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Circular RNA (circRNA) is a novel RNA with circular structures. It is conserved in various species, and characterized by high stability, high expression levels and tissue specificity. Meanwhile, it could serve as microRNA (miRNA) sponges, bind to RNA-binding proteins, or regulate transcription and protein translation. With the development of high-throughput sequencing and bioinformatics, circRNA was reported to participate in the pathogenesis of cancer. N6-methyladenosine (m6A) modification is the most common type of RNA modification in eukaryote RNA, which is a dynamic and reversible process regulated by m6A methyltransferase, m6A demethylase and m6A-binding proteins. M6A modification isinvolved in the regulation of RNA nuclear export, splicing, stability, translation and degradation, thus playing a key role in the occurrence and development of multiple human diseases, such as cancers, cardiovascular diseases. Recently, some researches demonstrated that m6A modification of circRNA was essential in the occurrence and development of malignant tumors, such as cervical cancer, colorectal carcinoma, hepatocellular carcinoma, non-small cell lung cancer, poorly differentiated adenocarcinoma of the stomach. In the current manuscript, we summarized the mechanism of m6A RNA modification, the roles of m6A modification in regulation of circRNA, and the effects of circRNA m6A modification on tumor. The potential clinical application value of m6A-modified circRNA was further discussed, as to provide some new ideas and ways for early diagnosis, clinical treatment and prognosis of tumors.
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In this study, the regulatory effect of the overexpression of polarity protein Lgl2 on the nuclear export ofinfluenza A virus nucleoprotein in infected cells was investigated. A stable Tet-Off inducible MDCK cell lineexpressing a fusion protein comprising Lgl2 and an enhanced yellow fluorescent protein were used. TCID50analysis and neuraminidase activity analysis revealed that replication of influenza A virus was inhibited in Lgl2overexpressing cells. By immunofluorescence microscopical observation at different time point post virusinfection, a retention of NP in cellular nucleus was found in Lgl2 overexpressing cells. Compared with normalMDCK cells, change in claudin-1 distribution between cell contacts caused by Lgl2 overexpression impairedthe barrier function of tight junction. These results suggest that changes in cell polarity induced by Lgl2overexpressing will affect virus NP transportation.
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@#The purpose of this study was to screen out the novel chromosome maintenance protein 1(CRM1)covalent targeting inhibitors by computer-assisted drug design(CADD), and to study their effects on the proliferation of extranodal nature killer/T cell lymphoma(ENKTL). A novel CRM1 inhibitor LFS-829 was designed based on the molecular structure of LFS-01 by means of ADME/T and covalent docking. The target binding of LFS-829 with CRM1 was analyzed by MALDI-TOF mass spectrometry. The effects of LFS-829 on the proliferation of extranodal NK/T cell lymphoma SNK6 and HANK-1 cells were detected by CCK-8. The cell morphology was observed by live cell workstation. Immunofluorescence experiments were used to analyze the effect of LFS-829 on nuclear export function of CRM1. The changes of NF-κB signaling pathway under different concentrations of LFS-829 were analyzed by Western blot, dual luciferase reporter gene assay and enzyme-linked immunosorbent assay. Apoptosis was detected by flow cytometry, and the expression of proteins related to apoptosis pathway was detected by Western blot. Tests of peripheral blood mononuclear lymphocyte(PBMC)toxicity, platelet toxicity and mouse acute toxicity were done to make sure that it is not harmful to human. LFS-829 could bind covalently to the cysteine residue of the hydrophobic active pocket of CRM1. LFS-829 could selectively kill SNK6 and HANK-1 cells, with IC50 of 366 nmol/L and 158 nmol/L in 72 h, respectively, and cell morphology was significantly changed. LFS-829 at 800 nmol/L significantly inhibited the nuclear export function of CRM1, promoted nuclear assembly of IκB-α, down-regulated the transcriptional activity of NF-κB signaling pathway, significantly up-regulated the expression of apoptotic pathway protein p53, cleaved Caspase 3 and cleaved Caspase 9 and induced apoptosis, with no obvious killing effect on PBMC or platelets. It did not cause substantial tissue damage to mice at the high dose of 300 mg/kg, which shows its great prospect of future application.
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Objective: To investigate the mechanisms of nuclear export signal of androgen receptor (NESAR) in the regulation of androgen receptor (AR) protein expression and stability in prostate cancer.Methods: The green fluorescent protein fusion protein expression vectors pEGFP-AR(1-918aa), pEGFP-NESAR (743-817aa), pEGFP-NAR (1-665aa) and pEGFP-NAR-NESAR, and lysine mutants of NESAR pEGFP-NESAR K776R, pEGFP-NESAR K807R and pEGFP-NESAR K776R/K807R, were transiently transfec-ted into prostate cancer cell line PC3.Fluorescence microscopy, Western blot and immunoprecipitation were used to detect NESAR regulation of androgen receptor stability.Results: Under the fluorescence microscope, NESAR-containing fusion proteins were cytoplasmic localization, and their fluorescence intensities were much weaker than those without NESAR.The expression levels of NESAR-containing fusion proteins were significantly lower than those without NESAR.The half-lives of GFP-NESAR and GFP-NAR-NESAR were less than 6 h, while the expression of GFP and GFP-NAR was relatively stable and the half-life was more than 24 h in the presence of cycloheximide.The expression levels of GFP-NESAR were significantly increased by proteasome inhibitor MG132 treatment in a dose-dependent manner;in contrast, MG132 did not show any significant effect on the protein levels of GFP.When new protein synthesis was blocked, MG132 could also prevent the degradation of GFP-NESAR in the transfected cells in the presence of cycloheximide, while it had no significant effect on GFP protein stability in the parallel experiment.GFP immunoprecipitation showed that the ubiquitination level of GFP-NESAR fusion protein was significantly higher than that of the GFP control.The mutations of lysine sites K776 and K807 in NESAR significantly reduced the level of ubiquitination, and showed increased protein stability, indicating that they were the key amino acid residues of NESAR ubiquitination.Conclusion: NESAR was unstable and decreased the stability of its fusion proteins.NESAR was the target of polyubiquitination and mediated the degradation of its fusion proteins through the ubiquitin-proteasome pathway in prostate cancer cells.Our research provides a new way to regulate the level and/or activity of AR proteins, thus helping us understand the molecular mechanisms of AR degradation and strict control of AR in the progression to castration-resistance.
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Abnormal localization of tumor suppressor proteins is a common feature of renal cancer. Nuclear export of these tumor suppressor proteins is mediated by chromosome region maintenance-1 (CRM1). Here, we investigated the antitumor eff ects of a novel reversible inhibitor of CRM1 on renal cancer cells. We found that S109 inhibits the CRM1-mediated nuclear export of RanBP1 and reduces protein levels of CRM1. Furthermore, the inhibitory eff ect of S109 on CRM1 is reversible. Our data demonstrated that S109 signifi cantly inhibits proliferation and colony formation of renal cancer cells. Cell cycle assay showed that S109 induced G1-phase arrest, followed by the reduction of Cyclin D1 and increased expression of p53 and p21. We also found that S109 induces nuclear accumulation of tumor suppressor proteins, Foxo1 and p27. Most importantly, mutation of CRM1 at Cys528 position abolished the eff ects of S109. Taken together, our results indicate that CRM1 is a therapeutic target in renal cancer and the novel reversible CRM1 inhibitor S109 can act as a promising candidate for renal cancer therapy.
Subject(s)
Active Transport, Cell Nucleus , Cell Cycle Checkpoints , Cell Cycle , Cell Proliferation , Cyclin D1 , Kidney Neoplasms , Tumor Suppressor ProteinsABSTRACT
Nuclear factor-E2-related factor 2(Nrf2)is a member of C′n′C transcription factor family.It is an important transcrip-tion factor for regulation of cellular redox status and can be seen in all kinds of tissues .Recent studies have demonstrated that rapid deg-radation of Nrf2 after gene-induced antioxidative stress is as important as transcription and activation of Nrf 2 and the nuclear export of Nrf2 is a prerequisite for rapid degradation of Nrf2 in the cytosol.This review focuses on the mechanism of nuclear export of Nrf 2.
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The function of the herpes simplex virus type 1(HSV-1)UL4 protein is still elusive. Our objective is to investigate the subcellular transport mechanism of the UL4 protein. In this study,fluorescence microscopy was employed to investigate the subcellular localization of UL4 and characterize the transport mechanism in living cells. By constructing a series of deletion mutants fused with enhanced yellow fluorescent protein(EYFP),the nuclear export signals(NES)of UL4 were for the first time mapped to amino acid residues 178 to 186. In addition,the N-terminal 19 amino acids are identified to be required for the granule-like cytoplasmic pattern of UL4.Furthermore,the UL4 protein was demonstrated to be exported to the cytoplasm through the NES in a chromosomal region maintenance 1(CRM l)-dependent manner involving RanGTP hydrolysis.
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Molecules can enter the nucleus by passive diffusion or active transport mechanisms, depending on their size. Small molecules up to size of 50-60 kDa or less than 10 nm in diameter can diffuse passively through the nuclear pore complex (NPC), while most proteins are transported by energy driven transport mechanisms. Active transport of viral proteins is mediated by nuclear localization signals (NLS), which were first identified in Simian Virus 40 large T antigen and had subsequently been identified in a large number of viral proteins. Usually they contain short stretches of lysine or arginine residues. These signals are recognized by the importin super-family (importin α and β) proteins that mediate the transport across the nuclear envelope through Ran-GTP. In contrast, only one class of the leucine-rich nuclear export signal (NES) on viral proteins is known at present. Chromosome region maintenance 1 (CRM1) protein mediates nuclear export of hundreds of viral proteins through the recognition of the leucine-rich NES.
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AIM: To identify the novel nuclear export signal by analyzing the DNA sequences and detecting the cell localization of different adenovirus ElA - associated protein BS69 isoforms. METHODS:BS69 DNA sequences in Emsebl database were blasted and the sequence of amino acids was aligned with the typical nuclear export signal. Different BS69 isoform fragments were cloned into pcDNA3.1 vector and transfected into Cos7 cells. The BS69 localization was observed by immunostaining and the function was verified by Western blotting. RESULTS: A novel nuclear export signal was found in BS69 isoform 2 but not in isoform 1.The isoform 2 was localized in cytoplasm and isoform 1 in nucleus, which was also consistent with the DNA sequence. The isoform 2 was involved in LMP1 - activated JNK phosphorylation whereas the isoform 1 was not. CONCLUSION: Different BS69 isoforms have different cellular localization. BS69 isoform 2 is localized in cytoplasm, interacting with Epstein - Barr virus latent membrane protein 1 and may be involved in nasopharyngeal carcinoma development.However, the isoform 1 is localized in nucleus and plays important roles in transcription.
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The herpes simplex virus type 1 (HSV-1) infected-cell protein 27 (ICP27) is an essential,highly conserved protein involved in various steps of HSV-1 gene regulation as well as in the shut-off of host gene expression during infection.It functions primarily at the post-transcriptional level in inhibiting precursor mRNA splicing and in promoting nuclear export of viral transcripts.Recently,many novel functions performed by the HSV-1 ICP27 protein were shown,including leptomycin B resistance,inhibition of the type I interferon signaling,regulation of the viral mRNA translation and determining the composition of HSV-1 virions.