Involvement of CNOT3 in mitotic progression through inhibition of MAD1 expression

Division of Oncology, Department of Cancer Biology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.
Biochemical and Biophysical Research Communications (Impact Factor: 2.3). 02/2012; 419(2):268-73. DOI: 10.1016/j.bbrc.2012.02.007
Source: PubMed


The stability of mRNA influences the dynamics of gene expression. The CCR4-NOT complex, the major deadenylase in mammalian cells, shortens the mRNA poly(A) tail and contributes to the destabilization of mRNAs. The CCR4-NOT complex plays pivotal roles in various physiological functions, including cell proliferation, apoptosis, and metabolism. Here, we show that CNOT3, a subunit of the CCR4-NOT complex, is involved in the regulation of the spindle assembly checkpoint, suggesting that the CCR4-NOT complex also plays a part in the regulation of mitosis. CNOT3 depletion increases the population of mitotic-arrested cells and specifically increases the expression of MAD1 mRNA and its protein product that plays a part in the spindle assembly checkpoint. We showed that CNOT3 depletion stabilizes the MAD1 mRNA, and that MAD1 knockdown attenuates the CNOT3 depletion-induced increase of the mitotic index. Basing on these observations, we propose that CNOT3 is involved in the regulation of the spindle assembly checkpoint through its ability to regulate the stability of MAD1 mRNA.

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    • "The cells, in turn, undergo caspase-dependent apoptosis, most likely due to the ER-stress induced by overproduction of the proteins that results from elevated levels of the stabilized mRNAs (Ito et al., 2011a,b). By contrast, knockdown of CNOT3 specifically increases the expression of MAD1 by stabilizing its mRNA and induces mitotic arrest of HeLa cells (Takahashi et al., 2012). "
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    ABSTRACT: The carbon catabolite repression 4 (CCR4)-negative on TATA-less (NOT) complex serves as one of the major deadenylases of eukaryotes. Although it was originally identified and characterized in yeast, recent studies have revealed that the CCR4-NOT complex also exerts important functions in mammals, -including humans. However, there are some differences in the composition and functions of the CCR4-NOT complex between mammals and yeast. It is noteworthy that each subunit of the CCR4-NOT complex has unique, multifunctional roles and is responsible for various physiological phenomena. This heterogeneity and versatility of the CCR4-NOT complex makes an overall understanding of this complex difficult. Here, we describe the functions of each subunit of the mammalian CCR4-NOT complex and discuss the molecular mechanisms by which it regulates homeostasis in mammals. Furthermore, a possible link between the disruption of the CCR4-NOT complex and various diseases will be discussed. Finally, we propose that the analysis of mice with each CCR4-NOT subunit knocked out is an effective strategy for clarifying its complicated functions and networks in mammals.
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    • "In addition to the nuclease subunits, several non-catalytic subunits are implicated in mRNA deadenylation (Tucker et al., 2002; Temme et al., 2004; Ito et al., 2011a,b; Takahashi et al., 2012). However , genetic analysis in Saccharomyces cerevisiae has shown that "
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    ABSTRACT: The shortening of the poly(A) tail of cytoplasmic mRNA (deadenylation) is a pivotal step in the regulation of gene expression in eukaryotic cells. Deadenylation impacts on both regulated mRNA decay as well as the rate of mRNA translation. An important enzyme complex involved in poly(A) shortening is the Ccr4-Not deadenylase. In addition to at least six non-catalytic subunits, it contains two distinct subunits with ribonuclease activity: a Caf1 subunit, characterized by a DEDD (Asp-Glu-Asp-Asp) domain, and a Ccr4 component containing an endonuclease-exonuclease-phosphatase (EEP) domain. In vertebrate cells, the complexity of the complex is further increased by the presence of paralogs of the Caf1 subunit (encoded by either CNOT7 or CNOT8) and the occurrence of two Ccr4 paralogs (encoded by CNOT6 or CNOT6L). In plants, there are also multiple Caf1 and Ccr4 paralogs. Thus, the composition of the Ccr4-Not complex is heterogeneous. The potential differences in the intrinsic enzymatic activities of the paralogs will be discussed. In addition, the potential redundancy, cooperation, and/or the extent of unique roles for the deadenylase subunits of the Ccr4-Not complex will be reviewed. Finally, novel approaches to study the catalytic roles of the Caf1 and Ccr4 subunits will be discussed.
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    ABSTRACT: Adipogenesis is an important component of adipose tissue development and is critically related to obesity. A cascade of transcription factors is involved in adipogenesis, in which peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer-binding proteins (C/EBPs) play pivotal roles. Bone morphogenetic proteins (BMPs) and Smad proteins are implicated in this cascade, although the precise regulatory mechanisms have yet to be elucidated. Here, we show that Tob2, a member of the Tob/BTG antiproliferative protein family, inhibits adipogenesis by interfering with Smad signaling. tob2 expression is downregulated in the white adipose tissue of high-fat diet-induced or genetically mutated obese mice. Consistent with this, tob2−/− mice exhibit increased adiposity with augmented expression of the genes encoding the type 1A BMP receptor (BMPR1A) and PPARγ2 as well as their target genes. We further show accelerated adipogenesis in primary tob2−/− preadipocytes. Furthermore, exogenously expressed Tob2 inhibits adipogenic differentiation of 3T3-L1 preadipocytes: the Tob2 protein suppresses PPARγ2 transcription by inhibiting BMP2-induced Smad1/5 phosphorylation through its interaction with Smad6 and by sequestering C/EBPα from the PPARγ2 promoter. Thus, Tob2 negatively regulates adipogenesis by inhibiting PPARγ2 expression.
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