CENP-I directly targets centromeric DNA to support CENP-A deposition and centromere maintenance.

The enrichment of histone H3 variant CENP-A is the epigenetic mark of centromere and initiates the assembly of the kinetochore at centromere. The kinetochore is a multi-subunit complex that ensures accurate attachment of microtubule centromere and faithful segregation of sister chromatids during mitosis. As a subunit of kinetochore, CENP-I localization at centromere also depends on CENP-A. However, whether and how CENP-I regulates CENP-A deposition and centromere identity remains unclear. Here, we identified that CENP-I directly interacts with the centromeric DNA and preferentially recognizes AT-rich elements of DNA via a consecutive DNA-binding surface formed by conserved charged residues at the end of N-terminal HEAT repeats. The DNA binding-deficient mutants of CENP-I retained the interaction with CENP-H/K and CENP-M, but significantly diminished the centromeric localization of CENP-I and chromosome alignment in mitosis. Moreover, the DNA binding of CENP-I is required for the centromeric loading of newly synthesized CENP-A. CENP-I stabilizes CENP-A nucleosomes upon binding to nucleosomal DNA instead of histones. These findings unveiled the molecular mechanism of how CENP-I promotes and stabilizes CENP-A deposition and would be insightful for understanding the dynamic interplay of centromere and kinetochore during cell cycle.

The tumor suppressor NF2 modulates TEAD4 stability and activity in Hippo signaling via direct interaction.

As an output effector of the Hippo signaling pathway, the TEAD transcription factor and co-activator YAP play crucial functions in promoting cell proliferation and organ size. The tumor suppressor NF2 has been shown to activate LATS1/2 kinases and interplay with the Hippo pathway to suppress the YAP-TEAD complex. However, whether and how NF2 could directly regulate TEAD remains unknown. We identified a direct link and physical interaction between NF2 and TEAD4. NF2 interacted with TEAD4 through its FERM domain and C-terminal tail and decreased the protein stability of TEAD4 independently of LATS1/2 and YAP. Furthermore, NF2 inhibited TEAD4 palmitoylation and induced the cytoplasmic translocation of TEAD4, resulting in ubiquitination and dysfunction of TEAD4. Moreover, the interaction with TEAD4 is required for NF2 function to suppress cell proliferation. These findings reveal an unanticipated role of NF2 as a binding partner and inhibitor of the transcription factor TEAD, shedding light on an alternative mechanism of how NF2 functions as a tumor suppressor through the Hippo signaling cascade.

The novel interaction mode among centromere sub-complex CENP-O/P/U/Q/R.

The kinetochore is essential for the accurate segregation of sister chromosome in the eukaryote cell. Among the kinetochore subunits, five proteins CENP-O/P/U/Q/R form a stable complex, referred to as CENP-O class, and are required for proper kinetochore function. Although the function and structure of yeast COMA complex (CENP-O/P/U/Q homologs) have been revealed extensively, the assembly mechanism and detail interactions among human CENP-O class are significantly different and remain largely unclear. Here, we identified the fragment (residues 241-360) of CENP-U and the C-terminal half of CENP-Q are essential to form a hetero-complex and interact with CENP-O/P sub-complex in vitro. We for the first time showed that CENP-R does not directly interact with CENP-O/P in vitro, but indeed interact with CENP-U and CENP-Q. Furthermore, both the N- and C-terminus of CENP-R are required for the interaction with CENP-U and CENP-Q. Our research pinpointed a novel interaction pattern that might shed light on the assembly mechanism of vertebrate CENP-O class.

The Tumor Suppressor Interferon Regulatory Factor 2 Binding Protein 2 Regulates Hippo Pathway in Liver Cancer by a Feedback Loop in Mice.

BACKGROUND AND AIMS: The conserved Hippo pathway regulates organ size, tissue homeostasis, and tumorigenesis. Interferon regulatory factor 2 binding protein 2 (IRF2BP2) was originally identified as a transcriptional corepressor. However, the association between IRF2BP2 and the Hippo pathway remains largely unknown. In addition, the biological function and regulation mechanism of IRF2BP2 in liver cancer are poorly understood. APPROACH AND RESULTS: In this study, we uncovered the clinical significance of IRF2BP2 in suppressing hepatocellular carcinogenesis. We showed that IRF2BP2, a direct target repressed by the Yes-associated protein (YAP)/TEA domain transcription factor 4 (TEAD4) transcriptional complex, inhibited YAP activity through a feedback loop. IRF2BP2 stabilized vestigial-like family member 4 (VGLL4) and further enhanced VGLL4's inhibitory function on YAP. Moreover, liver-specific IRF2BP2 overexpression suppressed tumor formation induced by Hippo pathway inactivation. CONCLUSIONS: These results revealed the important role of IRF2BP2 in repressing liver cancer progression and highlighted a feedback loop underlying the Hippo pathway in organ-size control and tumorigenesis.

Structural analysis of fungal CENP-H/I/K homologs reveals a conserved assembly mechanism underlying proper chromosome alignment.

The kinetochore is a proteinaceous complex that is essential for proper chromosome segregation. As a core member of the inner kinetochore, defects of each subunit in the CENP-H/I/K complex cause dysfunction of kinetochore that leads to chromosome mis-segregation and cell death. However, how the CENP-H/I/K complex assembles and promotes kinetochore function are poorly understood. We here determined the crystal structures of CENP-I N-terminus alone from Chaetomium thermophilum and its complex with CENP-H/K from Thielavia terrestris, and verified the identified interactions. The structures and biochemical analyses show that CENP-H and CENP-K form a heterodimer through both N- and C-terminal interactions. CENP-I integrates into the CENP-H/K complex by binding to the C-terminus of CENP-H, leading to formation of the ternary complex in which CENP-H is sandwiched between CENP-K and CENP-I. Our sequence comparisons and mutational analyses showed that this architecture of the CENP-H/I/K complex is conserved in human. Mutating the binding interfaces of CENP-H for either CENP-K or CENP-I significantly reduced their localizations at centromeres and induced massive chromosome alignment defects during mitosis, suggesting that the identified interactions are critical for CENP-H/I/K complex assembly at the centromere and kinetochore function. Altogether, our findings unveil the evolutionarily conserved assembly mechanism of the CENP-H/I/K complex that is critical for proper chromosome alignment.

An electrogenerated chemiluminescence aptasensor for lysozyme based on the interaction between Ru(bpy)3 2+ and cucurbit[8]uril.

Strong anodic Ru(bpy)3 2+ electrogenerated chemiluminescence (ECL) was obtained at a cucurbil[8]uril (CB[8]) modified electrode in neutral conditions without the need of an additional coreactant. An ECL aptasensor was fabricated based on the strong ECL emission as well as the host-guest interaction between DNA and CB[8]. Firstly, amino group-terminated complementary DNA (DNA-NH2 ) was firmly immobilized on CB[8]/glass carbon electrode, which could further increase ECL intensity. Then, a ferrocene group-terminated lysozyme aptamer (Fc-DNA) was hybridized with complementary DNA. The inhibiting effect of ferrocene on Ru(bpy)3 2+ ECL resulted in the apparent decrease in ECL signal. When the modified electrode was incubated in lysozyme, specific binding between lysozyme and its aptamer could release the ferrocene group from the electrode surface, and the ECL emission was recovered. As a result, an 'on-off-on' mode ECL aptasensor for lysozyme was fabricated. In the range 0.14-140 pg ml-1 , the increased ECL intensities exhibited excellent linearity with the logarithm of lysozyme concentrations, and the detection limit was calculated as 0.093 pg ml-1 (3σ). The proposed ECL aptasensor exhibited satisfactory analytical performance, revealing the potential application of CB[n]s in an ECL sensing field.

Structural insights into the intramolecular interactions of centromere protein CENP-I.

In mitosis, the accurate segregation of sister chromosomes relies on kinetochore, a multiple subunits complex assembled on centromere of each sister chromosome. As a core component of inner kinetochore, CENP-I plays important functions to mediate kinetochore assembly and supports the faithful chromosome segregation. The structures of the N-terminus and C-terminus of CENP-I homologs in complex with CENP-H/K have been reported, respectively. Unfortunately, the intramolecular interactions of CENP-I are poorly understood, and how CENP-I interacts with CENP-M remains unknown. Here, we verified a unique helix α11, which forms the intramolecular interactions with N-terminal HEAT repeats in fungal CENP-I. Deletion of the helix α11 exposed the hydrophobic surface and resulted in the in vitro protein aggregation of N-terminal HEAT repeats of fungal CENP-I. The corresponding helix and its intramolecular interaction are highly conserved in human CENP-I. Deletion of the corresponding helix in human CENP-I dramatically reduced the functional activity to interact with CENP-H and CENP-M. Mutations of the conserved residues on the helix in human CENP-I significantly weakened the binding to CENP-M, but not CENP-H, in HeLa cells. Therefore, our findings for the first time unveiled a conserved helix of CENP-I, which is important for the intramolecular interaction and function, and would be helpful for understanding the structure basis of how CENP-I mediates the kinetochore assembly during cell cycle and mitosis.

Research progresses on the molecular structure of the Hippo signaling pathway components.

The Hippo signaling pathway has been identified to be involved in development and tissue homeostasis during the past decade, and is evolutionarily conserved from Drosophila to mammals. It transduces the signal through a series of protein-protein interaction and kinase cascades, to control the cell number and organ size by inhibiting cell proliferation and promoting apoptosis. Dysregulation of the Hippo signaling pathway is associated with tumorigenesis and cancers, so it is a crucial target for cancer therapy and regeneration medicine. Most of the Hippo signaling pathway components have been identified, and the cellular function and molecular mechanism have been revealed by structural and functional researches. In this review, we summarize the molecular structure of Hippo signaling pathway components and related targeting inhibitors from a structural view. We hope to improve the understandings of the regulation mechanism of the Hippo signaling transduction, and facilitate further functional studies and potential therapeutic interventions.

Long non-coding RNA LncCplx2 regulates glucose homeostasis and pancreatic ß cell function.

OBJECTIVE: Numerous studies have highlighted the role of clock genes in diabetes disease and pancreatic ß cell functions. However, whether rhythmic long non-coding RNAs involve in this process is unknown. METHODS: RNA-seq and 3' rapid amplification of cDNA ends (RACE)-PCR were used to identify the rat LncCplx2 in pancreatic ß cells. The subcellular analysis with qRT-PCR and RNA-Scope were used to assess the localization of LncCplx2. The effects of LncCplx2 overexpression or knockout (KO) on the regulation of pancreatic ß cell functions were assessed in vitro and in vivo. RNA-seq, immunoblotting (IB), Immunoprecipitation (IP), RNA pull-down, and chromatin immunoprecipitation (ChIP)-PCR assays were employed to explore the regulatory mechanisms through LncRNA-protein interaction. Metabolism cage was used to measure the circadian behaviors. RESULTS: We first demonstrate that LncCplx2 is a conserved nuclear long non-coding RNA and enriched in pancreatic islets, which is driven by core clock transcription factor BMAL1. LncCplx2 is downregulated in the diabetic islets and repressed by high glucose, which regulates the insulin secretion in vitro and ex vivo. Furthermore, LncCplx2 KO mice exhibit diabetic phenotypes, such as high blood glucose and impaired glucose tolerance. Notably, LncCplx2 deficiency has significant effects on circadian behavior, including prolonged period duration, decreased locomotor activity, and reduced metabolic rates. Mechanistically, LncCplx2 recruits EZH2, a core subunit of polycomb repression complex 2 (PRC2), to the promoter of target genes, thereby silencing circadian gene expression, which leads to phase shifts and amplitude changes in insulin secretion and cell cycle genes. CONCLUSIONS: Our results propose LncCplx2 as an unanticipated transcriptional regulator in a circadian system and suggest a more integral mechanism for the coordination of circadian rhythms and glucose homeostasis.

Rapid isolation and cryo-EM characterization of synaptic vesicles from mammalian brain.

Synaptic vesicles (SVs) store and release neurotransmitters at chemical synapses. Precise regulation of SV trafficking, exocytosis and endocytosis is crucial for neural transmission. Biochemical characterization of SVs, which is essential for research into neurotransmitter uptake and release, requires effective in vitro isolation methods. Here, we describe an improved and simple purification protocol for isolating SVs from mouse brain within 6 h, achieving a yield of approximately 0.4 mg of SVs per single brain. The use of track-etch membrane filtration and iodixanol cushion ensured the uniform morphology of SVs and low contaminants in the sample. Cryo-electron microscopy was used to show that the in vitro isolated SVs retained intact membrane-associated proteins, and observation of SVs in hippocampal neurons using cryo-electron tomography confirmed the abundance of protein coating. Thus, our protocol allows effective isolation of SVs from small volumes of mammalian brain tissue, and the properties of the isolated SVs are close to those in vivo, making them suitable for biochemical analysis.

The Dual Roles of MAGE-C2 in p53 Ubiquitination and Cell Proliferation Through E3 Ligases MDM2 and TRIM28.

The tumor suppressor p53 is critical for the maintenance of genome stability and protection against tumor malignant transformation, and its homeostasis is usually regulated by ubiquitination. MDM2 is a major E3 ligase of p53 ubiquitination, and its activity is enhanced by TRIM28. TRIM28 also independently ubiquitinates p53 as an E3 ligase activated by MAGE-C2. Moreover, MAGE-C2 is highly expressed in various cancers, but the detailed mechanisms of MAGE-C2 involved in MDM2/TRIM28-mediated p53 ubiquitination remain unknown. Here, we found that MAGE-C2 directly interacts with MDM2 through its conserved MHD domain to inhibit the activity of MDM2 on p53 ubiquitination. Furthermore, TRIM28 acts as an MAGE-C2 binding partner and directly competes with MAGE-C2 for MDM2 interaction, thus releasing the inhibitory role of MAGE-C2 and promoting p53 ubiquitination. MAGE-C2 suppresses cell proliferation in TRIM28-deficient cells, but the overexpression of TRIM28 antagonizes the inhibitory role of MAGE-C2 and accumulates p53 ubiquitination to promote cell proliferation. This study clarified the molecular link of MAGE-C2 in two major E3 systems MDM2 and TRIM28 on p53 ubiquitination. Our results revealed the molecular function of how MAGE-C2 and TRIM28 contribute to p53 ubiquitination and cell proliferation, in which MAGE-C2 acts as a potential inhibitor of MDM2 and TRIM28 is a vital regulator for MAGE-C2 function in p53 protein level and cell proliferation. This work would be helpful to understand the regulation mechanism of tumor suppressor p53.

Multisite phosphorylation determines the formation of Ska-Ndc80 macro-complexes that are essential for chromosome segregation during mitosis.

The human Ska complex (Ska) localizing to both spindle microtubules and kinetochores is essential for proper chromosome segregation during mitosis. Although several mechanisms have been proposed to explain how Ska is recruited to kinetochores, it is still not fully understood. By analyzing Ska3 phosphorylation, we identified six critical Cdk1 sites, including the previously identified Thr358 and Thr360. Mutations of these sites to phospho-deficient alanine (6A) in cells completely abolished Ska3 localization to kinetochores and Ska functions in chromosome segregation. In vitro, Cdk1 phosphorylation on Ska enhanced WT, not phospho-deficient 6A, binding to Ndc80C. Strikingly, the phosphomimetic Ska 6D complex formed a stable macro-complex with Ndc80C, but Ska WT failed to do so. These results suggest that multisite Cdk1 phosphorylation-enabled Ska-Ndc80 binding is decisive for Ska localization to kinetochores and its functions. Moreover, we found that Ska decrease at kinetochores triggered by the microtubule-depolymerizing drug nocodazole is independent of Aurora B but can be overridden by Ska3 overexpression, suggestive of a role of spindle microtubules in promoting Ska kinetochore recruitment. Thus, based on the current and previous results, we propose that multisite Cdk1 phosphorylation is critical for the formation of Ska-Ndc80 macro-complexes that are essential for chromosome segregation.