Human carbon catabolite repressor protein (CCR4)-associative factor 1: cloning, expression and characterization of its interaction with the B-cell translocation protein BTG1

BTG1 mutation yields supercompetitive B cells primed for malignant transformation

Multicellular life requires altruistic cooperation between cells. The adaptive immune system is a notable exception, wherein germinal center B cells compete vigorously for limiting positive selection signals. Studying primary human lymphomas and developing new mouse models, we found that mutations affecting BTG1 disrupt a critical immune gatekeeper mechanism that strictly limits B cell fitness during antibody affinity maturation. This mechanism converted germinal center B cells into supercompetitors that rapidly outstrip their normal counterparts. This effect was conferred by a small shift in MYC protein induction kinetics but resulted in aggressive invasive lymphomas, which in humans are linked to dire clinical outcomes. Our findings reveal a delicate evolutionary trade-off between natural selection of B cells to provide immunity and potentially dangerous features that recall the more competitive nature of unicellular organisms.

The roles of BTG1 mRNA expression in cancers: A bioinformatics analysis

BTG1 (B-cell translocation gene 1) may inhibit proliferation and cell cycle progression, induce differentiation, apoptosis, and anti-inflammatory activity. The goal of this study was to clarify the clinicopathological and prognostic significances of BTG1 mRNA expression and related signal pathways in cancers. Using the Oncomine, TCGA (the cancer genome atlas), xiantao, UALCAN (The University of ALabama at Birmingham Cancer data analysis Portal), and Kaplan-Meier plotter databases, we undertook a bioinformatics study of BTG1 mRNA expression in cancers. BTG1 expression was lower in gastric, lung, breast and ovarian cancer than normal tissue due to its promoter methylation, which was the opposite to BTG1 expression. BTG1 expression was positively correlated with dedifferentiation and histological grading of gastric cancer (p < 0.05), with squamous subtype and young age of lung cancer (p < 0.05), with infrequent lymph node metastasis, low TNM staging, young age, white race, infiltrative lobular subtype, Her2 negativity, favorable molecular subtyping, and no postmenopause status of breast cancer (p < 0.05), and with elder age, venous invasion, lymphatic invasion, and clinicopathological staging of ovarian cancer (p < 0.05). BTG1 expression was negatively correlated with favorable prognosis of gastric, lung or ovarian cancer patients, but the converse was true for breast cancer (p < 0.05). KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis showed that the top signal pathways included cytokine-cytokine receptor interaction, cell adhesion molecules, chemokine, immune cell receptor and NF (nuclear factor)-κB signal pathways in gastric and breast cancer. The top hub genes mainly contained CD (cluster of differentiation) antigens in gastric cancer, FGF (fibroblast growth factor)-FGFR (FGF receptor) in lung cancer, NADH (nicotinamide adenine dinucleotide): ubiquinone oxidoreductase in breast cancer, and ribosomal proteins in ovarian cancer. BTG1 expression might be employed as a potential marker to indicate carcinogenesis and subsequent progression, even prognosis.

A conserved motif in human BTG1 and BTG2 proteins mediates interaction with the poly(A) binding protein PABPC1 to stimulate mRNA deadenylation

Antiproliferative BTG/Tob proteins interact directly with the CAF1 deadenylase subunit of the CCR4-NOT complex. This binding requires the presence of two conserved motifs, boxA and boxB, characteristic of the BTG/Tob APRO domain. Consistently, these proteins were shown to stimulate mRNA deadenylation and decay in several instances. Two members of the family, BTG1 and BTG2, were reported further to associate with the protein arginine methyltransferase PRMT1 through a motif, boxC, conserved only in this subset of proteins. We recently demonstrated that BTG1 and BTG2 also contact the first RRM domain of the cytoplasmic poly(A) binding protein PABPC1. To decipher the mode of interaction of BTG1 and BTG2 with partners, we performed nuclear magnetic resonance experiments as well as mutational and biochemical analyses. Our data demonstrate that, in the context of an APRO domain, the boxC motif is necessary and sufficient to allow interaction with PABPC1 but, unexpectedly, that it is not required for BTG2 association with PRMT1. We show further that the presence of a boxC motif in an APRO domain endows it with the ability to stimulate deadenylation in cellulo and in vitro. Overall, our results identify the molecular interface allowing BTG1 and BTG2 to activate deadenylation, a process recently shown to be necessary for maintaining T-cell quiescence.

CNOT7 modulates biological functions of ovarian cancer cells via AKT signaling pathway

AIMS

CNOT7 plays an important role in many biological processes, providing attractive opportunities for the treatment of malignant tumors. However, the functions and mechanism of CNOT7 in ovarian cancer (OC) have not been elucidated. The purpose of this study was to assess the role of CNOT7 in OC.

MATERIALS AND METHODS

SKOV3 and A2780 cells were chosen as the cell lines for the experiments of this manuscript via the analysis of the expression of CNOT7 protein and the mRNA level in ovarian surface epithelium (OSE) cells, SKOV3, HO8910 and A2780 cells. The expression of CNOT7 was detected by western blot assays and RT-PCR in A2780 and SKOV3 cells. The MTT assays, colony formation assays and EdU assays were used to measure cell proliferation when CNOT7 was knocked down or overexpressed in A2780 and SKOV3 cells. Furthermore, cell migration and invasion ability were achieved from transwell assays. Cell cycle and apoptosis rate after small interference RNA-CNOT7 (siRNA-CNOT7) were detected by flow cytometry assays. Finally, the cell proliferation, migration and invasion ability were detected when A2780 and SKOV3 cells with CNOT7 overexpression were treated with LY294002.

KEY FINDINGS

The expression of CNOT7 protein in OC cells, including SKOV3, HO8910 and A2780 cells were significantly higher than that in OSE cells (P < 0.05). The mRNA level of CNOT7 in HO8910 and A2780 cells were significantly higher than that in OSE cells (P < 0.01). However, the mRNA level of CNOT7 in SKOV3 cells was no significant difference compared with OSE cells (P > 0.05). The results suggested that knockdown of CNOT7 could inhibit the cell proliferation, migration and invasion ability in A2780 and SKOV3 cells, and increase cell apoptosis and autophagy. The expression of apoptosis-related molecules (PARP, Caspase3 and Caspase9) and autophagy-related protein (LC3B) were up-regulated after CNOT7 knockdown, while the expression of cycle-related protein (CDK6) and the anti-apoptotic gene (Bcl2) were downregulated. Meanwhile, the opposite results were observed when CNOT7 was overexpressed in A2780 and SKOV3 cells. It is worth noting that the effect of CNOT7 overexpression in A2780 and SKOV3 cells could be partially or completely eliminated by treatment with AKT inhibitor LY294002.

SIGNIFICANCE

CNOT7 has a carcinogenic effect in OC, and the carcinogenic effect may be achieved via the AKT signaling pathway.

Alzheimer's disease master regulators analysis: search for potential molecular targets and drug repositioning candidates

Background

Alzheimer’s disease (AD) is a multifactorial and complex neuropathology that involves impairment of many intricate molecular mechanisms. Despite recent advances, AD pathophysiological characterization remains incomplete, which hampers the development of effective treatments. In fact, currently, there are no effective pharmacological treatments for AD. Integrative strategies such as transcription regulatory network and master regulator analyses exemplify promising new approaches to study complex diseases and may help in the identification of potential pharmacological targets.

Methods

In this study, we used transcription regulatory network and master regulator analyses on transcriptomic data of human hippocampus to identify transcription factors (TFs) that can potentially act as master regulators in AD. All expression profiles were obtained from the Gene Expression Omnibus database using the GEOquery package. A normal hippocampus transcription factor-centered regulatory network was reconstructed using the ARACNe algorithm. Master regulator analysis and two-tail gene set enrichment analysis were employed to evaluate the inferred regulatory units in AD case-control studies. Finally, we used a connectivity map adaptation to prospect new potential therapeutic interventions by drug repurposing.

Results

We identified TFs with already reported involvement in AD, such as ATF2 and PARK2, as well as possible new targets for future investigations, such as CNOT7, CSRNP2, SLC30A9, and TSC22D1. Furthermore, Connectivity Map Analysis adaptation suggested the repositioning of six FDA-approved drugs that can potentially modulate master regulator candidate regulatory units (Cefuroxime, Cyproterone, Dydrogesterone, Metrizamide, Trimethadione, and Vorinostat).

Conclusions

Using a transcription factor-centered regulatory network reconstruction we were able to identify several potential molecular targets and six drug candidates for repositioning in AD. Our study provides further support for the use of bioinformatics tools as exploratory strategies in neurodegenerative diseases research, and also provides new perspectives on molecular targets and drug therapies for future investigation and validation in AD.

Electronic supplementary material

The online version of this article (10.1186/s13195-018-0394-7) contains supplementary material, which is available to authorized users.

Nanos genes and their role in development and beyond

The hallmark of Nanos proteins is their typical (CCHC)2 zinc finger motif (zf-nanos). Animals have one to four nanos genes. For example, the fruit fly and demosponge have only one nanos gene, zebrafish and humans have three, and Fugu rubripes has four. Nanos genes are mainly known for their evolutionarily preserved role in germ cell survival and pluripotency. Nanos proteins have been reported to bind the C-terminal RNA-binding domain of Pumilio to form a post-transcriptional repressor complex. Several observations point to a link between the miRNA-mediated repression complex and the Nanos/Pumilio complex. Repression of the E2F3 oncogene product is, indeed, mediated by cooperation between the Nanos/Pumilio complex and miRNAs. Another important interaction partner of Nanos is the CCR4-NOT deadenylase complex. Besides the tissue-specific contribution of Nanos proteins to normal development, their ectopic expression has been observed in several cancer cell lines and various human cancers. An inverse correlation between the expression levels of human Nanos1 and Nanos3 and E-cadherin was observed in several cancer cell lines. Loss of E-cadherin, an important cell-cell adhesion protein, contributes to tumor invasion and metastasis. Overexpression of Nanos3 induces epithelial-mesenchymal transition in lung cancer cell lines partly by repressing E-cadherin. Other than some most interesting data from Nanos knockout mice, little is known about mammalian Nanos proteins, and further research is needed. In this review, we summarize the main roles of Nanos proteins and discuss the emerging concept of Nanos proteins as oncofetal antigens.

The many faces of IKZF1 in B-cell precursor acute lymphoblastic leukemia

Transcription factor IKZF1 (IKAROS) acts as a critical regulator of lymphoid differentiation and is frequently deleted or mutated in B-cell precursor acute lymphoblastic leukemia. IKZF1 gene defects are associated with inferior treatment outcome in both childhood and adult B-cell precursor acute lymphoblastic leukemia and occur in more than 70% of BCR-ABL1-positive and BCR-ABL1-like cases of acute lymphoblastic leukemia. Over the past few years, much has been learned about the tumor suppressive function of IKZF1 during leukemia development and the molecular pathways that relate to its impact on treatment outcome. In this review, we provide a concise overview on the role of IKZF1 during normal lymphopoiesis and the pathways that contribute to leukemia pathogenesis as a consequence of altered IKZF1 function. Furthermore, we discuss different mechanisms by which IKZF1 alterations impose therapy resistance on leukemic cells, including enhanced cell adhesion and modulation of glucocorticoid response.

Alternative splicing of CNOT7 diversifies CCR4-NOT functions

The CCR4-associated factor CAF1, also called CNOT7, is a catalytic subunit of the CCR4–NOT complex, which has been implicated in all aspects of the mRNA life cycle, from mRNA synthesis in the nucleus to degradation in the cytoplasm. In human cells, alternative splicing of the CNOT7 gene yields a second CNOT7 transcript leading to the formation of a shorter protein, CNOT7 variant 2 (CNOT7v2). Biochemical characterization indicates that CNOT7v2 interacts with CCR4–NOT subunits, although it does not bind to BTG proteins. We report that CNOT7v2 displays a distinct expression profile in human tissues, as well as a nuclear sub-cellular localization compared to CNOT7v1. Despite a conserved DEDD nuclease domain, CNOT7v2 is unable to degrade a poly(A) tail in vitro and preferentially associates with the protein arginine methyltransferase PRMT1 to regulate its activity. Using both in vitro and in cellulo systems, we have also demonstrated that CNOT7v2 regulates the inclusion of CD44 variable exons. Altogether, our findings suggest a preferential involvement of CNOT7v2 in nuclear processes, such as arginine methylation and alternative splicing, rather than mRNA turnover. These observations illustrate how the integration of a splicing variant inside CCR4–NOT can diversify its cell- and tissue-specific functions.

BTG1 expression correlates with pathogenesis, aggressive behaviors and prognosis of gastric cancer: a potential target for gene therapy

Here, we found that BTG1 overexpression inhibited proliferation, migration and invasion, induced G₂/M arrest, differentiation, senescence and apoptosis in BGC-823 and MKN28 cells (p < 0.05). BTG1 transfectants showed a higher mRNA expression of Cyclin D1 and Bax, but a lower mRNA expression of cdc2, p21, mTOR and MMP-9 than the control and mock (p < 0.05). After treated with cisplatin, MG132, paclitaxel and SAHA, both BTG1 transfectants showed lower mRNA viability and higher apoptosis than the control in both time- and dose-dependent manners (p < 0.05) with the hypoexpression of chemoresistance-related genes (slug, CD147, GRP78, GRP94, FBXW7 TOP1, TOP2 and GST-π). BTG1 expression was restored after 5-aza-2′-deoxycytidine treatment in gastric cancer cells. BTG1 expression was statistically lower in gastric cancer than non-neoplastic mucosa and metastatic cancer in lymph node (p < 0.05). BTG1 expression was positively correlated with depth of invasion, lymphatic and venous invasion, lymph node metastasis, TNM staging and worse prognosis (p < 0.05). The diffuse-type carcinoma showed less BTG1 expression than intestinal- and mixed-type ones (p < 0.05). BTG1 overexpression suppressed tumor growth and lung metastasis of gastric cancer cells by inhibiting proliferation, enhancing autophagy and apoptosis in xenograft models. It was suggested that down-regulated BTG1 expression might promote gastric carcinogenesis partially due to its promoter methylation. BTG1 overexpression might reverse the aggressive phenotypes and be employed as a potential target for gene therapy of gastric cancer.

The Ccr4-Not complex is a key regulator of eukaryotic gene expression

The Ccr4‐Not complex is a multisubunit complex present in all eukaryotes that contributes to regulate gene expression at all steps, from production of messenger RNAs (mRNAs) in the nucleus to their degradation in the cytoplasm. In the nucleus it influences the post‐translational modifications of the chromatin template that has to be remodeled for transcription, it is present at sites of transcription and associates with transcription factors as well as with the elongating polymerase, it interacts with the factors that prepare the new transcript for export to the cytoplasm and finally is important for nuclear quality control and influences mRNA export. In the cytoplasm it is present in polysomes where mRNAs are translated and in RNA granules where mRNAs will be redirected upon inhibition of translation. It influences mRNA translatability, and is needed during translation, on one hand for co‐translational protein interactions and on the other hand to preserve translation that stalls. It is one of the relevant players during co‐translational quality control. It also interacts with factors that will repress translation or induce mRNA decapping when recruited to the translating template. Finally, Ccr4‐Not carries deadenylating enzymes and is a key player in mRNA decay, generic mRNA decay that follows normal translation termination, co‐translational mRNA decay of transcripts on which the ribosomes stall durably or which carry a non‐sense mutation and finally mRNA decay that is induced by external signaling for a change in genetic programming. Ccr4‐Not is a master regulator of eukaryotic gene expression. WIREs RNA 2016, 7:438–454. doi: 10.1002/wrna.1332

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Control of the Cell Cycle in Adult Neurogenesis and its Relation with Physical Exercise

In the adult brain the neurogenesis is mainly restricted to two neurogenic regions: newly generated neurons arise at the subventricular zone (SVZ) of the lateral ventricle and at the subgranular zone of the hippocampal subregion named the dentate gyrus. The hippocampus is involved in learning and memory paradigms and the generation of new hippocampal neurons has been hypothesized to be a pivotal form of plasticity involved in the process. Moreover the dysregulation of hippocampal adult neurogenesis has been recognized and could anticipate several varieties of brain disease such as Alzheimer disease, epilepsy and depression. Over the last few decades numerous intrinsic, epigenetic and environmental factors have been revealed to deeply influence the process of adult neurogenesis, although the underlying mechanisms remain largely unknown. Growing evidence indicates that physical exercise represents one of the main extrinsic factor able to profoundly increase hippocampal adult neurogenesis, by altering neurochemistry and function of newly generated neurons. The present review surveys how neurogenesis can be modulated by cell cycle kinetics and highlights the putative role of the cell cycle length as a key component of the beneficial effect of running for hippocampal adult neurogenesis, both in physiological conditions and in the presence of defective neurogenesis.

Depletion of poly(A)-specific ribonuclease (PARN) inhibits proliferation of human gastric cancer cells by blocking cell cycle progression

Regulation of mRNA decay plays a crucial role in the post-transcriptional control of cell growth, survival, differentiation, death and senescence. Deadenylation is a rate-limiting step in the silence and degradation of the bulk of highly regulated mRNAs. However, the physiological functions of various deadenylases have not been fully deciphered. In this research, we found that poly(A)-specific ribonuclease (PARN) was upregulated in gastric tumor tissues and gastric cancer cell lines MKN28 and AGS. The cellular function of PARN was investigated by stably knocking down the endogenous PARN in the MKN28 and AGS cells. Our results showed that PARN-depletion significantly inhibited the proliferation of the two types of gastric cancer cells and promoted cell death, but did not significantly affect cell motility and invasion. The depletion of PARN arrested the gastric cancer cells at the G0/G1 phase by upregulating the expression levels of p53 and p21 but not p27. The mRNA stability of p53 was unaffected by PARN-knockdown in both types of cells. A significant stabilizing effect of PARN-depletion on p21 mRNA was observed in the AGS cells but not in the MKN28 cells. We further showed that the p21 3'-UTR triggered the action of PARN in the AGS cells. The dissimilar observations between the MKN28 and AGS cells as well as various stress conditions suggested that the action of PARN strongly relied on protein expression profiles of the cells, which led to heterogeneity in the stability of PARN-targeted mRNAs.

Down-regulation of BTG1 by miR-454-3p enhances cellular radiosensitivity in renal carcinoma cells

BACKGROUND

B cell translocation gene 1 (BTG1) has long been recognized as a tumor suppressor gene. Recent reports demonstrated that BTG1 plays an important role in progression of cell cycle and is involved in cellular response to stressors. However, the microRNAs mediated regulatory mechanism of BTG1 expression has not been reported so far. MicroRNAs can effectively influence tumor radiosensitivity by preventing cell cycle progression, resulting in enhancement of the cytotoxicity of radiotherapy efficacy. This study aimed to demonstrating the effects of microRNAs on the BTG1 expression and cellular radiosensitivity.

METHODS

The human renal carcinoma 786-O cells were treated with 5 Gy of X-rays. Expressions of BTG1 gene and miR-454-3p, which was predicted to target BTG1 by software algorithm, were analyzed by quantitative polymerase chain reaction. Protein expressions were assessed by Western blot. Luciferase assays were used to quantify the interaction between BTG1 3'-untranslated region (3'-UTR) and miR-454-3p. The radiosensitivity was quantified by the assay of cell viability, colony formation and caspase-3 activity.

RESULTS

The expression of the BTG1 gene in 786-O cells was significantly elevated after treatments with X-ray irradiation, DMSO, or serum starvation. The up-regulation of BTG1 after irradiation reduced cellular radiosensitivity as demonstrated by the enhanced cell viability and colony formation, as well as the repressed caspase-3 activity. In comparison, knock down of BTG1 by siRNA led to significantly enhanced cellular radiosensitivity. It was found that miR-454-3p can regulate the expression of BTG1 through a direct interaction with the 3'-UTR of BTG1 mRNA. Decreasing of its expression level correlates well with BTG1 up-regulation during X-ray irradiation. Particularly, we observed that over-expression of miR-454-3p by transfection inhibited the BTG1 expression and enhanced the radiosensitivity. In addition, cell cycle analysis showed that over-expression of miR-454-3p shifted the cell cycle arrest from G2/M phase to S phase.

CONCLUSIONS

Our results indicate that BTG1 is a direct target of miR-454-3p. Down-regulation of BTG1 by miR-454-3p renders tumor cells sensitive to radiation. These results may shed light on the potential application in tumor radiotherapy.

Accumulation of cytolytic CD8+ T cells in B16-melanoma and proliferation of mature T cells in TIS21-knockout mice after T cell receptor stimulation

In vivo and in vitro effects of TIS21 gene on the mature T cell activation and antitumor activities were explored by employing MO5 melanoma orthograft and splenocytes isolated from the TIS21-knockout (KO)(2) mice. Proliferation and survival of mature T cells were significantly increased in the KO than the wild type (WT3)e cells, indicating that TIS21 inhibits the rate of mature T cell proliferation and its survival. In MO5 melanoma orthograft model, the KO mice recruited much more CD8(+) T cells into the tumors at around day 14 after tumor cell injection along with reduced tumor volumes compared with the WT. The increased frequency of granzyme B+ CD8+ T cells in splenocytes of the KO mice compared with the WT may account for antitumor-immunity of TIS21 gene in the melanoma orthograft. In contrast, reduced frequencies of CD107a+ CD8+ T cells in the splenocytes of KO mice may affect the loss of CD8+ T cell infiltration in the orthograft at around day 19. These results indicate that TIS21 exhibits antiproliferative and proapoptotic effects in mature T cells, and differentially affects the frequencies of granzyme B+ CD8+ T-cells and CD107a+ CD8+ T-cells, thus transiently regulating in vivo anti-tumor immunity.

The role of antiproliferative gene Tob1 in the immune system

Tob1 (transducer of ERBB2-1, TOB1 is humans) is a member of the antiproliferative (APRO) family of proteins that controls cell cycle progression in several cell types. In addition, Tob1 has been implicated in diverse cellular mechanisms such as embryonic dorsal development, and T helper 17 (Th17) cell function. More recently, evidence linking Tob1 function to experimental and human immune related disorders has mounted, thus underscoring the potential of this molecule as a biomarker and as a therapeutic target. This article reviews these functions with an emphasis on their implications for human autoimmune diseases such as multiple sclerosis.

Insights into the structure and architecture of the CCR4-NOT complex

The CCR4–NOT complex is a highly conserved, multifunctional machinery with a general role in controlling mRNA metabolism. It has been implicated in a number of different aspects of mRNA and protein expression, including mRNA degradation, transcription initiation and elongation, ubiquitination, and protein modification. The core CCR4–NOT complex is evolutionarily conserved and consists of at least three NOT proteins and two catalytic subunits. The L-shaped complex is characterized by two functional modules bound to the CNOT1/Not1 scaffold protein: the deadenylase or nuclease module containing two enzymes required for deadenylation, and the NOT module. In this review, we will summarize the currently available information regarding the three-dimensional structure and assembly of the CCR4–NOT complex, in order to provide insight into its roles in mRNA degradation and other biological processes.

BTG1 expression correlates with the pathogenesis and progression of ovarian carcinomas

BTG (B-cell translocation gene) can inhibit cell proliferation, metastasis, and angiogenesis and regulate cell cycle progression and differentiation in a variety of cell types. We aimed to clarify the role of BTG1 in ovarian carcinogenesis and progression. A BTG1-expressing plasmid was transfected into ovarian carcinoma cells and their phenotypes and related proteins were examined. BTG1 mRNA expression was detected in ovarian normal tissue (n = 17), ovarian benign tumors (n = 12), and ovarian carcinoma (n = 64) using real-time RT-PCR. Ectopic BTG1 expression resulted in lower growth rate, high cisplatin sensitivity, G₁ arrest, apoptosis, and decreased migration and invasion. Phosphoinositide 3-kinase, protein kinase B, Bcl-xL, survivin, vascular endothelial growth factor, and matrix metalloproteinase-2 mRNA and protein expression was reduced in transfectants as compared to control cells. There was higher expression of BTG1 mRNA in normal tissue than in carcinoma tissue (p = 0.001) and in benign tumors than in carcinoma tissue (p = 0.027). BTG1 mRNA expression in International Federation of Gynecology and Obstetrics (FIGO) stage I/II ovarian carcinomas was higher than that in FIGO stage III/IV ovarian carcinomas (p = 0.038). Altered BTG1 expression might play a role in the pathogenesis and progression of ovarian carcinoma by modulating proliferation, migration, invasion, the cell cycle, and apoptosis.

hCAF1/CNOT7 regulates interferon signalling by targeting STAT1

Stringent regulation of the interferon (IFN) signalling pathway is essential for maintaining the immune response to pathogens and tumours. The transcription factor STAT1 is a crucial mediator of this response. Here, we show that hCAF1/CNOT7 regulates class I and II IFN pathways at different crucial steps. In resting cells, hCAF1 can control STAT1 trafficking by interacting with the latent form of STAT1 in the cytoplasm. IFN treatment induces STAT1 release, suggesting that hCAF1 may shield cytoplasmic STAT1 from undesirable stimulation. Consistently, hCAF1 silencing enhances STAT1 basal promoter occupancy associated with increased expression of a subset of STAT1-regulated genes. Consequently, hCAF1 knockdown cells exhibit an increased protection against viral infection and reduced viral replication. Furthermore, hCAF1 participates in the extinction of the IFN signal, through its deadenylase activity, by speeding up the degradation of some STAT1-regulated mRNAs. Since abnormal and unbalanced JAK/STAT activation is associated with immune disorders and cancer, hCAF1 could play a major role in innate immunity and oncogenesis, contributing to tumour escape.

Rapid estrogen receptor signaling is essential for the protective effects of estrogen against vascular injury

BACKGROUND

Clinical trial and epidemiological data support that the cardiovascular effects of estrogen are complex, including a mixture of both potentially beneficial and harmful effects. In animal models, estrogen protects females from vascular injury and inhibits atherosclerosis. These effects are mediated by estrogen receptors (ERs), which, when bound to estrogen, can bind to DNA to directly regulate transcription. ERs can also activate several cellular kinases by inducing a rapid nonnuclear signaling cascade. However, the biological significance of this rapid signaling pathway has been unclear.

METHODS AND RESULTS

In the present study, we develop a novel transgenic mouse in which rapid signaling is blocked by overexpression of a peptide that prevents ERs from interacting with the scaffold protein striatin (the disrupting peptide mouse). Microarray analysis of ex vivo treated mouse aortas demonstrates that rapid ER signaling plays an important role in estrogen-mediated gene regulatory responses. Disruption of ER-striatin interactions also eliminates the ability of estrogen to stimulate cultured endothelial cell migration and to inhibit cultured vascular smooth muscle cell growth. The importance of these findings is underscored by in vivo experiments demonstrating loss of estrogen-mediated protection against vascular injury in the disrupting peptide mouse after carotid artery wire injury.

CONCLUSIONS

Taken together, these results support the concept that rapid, nonnuclear ER signaling contributes to the transcriptional regulatory functions of ER and is essential for many of the vasoprotective effects of estrogen. These findings also identify the rapid ER signaling pathway as a potential target for the development of novel therapeutic agents.

A low-cost affinity purification system using β-1,3-glucan recognition protein and curdlan beads

Silkworm β-1,3-glucan recognition protein (βGRP) tightly and specifically associates with β-1,3-glucan. We report here an affinity purification system named the 'GRP system', which uses the association between the β-1,3-glucan recognition domain of βGRP (GRP-tag), as an affinity tag, and curdlan beads. Curdlan is a water-insoluble β-1,3-glucan reagent, the low cost of which (about 100 JPY/g) allows the economical preparation of beads. Curdlan beads can be readily prepared by solubilization in an alkaline solution, followed by neutralization, sonication and centrifugation. We applied the GRP system to preparation of several proteins and revealed that the expression levels of the GRP-tagged proteins in soluble fractions were two or three times higher than those of the glutathione S-transferase (GST)-tagged proteins. The purity of the GRP-tagged proteins on the curdlan beads was comparable to that of the GST-tagged proteins on glutathione beads. The chemical stability of the GRP system was more robust than conventional affinity systems under various conditions, including low pH (4-6). Biochemical and structural analyses revealed that proteins produced using the GRP system were structurally and functionally active. Thus, the GRP system is suitable for both the large- and small-scale preparation of recombinant proteins for functional and structural analyses.

The Ccr4--not complex

The Ccr4-Not complex is a unique, essential and conserved multi-subunit complex that acts at the level of many different cellular functions to regulate gene expression. Two enzymatic activities, namely ubiquitination and deadenylation, are provided by different subunits of the complex. However, studies over the last decade have demonstrated a tantalizing multi-functionality of this complex that extends well beyond its identified enzymatic activities. Most of our initial knowledge about the Ccr4-Not complex stemmed from studies in yeast, but an increasing number of reports on this complex in other species are emerging. In this review we will discuss the structure and composition of the complex, and describe the different cellular functions with which the Ccr4-Not complex has been connected in different organisms. Finally, based upon our current state of knowledge, we will propose a model to explain how one complex can provide such multi-functionality. This model suggests that the Ccr4-Not complex might function as a "chaperone platform".

The structural basis for deadenylation by the CCR4-NOT complex

The CCR4-NOT complex is a highly conserved, multifunctional machinery controlling mRNA metabolism. Its components have been implicated in several aspects of mRNA and protein expression, including transcription initiation, elongation, mRNA degradation, ubiquitination, and protein modification. In this review, we will focus on the role of the CCR4-NOT complex in mRNA degradation. The complex contains two types of deadenylase enzymes, one belonging to the DEDD-type family and one belonging to the EEP-type family, which shorten the poly(A) tails of mRNA. We will review the present state of structure-function analyses into the CCR4-NOT deadenylases and summarize current understanding of their roles in mRNA degradation. We will also review structural and functional work on the Tob/BTG family of proteins, which are known to interact with the CCR4-NOT complex and which have been reported to suppress deadenylase activity in vitro.

BTG/TOB factors impact deadenylases

BTG/TOB factors are a family of antiproliferative proteins whose expression is altered in numerous cancers. They have been implicated in cell differentiation, development and apoptosis. Although proposed to affect transcriptional regulation, these factors interact with CAF1, a subunit of the main eukaryotic deadenylase, and with poly(A)-binding-proteins, strongly suggesting a role in post-transcriptional regulation of gene expression. The recent determination of the structures of BTG2, TOB1 N-terminal domain (TOB1N138) and TOB1N138-CAF1 complexes support a role for BTG/TOB proteins in mRNA deadenylation, a function corroborated by recently published functional characterizations. We highlight molecular mechanisms by which BTG/TOB proteins influence deadenylation and discuss the need for a better understanding of BTG/TOB physiological functions.

The Ccr4-NOT deadenylase subunits CNOT7 and CNOT8 have overlapping roles and modulate cell proliferation

Accurate gene expression requires the precise control of mRNA levels, which are determined by the relative rates of nuclear (pre-)mRNA synthesis and processing, and cytoplasmic mRNA turnover. A key step in mRNA degradation is the removal of the poly(A) tail, which involves several deadenylases including components of the Ccr4-Not complex. Here, we focused on the role of the human paralogues CNOT7 (hCaf1/Caf1a) and CNOT8 (hPop2/Caf1b/Calif), which possess deadenylase activity mediated by DEDD nuclease domains. We show that efficient proliferation requires both subunits, although combined knockdown of CNOT7 and CNOT8 further reduces cell proliferation indicating partial redundancy between these proteins. Interestingly, the function of CNOT7 in cell proliferation partly depends on its catalytic activity. On the other hand, the interaction between CNOT7 and BTG2, a member of the antiproliferative BTG/Tob family involved in transcription and mRNA decay appears less important for proliferation of MCF7 cells, suggesting that CNOT7 does not function solely in conjunction with BTG2. Further analysis of gene expression profiles of CNOT7 and/or CNOT8 knockdown cells underscores the partial redundancy between these subunits and suggests that regulation of several genes, including repression of the antiproliferative genes MSMB and PMP22, by the Ccr4-Not complex contributes to cell proliferation.

Structural basis for the antiproliferative activity of the Tob-hCaf1 complex

The Tob/BTG family is a group of antiproliferative proteins containing two highly homologous regions, Box A and Box B. These proteins all associate with CCR4-associated factor 1 (Caf1), which belongs to the ribonuclease D (RNase D) family of deadenylases and is a component of the CCR4-Not deadenylase complex. Here we determined the crystal structure of the complex of the N-terminal region of Tob and human Caf1 (hCaf1). Tob exhibited a novel fold, whereas hCaf1 most closely resembled the catalytic domain of yeast Pop2 and human poly(A)-specific ribonuclease. Interestingly, the association of hCaf1 was mediated by both Box A and Box B of Tob. Cell growth assays using both wild-type and mutant proteins revealed that deadenylase activity of Caf1 is not critical but complex formation is crucial to cell growth inhibition. Caf1 tethers Tob to the CCR4-Not deadenylase complex, and thereby Tob gathers several factors at its C-terminal region, such as poly(A)-binding proteins, to exert antiproliferative activity.

Tob, a member of the APRO family, regulates immunological quiescence and tumor suppression

Cellular quiescence is a state characterized by decreased cell size and metabolic activity. Quiescence acts to reduce the resources, energy and space. Quiescence might also protect cells from accumulating metabolic damage that could result in malignancy. Recent studies have shown that cell quiescence is an actively maintained rather than a default state in the absence of signals. Quiescence factors represent potential tumor suppressor genes because alterations in their expression or function contribute to progression of malignancies. There is growing evidence that quiescence is under active transcriptional control. The regulation of cell proliferation involves dozens of extracellular signals and intracellular factors of various types. In the present review we will focus on the role of Tob, a member of the APRO family members in regulating cellular quiescence and inhibition of cellular proliferation.

The BTG2 protein is a general activator of mRNA deadenylation

BTG2 is a prototype member of the BTG/Tob family of antiproliferative proteins, originally identified as a primary response gene induced by growth factors and tumour promoters. Its expression has been linked to diverse cellular processes such as cell-cycle progression, differentiation or apoptosis. BTG2 has also been shown to interact with the Pop2/Caf1 deadenylase. Here, we demonstrate that BTG2 is a general activator of mRNA decay, thereby contributing to gene expression control. Detailed characterizations of BTG2 show that it enhances deadenylation of all transcripts tested. Our results demonstrate that Caf1 nuclease activity is required for efficient deadenylation in mammalian cells and that the deadenylase activities of both Caf1 and its Ccr4 partner are required for Btg2-induced poly(A) degradation. General activation of deadenylation may represent a new mode of global regulation of gene expression, which could be important to allow rapid resetting of protein production during development or after specific stresses. This may constitute a common function for BTG/Tob family members.

Multifunctional deadenylase complexes diversify mRNA control

Dynamic changes of the lengths of mRNA poly(A) tails are catalysed by diverse deadenylase enzymes. Modulating the length of the poly(A) tail of an mRNA is a widespread means of controlling protein production and mRNA stability. Recent insights illuminate the specialized activities, biological functions and regulation of deadenylases. We propose that the recruitment of multifunctional deadenylase complexes provides unique opportunities to control mRNAs and that the heterogeneity of the deadenylase complexes is exploited to control translation and mRNA stability.

Crystallization and preliminary crystallographic analysis of the Tob-hCaf1 complex

The Tob/BTG family is a group of antiproliferative proteins that contain two highly homologous regions named Box A and Box B. These proteins all associate with CCR4-associated factor 1 (Caf1), which belongs to the ribonuclease D family of deadenylases. The antiproliferative region of human Tob (residues 1-138) and intact hCaf1 were co-expressed in Escherichia coli, purified and successfully cocrystallized. The crystal belongs to the tetragonal space group I422, with unit-cell parameters a = b = 150.9, c = 113.9 A, and is estimated to contain one heterodimer per asymmetric unit. The crystal diffracted to around 2.6 A resolution.

Human TOB, an antiproliferative transcription factor, is a poly(A)-binding protein-dependent positive regulator of cytoplasmic mRNA deadenylation

In mammalian cells, mRNA decay begins with deadenylation, which involves two consecutive phases mediated by the PAN2-PAN3 and the CCR4-CAF1 complexes, respectively. The regulation of the critical deadenylation step and its relationship with RNA-processing bodies (P-bodies), which are thought to be a site where poly(A)-shortened mRNAs get degraded, are poorly understood. Using the Tet-Off transcriptional pulsing approach to investigate mRNA decay in mouse NIH 3T3 fibroblasts, we found that TOB, an antiproliferative transcription factor, enhances mRNA deadenylation in vivo. Results from glutathione S-transferase pull-down and coimmunoprecipitation experiments indicate that TOB can simultaneously interact with the poly(A) nuclease complex CCR4-CAF1 and the cytoplasmic poly(A)-binding protein, PABPC1. Combining these findings with those from mutagenesis studies, we further identified the protein motifs on TOB and PABPC1 that are necessary for their interaction and found that interaction with PABPC1 is necessary for TOB's deadenylation-enhancing effect. Moreover, our immunofluorescence microscopy results revealed that TOB colocalizes with P-bodies, suggesting a role of TOB in linking deadenylation to the P-bodies. Our findings reveal a new mechanism by which the fate of mammalian mRNA is modulated at the deadenylation step by a protein that recruits poly(A) nuclease(s) to the 3' poly(A) tail-PABP complex.

Capsicum annuum CCR4-associated factor CaCAF1 is necessary for plant development and defence response

The CCR4-associated factor 1 (CAF1) protein belongs to the CCR4-NOT complex, which is an evolutionary conserved protein complex and plays an important role in the control of transcription and mRNA decay in yeast and mammals. To investigate the function of CAF1 in plants, we performed gain- and loss-of-function studies by overexpression of the pepper CAF1 (CaCAF1) in tomato and virus-induced gene silencing (VIGS) of the gene in pepper plants. Overexpression of CaCAF1 in tomato resulted in significant growth enhancement, with increasing leaf thickness, and enlarged cell size by more than twofold when compared with the control plants. A transmission electron microscopic analysis revealed that the CaCAF1-transgenic tomato plants had thicker cell walls and cuticle layers than the control plants. In addition to developmental changes, overexpression of CaCAF1 in tomato plants resulted in enhanced resistance against the oomycete pathogen Phytophthora infestans. Additionally, microarray, northern and real-time polymerase chain reaction analyses of CaCAF1-transgenic tomato plants revealed that multiple genes were constitutively upregulated, including genes involved in polyamine biosynthesis, defence reactions and cell-wall organogenesis. In contrast, VIGS of CaCAF1 in pepper plants caused significant growth retardation and enhanced susceptibility to the pepper bacterial spot pathogen Xanthomonas axonopodis pv. vesicatoria. Our results suggest roles for plant CAF1 in normal growth and development, as well as in defence against pathogens.

Cnot7-null mice exhibit high bone mass phenotype and modulation of BMP actions

Cnot7 is a recently identified regulator of spermatogenesis in adult mice. Because Cnot7 binds to Tob, a BMP inhibitor shown to be involved in bone metabolism, we examined whether Cnot7 is involved in bone mass regulation by using adult Cnot7 deficient mice. Cnot7-/- mice exhibited a high bone mass phenotype. This was associated with an increase in bone formation rate but not with any alteration in bone resorption parameters. On BMP treatment, Cnot7-/- cells expressed higher levels of alkaline phosphatase compared with control cells. Direct BMP2 injection induced larger bone mass in Cnot7-/- calvaria than control in vivo. These observations revealed that Cnot7 is an endogenous suppressor of bone mass and inhibits BMP actions in osteoblasts.

INTRODUCTION

The molecular mechanisms involved in the determination of bone mass have been gradually understood based on recent analyses. Cnot7 (Ccr4-Not complex 7) is a component of transcriptional Ccr4-Not complex, is conserved from yeast to human, and binds to Tob, but its function in bone is not understood.

MATERIALS AND METHODS

To elucidate the role of involvement of Cnot7 in bone mass determination, we examined the bone of adult male Cnot7-null and heterozygous mice based on microCT analyses, histomorphometry, cell cultures, and in vivo BMP assays.

RESULTS

Cnot7-/- mice showed an increase in bone mass levels by >50% compared with controls. Analyses of the histomorphometric parameters indicated that bone formation activity in Cnot7-/- mice was enhanced, whereas bone resorption activity was not altered. These effects on osteoblasts were cell autonomous because mineralized nodule formation was enhanced in the cultures of bone marrow cells prepared from Cnot7-/- mice. In vitro analyses to elucidate Cnot7 effects revealed that BMP-induced expression of alkaline phosphatase in Cnot7-/- calvaria-derived osteoblastic cells was enhanced compared with controls. Moreover, BMP injection-induced new bone formation in vivo was enhanced in Cnot7-/- mice.

CONCLUSIONS

These observations indicated that Cnot7 is an endogenous suppressor of bone mass in adult mice and inhibits BMP actions.

Tob genes in development and homeostasis

Members of the Btg/Tob protein family share a conserved N-terminal region that confers the activity to inhibit cell proliferation. Tob1 and Tob2 proteins, which constitute a Tob subfamily, have a longer C-terminal region than BTG proteins. Apparently, genomes of invertebrates and teleost species contain only a single Tob locus, whereas genomes of mammalian, avian, and amphibian species contain two Tob loci (Tob1 and Tob2). Tob genes are expressed in oocytes, sperm, early embryos, and various adult tissues, depending on the species. Recent reports indicate that Tob proteins play important roles in spermatogenesis, embryonic dorsoventral patterning, osteogenesis, T-cell activation, and learning and memory. Accumulating evidence supports the hypothesis that Tob proteins act primarily as transcriptional repressors in several signaling pathways.

hCAF1, a new regulator of PRMT1-dependent arginine methylation

Protein arginine methylation is an emergent post-translational modification involved in a growing number of cellular processes, including transcriptional regulation, cell signaling, RNA processing and DNA repair. Although protein arginine methyltransferase 1 (PRMT1) is the major arginine methyltransferase in mammals, little is known about the regulation of its activity, except for the regulation induced by interaction with the antiproliferative protein BTG1 (B-cell translocation gene 1). Since the protein hCAF1 (CCR4-associated factor 1) was described to interact with BTG1, we investigated a functional link between hCAF1 and PRMT1. By co-immunoprecipitation and immunofluorescence experiments we demonstrated that endogenous hCAF1 and PRMT1 interact in vivo and colocalize in nuclear speckles, a sub-nuclear compartment enriched in small nuclear ribonucleoproteins and splicing factors. In vitro methylation assays indicated that hCAF1 is not a substrate for PRMT1-mediated methylation, but it regulates PRMT1 activity in a substrate-dependent manner. Moreover, small interfering RNA (siRNA)-mediated silencing of hCAF1 in MCF-7 cells significantly modulates the methylation of endogenous PRMT1 substrates. Finally, we demonstrated that in vitro and in the cellular context, hCAF1 regulates the methylation of Sam68 and histone H4, two PRMT1 substrates. Since hCAF1 and PRMT1 have been involved in the regulation of transcription and RNA metabolism, we speculate that hCAF1 and PRMT1 could contribute to the crosstalk between transcription and RNA processing.

B cell translocation gene 1 contributes to antisense Bcl-2-mediated apoptosis in breast cancer cells

The antiapoptotic protein Bcl-2 is overexpressed in a majority of breast cancers, and is associated with a diminished apoptotic response and resistance to various antitumor agents. Bcl-2 inhibition is currently being explored as a possible strategy for sensitizing breast cancer cells to standard chemotherapeutic agents. Antisense Bcl-2 oligonucleotides represent one method for blocking the antiapoptotic effects of Bcl-2. In this study, we show that antisense Bcl-2 efficiently blocks Bcl-2 expression, resulting in the apoptosis of breast cancer cells. Antisense Bcl-2-mediated cytotoxicity was associated with the induction of the B cell translocation gene 1 (BTG1). Importantly, knockdown of BTG1 reduced antisense Bcl-2-mediated cytotoxicity in breast cancer cells. Furthermore, BTG1 expression seems to be negatively regulated by Bcl-2, and exogenous expression of BTG1 induced apoptosis. These results suggest that BTG1 is a Bcl-2-regulated mediator of apoptosis in breast cancer cells, and that its induction contributes to antisense Bcl-2-mediated cytotoxic effects.

Human Ccr4-Not complex is a ligand-dependent repressor of nuclear receptor-mediated transcription

The Ccr4-Not complex is a highly conserved regulator of mRNA metabolism. The transcription regulatory function of this complex in higher eukaryotes, however, is largely unexplored. Here we report that CNOT1, the large human subunit, represses the ligand-dependent transcriptional activation function of oestrogen receptor (ER) alpha. Promoter recruitment assays indicate that CNOT1 contains an intrinsic ability to mediate transcriptional repression. Furthermore, CNOT1 can interact with the ligand-binding domain of ERalpha in a hormone-dependent fashion and is recruited with other Ccr4-Not subunits to endogenous oestrogen-regulated promoters dependent on the presence of ligand. In addition, siRNA-mediated depletion of endogenous CNOT1 or other Ccr4-Not subunits in breast cancer cells results in deregulation of ERalpha target genes. Finally, CNOT1 interacts in a ligand-dependent manner with RXR and represses transcription mediated by several RXR heterodimers. These findings define a function for the human Ccr4-Not complex as a transcriptional repressor of nuclear receptor signalling that is relevant for the understanding of molecular pathways involved in cancer.

Change of the cell cycle after flutamide treatment in prostate cancer cells and its molecular mechanism

AIM

To explore the effect of androgen receptor (AR) on the expression of the cell cycle-related genes, such as CDKN1A and BTG1, in prostate cancer cell line LNCaP.

METHODS

After AR antagonist flutamide treatment and confirmation of its effect by phase contrast microscope and flow cytometry, the differential expression of the cell cycle-related genes was analyzed by a cDNA microarray. The flutamide treated cells were set as the experimental group and the LNCaP cells as the control. We labeled cDNA probes of the experimental group and control group with Cy5 and Cy3 dyes, respectively, through reverse transcription. Then we hybridized the cDNA probes with cDNA microarrays, which contained 8 126 unique human cDNA sequences and the chip was scanned to get the fluorescent values of Cy5 and Cy3 on each spot. After primary analysis, reverse transcription polymerase chain reaction (RT-PCR) tests were carried out to confirm the results of the chips.

RESULTS

After AR antagonist flutamide treatment, three hundred and twenty-six genes (3.93%) expressed differentially, 97 down-regulated and 219 up-regulated. Among them, eight up-regulated genes might be cell cycle-related, namely CDC10, NRAS, BTG1, Wee1, CLK3, DKFZP564A122, CDKN1A and BTG2. The CDKN1A and BTG1 gene mRNA expression was confirmed to be higher in the experimental group by RT-PCR, while p53 mRNA expression had no significant changes.

CONCLUSION

Flutamide treatment might up-regulate CDKN1A and BTG1 expression in prostate cancer cells. The protein expressions of CDKN1A and BTG1 play an important role in inhibiting the proliferation of cancer cells. CDKN1A has a great impact on the cell cycle of prostate cancer cells and may play a role in the cancer cells in a p53-independent pathway. The prostate cancer cells might affect the cell cycle-related genes by activating AR and thus break the cell cycle control.

Nuclear localization of Tob is important for regulation of its antiproliferative activity

TOB: is a member of an antiproliferative gene family that includes btg1, pc3/tis21/btg2, pc3b, ana/btg3, and tob2. Exogenous overexpression of the family proteins suppresses cell proliferation. These proteins participate in transcriptional regulation of several genes. Here, we show that Tob is a nuclear protein that is imported into the nucleus through a nuclear localization signal (NLS)-mediated mechanism. Mutation in the NLS sequence of Tob affects its nuclear localization and impairs antiproliferative activity. Additionally, Tob contains a nuclear export signal (NES). In oncogenic ErbB2-transformed cells, nuclear export of Tob is facilitated by NES-mediated mechanism, resulting in decrease of its antiproliferative activity. These results indicate that regulation of nuclear localization of Tob is important for its antiproliferative activity.

FoxO3a regulates erythroid differentiation and induces BTG1, an activator of protein arginine methyl transferase 1

Erythropoiesis requires tight control of expansion, maturation, and survival of erythroid progenitors. Because activation of phosphatidylinositol-3-kinase (PI3K) is required for erythropoietin/stem cell factor-induced expansion of erythroid progenitors, we examined the role of the PI3K-controlled Forkhead box, class O (FoxO) subfamily of Forkhead transcription factors. FoxO3a expression and nuclear accumulation increased during erythroid differentiation, whereas untimely induction of FoxO3a activity accelerated differentiation of erythroid progenitors to erythrocytes. We identified B cell translocation gene 1 (BTG1)/antiproliferative protein 2 as a FoxO3a target gene in erythroid progenitors. Promoter studies indicated BTG1 as a direct target of FoxO3a. Expression of BTG1 in primary mouse bone marrow cells blocked the outgrowth of erythroid colonies, which required a domain of BTG1 that binds protein arginine methyl transferase 1. During erythroid differentiation, increased arginine methylation coincided with BTG1 expression. Concordantly, inhibition of methyl transferase activity blocked erythroid maturation without affecting expansion of progenitor cells. We propose FoxO3a-controlled expression of BTG1 and subsequent regulation of protein arginine methyl transferase activity as a novel mechanism controlling erythroid expansion and differentiation.

CCR4-associated factor CAF1 is an essential factor for spermatogenesis

The CCR4-associated protein CAF1 has been demonstrated to play several roles in the control of transcription and of mRNA decay. To gain further insight into its physiological function, we generated CAF1-deficient mice. They are viable, healthy, and normal in appearance; however, mCAF1(-/-) male mice are sterile. The crossing of mCAF1(+/-) mice gave a Mendelian ratio of mCAF1(+/+), mCAF1(+/-), and mCAF1(-/-) pups, indicating that haploid mCAF1-deficient germ cells differentiate normally. The onset of the defect occurs during the first wave of spermatogenesis at 19 to 20 days after birth, during progression of pachytene spermatocytes to haploid spermatids and spermatozoa. Early disruption of spermatogenesis was evidenced by Sertoli cell vacuolization and tubular disorganization. The most mature germ cells were the most severely depleted, but progressively all germ cells were affected, giving Sertoli cell-only tubes, large interstitial spaces, and small testes. This phenotype could be linked to a defect(s) in germ cells and/or to inadequate Sertoli cell function, leading to seminiferous tubule disorganization and finally to a total disappearance of germ cells. The mCAF1-deficient mouse provides a new model of failed spermatogenesis in the adult that may be relevant to some cases of human male sterility.

An anti-proliferative gene BTG1 regulates angiogenesis in vitro

B-cell translocation gene 1 (BTG1) is a member of the anti-proliferative gene family that regulates cell growth and differentiation. To clarify the role of BTG1 in angiogenesis, we examined the regulation of BTG1 expression in cultured endothelial cells and characterized its function in in vitro models of angiogenesis. BTG1 mRNA was abundantly expressed in quiescent endothelial cells. Addition of serum and angiogenic growth factors decreased BTG1 mRNA levels in endothelial cells. In contrast, BTG1 mRNA was up-regulated in tube-forming endothelial cells on Matrigel. This up-regulation was partially blocked by neutralizing antibody against transforming growth factor-beta (TGF-beta), and TGF-beta increased BTG1 mRNA levels. Inhibition of endogenous BTG1 by overexpression of antisense BTG1 resulted in inhibited network formation, and overexpression of sense BTG1 augmented tube formation in these cell lines. BTG1-overexpressing endothelial cells displayed increased cell migration. These findings suggest that BTG1 may play an important role in the process of angiogenesis.

The CCR4-NOT complex plays diverse roles in mRNA metabolism

It is increasingly clear that the synthesis of eukaryotic mRNA involves an integrated series of events involving large multisubunit protein complexes. The evolutionarily conserved CCR4-NOT complex of proteins has been found to be involved in several aspects of mRNA formation, including repression and activation of mRNA initiation, control of mRNA elongation, and the deadenylation and subsequent degradation of mRNA. Its roles in such diverse processes make the CCR4-NOT complex central to the regulation of mRNA metabolism. In this review we describe the CCR4-NOT complex, its constituents, and its organization, discussing both the well characterized yeast proteins and their higher eukaryotic orthologs. The known biochemical roles of the individual components and of the complex are described with particular emphasis on the two known functions of the complex, repression of TFIID action and deadenylation of mRNA. Finally, the functional diversity of the CCR4-NOT complex is related to its mediating responses from a number of cellular signaling pathways.

Analysis of the transcription regulator, CNOT7, as a candidate chromosome 8 tumor suppressor gene in colorectal cancer

Loss of heterozygosity (LOH) on the short arm of chromosome 8 occurs at high frequencies in many tumor types, including colorectal carcinoma. We have previously used microcell-mediated chromosome transfer (MMCT) to map an approximately 7.7 Mb colorectal cancer suppressor region (CRCSR) at 8p22-23.1. We have now taken a candidate gene approach to identify the putative tumor suppressor gene located within the CRCSR. CNOT7 encodes a subunit of the CCR4-Not transcription complex and is located at 8p22. We showed that CNOT7 is expressed in normal colonic mucosa and in colonic crypt cells, as well as in colorectal cell lines and primary tumors. We assembled a panel of 88 primary colorectal tumors comprising 20 MSI-high (high microsatellite instability), 19 MSI-low and 49 MSS (microsatellite stable) tumors for mutation analysis of the CNOT7 gene. Denaturing high-performance liquid chromatography (DHPLC) analysis of the entire coding region of the CNOT7 gene revealed only one somatic missense mutation in an MSS tumor. The rarity of somatic mutations in CNOT7, and its expression in primary colorectal tumors and cell lines, suggests that CNOT7 is not the target tumor suppressor gene in the 8p22-23.1 CRCSR.

Global control of gene expression in yeast by the Ccr4-Not complex

The Ccr4-Not complex is a global regulator of gene expression that is conserved from yeast to human. It is a large complex that in the yeast Saccharmyces cerevisiae exists in two prominent forms of 0.9-1.2 and 1.9-2 MDa, and consists of at least nine core subunits: the five Not proteins (Not1p to Not5p), Caf1p, Caf40p, Caf130p and Ccr4p. It was initially described to be a global regulator of transcription, based upon the observation that the levels of many transcripts were increased or decreased in mutants. However, the recent finding that Caf1p and Ccr4p encode the major yeast deadenylase has suggested that this complex may additionally play a role in RNA degradation. In this review, the events that led to the identification of the Ccr4-Not complex are described and the elements that clearly demonstrate that the Ccr4-Not complex regulates many different cellular functions are discussed, including RNA degradation and transcription initiation. The evidence points to a role for the Ccr4-Not complex as a regulatory platform that senses nutrient levels and stress.

BTG2 antiproliferative protein interacts with the human CCR4 complex existing in vivo in three cell-cycle-regulated forms

The yeast CCR4-NOT complex exists in two forms (1.0 and 1.9 MDa) that share several common subunits, including yCCR4, yCAF1 and five NOT proteins (NOT1-5). Here, we report that different complexes containing mammalian homologs of CCR4-NOT subunits exist in mammalian cells, with estimated sizes of approximately 1.9 MDa, approximately 1 MDa and approximately 650 kDa, and that BTG2, a member of a protein family with antiproliferative functions, can associate with these complexes. Immunoprecipitation and gel filtration experiments established that BTG2 interacts in vivo with hCCR4 protein via hCAF1 and hPOP2. Moreover, we show that hCCR4, as well as hCAF1 and BTG2, modulate the transcription regulation mediated by ERalpha. Finally, we demonstrate that the cellular localization of hCAF1 and the cell content in hCAF1-containing complexes change as cells progress from quiescence to S phase. These findings suggest that the different regulatory pathways in which hCAF1 is involved, notably transcription regulation and mRNA turnover, may occur through distinct CCR4 complexes in the course of cell-cycle progression.

Rapid deadenylation triggered by a nonsense codon precedes decay of the RNA body in a mammalian cytoplasmic nonsense-mediated decay pathway

Nonsense-mediated mRNA decay (NMD) is an RNA surveillance pathway that detects and destroys aberrant mRNAs containing nonsense or premature termination codons (PTCs) in a translation-dependent manner in eukaryotes. In yeast, the NMD pathway bypasses the deadenylation step and directly targets PTC-containing messages for decapping, followed by 5'-to-3' exonuclease digestion of the RNA body. In mammals, most PTC-containing mRNAs are subject to active nucleus-associated NMD. Here, using two distinct transcription-pulsing approaches to monitor mRNA deadenylation and decay kinetics, we demonstrate the existence of an active cytoplasmic NMD pathway in mammalian cells. In this pathway, a nonsense codon triggers accelerated deadenylation that precedes decay of the PTC-containing mRNA body. Transcript is stabilized when accelerated deadenylation is impeded by blocking translation initiation; by ectopically expressing two RNA-binding proteins, UNR and NSAP1; or by ectopically expressing a UPF1 dominant-negative mutant. These results are consistent with the notion that the nonsense codon can function in the cytoplasm by promoting rapid removal of the poly(A) tail as a necessary first step in the decay process.