cDNA cloning and characterization of a novel gene encoding the MLF1-interacting protein MLF1IP

Myeloid leukemia factor 1: A "double-edged sword" in health and disease

The occurrence and development of malignancies are closely related to abnormal cell cycle regulation. Myeloid leukemia factor 1 (MLF1) is a small nucleocytoplasmic shuttling protein associated with cell cycle exit, apoptosis, and certain immune functions. Therefore, it is pertinent to explore the role of MLF1 in health and diseases. Studies to date have suggested that MLF1 could act as a double-edged sword, regulating biochemical activities directly or indirectly. In hematopoietic cells, it serves as a protective factor for the development of lineages, and in malignancies, it serves as an oncogenesis factor. The diversity of its functions depends on the binding partners, including tumor inhibitors, scaffolding molecules, mitochondrial membrane proteins, and transcription factors. Emerging evidence indicates that MLF1 influences immune responses as well. This paper reviews the structure, biological function, and research progress on MLF1 in health and diseases to provide new insights for future research.

A positive feedback loop of CENPU/E2F6/E2F1 facilitates proliferation and metastasis via ubiquitination of E2F6 in hepatocellular carcinoma

Centromere protein U (CENPU), a centromere-binding protein required for cellular mitosis, has been reported to be closely associated with carcinogenesis in multiple malignancies; however, the role of CENPU in hepatocellular carcinoma (HCC) is still unclear. Herein, we investigated its biological role and molecular mechanism in the development of HCC. High CENPU expression in HCC tissue was observed and correlated positively with a poor prognosis in HCC patients. CENPU knockdown inhibited the proliferation, metastasis, and G1/S transition of HCC cells in vivo and in vitro, while ectopic expression of CENPU exerted the opposite effects. Mechanistically, CENPU physically interacted with E2F6 and promoted its ubiquitin-mediated degradation, thus affecting the transcription level of E2F1 and further accelerating the G1/S transition to promote HCC cell proliferation. E2F1 directly binds to the CENPU promoter and increases the transcription of CENPU, thereby forming a positive regulatory loop. Collectively, our findings indicate a crucial role for CENPU in E2F1-mediated signalling for cell cycle progression and reveal a role for CENPU as a predictive biomarker and therapeutic target for HCC patients.

Visualization, benchmarking and characterization of nested single-cell heterogeneity as dynamic forest mixtures

A major topic of debate in developmental biology centers on whether development is continuous, discontinuous, or a mixture of both. Pseudo-time trajectory models, optimal for visualizing cellular progression, model cell transitions as continuous state manifolds and do not explicitly model real-time, complex, heterogeneous systems and are challenging for benchmarking with temporal models. We present a data-driven framework that addresses these limitations with temporal single-cell data collected at discrete time points as inputs and a mixture of dependent minimum spanning trees (MSTs) as outputs, denoted as dynamic spanning forest mixtures (DSFMix). DSFMix uses decision-tree models to select genes that account for variations in multimodality, skewness and time. The genes are subsequently used to build the forest using tree agglomerative hierarchical clustering and dynamic branch cutting. We first motivate the use of forest-based algorithms compared to single-tree approaches for visualizing and characterizing developmental processes. We next benchmark DSFMix to pseudo-time and temporal approaches in terms of feature selection, time correlation, and network similarity. Finally, we demonstrate how DSFMix can be used to visualize, compare and characterize complex relationships during biological processes such as epithelial-mesenchymal transition, spermatogenesis, stem cell pluripotency, early transcriptional response from hormones and immune response to coronavirus disease. Our results indicate that the expression of genes during normal development exhibits a high proportion of non-uniformly distributed profiles that are mostly right-skewed and multimodal; the latter being a characteristic of major steady states during development. Our study also identifies and validates gene signatures driving complex dynamic processes during somatic or germline differentiation.

Overexpression of MLF1IP promotes colorectal cancer cell proliferation through BRCA1/AKT/p27 signaling pathway

BACKGROUND AND OBJECTIVE

MLF1IP has been correlated with the progression and prognosis of a few tumors. However, the role of MLF1IP in colorectal cancer remains unclear. Here, we examined the expression and function of MLF1IP in colorectal cancer and investigated possible molecular mechanisms.

METHODS

MLF1IP expressions in colorectal cancer tissues and cell lines were detected by quantitative real-time PCR, western blotting, and immunohistochemistry. In vitro and in vivo assays were performed to explore the function and underlying molecular mechanisms of MLF1IP in colorectal cancer.

RESULTS

The expression levels of MLF1IP were significantly up-regulated in colorectal cancer tissues and CRC cell lines (P < 0.05). High expression of MLF1IP was significantly associated with TNM stage, T classification, lymph node involvement, distant metastasis, and poor patient survival (all P < 0.05). Overexpressing MLF1IP promoted while silencing MLF1IP inhibited, the proliferation and clonogenicity of colorectal cancer cells and tumorigenicity in NOD/SCID mice (P < 0.05). In addition, we demonstrated that the pro-proliferative effect of MLF1IP on colorectal cancer cells was associated with mediating the G1-to-S phase transition. MLF1IP knockdown enhanced BRCA1 activity concomitantly with p-AKT downregulation and p27 upregulation, while overexpression of MLF1IP has the opposite effect. Moreover, upregulation of BRCA1 can partially abolish the proliferative activity of MLF1IP.

CONCLUSIONS

These findings suggest that MLF1IP may promote proliferation and tumorigenicity of colorectal cancer cells via BRCA1/AKT/p27 signaling axis, and thereby provides potential targets for colorectal cancer therapy.

Abnormal Expression of Centromere Protein U Is Associated with Hepatocellular Cancer Progression

Background

Hepatocellular carcinoma (HCC) is one of the most common malignancies globally, but its molecular mechanism is unclear. Abnormal expression of centromere protein U (CENPU) is closely related to diverse human cancers. The purpose of this article was to evaluate the function and potential mechanisms of CENPU in HCC development.

Methods

We performed bioinformatics analysis of The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO), Gene Expression Profiling Interactive Analysis (GEPIA), and Kaplan-Meier plotter databases to investigate the clinical significance and prognostic value of CENPU in HCC. Western blotting and immunohistochemical staining were used to measure protein expression, while reverse transcription-quantitative polymerase chain reaction (qRT-PCR) was used to determine mRNA expression. Cell Counting Kit8 (CCK-8) and colony formation assays were conducted to examine cell proliferation. Transwell and wound healing assays were used to assess cell migration and invasion. Gene set enrichment analysis (GSEA) was used to explore the potential signaling pathways of CENPU involved in HCC.

Results

High expression of CENPU in HCC was predicted by public database analysis and indicated a poor prognosis. CENPU expression was significantly higher in HCC tissues and cells than in normal tissues and cell. In vitro, CENPU promoted the proliferation, migration, and invasion of HCC cells. GSEA results indicated that CENPU was linked to the Notch signaling pathway, and our research supported this prediction.

Conclusion

CENPU promotes the malignant biological process of HCC and may be a promising target for HCC treatment.

Identification of Key Biomarkers and Pathways in Small-Cell Lung Cancer Using Biological Analysis

BACKGROUND

Small-cell lung cancer (SCLC) is a major cause of carcinoma-related deaths worldwide. The aim of this study was to identify the key biomarkers and pathways in SCLC using biological analysis.

METHODS

Key genes involved in the development of SCLC were identified by downloading three datasets from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were screened using the GEO2R online analyzer; for the functional annotation and pathway enrichment analysis of genes, Funrich software was used. Construction of protein-to-protein interaction (PPI) networks was accomplished using the Search Tool for the Retrieval of Interacting Genes (STRING), and network visualization and module identification were performed using Cytoscape.

RESULTS

A total of 268 DEGs were ultimately obtained. The enriched functions and pathways of the upregulated DEGs included cell cycle, mitotic, and DNA replication, and the downregulated DEGs were enriched in epithelial-to-mesenchymal transition, serotonin degradation, and noradrenaline. Analysis of significant modules demonstrated that the upregulated genes are primarily concentrated in functions related to cell cycle and DNA replication. Kaplan-Meier analysis of hub genes revealed that they may promote the carcinogenesis and progression of SCLC. The result of ONCOMINE demonstrated that these 10 hub genes were significantly overexpressed in SCLC compared with normal samples.

CONCLUSION

Identification of the molecular functions and signaling pathways of participating DEGs can deepen the current understanding of the molecular mechanisms of SCLC. The knowledge gained from this work may contribute to the development of treatment options and improve the prognosis of SCLC in the future.

The lncRNA GATA3-AS1/miR-495-3p/CENPU axis predicts poor prognosis of breast cancer via the PLK1 signaling pathway

The function of centromere protein U (CENPU) gene in breast cancer has not been well understood. Therefore, we explored the expression profiles of CENPU gene in breast carcinoma to better understand the functions of this gene, as well as the relationship between CENPU expression and the prognosis of breast carcinoma patients. Our results indicate that CENPU was expressed at significantly higher levels in cancerous tissues than in normal tissues. Furthermore, CENPU expression correlated significantly with many clinicopathological characteristics of breast cancer. In addition, we discovered that high levels of CENPU expression predicted poor prognosis in patients with breast cancer. Functional investigation revealed that 180 genes exhibited co-expression with CENPU. Functional annotation indicated that 17 of these genes were involved in the PLK1 signaling pathway, with most of them (16/17) being expressed at significantly higher levels in malignant tissues compared with normal controls and correlating with a poor prognosis. Subsequently, we found that four miRNAs, namely hsa-miR-543, hsa-miR-495-3p, hsa-miR-485-3p, and hsa-miR-337-3p, could be regarded as potential CENPU expression regulators. Then, five lncRNAs were predicted to potentially bind to the four miRNAs. Combination of the results from expression, survival, correlation analysis and functional experiments analysis demonstrated the link between lncRNA GATA3-AS1/miR-495-3p/CENPU axis and prognosis of breast cancer. In conclusion, CENPU could be involved in cell cycle progression through PLK1 signaling pathway.

CENP-50 is required for papilloma development in the two-stage skin carcinogenesis model

CENP‐50/U is a component of the CENP‐O complex (CENP‐O/P/Q/R/U) and localizes to the centromere throughout the cell cycle. Aberrant expression of CENP‐50/U has been reported in many types of cancers. However, as Cenp‐50/U‐deficient mice die during early embryogenesis, its functions remain poorly understood in vivo. To investigate the role of Cenp‐50/U in skin carcinogenesis, we generated Cenp‐50/U conditional knockout (K14Cre^ER‐Cenp‐50/U^fl/fl) mice and subjected them to the 7,12‐dimethylbenz(a)anthracene (DMBA)/terephthalic acid (TPA) chemical carcinogenesis protocol. As a result, early‐stage papillomas decreased in Cenp‐50/U‐deficient mice. In contrast, Cenp‐50/U‐deficient mice demonstrated almost the same carcinoma incidence as control mice. Furthermore, mRNA expression analysis using DMBA/TPA‐induced papillomas and carcinomas revealed that Cenp‐50/U expression levels in papillomas were significantly higher than in carcinomas. These results suggest that Cenp‐50/U functions mainly in early papilloma development and it has little effect on malignant conversion.

NPM and NPM-MLF1 interact with chromatin remodeling complexes and influence their recruitment to specific genes

Nucleophosmin (NPM1) is frequently mutated or subjected to chromosomal translocation in acute myeloid leukemia (AML). NPM protein is primarily located in the nucleus, but the recurrent NPMc+ mutation, which creates a nuclear export signal, is characterized by cytoplasmic localization and leukemogenic properties. Similarly, the NPM-MLF1 translocation product favors the partial cytoplasmic retention of NPM. Regardless of their common cellular distribution, NPM-MLF1 malignancies engender different effects on hematopoiesis compared to NPMc+ counterparts, highlighting possible aberrant nuclear function(s) of NPM in NPMc+ and NPM-MLF1 AML. We performed a proteomic analysis and found that NPM and NPM-MLF1 interact with various nuclear proteins including subunits of the chromatin remodeling complexes ISWI, NuRD and P/BAF. Accordingly, NPM and NPM-MLF1 are recruited to transcriptionally active or repressed genes along with NuRD subunits. Although the overall gene expression program in NPM knockdown cells is similar to that resulting from NPMc+, NPM-MLF1 expression differentially altered gene transcription regulated by NPM. The abnormal gene regulation imposed by NPM-MLF1 can be characterized by the enhanced recruitment of NuRD to gene regulatory regions. Thus, different mechanisms would orchestrate the dysregulation of NPM function in NPMc+- versus NPM1-MLF1-associated leukemia.

NPMc+ mutation is the most common mutation in acute myeloid leukemia (AML) with prevalence in one third of all AML cases. NPM can also be involved in leukemogenic translocation including the t(3;5)(q25;q34) NPM-MLF1 translocation, which is associated to bad clinical course but remains poorly defined. We are reporting that NPM and the leukemogenic NPM-MLF1 play central role in chromatin organization and gene regulation in hematopoietic cells. A proteomic analysis provided the evidence that NPM and NPM-MLF1 are interacting with the chromatin remodeling complexes NuRD, P/BAF and ISWI in hematopoietic cells. The NPM nuclear depletion, such as imposed by the leukemogenic NPMc+ mutation, or the expression of NPM-MLF1 favors the uncontrolled recruitment of the CHD4/NuRD to chromatin and the abnormal regulation of NPM-target genes. Our results suggest that the abnormal gene regulation forced by NPM-MLF1 is different than the loss of nuclear function imposed by NPMc+, and it can be characterized by the enhanced recruitment of CHD4/NuRD to genes. Thus, NPM-MLF1 is likely to promote hematopoietic malignancies by disruption of gene regulation imposed by the NuRD activity.

Centromere protein U expression promotes non-small-cell lung cancer cell proliferation through FOXM1 and predicts poor survival

Purpose

Centromere protein U (CENPU) abnormally exhibits high expression in various types of human tumor tissues and participates in tumor progression; however, its expression pattern and biological function in lung cancer have not yet been elucidated. In the present study, we explored the clinical significance and biological function of CENPU in lung cancer.

Materials and methods

The Cancer Genome Atlas (TCGA) data analyses, quantitative real-time PCR (RT-PCR), and Western blotting were performed to quantify CENPU and FOXM1 expression in non-small-cell lung cancer (NSCLC) samples. Survival data were obtained from Kaplan–Meier plotter or PROGgene V2 prognostic database. The function of CENPU in lung cancer cell proliferation was determined using 5-ethynyl-2′-deoxyuridine (EdU), Cell Counting Kit-8 (CCK-8), and cell cycle assays, and the underlying mechanism was determined through bioinformatic analyses and validated by in vitro siRNA or plasmid transfection experiments.

Results

CENPU was abnormally overexpressed in NSCLC samples compared with matched paired normal tissues. Higher expression of CENPU predicted worse overall survival (OS) and relapse-free survival (RFS) in NSCLC patients. Knockdown of CENPU expression by siRNA significantly inhibited proliferation and delayed cell cycle progression of lung cancer cells. To figure out the mechanism, bioinformatic analyses were performed and the results showed that the transcription factor, FOXM1, positively correlated with CENPU. Further in vitro experiments indicated that FOXM1 was the possible downstream transcription factor of CENPU as the knockdown of CENPU led to lower expression of FOXM1 and the overexpression of FOXM1 significantly reversed the inhibition of proliferation caused by CENPU knockdown. Furthermore, FOXM1 was highly expressed in NSCLC. The knockdown of FOXM1 also attenuated proliferation and induced G1 arrest in lung cancer cells.

Conclusion

CENPU was highly expressed in NSCLC tissues, wherein it promoted lung cancer cell proliferation via the transcription factor, FOXM1, which could be a potential target for therapeutic strategies.

The effect of centromere protein U silencing by lentiviral mediated RNA interference on the proliferation and apoptosis of breast cancer

Centromere protein U (CENPU) is a novel transcriptional repressor that is associated with different types of cancer. However, its function in breast cancer is poorly understood. In the present study, it was identified that CENPU was highly expressed in breast cancer tissues compared with expression in normal breast tissues (P=0.001). Furthermore, the CENPU mRNA level in tumors was often elevated, compared with the matched adjacent normal breast cancer tissue specimens in the dataset from The Cancer Genome Atlas database (n=106; P<0.001). To understand the function of CENPU in human breast carcinogenesis, its effects on the proliferation, apoptosis and cell cycle progression of MDA-MB-231 cells were examined using the lentiviral-mediated CENPU knockdown approach. The RNA and protein expression levels in the transfected cells were monitored using reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. The mRNA and protein expression levels of the CENPU gene were significantly lower in the CENPU-shRNA transfected cells than in the control (P<0.01), indicating successful gene expression knockdown. Post-transfection, cell counting and MTT analysis revealed that the proliferation activity was significantly suppressed in CENPU knockdown cells relative to the control (P<0.01). Additionally, fluorescence activated cell sorting analysis revealed that the (G2+S) phase fraction was significantly declined in CENPU knockdown cells relative to the control; while the G1 phase fraction was significantly increased (P<0.01) and the percentage of the apoptotic cells was significantly increased (P<0.01). In conclusion, downregulation of CENPU gene expression may inhibit cell proliferation and cell cycle progression, and increase the apoptosis of the breast cancer cells. These results suggested a possible function of this protein in breast cancer pathogenesis and prognosis.

Myeloid leukemia factor functions in anti-WSSV immune reaction of kuruma shrimp, Marsupenaeus japonicus

Myeloid leukemia factor (MLF) plays an important role in development, cell cycle, myeloid differentiation, and regulates the RUNX transcription factors. However, the function of MLF in immunity is still unclear. In this study, an MLF was identified and characterized in kuruma shrimp Marsupenaeus japonicus, and named as MjMLF. The full-length cDNA of MjMLF contained 1111 nucleotides, which had an opening reading frame of 816 bp encoding a protein of 272 amino acids with an MLF1-interacting protein domain. MjMLF could be ubiquitously detected in different tissues of shrimp at the transcriptional level. The expression pattern analysis showed that MjMLF could be upregulated in shrimp hemocytes and hepatopancreas after white spot syndrome virus challenge. The RNA interference and protein injection assay showed that MjMLF could inhibit WSSV replication in vivo. Flow cytometry assay showed that MjMLF could induce hemocytes apoptosis which functioned in the shrimp antiviral reaction. All the results suggested that MjMLF played an important role in the antiviral immune reaction of kuruma shrimp. The research indicated that MjMLF might function as a novel regulator to inhibit WSSV replication in shrimp.

Centromere protein U is a potential target for gene therapy of human bladder cancer

To investigate the role of centromere protein U (CENPU) in human bladder cancer (BCa), CENPU gene expression was evaluated in human BCa tissues. We used real-time quantitative PCR (qPCR) and found that CENPU gene expression in human BCa tissues was higher compared to that observed in cancer-adjacent normal tissues. High CENPU expression was found to be strongly correlated with tumor size and TNM stage. Kaplan-Meier survival analysis indicated that high CENPU levels were associated with reduced survival. We used a lentivirus to silence endogenous CENPU gene expression in the BCa T24 cell line. CENPU knockdown was confirmed by qPCR. Cellomic imaging and BrdU assays showed that cell proliferation was significantly reduced in the CENPU-silenced cells compared to that noted in the control cells. Flow cytometry revealed that in the CENPU-silenced cells the cell cycle was arrested at the G1 phase relative to that in the control cells. In addition, apoptosis was significantly increased in the CENPU-silenced cells. Giemsa staining showed that CENPU-silenced cells, compared to control cells, displayed a significantly lower number of cell colonies. The genome-wide effect of CENPU knockdown showed that a total of 1,274 differentially expressed genes was found, including 809 downregulated genes and 465 upregulated genes. Network analysis by Ingenuity Pathway Analysis (IPA) resulted in 25 distinct signaling pathways, including the top-ranked network: ‘Cellular compromise, organismal injury and abnormalities, skeletal and muscular disorders’. In-depth IPA analysis revealed that CENPU was associated with the HMGB1 signaling pathway. qPCR and western blot analysis demonstrated that in the HMGB1 signaling pathway, CENPU knockdown downregulated expression levels of ILB, CXCL8, RAC1 and IL1A. In conclusion, our data may provide a potential pathway signature for therapeutic targets with which to treat BCa.

MLF1IP promotes normal erythroid proliferation and is involved in the pathogenesis of polycythemia vera

Myelodysplasia/myeloid leukemia factor 1-interacting protein (MLF1IP) appears to be an erythroid lineage-specific gene in mice; however, its role in normal erythropoiesis and erythropoietic disorders have not yet been elucidated. Here, we found that MLF1IP is abundantly expressed in human erythroid progenitor cells and that MLF1IP-deficiency reduces cell proliferation resulting from cell cycle arrest. Moreover, MLF1IP expression is exclusively elevated in CFU-E cells from polycythemia vera (PV) patients, and MLF1IP transgenic mice develop a PV-like disorder. Further analyses revealed that the erythroid progenitors and early-stage erythroblasts from these transgenic mice expand by up-regulating cyclin D2 and down-regulating p27 and p21. Thus, our data demonstrate that MLF1IP promotes erythroid proliferation and is involved in the pathogenesis of PV, suggesting that it might be a novel molecular target for erythropoietic disorders.

MLF1 is a proapoptotic antagonist of HOP complex-mediated survival

In the HAX1/HtrA2-OMI/PARL (HOP) mitochondrial protein complex, anti-apoptotic signals are generated by cleavage and activation of the serine protease HtrA2/OMI by the rhomboid protease PARL upon recruitment of both proteases to inner mitochondrial membrane protein HAX1 (HS1-associated protein X-1). Here we report the negative regulation of the HOP complex by human leukemia-associated myeloid leukemia factor 1 (MLF1). We demonstrate that MLF1 physically and functionally associates with HAX1 and HtrA2. Increased interaction of MLF1 with HAX1 and HtrA2 displaces HtrA2 from the HOP complex and inhibits HtrA2 cleavage and activation, resulting in the apoptotic cell death. Conversely, over-expressed HAX1 neutralizes MLF1's effect and inhibits MLF1-induced apoptosis. Importantly, Mlf1 deletion reverses B- and T-cell lymphopenia and significantly ameliorates the progressive striatal and cerebellar neurodegeneration observed in Hax1^-/- mice, with a doubling of the lifespan of Mlf1^-/-/Hax1^-/- animals compared to Hax1^-/- animals. Collectively, these data indicate that MLF1 serves as a proapoptotic antagonist that interacts with the HOP mitochondrial complex to modulate cell survival.

MLF1IP is correlated with progression and prognosis in luminal breast cancer

Myeloid leukemia factor 1-interacting protein (MLF1IP) has been found to be involved in the progression of several malignancies. The potential correlation between MLF1IP and clinical outcome in patients with luminal breast cancer, however, remains unknown. In the present study, we demonstrated that MLF1IP was significantly upregulated in luminal breast cancer tissue compared with adjacent normal tissue both in validated cohort and TCGA cohort. Upregulated expression of MLF1IP was correlated with more often lymph node metastasis and negative progesterone receptor expression in TCGA cohorts. Kaplan-Meier analysis indicated that patients with high MLF1IP expression had significantly lower overall survival. Moreover, multivariate analysis revealed that high MLF1IP expression was independent high risk factor as well as old age (>60) and distant metastasis. This study provides new insights and evidences that MLF1IP over-expression plays important roles in progression of luminal breast cancer. However, the precise cellular mechanisms for MLF1IP in luminal breast cancer need to be further explored.

Detection of genes associated with developmental competence of bovine oocytes

The developmental competence of oocytes is acquired progressively during folliculogenesis and is linked to follicular size. It has been documented that oocytes originating from larger follicles exhibit a greater ability to develop to the blastocyst stage. The differences in cytoplasmic factors such as mRNA transcripts could explain the differences in oocyte developmental potential. We used bovine oligonucleotide microarrays to characterize differences between the gene expression profiles of germinal vesicle stage (GV) oocytes with greater developmental competence from medium follicles (MF) and those with less developmental competence from small follicles (SF). After normalizing the microarray data, our analysis found differences in the level of 60 transcripts (≥1.4 fold), corresponding to 49 upregulated and 11 downregulated transcripts in MF oocytes compared to SF oocytes. The gene expression data were classified according to gene ontology, the majority of the genes were associated with the regulation of transcription, translation, the cell cycle, and mitochondrial activity. A subset of 16 selected genes was validated for GV oocytes by quantitative real-time RT-PCR; significant differences (P˂0.01) were found in the level of TAF1A, MTRF1L, ATP5C1, UBL5 and MAP3K13 between the MF and SF oocytes. After maturation the transcript level remained stable for ATP5F1, BRD7, and UBL5 in both oocyte categories. The transcript level of another 13 genes substantially dropped in the MF and/or SF oocytes. It can be concluded that the developmental competence of bovine oocytes and embryos may be a quantitative trait dependent on small changes in the transcription profiles of many genes.

MLF1 interacting protein: a potential gene therapy target for human prostate cancer?

Here, we investigated the role of one gene that has been previously associated with human prostate carcinoma cells-myelodysplasia/myeloid leukemia factor 1 interacting protein (MLF1IP)-in order to better ascertain its role in human prostate carcinogenesis. The prostate cancer cell line PC-3 was lentivirally transfected to silence endogenous MLF1IP gene expression, which was confirmed by real-time quantitative PCR (RT-qPCR). Cellomics ArrayScan VTI imaging and MTT assays were conducted to assess cell proliferation. Cell cycle phase arrest and apoptosis were assayed by flow cytometry. Colony formation was assessed by fluorescence microscopy. MLF1IP gene expression was also analyzed by RT-qPCR in sixteen prostate cancer tissue samples and six healthy control prostate tissue samples from human patients. Cell proliferation was significantly inhibited in MLF1IP-silenced cells relative to control cells. G1 phase, S and G2/M phase cell counts were not significantly changed in MLF1IP-silenced cells relative to control cells. Apoptosis was significantly increased in MLF1IP-silenced cells, while MLF1IP-silenced cells displayed a significantly reduced number of cell colonies, compared to control cells. The 16 human prostate cancer tissue samples revealed no clear upregulation or downregulation in MLF1IP gene expression. MLF1IP significantly promotes prostate cancer cell proliferation and colony formation and significantly inhibits apoptosis without affecting cell cycle phase arrest. Further study is required to conclusively determine whether MLF1IP is upregulated in human prostate cancer tumors and to determine the precise cellular mechanism(s) for MLF1IP in prostate carcinogenesis.

Selective blockade of cancer cell proliferation and anchorage-independent growth by Plk1 activity-dependent suicidal inhibition of its polo-box domain

Polo-like kinase 1 (Plk1) plays a critical role in proper M-phase progression and cell proliferation. Plk1 is overexpressed in a broad spectrum of human cancers and is considered an attractive anticancer drug target. Although a large number of inhibitors targeting the catalytic domain of Plk1 have been developed, these inhibitors commonly exhibit a substantial level of cross-reactivity with other structurally related kinases, thus narrowing their applicable dose for patient treatment. Plk1 contains a C-terminal polo-box domain (PBD) that is essentially required for interacting with its binding targets. However, largely due to the lack of both specific and membrane-permeable inhibitors, whether PBD serves as an alternative target for the development of anticancer therapeutics has not been rigorously examined. Here, we used an intracellularly expressed 29-mer-long PBIP1-derived peptide (i.e., PBIPtide), which can be converted into a "suicidal" PBD inhibitor via Plk1-dependent self-priming and binding. Using this highly specific and potent system, we showed that Plk1 PBD inhibition alone is sufficient for inducing mitotic arrest and apoptotic cell death in cancer cells but not in normal cells, and that cancer cell-selective killing can occur regardless of the presence or absence of oncogenic RAS mutation. Intriguingly, PBD inhibition also effectively prevented anchorage-independent growth of malignant cancer cells. Thus, targeting PBD represents an appealing strategy for anti-Plk1 inhibitor development. Additionally, PBD inhibition-induced cancer cell-selective killing may not simply stem from activated RAS alone but, rather, from multiple altered biochemical and physiological mechanisms, which may have collectively contributed to Plk1 addiction in cancer cells.

Structural analysis of in silico mutant experiments of human inner-kinetochore structure

Large multi-molecular complexes like the kinetochore are lacking of suitable methods to determine their spatial structure. Here, we use and evaluate a novel modeling approach that combines rule-bases reaction network models with spatial molecular geometries. In particular, we introduce a method that allows to study in silico the influence of single interactions (e.g. bonds) on the spatial organization of large multi-molecular complexes and apply this method to an extended model of the human inner-kinetochore. Our computational analysis method encompasses determination of bond frequency, geometrical distances, statistical moments, and inter-dependencies between bonds using mutual information. For the analysis we have extend our previously reported human inner-kinetochore model by adding 13 new protein interactions and three protein geometry details. The model is validated by comparing the results of in silico with reported in vitro single protein deletion experiments. Our studies revealed that most simulations mimic the in vitro behavior of the kinetochore complex as expected. To identify the most important bonds in this model, we have created 39 mutants in silico by selectively disabling single protein interactions. In a total of 11,800 simulation runs we have compared the resulting structures to the wild-type. In particular, this allowed us to identify the interaction Cenp-W-H3 and Cenp-S-Cenp-X as having the strongest influence on the inner-kinetochore's structure. We conclude that our approach can become a useful tool for the in silico dynamical study of large, multi-molecular complexes.

Drosophila myeloid leukemia factor acts with DREF to activate the JNK signaling pathway

Drosophila myelodysplasia/myeloid leukemia factor (dMLF), a homolog of human MLF1, oncogene was first identified by yeast two-hybrid screen using the DNA replication-related element-binding factor (DREF) as bait. DREF is a transcription factor that regulates proliferation-related genes in Drosophila. It is known that overexpression of dMLF in the wing imaginal discs through the engrailed-GAL4 driver causes an atrophied wing phenotype associated with the induction of apoptosis. However, the precise mechanisms involved have yet to be clarified. Here, we found the atrophied phenotype to be suppressed by loss-of-function mutation of Drosophila Jun N-terminal kinase (JNK), basket (bsk). Overexpression of dMLF induced ectopic JNK activation in the wing disc monitored with the puckered-lacZ reporter line, resulting in induction of apoptosis. The DREF-binding consensus DRE sequence could be shown to exist in the bsk promoter. Chromatin immunoprecipitation assays in S2 cells with anti-dMLF IgG and quantitative real-time PCR revealed that dMLF binds specifically to the bsk promoter region containing the DRE sequence. Furthermore, using a transient luciferase expression assay, we provide evidence that knockdown of dMLF reduced bsk gene promoter activity in S2 cells. Finally, we show that dMLF interacts with DREF in vivo. Altogether, these data indicate that dMLF acts with DREF to stimulate the bsk promoter and consequently activates the JNK pathway to promote apoptosis.

Mechanisms underlying Plk1 polo-box domain-mediated biological processes and their physiological significance

Mammalian polo-like kinase 1 (Plk1) has been studied intensively as a key regulator of various cell cycle events that are critical for proper M-phase progression. The polobox domain (PBD) present in Plk1's C-terminal noncatalytic region has been shown to play a central role in targeting the N-terminal kinase domain of Plk1 to specific subcellular locations. Subsequent studies reveal that PBD binds to a phosphorylated motif generated by one of the two mechanisms-self-priming by Plk1 itself or non-selfpriming by a Pro-directed kinase, such as Cdc2. Here, we comparatively review the differences in the biochemical steps of these mechanisms and discuss their physiological significance. Considering the diverse functions of Plk1 during the cell cycle, a better understanding of how the catalytic activity of Plk1 functions in concert with its cisacting PBD and how this coordinated process is intricately regulated to promote Plk1 functions will be important for providing new insights into different mechanisms underlying various Plk1-mediated biological events that occur at the multiple stages of the cell cycle.

Identification of TNM stage-specific genes in lung adenocarcinoma by genome-wide expression profiling

The present study aimed to investigate the molecular basis of lung cancer development using a microarray to identify the differentially-expressed genes associated with the various tumor-node-metastasis (TNM) stages of lung adenocarcinoma. This subtype of lung cancer has increased in incidence within recent years in China. A 35K oligo gene array covering ~25,100 genes was used to screen the differentially-expressed genes among 90 lung adenocarcinoma samples of various TNM stages. To verify the data from the gene arrays, three genes [human zinc finger-containing, Miz1, PIAS-like protein on chromosome 7 (Zimp7), GINS complex subunit 2 (GINS2) and NSAID activated gene 1 (NAG-1)] were validated using quantitative (q)PCR in an alternative set of samples to the gene array. A total of 640 genes were identified that were differentially-expressed in lung adenocarcinoma compared with the surrounding normal lung tissues. From these 640 candidate genes, 10 were observed to be differentially-expressed among TNM stages I, II and IIIA, of which, the Zimp7, GINS2 and NAG-1 genes were reported for the first time to be expressed at high levels in lung adenocarcinoma. The results of the qPCR for the three genes were consistent with those from the gene array. In total, 10 candidate genes were identified to be associated with the various TNM stages of lung adenocarcinoma in the population studied, which may provide new insights into the molecular basis underlying the development of lung adenocarcinoma and offer new targets for the diagnosis, therapy and prognosis.

Investigation of tissue-specific expression and functions of MLF1-IP during development and in the immune system

Myeloid leukemia factor 1-interacting protein (MLF1-IP) has been found to exert functions in mitosis, although studies have been conducted only in cell lines up to now. To understand its roles during ontogeny and immunity, we analyzed its mRNA expression pattern by in situ hybridization and generated MLF1-IP gene knockout (KO) mice. MLF1-IP was expressed at elevated levels in most rudimentary tissues during the mid-gestation stage, between embryonic day 9.5 (e9.5) and e15.5. It declined afterwards in these tissues, but was very high in the testes and ovaries in adulthood. At post-natal day 10 (p10), the retina and cerebellum still expressed moderate MLF1-IP levels, although these tissues do not contain fast-proliferating cells at this stage. MLF1-IP expression in lymphoid organs, such as the thymus, lymph nodes, spleen and bone marrow, was high between e15.5 and p10, and decreased in adulthood. MLF1-IP KO embryos failed to develop beyond e6.5. On the other hand, MLF1-IP(+/-) mice were alive and fertile, with no obvious anomalies. Lymphoid organ size, weight, cellularity and cell sub-populations in MLF1-IP(+/-) mice were in the normal range. The functions of MLF1-IP(+/-) T cells and naïve CD4 cells, in terms of TCR-stimulated proliferation and Th1, Th17 and Treg cell differentiation in vitro, were comparable to those of wild type T cells. Our study demonstrates that MLF1-IP performs unique functions during mouse embryonic development, particularly around e6.5, when there was degeneration of epiblasts. However, the cells could proliferate dozens of rounds without MLF1-IP. MLF1-IP expression at about 50% of its normal level is sufficient to sustain mice life and the development of their immune system without apparent abnormalities. Our results also raise an intriguing question that MLF1-IP might have additional functions unrelated to cell proliferation.

Subcellular localization of full-length human myeloid leukemia factor 1 (MLF1) is independent of 14-3-3 proteins

Myeloid leukemia factor 1 (MLF1) is associated with the development of leukemic diseases such as acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). However, information on the physiological function of MLF1 is limited and mostly derived from studies identifying MLF1 interaction partners like CSN3, MLF1IP, MADM, Manp and the 14-3-3 proteins. The 14-3-3-binding site surrounding S34 is one of the only known functional features of the MLF1 sequence, along with one nuclear export sequence (NES) and two nuclear localization sequences (NLS). It was recently shown that the subcellular localization of mouse MLF1 is dependent on 14-3-3 proteins. Based on these findings, we investigated whether the subcellular localization of human MLF1 was also directly 14-3-3-dependent. Live cell imaging with GFP-fused human MLF1 was used to study the effects of mutations and deletions on its subcellular localization. Surprisingly, we found that the subcellular localization of full-length human MLF1 is 14-3-3-independent, and is probably regulated by other as-yet-unknown proteins.

Establishment of the vertebrate kinetochores

The centromere is essential for accurate chromosome segregation during mitosis and meiosis to achieve transmission of genetic information to daughter cells. To facilitate accurate chromosome segregation, the centromere serves several specific functions, including microtubule binding, spindle-checkpoint control, and sister chromatid cohesion. The kinetochore is formed on the centromere to achieve these functions. To understand kinetochore structure and function, it is critical to identify the protein components of the kinetochore and characterize the functional properties of each component. Here, we review recent progress with regard to the molecular architecture of the kinetochore and discuss the future directions for centromere biology.

Step-wise assembly, maturation and dynamic behavior of the human CENP-P/O/R/Q/U kinetochore sub-complex

Kinetochores are multi-protein megadalton assemblies that are required for attachment of microtubules to centromeres and, in turn, the segregation of chromosomes in mitosis. Kinetochore assembly is a cell cycle regulated multi-step process. The initial step occurs during interphase and involves loading of the 15-subunit constitutive centromere associated complex (CCAN), which contains a 5-subunit (CENP-P/O/R/Q/U) sub-complex. Here we show using a fluorescent three-hybrid (F3H) assay and fluorescence resonance energy transfer (FRET) in living mammalian cells that CENP-P/O/R/Q/U subunits exist in a tightly packed arrangement that involves multifold protein-protein interactions. This sub-complex is, however, not pre-assembled in the cytoplasm, but rather assembled on kinetochores through the step-wise recruitment of CENP-O/P heterodimers and the CENP-P, -O, -R, -Q and -U single protein units. SNAP-tag experiments and immuno-staining indicate that these loading events occur during S-phase in a manner similar to the nucleosome binding components of the CCAN, CENP-T/W/N. Furthermore, CENP-P/O/R/Q/U binding to the CCAN is largely mediated through interactions with the CENP-N binding protein CENP-L as well as CENP-K. Once assembled, CENP-P/O/R/Q/U exchanges slowly with the free nucleoplasmic pool indicating a low off-rate for individual CENP-P/O/R/Q/U subunits. Surprisingly, we then find that during late S-phase, following the kinetochore-binding step, both CENP-Q and -U but not -R undergo oligomerization. We propose that CENP-P/O/R/Q/U self-assembles on kinetochores with varying stoichiometry and undergoes a pre-mitotic maturation step that could be important for kinetochores switching into the correct conformation necessary for microtubule-attachment.

Myeloid leukemia factor: a return ticket from human leukemia to fly hematopoiesis

Even though deregulation of human MLF1, the founding member of the Myeloid Leukemia Factor family, has been associated with acute myeloid leukemia, the function and mode of action of this family of genes have remained rather mysterious. Yet, recent findings in Drosophila shed new light on their biological activity and suggest that they play an important role in hematopoiesis and leukemia, notably by regulating the stability of RUNX transcription factors, another family of conserved proteins with prominent roles in normal and malignant blood cell development.

Structural insights of the MLF1/14-3-3 interaction

Myeloid leukaemia factor 1 (MLF1) binds to 14-3-3 adapter proteins by a sequence surrounding Ser34 with the functional consequences of this interaction largely unknown. We present here the high-resolution crystal structure of this binding motif [MLF1(29-42)pSer34] in complex with 14-3-3ε and analyse the interaction with isothermal titration calorimetry. Fragment-based ligand discovery employing crystals of the binary 14-3-3ε/MLF1(29-42)pSer34 complex was used to identify a molecule that binds to the interface rim of the two proteins, potentially representing the starting point for the development of a small molecule that stabilizes the MLF1/14-3-3 protein-protein interaction. Such a compound might be used as a chemical biology tool to further analyse the 14-3-3/MLF1 interaction without the use of genetic methods. Database Structural data are available in the Protein Data Bank under the accession number(s) 3UAL [14-3-3ε/MLF1(29-42)pSer34 complex] and 3UBW [14-3-3ε/MLF1(29-42)pSer34/3-pyrrolidinol complex] Structured digital abstract •  14-3-3 epsilon and MLF1 bind by x-ray crystallography (View interaction) •  14-3-3 epsilon and MLF1 bind by isothermal titration calorimetry (View Interaction: 1, 2).

Mammalian polo-like kinase 1-dependent regulation of the PBIP1-CENP-Q complex at kinetochores

Mammalian polo-like kinase 1 (Plk1) plays a pivotal role during M-phase progression. Plk1 localizes to specific subcellular structures through the targeting activity of the C-terminal polo-box domain (PBD). Disruption of the PBD function results in improper bipolar spindle formation, chromosome missegregation, and cytokinesis defect that ultimately lead to the generation of aneuploidy. It has been shown that Plk1 recruits itself to centromeres by phosphorylating and binding to a centromere scaffold, PBIP1 (also called MLF1IP and CENP-U[50]) through its PBD. However, how PBIP1 itself is targeted to centromeres and what roles it plays in the regulation of Plk1-dependent mitotic events remain unknown. Here, we demonstrated that PBIP1 directly interacts with CENP-Q, and this interaction was mutually required not only for their stability but also for their centromere localization. Plk1 did not appear to interact with CENP-Q directly. However, Plk1 formed a ternary complex with PBIP1 and CENP-Q through a self-generated p-T78 motif on PBIP1. This complex formation was central for Plk1-dependent phosphorylation of PBIP1-bound CENP-Q and delocalization of the PBIP1-CENP-Q complex from mitotic centromeres. This study reveals a unique mechanism of how PBIP1 mediates Plk1-dependent phosphorylation event onto a third protein, and provides new insights into the mechanism of how Plk1 and its recruitment scaffold, PBIP1-CENP-Q complex, are localized to and delocalized from centromeres.

The pathogenic E. coli type III effector EspZ interacts with host CD98 and facilitates host cell prosurvival signalling

Enterohaemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC respectively) are diarrhoeal pathogens that cause the formation of attaching and effacing (A/E) lesions on infected host cells. These pathogens encode a type III secretion system (T3SS) used to inject effector proteins directly into host cells, an essential requirement for virulence. In this study, we identified a function for the type III secreted effector EspZ. Infection with EPEC DeltaespZ caused increased cytotoxicity in HeLa and MDCK cells compared with wild-type EPEC, and expressing espZ in cells abrogated this effect. Using yeast two-hybrid, proteomics, immunofluorescence and co-immunoprecipitation, it was demonstrated that EspZ interacts with the host protein CD98, which contributes to protection against EPEC-mediated cytotoxicity. EspZ enhanced phosphorylation of focal adhesion kinase (FAK) and AKT during infection with EPEC, but CD98 only appeared to facilitate FAK phosphorylation. This study provides evidence that EspZ and CD98 promote host cell survival mechanisms involving FAK during A/E pathogen infection.

20,23-dihydroxyvitamin D3, novel P450scc product, stimulates differentiation and inhibits proliferation and NF-kappaB activity in human keratinocytes

We have examined effects of the 20,23-dihydroxyvitamin D3 (20,23(OH)2D3), on differentiation and proliferation of human keratinocytes and the anti-inflammatory potential of 20,23(OH)2D3 from its action on nuclear factor-kappaB (NF-kappaB). 20,23(OH)2D3 inhibited growth of keratinocytes with a potency comparable to that for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Cell cycle analysis showed that this inhibition was associated with G1/G0 and G2/M arrests. 20,23(OH)2D3 stimulated production of involucrin mRNA and inhibited production of cytokeratin 14 mRNA in a manner similar to that seen for 1,25(OH)2D3. Flow cytometry showed that these effects were accompanied by increased involucrin protein expression, and an increase in the cell size and granularity. Silencing of the vitamin D receptor (VDR) by corresponding siRNA abolished the stimulatory effect on involucrin gene expression demonstrating an involvement of VDR in 20,23(OH)2D3 action. This mode of action was further substantiated by stimulation of CYP24 gene expression and stimulation of the CYP24 promoter-driven reporter gene activity. 20,23(OH)2D3 displayed several fold lower potency for induction of CYP24 gene expression than 1,25(OH)2D3. Finally, 20,23(OH)2D3 inhibited the transcriptional activity of NF-kappaB in keratinocytes as demonstrated by EMSA, NF-kappaB-driven reporter gene activity assays and measurements of translocation of p65 from the cytoplasm to the nucleus. These inhibitory effects were connected with stimulation of the expression of IkappaBalpha with subsequent sequestration of NF-kappaB in the cytoplasm and consequent attenuation of transcriptional activity. In summary, we have characterized 20,23(OH)2D3 as a novel secosteroidal regulator of keratinocytes proliferation and differentiation and a modifier of their immune activity.

The effects of immunostimulation through dietary manipulation in the rainbow trout; evaluation of mucosal immunity

Immunostimulant-containing diets are commonly used in aquaculture to enhance the resistance of cultured fish to disease and stress. Although widespread in use, there have been conflicting results published, and surprisingly little is known about the regulation of immune response-related genes in tissues key to mucosal immunity induced by immunostimulant dietary feeding. Using a salmonid-specific microarray platform enriched with immune-related genes and in situ hybridization, we investigated dietary acclimation in two organs relevant to mucosal immunity, the gills and the intestine, in the rainbow trout (Oncorhynchus mykiss). Immunostimulant diets significantly changed gene expression profiles and gene distribution in a tissue-specific manner: genes and functional Gene Ontology categories involved in immunity were differently expressed at portals of entry where significant changes in genes and functional groups related to remodeling processes and antigen presentation were observed. Furthermore, genes involved in chemotaxis, cell differentiation, antigen-presenting capacity and tissue remodeling were localized in both organs.

20-Hydroxycholecalciferol, product of vitamin D3 hydroxylation by P450scc, decreases NF-kappaB activity by increasing IkappaB alpha levels in human keratinocytes

The side chain of vitamin D3 is hydroxylated in a sequential manner by cytochrome P450scc (CYP11A1) to form 20-hydroxycholecalciferol, which can induce growth arrest and differentiation of both primary and immortalized epidermal keratinocytes. Since nuclear factor-κB (NF-κB) plays a pivotal role in the regulation of cell proliferation, differentiation and apoptosis, we examined the capability of 20-hydroxycholecalciferol to modulate the activity of NF-κB, using 1,25-dihydroxycholecalciferol (calcitriol) as a positive control. 20-hydroxycholecalciferol inhibits the activation of NFκB DNA binding activity as well as NF-κB-driven reporter gene activity in keratinocytes. Also, 20-hydroxycholecalciferol induced significant increases in the mRNA and protein levels of the NF-κB inhibitor protein, IκBα, in a time dependent manner, while no changes in total NF-κB-p65 mRNA or protein levels were observed. Another measure of NF-κB activity, p65 translocation from the cytoplasm into the nucleus was also inhibited in extracts of 20-hydroxycholecalciferol treated keratinocytes. Increased IκBα was concomitantly observed in cytosolic extracts of 20-hydroxycholecalciferol treated keratinocytes, as determined by immunoblotting and immunofluorescent staining. In keratinocytes lacking vitamin D receptor (VDR), 20-hydroxycholecalciferol did not affect IκBα mRNA levels, indicating that it requires VDR for its action on NF-κB activity. Comparison of the effects of calcitrol, hormonally active form of vitamin D3, with 20-hydrocholecalciferol show that both agents have a similar potency in inhibiting NF-κB. Since NF-κB is a major transcription factor for the induction of inflammatory mediators, our findings indicate that 20-hydroxycholecalciferol may be an effective therapeutic agent for inflammatory and hyperproliferative skin diseases.

Self-regulated mechanism of Plk1 localization to kinetochores: lessons from the Plk1-PBIP1 interaction

Mammalian polo-like kinase 1 (Plk1) has been studied extensively as a critical element in regulating various mitotic events during M-phase progression. Plk1 function is spatially regulated through the targeting activity of the conserved polo-box domain (PBD) present in the C-terminal non-catalytic region. Recent progress in our understanding of Plk1 localization to the centromeres shows that Plk1 self-regulates its initial recruitment by phosphorylating a centromeric component PBIP1 and generating its own PBD-binding site. Paradoxically, Plk1 also induces PBIP1 delocalization and degradation from the mitotic kinetochores late in the cell cycle, consequently permitting itself to bind to other kinetochore components. Thus, PBIP1-dependent self-recruitment of Plk1 to the interphase centromeres serves as a prelude to the efficient delivery of Plk1 itself to other kinetochore components whose interactions with Plk1 are vital for proper mitotic progression.

Shuttling imbalance of MLF1 results in p53 instability and increases susceptibility to oncogenic transformation

Myeloid leukemia factor 1 (MLF1) stabilizes the activity of the tumor suppressor p53 by suppressing its E3 ubiquitin ligase, COP1, through a third component of the COP9 signalosome (CSN3). However, little is known about how MLF1 functions upstream of the CSN3-COP1-p53 pathway and how its deregulation by the formation of the fusion protein nucleophosmin (NPM)-MLF1, generated by t(3;5)(q25.1;q34) chromosomal translocation, leads to leukemogenesis. Here we show that MLF1 is a cytoplasmic-nuclear-shuttling protein and that its nucleolar localization on fusing with NPM prevents the full induction of p53 by both genotoxic and oncogenic cellular stress. The majority of MLF1 was located in the cytoplasm, but the treatment of cells with leptomycin B rapidly induced a nuclear accumulation of MLF1. A mutation of the nuclear export signal (NES) motif identified in the MLF1 sequence enhanced the antiproliferative activity of MLF1. The fusion of MLF1 with NPM translocated MLF1 to the nucleolus and abolished the growth-suppressing activity. The introduction of NPM-MLF1 into early-passage murine embryonic fibroblasts allowed the cells to escape from cellular senescence at a markedly earlier stage and induced neoplastic transformation in collaboration with the oncogenic form of Ras. Interestingly, disruption of the MLF1-derived NES sequence completely abolished the growth-promoting activity of NPM-MLF1 in murine fibroblasts and hematopoietic cells. Thus, our results provide important evidence that the shuttling of MLF1 is critical for the regulation of cell proliferation and a disturbance in the shuttling balance increases the cell's susceptibility to oncogenic transformation.

Non-pathogenic protein aggregates in skeletal muscle in MLF1 transgenic mice

Protein aggregate formation in muscle is thought to be pathogenic and associated with clinical weakness. Over-expression of either wild type or a mutant form of myeloid leukemia factor 1 (MLF1) in transgenic mouse skeletal muscle and in cultured cells resulted in aggregate formation. Aggregates were detected in MLF1 transgenic mice at 6 weeks of age, and increased in size with age. However, histological examination of skeletal muscles of MLF1 transgenic mice revealed no pathological changes other than the aggregates, and RotaRod testing did not detect functional deficits. MLF1 has recently been identified as a protein that could neutralize the toxicity of intracellular protein aggregates in a Drosophila model of Huntington's disease (HD). We also demonstrate that MLF1 interacts with MRJ, a heat shock protein, which can independently neutralize the toxicity of intracellular protein aggregates in the Drosophila HD model. Our data suggest that over-expression of MLF1 has no significant impact on skeletal muscle function in mice; that progressive formation of protein aggregates in muscle are not necessarily pathogenic; and that MLF1 and MRJ may function together to ameliorate the toxic effects of polyglutamine or mutant proteins in myodegenerative diseases such as inclusion body myositis and oculopharyngeal muscular dystrophy, as well as neurodegenerative disease.

Myeloid Leukemia Factor 1 Associates with a Novel Heterogeneous Nuclear Ribonucleoprotein U-like Molecule

Myeloid leukemia factor 1 (MLF1) is an oncoprotein associated with hemopoietic lineage commitment and acute myeloid leukemia. Here we show that Mlf1 associated with a novel binding partner, Mlf1-associated nuclear protein (Manp), a new heterogeneous nuclear ribonucleoprotein (hnRNP) family member, related to hnRNP-U. Manp localized exclusively in the nucleus and could redirect Mlf1 from the cytoplasm into the nucleus. The nuclear content of Mlf1 was also regulated by 14-3-3 binding to a canonical 14-3-3 binding motif within the N terminus of Mlf1. Significantly Mlf1 contains a functional nuclear export signal and localized primarily to the nuclei of hemopoietic cells. Mlf1 was capable of binding DNA, and microarray analysis revealed that it affected the expression of several genes, including transcription factors. In summary, this study reveals that Mlf1 translocates between nucleus and cytoplasm, associates with a novel hnRNP, and influences gene expression.

Self-regulated Plk1 recruitment to kinetochores by the Plk1-PBIP1 interaction is critical for proper chromosome segregation

The polo-box domain (PBD) of mammalian polo-like kinase 1 (Plk1) is essential in targeting its catalytic activity to specific subcellular structures critical for mitosis. The mechanism underlying Plk1 recruitment to the kinetochores and the role of Plk1 at this site remain elusive. Here, we demonstrate that a PBD-binding protein, PBIP1, is crucial for recruiting Plk1 to the interphase and mitotic kinetochores. Unprecedentedly, Plk1 phosphorylated PBIP1 at T78, creating a self-tethering site that specifically interacted with the PBD of Plk1, but not Plk2 or Plk3. Later in mitosis, Plk1 also induced PBIP1 degradation in a T78-dependent manner, thereby enabling itself to interact with other components critical for proper kinetochore functions. Absence of the p-T78-dependent Plk1 localization induced a chromosome congression defect and compromised the spindle checkpoint, ultimately leading to aneuploidy. Thus, Plk1 self-regulates the Plk1-PBIP1 interaction to timely localize to the kinetochores and promote proper chromosome segregation.

Nucleophosmin: a versatile molecule associated with hematological malignancies

Nucleophosmin (NPM) is a nucleolar phosphoprotein that plays multiple roles in ribosome assembly and transport, cytoplasmic-nuclear trafficking, centrosome duplication and regulation of p53. In hematological malignancies, the NPM1 gene is frequently involved in chromosomal translocation, mutation and deletion. The NPM1 gene on 5q35 is translocated with the anaplastic lymphoma kinase (ALK) gene in anaplastic large cell lymphoma with t(2;5). The MLF1 and RARA genes are fused with NPM1 in myelodysplastic syndrome and acute myeloid leukemia (AML) with t(3;5) and acute promyelocytic leukemia with t(5;17), respectively. In each fused protein, the N-terminal NPM portion is associated with oligomerization of a partner protein leading to altered signal transduction or transcription. Recently, mutations of exon 12 have been found in a significant proportion of de novo AML, especially in those with a normal karyotype. Mutant NPM is localized aberrantly in the cytoplasm, but the molecular mechanisms for leukemia remain to be studied. Studies of knock-out mice have revealed new aspects regarding NPM1 as a tumor-suppressor gene. This review focuses on the clinical significance of the NPM1 gene in hematological malignancies and newly discovered roles of NPM associated with oncogenesis.

Comprehensive analysis of the ICEN (Interphase Centromere Complex) components enriched in the CENP-A chromatin of human cells

The centromere is a chromatin structure essential for correct segregation of sister chromatids, and defects in this region often lead to aneuploidy and cancer. We have previously reported purification of the interphase centromere complex (ICEN) from HeLa cells, and have demonstrated the presence of 40 proteins (ICEN1-40), along with CENP-A, -B, -C, -H and hMis6, by proteomic analysis. Here we report analysis of seven ICEN components with unknown function. Centromere localization of EGFP-tagged ICEN22, 24, 32, 33, 36, 37 and 39 was observed in transformant cells. Depletion of each of these proteins by short RNA interference produced abnormal metaphase cells carrying misaligned chromosomes and also produced cells containing aneuploid chromosomes, implying that these ICEN proteins take part in kinetochore functions. Interestingly, in the ICEN22, 32, 33, 37 or 39 siRNA-transfected cells, CENP-H and hMis6 signals disappeared from all the centromeres in abnormal mitotic cells containing misaligned chromosomes. These results suggest that the seven components of the ICEN complex are predominantly localized at the centromeres and are required for kinetochore function perhaps through or not through loading of CENP-H and hMis6 onto the centromere.

The human CENP-A centromeric nucleosome-associated complex

The basic element for chromosome inheritance, the centromere, is epigenetically determined in mammals. The prime candidate for specifying centromere identity is the array of nucleosomes assembled with CENP-A, the centromere-specific histone H3 variant. Here, we show that CENP-A nucleosomes directly recruit a proximal CENP-A nucleosome associated complex (NAC) comprised of three new human centromere proteins (CENP-M, CENP-N and CENP-T), along with CENP-U(50), CENP-C and CENP-H. Assembly of the CENP-A NAC at centromeres is dependent on CENP-M, CENP-N and CENP-T. Facilitates chromatin transcription (FACT) and nucleophosmin-1 (previously implicated in transcriptional chromatin remodelling and as a multifunctional nuclear chaperone, respectively) are absent from histone H3-containing nucleosomes, but are stably recruited to CENP-A nucleosomes independent of CENP-A NAC. Seven new CENP-A-nucleosome distal (CAD) centromere components (CENP-K, CENP-L, CENP-O, CENP-P, CENP-Q, CENP-R and CENP-S) are identified as assembling on the CENP-A NAC. The CENP-A NAC is essential, as disruption of the complex causes errors of chromosome alignment and segregation that preclude cell survival despite continued centromere-derived mitotic checkpoint signalling.

The constitutive centromere component CENP-50 is required for recovery from spindle damage

We identified CENP-50 as a novel kinetochore component. We found that CENP-50 is a constitutive component of the centromere that colocalizes with CENP-A and CENP-H throughout the cell cycle in vertebrate cells. To determine the precise role of CENP-50, we examined its role in centromere function by generating a loss-of-function mutant in the chicken DT40 cell line. The CENP-50 knockout was not lethal; however, the growth rate of cells with this mutation was slower than that of wild-type cells. We observed that the time for CENP-50-deficient cells to complete mitosis was longer than that for wild-type cells. Centromeric localization of CENP-50 was abolished in both CENP-H- and CENP-I-deficient cells. Coimmunoprecipitation experiments revealed that CENP-50 interacted with the CENP-H/CENP-I complex in chicken DT40 cells. We also observed severe mitotic defects in CENP-50-deficient cells with apparent premature sister chromatid separation when the mitotic checkpoint was activated, indicating that CENP-50 is required for recovery from spindle damage.

Regulation of myeloid leukemia factor-1 interacting protein (MLF1IP) expression in glioblastoma

The myelodysplasia/myeloid leukemia factor 1-interacting protein MLF1IP is a novel gene which encodes for a putative transcriptional repressor. It is localized to human chromosome 4q35.1 and is expressed in both the nuclei and cytoplasm of cells. Northern and Western blot analyses have revealed MLF1IP to be present at very low amounts in normal brain tissues, whereas a number of human and rat glioblastoma (GBM) cell lines demonstrated a high level expression of the MLF1IP protein. Immunohistochemical analysis of rat F98 and C6 GBM tumor models showed that MLF1IP was highly expressed in the tumor core where it was co-localized with MLF1 and nestin. Moreover, MLF1IP expression was elevated in the contralateral brain where no tumor cells were detected. These observations, together with previous data demonstrating a role for MLF1IP in erythroleukemias, suggest a possible function for this protein in glioma pathogenesis and potentially in other types of malignancies.

Identification of Novel and Known Oocyte-Specific Genes Using Complementary DNA Subtraction and Microarray Analysis in Three Different Species1

The main objective of the present study was to identify novel oocyte-specific genes in three different species: bovine, mouse, and Xenopus laevis. To achieve this goal, two powerful technologies were combined: a polymerase chain reaction (PCR)-based cDNA subtraction, and cDNA microarrays. Three subtractive libraries consisting of 3456 clones were established and enriched for oocyte-specific transcripts. Sequencing analysis of the positive insert-containing clones resulted in the following classification: 53% of the clones corresponded to known cDNAs, 26% were classified as uncharacterized cDNAs, and a final 9% were classified as novel sequences. All these clones were used for cDNA microarray preparation. Results from these microarray analyses revealed that in addition to already known oocyte-specific genes, such as GDF9, BMP15, and ZP, known genes with unknown function in the oocyte were identified, such as a MLF1-interacting protein (MLF1IP), B-cell translocation gene 4 (BTG4), and phosphotyrosine-binding protein (xPTB). Furthermore, 15 novel oocyte-specific genes were validated by reverse transcription-PCR to confirm their preferential expression in the oocyte compared to somatic tissues. The results obtained in the present study confirmed that microarray analysis is a robust technique to identify true positives from the suppressive subtractive hybridization experiment. Furthermore, obtaining oocyte-specific genes from three species simultaneously allowed us to look at important genes that are conserved across species. Further characterization of these novel oocyte-specific genes will lead to a better understanding of the molecular mechanisms related to the unique functions found in the oocyte.