in comparison with CYGB.Approach & resultsWe characterized the biological activities of globins in cultured human HSCs (HHSteCs) and their effects on carbon tetrachloride (CCl4)-induced cirrhosis in mice. All globins demonstrated greater antioxidant capacity than glutathione in cell-free systems. Cellular fractionation revealed endocytosis of extracellular MB, NGB, and CYGB, but not HB; endocytosed globins localized to intracellular membranous, cytoplasmic, and cytoskeletal fractions. MB, NGB, and CYGB, but not HB, scavenged reactive oxygen species generated spontaneously or stimulated by H2O2 or transforming growth factor β1 in HHSteCs and reduced collagen 1A1 production via suppressing COL1A1 promoter activity. Disulfide bond-mutant NGB displayed decreased heme and superoxide scavenging activity and reduced collagen inhibitory capacity. RNA sequencing of MB- and NGB-treated HHSteCs revealed downregulation of extracellular matrix–encoding and fibrosis-related genes and HSC deactivation markers. Upregulation of matrix metalloproteinase (MMP)-1 was observed following MB and NGB treatment, and MMP-1 knockdown partially reversed globin-mediated effects on secreted collagen. Importantly, administration of MB, NGB, and CYGB suppressed CCl4-induced mouse liver fibrosis.ConclusionsThese findings revealed unexpected roles for MB and NGB in deactivating HSCs and inhibiting liver fibrosis development, suggesting that globin therapy may represent a new strategy for combating fibrotic liver disease.

Deubiquitylating enzymes (DUBs) regulate numerous cellular functions by removing ubiquitin modifications. We examined the effects of 88 human DUBs on linear ubiquitin chain assembly complex (LUBAC)-induced NF-κB activation, and identified OTUD1 as a potent suppressor. OTUD1 regulates the canonical NF-κB pathway by hydrolysing K63-linked ubiquitin chains from NF-κB signalling factors, including LUBAC. OTUD1 negatively regulates the canonical NF-κB activation, apoptosis, and necroptosis, whereas OTUD1 upregulates the interferon (IFN) antiviral pathway. The N-terminal intrinsically disordered region of OTUD1, which contains an EGTE motif, is indispensable for KEAP1-binding and NF-κB suppression. OTUD1 is involved in the KEAP1-mediated antioxidant response and reactive oxygen species (ROS)-induced cell death, oxeiptosis. In Otud1-/--mice, inflammation, oxidative damage, and cell death were enhanced in inflammatory bowel disease, acute hepatitis, and sepsis models. Thus, OTUD1 is a crucial regulator for the inflammatory, innate immune, and oxidative stress responses and ROS-associated cell death pathways.

The linear ubiquitin chain assembly complex (LUBAC), which is composed of RING finger protein 31 (RNF31), RANBP2-type and C3HC4-type zinc finger containing 1 and SHANK-associated RH domain interactor subunits, is the only ubiquitin ligase to generate Met1-linked linear ubiquitin chains. Linear ubiquitin chains regulate canonical NF-κB activation and cell death. Single nucleotide polymorphisms in RNF31, such as Q584H and Q622L, are known to cause the activated B cell-like subtype of diffuse large B cell lymphoma (ABC-DLBCL) because of enhanced LUBAC-mediated NF-κB activation. The present study identified a novel Q622H polymorphism of RNF31 in two patients with lung cancer, one of whom had concurrent ABC-DLBCL. Immunohistochemical analyses revealed that although the expression of RNF31 was elevated in both patients, only the ABC-DLBCL specimen showed increased NF-κB activation. Cancer panel analysis showed that the Q622H-related ABC-DLBCL did not harbor co-mutations that were previously reported in Q584H-/Q622L-related ABC-DLBCL. Furthermore, in contrast to Q584H and Q622L, Q622H showed no enhancement effects on LUBAC and NF-κB activity in vitro compared with wild-type RNF31. The present study's structural prediction suggested that the electrostatic interaction related to the Q622 residue may not have had an important role in LUBAC formation. In conclusion, the molecular mechanism and mutational background of RNF31 Q622H differed from that of RNF31 Q584H or Q622L. Furthermore, RNF31 Q622H appeared not to induce NF-κB activation in lung cancer.

Spinocerebellar ataxia (SCA) type 17-digenic TBP/STUB1 disease (SCA17-DI) has been recently segregated from SCA17, caused by digenic inheritance of two gene mutations – intermediate polyglutamine-encoding CAG/CAA repeat expansions (polyQ) in TBP ( TBP 41 − 49 ) and STUB1 heterozygosity – the former being associated with SCA17, and the latter with SCA48 and SCAR16 (autosomal recessive). In SCA17, most patients carry intermediate TBP 41 − 49 alleles but show incomplete penetrance, and the missing heritability can be explained by a new entity whereby TBP 41 − 49 requires the STUB1 variant to be symptomatic. The STUB1 gene encodes the chaperone-associated E3 ubiquitin ligase (CHIP) involved in ubiquitin-mediated proteasomal control of protein homeostasis. However, reports of the neuropathology are limited and role of STUB1 mutations in SCA17-DI remain unknown. Here we report the clinicopathologic features of identical twin siblings, one of whom was autopsied and was found to carry an intermediate allele (41 and 38 CAG/CAA repeats) in TBP and a heterozygous missense mutation in STUB1 (p.P243L). These patients developed autosomal recessive Huntington’s disease-like symptoms. Brain MRI showed diffuse atrophy of the cerebellum and T2WI revealed hyperintense lesions in the basal ganglia and periventricular deep white matter. The brain histopathology of the patient shared features characteristic of SCA17, such as degeneration of the cerebellar cortex and caudate nucleus, and presence of 1C2-positive neurons. Here we show that mutant CHIP fails to generate the polyubiquitin chain due to disrupted folding of the entire U box domain, thereby affecting the E3 activity of CHIP. When encountering patients with cerebellar ataxia, especially those with Huntington’s disease-like symptoms, genetic testing for STUB1 as well as TBP should be conducted for diagnosis of SCA17-DI, even in cases of sporadic or autosomal recessive inheritance.

Abstract Saliva contributes to the innate immune system, which suggests that it can prevent SARS-CoV-2 entry. We studied the ability of healthy salivary proteins to bind to angiotensin-converting enzyme 2 (ACE2) using biolayer interferometry and pull-down assays. Their effects on binding between the receptor-binding domain of the SARS-CoV-2 spike protein S1 (S1) and ACE2 were determined using an enzyme-linked immunosorbent assay. Saliva bound to ACE2 and disrupted the binding of S1 to ACE2 and four ACE2-binding salivary proteins were identified, including cationic histone H2A and neutrophil elastase, which inhibited the S1-ACE2 interaction. Calf thymus histone (ct-histone) also inhibited binding as effectively as histone H2A. The results of a cell-based infection assay indicated that ct-histone suppressed SARS-CoV-2 pseudoviral invasion into ACE2-expressing host cells. Manufactured polypeptides, such as ε-poly-L-lysine, also disrupted S1-ACE2 binding, indicating the importance of the cationic properties of salivary proteins in ACE2 binding. Overall, we demonstrated that positively charged salivary proteins are a barrier against SARS-CoV-2 entry by cloaking the negatively charged surface of ACE2 and provided a view that the cationic polypeptides represent a preventative and therapeutic treatment against COVID-19.