Mechanical study of alisol B 23-acetate on methionine and choline deficient diet-induced nonalcoholic steatohepatitis based on untargeted metabolomics.

Alisol B 23-acetate (AB23A) has been demonstrated to have beneficial effects on nonalcoholic steatohepatitis (NASH). However, the mechanisms of AB23A on NASH remain unclear. This study aimed to investigate the mechanisms underlying the metabolic regulatory effects of AB23A on NASH. We used AB23A to treat mice with NASH, which was induced by a methionine and choline deficient (MCD) diet. We initially investigated therapeutic effect and resistance to oxidation and inflammation of AB23A on NASH. Subsequently, we performed untargeted metabolomic analyses and relative validation assessments to evaluate the metabolic regulatory effects of AB23A. AB23A reduced lipid accumulation, ameliorated oxidative stress and decreased pro-inflammatory cytokines in the liver. Untargeted metabolomic analysis found that AB23A altered the metabolites of liver. A total of 55 differential metabolites and three common changed pathways were screened among the control, model and AB23A treatment groups. Further tests validated the effects of AB23A on modulating common changed pathway-involved factors. AB23A treatment can ameliorate NASH by inhibiting oxidative stress and inflammation. The mechanism of AB23A on NASH may be related to the regulation of alanine, aspartate and glutamate metabolism, d-glutamine and d-glutamate metabolism, and arginine biosynthesis pathways.

Two Undescribed Protostane Triterpenoids from the Rhizome of Alisma plantago-aquatica.

Two undescribed protostane triterpenoids, 11-deoxy-13(17),15-dehydro-alisol B 23-acetate (2) and alisol S (3), together with 21 known ones (1, 4-23), were isolated from the dried rhizome of Alisma plantago-aquatica. Of these compounds, 13(17),15-Dehydro-alisol B 23-acetate (1) and 11-deoxy-13(17),15-dehydro-alisol B 23-acetate (2) are two protostane triterpenoids containing conjugated double bonds in the five-membered ring D that are rarely found from nature resource, while alisol S (3) is a protostane triterpenoid with undescribed tetrahydrofuran moiety linked via C20 -O-C24 at the side chain. Additionally, compound 18 is a new natural product, and cycloartenol triterpenoid 23 is a non protostane triterpenoid firstly isolated from genus Alisma. Their structures were elucidated by extensive spectral analysis of the UV, IR, MS, 1D and 2D NMR, and comparison of the experimental and calculated CD curves.

Inhibition of nucleophosmin/B23 sensitizes ovarian cancer cells to immune check-point blockade via PD-L1 in ovarian cancer.

BACKGROUND: Immune checkpoint inhibitors (ICIs) that against programmed cell death protein-1 (PD-1) and its ligand PD-L1 have been approved as a promising treatment of many human cancers. However, the responses to these ICIs were limited in patients with ovarian cancer. Studies have indicated that the response to PD-1/PD-L1 blockade might be correlated with the PD-L1 expression level in cancer cells. Nucleophosmin (NPM/B23) was found to be a potential target for immunotherapy. Whether NPM/B23 plays a role in cancer-associated immunity, such as PD-1/PD-L1 axis, and its underlying mechanisms remain largely unknown in ovarian cancer. METHODS: We applied ovarian cancer cell lines as research models. The effect of modulating PD-L1 by NPM/B23 was subsequently confirmed via Western blot, flow cytometry, qRT-PCR, luciferase reporter assays, and immunoprecipitation. Protein stability and ubiquitin assay assays were used to analyze the interplay between NPM/B23 and NF-ĸB/p65 in PD-L1 regulation. The MOSEC/Luc xenograft mouse model was used to validate the role of NPM/B23-PD-L1 through tumor growth in vivo. RESULTS: Our results revealed that NPM/B23 negatively regulates PD-L1 expression via a protein complex with NF-κB/p65 and through an IFN-γ pathway. Moreover, NPM/B23 inhibitor/modulator sensitized ovarian cancer cells to the anti-PD-1 antibody by regulating PD-L1 expression in the immunocompetent mouse model. Compared to anti-PD-1 antibody alone, a combination of anti-PD-1 antibody and NPM/B23 inhibitor/modulator showed reduced tumorigenesis and increased CD8+ T-cell expansion, thus contributing to prolonged survival on MOSEC/Luc-bearing mouse model. CONCLUSION: Targeting NPM/B23 is a novel and potential therapeutic approach to sensitize ovarian cancer cells to immunotherapy.

Plasma microRNA Profiling in Type 2 Diabetes Mellitus: A Pilot Study.

Type 2 diabetes mellitus (T2D) is a chronic metabolic disease characterized by insulin resistance and ß-cell dysfunction and leading to many micro- and macrovascular complications. In this study we analyzed the circulating miRNA expression profiles in plasma samples from 44 patients with T2D and 22 healthy individuals using next generation sequencing and detected 229 differentially expressed miRNAs. An increased level of miR-5588-5p, miR-125b-2-3p, miR-1284, and a reduced level of miR-496 in T2D patients was verified. We also compared the expression landscapes in the same group of patients depending on body mass index and identified differential expression of miR-144-3p and miR-99a-5p in obese individuals. Identification and functional analysis of putative target genes was performed for miR-5588-5p, miR-125b-2-3p, miR-1284, and miR-496, showing chromatin modifying enzymes and apoptotic genes being among the significantly enriched pathways.

Molecular Tuning in Diaryl-Capped Pyrrolo[2,3-d:5,4-d']bisthiazoles: Effects of Terminal Aryl Unit and Comparison to Dithieno[3,2-b:2',3'-d]pyrrole Analogues.

A series of six conjugated oligomers consisting of a central pyrrolo[2,3-d:5,4-d']bisthiazole (PBTz) end-capped with either thienyl, furyl, or phenyl groups have been prepared from N-alkyl-and N-aryl-pyrrolo[2,3-d:5,4-d']bisthiazoles via Stille and Negishi cross-coupling. The full oligomeric series was thoroughly investigated via photophysical and electrochemical studies, in parallel with density functional theory (DFT) calculations, in order to correlate the cumulative effects of both aryl end-groups and N-functionalization on the resulting optical and electronic properties. Through comparison with the analogous dithieno[3,2-b:2',3'-d]pyrrole (DTP) materials, the effect of replacing DTP with PBTz on the material HOMO energy and visible light absorption is quantified.

A naturally occurring FXR agonist, alisol B 23-acetate, protects against renal ischemia-reperfusion injury.

The ligand-activated nuclear receptor, farnesoid X receptor (FXR), plays a pivotal role in regulating renal function. Activation of FXR by its specific agonists exerts renoprotective action in animals with acute kidney injury (AKI). In the present study, we aimed to identify naturally occurring agonists of FXR with potential as therapeutic agents in renal ischemia-reperfusion injury. In vitro and in vivo FXR activation was determined by a dual-luciferase assay, docking analysis, site-directed mutagenesis, and whole kidney transcriptome analysis. Wild-type (WT) and FXR knockout (FXR-/-) mice were used to determine the effect of potential FXR agonist on renal ischemia-reperfusion injury (IRI). We found that alisol B 23-acetate (ABA), a major active triterpenoid extracted from Alismatis rhizoma, a well-known traditional Chinese medicine, can activate renal FXR and induce FXR downstream gene expression in mouse kidney. ABA treatment significantly attenuated renal ischemia-reperfusion-induced AKI in WT mice but not in FXR-/- mice. Our results demonstrate that ABA can activate renal FXR to exert renoprotection against ischemia-reperfusion injury-induced AKI. Therefore, ABA may represent a potential therapeutic agent in the treatment of ischemic AKI.NEW & NOTEWORTHY In the present study, we found that alisol B 23-acetate (ABA), an identified natural farnesoid X receptor (FXR) agonist from the well-known traditional Chinese medicine Alismatis rhizoma, protects against ischemic acute kidney injury (AKI) in an FXR-dependent manner, as reflected by improved renal function, reduced renal tubular apoptosis, ameliorated oxidative stress, and suppressed inflammatory factor expression. Therefore, ABA may have great potential as a novel therapeutic agent in the treatment of AKI in the future.

Targeting CK2 mediated signaling to impair/tackle SARS-CoV-2 infection: a computational biology approach.

BACKGROUND: Similarities in the hijacking mechanisms used by SARS-CoV-2 and several types of cancer, suggest the repurposing of cancer drugs to treat Covid-19. CK2 kinase antagonists have been proposed for cancer treatment. A recent study in cells infected with SARS-CoV-2 found a significant CK2 kinase activity, and the use of a CK2 inhibitor showed antiviral responses. CIGB-300, originally designed as an anticancer peptide, is an antagonist of CK2 kinase activity that binds to the CK2 phospho-acceptor sites. Recent preliminary results show the antiviral activity of CIGB-300 using a surrogate model of coronavirus. Here we present a computational biology study that provides evidence, at the molecular level, of how CIGB-300 may interfere with the SARS-CoV-2 life cycle within infected human cells. METHODS: Sequence analyses and data from phosphorylation studies were combined to predict infection-induced molecular mechanisms that can be interfered by CIGB-300. Next, we integrated data from multi-omics studies and data focusing on the antagonistic effect on the CK2 kinase activity of CIGB-300. A combination of network and functional enrichment analyses was used. RESULTS: Firstly, from the SARS-CoV studies, we inferred the potential incidence of CIGB-300 in SARS-CoV-2 interference on the immune response. Afterwards, from the analysis of multiple omics data, we proposed the action of CIGB-300 from the early stages of viral infections perturbing the virus hijacking of RNA splicing machinery. We also predicted the interference of CIGB-300 in virus-host interactions that are responsible for the high infectivity and the particular immune response to SARS-CoV-2 infection. Furthermore, we provided evidence of how CIGB-300 may participate in the attenuation of phenotypes related to muscle, bleeding, coagulation and respiratory disorders. CONCLUSIONS: Our computational analysis proposes putative molecular mechanisms that support the antiviral activity of CIGB-300.

The probiotic effects of AB23A on high-fat-diet-induced non-alcoholic fatty liver disease in mice may be associated with suppressing the serum levels of lipopolysaccharides and branched-chain amino acids.

Alisol B 23-acetate (AB23A) is a natural triterpenoid isolated from Rhizoma alisamatis that has been widely used as a traditional Chinese medicine (TCM). Previous studies have documented the beneficial effect of AB23A on non-alcoholic fatty liver disease (NAFLD), but the functional interactions between gut microbiota and the anti-NAFLD effect of AB23A remain unclear. In this study, we investigated the benefits of experimental treatment with AB23A on gut microbiota dysbiosis in NAFLD with an obesity model. C57BL/6J mice were administrated a high-fat diet (HFD) with or without AB23A for 12 weeks. AB23A significantly improved metabolic phenotype in the HFD-fed mice. Moreover, results of 16S rRNA gene-based amplicon sequencing in each group reveled that AB23A not only reduced the abundance of the Firmicutes/Bacteroidaeota ratio and Actinobacteriota/Bacteroidaeota ratio, but regulated the abundance of the top 10 genera, including norank_f__Muribaculaceae, Lactobacillus, Ileibacterium, Turicibacter, Faecalibaculum, the Lachnospiraceae_NK4A136_group, unclassified_f__Lachnospiraceae, and norank_f__Lachnospiraceae. AB23A significantly reduced the serum levels of lipopolysaccharide and branched-chain amino acids, which are positively correlated with the abundances of Ileibacterium and Turicibacter. Moreover, AB23A led to remarkable reductions in the activation of TLR4, NF-κB, and mTOR, and upregulated the expression of tight junction proteins, including ZO-1 and occludin. These results revealed that AB23A displayed a prebiotic capacity in HFD-fed NAFLD mice.

Nucleophosmin in Its Interaction with Ligands.

Nucleophosmin (NPM1) is a mainly nucleolar protein that shuttles between nucleoli, nucleoplasm and cytoplasm to fulfill its many functions. It is a chaperone of both nucleic acids and proteins and plays a role in cell cycle control, centrosome duplication, ribosome maturation and export, as well as the cellular response to a variety of stress stimuli. NPM1 is a hub protein in nucleoli where it contributes to nucleolar organization through heterotypic and homotypic interactions. Furthermore, several alterations, including overexpression, chromosomal translocations and mutations are present in solid and hematological cancers. Recently, novel germline mutations that cause dyskeratosis congenita have also been described. This review focuses on NPM1 interactions and inhibition. Indeed, the list of NPM1 binding partners is ever-growing and, in recent years, many studies contributed to clarifying the structural basis for NPM1 recognition of both nucleic acids and several proteins. Intriguingly, a number of natural and synthetic ligands that interfere with NPM1 interactions have also been reported. The possible role of NPM1 inhibitors in the treatment of multiple cancers and other pathologies is emerging as a new therapeutic strategy.

[Recommendations on quality standards of Alismatis Rhizoma in Chinese Pharmacopoeia(2020 edition)].

The present research was launched to improve the quality standards of Alismatis Rhizoma and supply scientific evidence and recommendations for the quality control of Alismatis Rhizoma in Chinese Pharmacopoeia(Ch. P) 2020 edition. The contents of water, total ash, heavy metals and deleterious element, pesticide residues and alcohol-soluble extract were analyzed according to the methods listed in the volume Ⅳ of Ch. P 2015 edition. Alisol B 23-acetate, alisol C 23-acetate and reference herbs were used to identify Alismatis Rhizoma by TLC method, which was developed by using a mixture of dichloromethane-methanol(15∶1) as developing solvent on silica gel GF_(254 )precoated plates. In HPLC method, alisol B 23-acetate and alisol C 23-acetate were separated with acetonitrile-water as the mobile phase and detected at 208 nm and 246 nm, respectively. Thirty-seven batches of crude drugs, thirty batches of prepared slices and nineteen batches of salt prepared slices of Alismatis Rhizoma were determined according to the methods established. The quality standards established based on the research results were specific and repeatable, and suitable for the quality evaluation of Alismatis Rhizoma. We recommended that the botanical sources, TLC examination, alcohol-soluble extract of salt prepared slices and content determination should be revised in the Ch. P 2020 edition.

B23/Nucleophosmin promotes reconstitution of synaptic path in hippocampus after injury.

B23, also known as nucleophosmin (NPM), is multifunctional protein directly implicated in cell proliferation, cell cycle progression, and cell survival. In the current study, in addition to confirming its anti-apoptotic function in neuronal survival, we demonstrated that the spatial-temporal expression profile of B23 during development of hippocampal neurons is high in the embryonic stage, down-regulated after birth, and preferentially localized at the tips of growing neuritis and branching points. Overexpression of B23 promotes axon growth with abundant branching points in growing hippocampal neurons, but depletion of B23 impairs axon growth, leading to neuronal death. Following injury to the trisynaptic path in hippocampal slice, overexpression of B23 remarkably increased the number and length of regenerative fibers in the mossy fiber path. Our study suggests that B23 expression in developing neurons is essential for neuritogenesis and axon growth and that up-regulation of B23 may be a strategy for enhancing the reconstitution of synaptic paths after injury to hippocampal synapses.

[Features of the Structure and Expression of NPM and NCL Genes in Cutaneous Melanoma].

Malignant cutaneous melanoma (CM) is an extremely aggressive cancer characterized by a high level of metastatic activity and unfavorable prognosis due to a high incidence of relapses, as well as resistance to standard chemotherapy. Cutaneous melanoma accounts for 80% of deaths from malignant skin tumors. Nucleolin/C23 and nucleophosmin/B23, which constitute altogether ~70% of the nucleolus volume, are promising targets for molecular therapy of melanoma. These proteins perform many important functions in the cell, so disruption of the NCL and/or NPM gene structure and abnormal expression of the C23 and B23 proteins they encode, can lead to unlimited cell proliferation and progression of a tumor. Therefore, investigation of the structure and expression of these genes is a topical problem, which is important for understanding the mechanisms of CM carcinogenesis and for the development of new therapeutic approaches. This paper describes new NCL and NPM polymorphisms, as well as the levels of C23 and B23 expression in normal tissues, CM and mucosal melanoma.

[Exploration of objective quality evaluation parameter of Alismatis Rhizoma decoction pieces].

To establish a quality constant evaluation system of Alismatis Rhizoma decoction pieces,in order to provide reference for regulating the market circulation of this decoction pieces. A total of 18 batches of Alismatis Rhizoma decoction pieces were collected from different pharmaceutical factories,and the morphological parameters of each sample were tested. The content of alisol B 23-acetate in Alismatis Rhizoma decoction pieces was determined by HPLC in the 2015 edition of Chinese Pharmacopoeia,and the parameters such as quality constant and relative quality constant were calculated. The quality constant range of 18 batches of Alismatis Rhizoma decoction pieces was 0. 390-2. 076. If 18 batches of Alismatis Rhizoma decoction pieces were divided into 3 grades,taking 80% of the maximum quality constant as first grade,50% to 80% as second grade,and the rest as third grade,then the quality constant of firstgrade samples was ≥1. 66,the quality constant of second-grade samples was ≥1. 04 and <1. 66,and the quality constant of third-grade samples was <1. 04. The established quality constant evaluation method is objective and feasible,which can be used to classify the grade of Alismatis Rhizoma decoction pieces and provide a reference method to control the quality of this decoction pieces.

Dithieno[3,2-b:2',3'-d]pyrrole Cored p-Type Semiconductors Enabling 20 % Efficiency Dopant-Free Perovskite Solar Cells.

Organic p-type semiconductors with tunable structures offer great opportunities for hybrid perovskite solar cells (PVSCs). We report herein two dithieno[3,2-b:2',3'-d]pyrrole (DTP) cored molecular semiconductors prepared through π-conjugation extension and an N-alkylation strategy. The as-prepared conjugated molecules exhibit a highest occupied molecular orbital (HOMO) level of -4.82 eV and a hole mobility up to 2.16×10-4  cm2 V-1 s-1 . Together with excellent film-forming and over 99 % photoluminescence quenching efficiency on perovskite, the DTP based semiconductors work efficiently as hole-transporting materials (HTMs) for n-i-p structured PVSCs. Their dopant-free MA0.7 FA0.3 PbI2.85 Br0.15 devices exhibit a power conversion efficiency over 20 %, representing one of the highest values for un-doped molecular HTMs based PVSCs. This work demonstrates the great potential of using a DTP core in designing efficient semiconductors for dopant-free PVSCs.

Alisol B 23-acetate-induced HepG2 hepatoma cell death through mTOR signaling-initiated G1 cell cycle arrest and apoptosis: A quantitative proteomic study.

OBJECTIVE: The present study aimed to investigate the molecular events in alisol B 23-acetate (ABA) cytotoxic activity against a liver cancer cell line. METHODS: First, we employed a quantitative proteomics approach based on stable isotope labeling by amino acids in cell culture (SILAC) to identify the different proteins expressed in HepG2 liver cancer cells upon exposure to ABA. Next, bioinformatics analyses through DAVID and STRING on-line tools were used to predict the pathways involved. Finally, we applied functional validation including cell cycle analysis and Western blotting for apoptosis and mTOR pathway-related proteins to confirm the bioinformatics predictions. RESULTS: We identified 330 different proteins with the SILAC-based quantitative proteomics approach. The bioinformatics analysis and the functional validation revealed that the mTOR pathway, ribosome biogenesis, cell cycle, and apoptosis pathways were differentially regulated by ABA. G1 cell cycle arrest, apoptosis and mTOR inhibition were confirmed. CONCLUSIONS: ABA, a potential mTOR inhibitor, induces the disruption of ribosomal biogenesis. It also affects the mTOR-MRP axis to cause G1 cell cycle arrest and finally leads to cancer cell apoptosis.

RNA-dependent disassembly of nuclear bodies.

Nuclear bodies are membraneless organelles that play important roles in genome functioning. A specific type of nuclear bodies known as interphase prenucleolar bodies (iPNBs) are formed in the nucleoplasm after hypotonic stress from partially disassembled nucleoli. iPNBs are then disassembled, and the nucleoli are reformed simultaneously. Here, we show that diffusion of B23 molecules (also known as nucleophosmin, NPM1) from iPNBs, but not fusion of iPNBs with the nucleoli, contributes to the transfer of B23 from iPNBs to the nucleoli. Maturation of pre-ribosomal RNAs (rRNAs) and the subsequent outflow of mature rRNAs from iPNBs led to the disassembly of iPNBs. We found that B23 transfer was dependent on the synthesis of pre-rRNA molecules in nucleoli; these pre-rRNA molecules interacted with B23 and led to its accumulation within nucleoli. The transfer of B23 between iPNBs and nucleoli was accomplished through a nucleoplasmic pool of B23, and increased nucleoplasmic B23 content retarded disassembly, whereas B23 depletion accelerated disassembly. Our results suggest that iPNB disassembly and nucleolus assembly might be coupled through RNA-dependent exchange of nucleolar proteins, creating a highly dynamic system with long-distance correlations between spatially distinct processes.

Alisol B-23-acetate, a tetracyclic triterpenoid isolated from Alisma orientale, induces apoptosis in human lung cancer cells via the mitochondrial pathway.

Alisol B-23-acetate (AB23A), a tetracyclic triterpenoid isolated from the rhizome of Alisma orientale, has been reported to exert anti-proliferative activities in human colon, ovarian and gastric cancer cells. However, the anti-cancer effect of this compound on human lung cancer cells has not yet been thoroughly elucidated. In the present study, we investigated the effects of AB23A on the cell viability and apoptosis in human lung cancer A549 and NCI-H292 cells. The results indicated that AB23A inhibited the growth of A549 and NCI-H292 cells in dose- and time-dependent manner, however, there was only weak cytotoxicity on normal bronchial epithelial cells. The induction of apoptosis by AB23A was demonstrated by DAPI and annexin-V-FITC/PI staining. Further investigation revealed that AB23A decreased mitochondrial membrane potential (MMP) and up regulated reactive oxygen species (ROS) level. Meanwhile, the increased Bax/Bcl-2 ratio, activated caspase-3, caspase-9 and PARP were observed. In addition, AB23A increased the release of cytochrome c from mitochondria and the translocation of apoptotic inducing factor (AIF) into nuclei. Taken together, these results indicated that AB23A induced apoptosis by activating the intrinsic pathway, and suggested that AB23A can be used as a potential modulating agent in lung cancer.

LncRNA Gm5091 alleviates alcoholic hepatic fibrosis by sponging miR-27b/23b/24 in mice.

The regulatory roles of lncRNAs in the development of alcoholic hepatic fibrosis (AHF) have not been revealed. Here, we found lncRNA Gm5091 was being downregulated in mouse hepatic stellate cells (HSCs) during AHF. Then, Gm5091 was, respectively, overexpressed and knocked down in alcohol-treated primary HSCs. Our results showed that Gm5091 negatively regulated cell migration, ROS content, IL-1ß secretion, and expression of Collagen I and markers of HSC activation including α-SMA and Desmin. Furthermore, bioinformatics analysis showed that Gm5091 sequence contained binding sites of miR-27b, miR-23b, and miR-24, and we proved that miR-27b/23b/24 all bound to Gm5091 by using RNA pull-down assay. Full-length Gm5091 could decrease the miR-27b/23b/24 levels, but the truncated Gm5091 deleting the binding sites could not. Finally, we confirmed that full-length Gm5091 could alleviate AHF in vivo, but the truncated Gm5091 could not. In conclusion, lncRNA Gm5091 alleviates mouse AHF by sponging miR-27b/23b/24.

Synthesis and Characterization of Bis[1]benzothieno[3,2-b:2',3'-d]pyrroles: Quantitative Effects of Benzannulation on Dithieno[3,2-b:2',3'-d]pyrroles.

The synthesis of four N-functionalized bis[1]benzothieno[3,2-b:2',3'-d]pyrroles (BBTPs) is reported in order to provide a more detailed characterization of these fused-ring units, as well as increase the scope of known BBTP units available for application to conjugated materials. The optical, electronic, and structural properties of the resulting BBTP units have been compared to the parent N-alkyl- and N-aryl-dithieno[3,2-b:2',3'-d]pyrroles (DTPs), as well as their corresponding 2,6-diphenyl derivatives, in order to fully quantify the relative electronic effects resulting from benzannulation of the parent DTP building block. Such comparative analysis reveals that benzannulation results in a red-shifted absorbance, but to a lesser extent than simple phenyl-capping of the DTP. More surprising is that benzannulation results in stabilization of the BBTP HOMO, compared to the destabilization normally observed with extending the conjugation length of the backbone.

A charge-dependent mechanism is responsible for the dynamic accumulation of proteins inside nucleoli.

The majority of known nucleolar proteins are freely exchanged between the nucleolus and the surrounding nucleoplasm. One way proteins are retained in the nucleoli is by the presence of specific amino acid sequences, namely nucleolar localization signals (NoLSs). The mechanism by which NoLSs retain proteins inside the nucleoli is still unclear. Here, we present data showing that the charge-dependent (electrostatic) interactions of NoLSs with nucleolar components lead to nucleolar accumulation as follows: (i) known NoLSs are enriched in positively charged amino acids, but the NoLS structure is highly heterogeneous, and it is not possible to identify a consensus sequence for this type of signal; (ii) in two analyzed proteins (NF-κB-inducing kinase and HIV-1 Tat), the NoLS corresponds to a region that is enriched for positively charged amino acid residues; substituting charged amino acids with non-charged ones reduced the nucleolar accumulation in proportion to the charge reduction, and nucleolar accumulation efficiency was strongly correlated with the predicted charge of the tested sequences; and (iii) sequences containing only lysine or arginine residues (which were referred to as imitative NoLSs, or iNoLSs) are accumulated in the nucleoli in a charge-dependent manner. The results of experiments with iNoLSs suggested that charge-dependent accumulation inside the nucleoli was dependent on interactions with nucleolar RNAs. The results of this work are consistent with the hypothesis that nucleolar protein accumulation by NoLSs can be determined by the electrostatic interaction of positively charged regions with nucleolar RNAs rather than by any sequence-specific mechanism.