Human Pumilio Proteins Recruit Multiple Deadenylases to Efficiently Repress Messenger RNAs.
ABSTRACT PUF proteins are a conserved family of eukaryotic RNA-binding proteins that regulate specific mRNAs: they control many processes including stem cell proliferation, fertility, and memory formation. PUFs repress protein expression from their target mRNAs but the mechanism by which they do so remains unclear, especially for humans. Humans possess two PUF proteins, PUM1 and PUM2, which exhibit similar RNA binding specificities. Here we report new insights into their regulatory activities and mechanisms of action. We developed functional assays to measure sequence-specific repression by PUM1 and PUM2. Both robustly inhibit translation and promote mRNA degradation. Purified PUM complexes were found to contain subunits of the CCR4-NOT (CNOT) complex, which contains multiple enzymes that catalyze mRNA deadenylation. PUMs interact with the CNOT deadenylase subunits in vitro. We used three approaches to determine the importance of deadenylases for PUM repression. First, dominant-negative mutants of CNOT7 and CNOT8 reduced PUM repression. Second, RNA interference depletion of the deadenylases alleviated PUM repression. Third, the poly(A) tail was necessary for maximal PUM repression. These findings demonstrate a conserved mechanism of PUF-mediated repression via direct recruitment of the CCR4-POP2-NOT deadenylase leading to translational inhibition and mRNA degradation. A second, deadenylation independent mechanism was revealed by the finding that PUMs repress an mRNA that lacks a poly(A) tail. Thus, human PUMs are repressors capable of deadenylation-dependent and -independent modes of repression.
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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.Frontiers in Genetics 08/2014; 5:286. DOI:10.3389/fgene.2014.00286
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ABSTRACT: T cells reactive to tumor antigens and viral antigens lose their reactivity when exposed to the antigen-rich environment of a larger tumor bed or viral load. Such non-responsive T cells are termed exhausted. T cell exhaustion affects both CD8+ and CD4+ T cells. T cell exhaustion is attributed to the functional impairment of T cells to produce cytokines, of which the most important may be Interleukin 2 (IL2). IL2 performs functions critical for the elimination of cancer cells and virus infected cells. In one such function, IL2 promotes CD8+ T cell and natural killer (NK) cell cytolytic activities. Other functions include regulating naïve T cell differentiation into Th1 and Th2 subsets upon exposure to antigens. Thus, the signaling pathways contributing to T cell exhaustion could be linked to the signaling pathways contributing to IL2 loss. This review will discuss the process of T cell exhaustion and the signaling pathways that could be contributing to T cell exhaustion.Cytokine 12/2014; 71(2). DOI:10.1016/j.cyto.2014.11.024 · 2.87 Impact Factor
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ABSTRACT: A crucial event in animal development is the specification of primordial germ cells (PGCs), which become the stem cells that create sperm and eggs. How PGCs are created provides a valuable paradigm for understanding stem cells in general. We find that the PGCs of the sea urchin Strongylocentrotus purpuratus exhibit broad transcriptional repression, yet enrichment for a set of inherited mRNAs. Enrichment of several germline determinants in the PGCs requires the RNA-binding protein Nanos to target the transcript that encodes CNOT6, a deadenylase, for degradation in the PGCs, thereby creating a stable environment for RNA. Misexpression of CNOT6 in the PGCs results in their failure to retain Seawi transcripts and Vasa protein. Conversely, broad knockdown of CNOT6 expands the domain of Seawi RNA as well as exogenous reporters. Thus, Nanos-dependent spatially restricted CNOT6 differential expression is used to selectively localize germline RNAs to the PGCs. Our findings support a 'time capsule' model of germline determination, whereby the PGCs are insulated from differentiation by retaining the molecular characteristics of the totipotent egg and early embryo.Development 08/2014; 141(16). DOI:10.1242/dev.110395 · 6.27 Impact Factor