Transcriptional analysis of pluripotency reveals the Hippo pathway as a barrier to reprogramming

Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, and Diabetes Center, South San Francisco, CA, USA.
Human Molecular Genetics (Impact Factor: 6.39). 02/2012; 21(9):2054-67. DOI: 10.1093/hmg/dds023
Source: PubMed


Pluripotent stem cells are derived from culture of early embryos or the germline and can be induced by reprogramming of somatic cells. Barriers to reprogramming that stabilize the differentiated state and have tumor suppression functions are expected to exist. However, we have a limited understanding of what such barriers might be. To find novel barriers to reprogramming to pluripotency, we compared the transcriptional profiles of the mouse germline with pluripotent and somatic cells, in vivo and in vitro. There is a remarkable global expression of the transcriptional program for pluripotency in primordial germ cells (PGCs). We identify parallels between PGC reprogramming to pluripotency and human germ cell tumorigenesis, including the loss of LATS2, a tumor suppressor kinase of the Hippo pathway. We show that knockdown of LATS2 increases the efficiency of induction of pluripotency in human cells. LATS2 RNAi, unlike p53 RNAi, specifically enhances the generation of fully reprogrammed iPS cells without accelerating cell proliferation. We further show that LATS2 represses reprogramming in human cells by post-transcriptionally antagonizing TAZ but not YAP, two downstream effectors of the Hippo pathway. These results reveal transcriptional parallels between germ cell transformation and the generation of iPS cells and indicate that the Hippo pathway constitutes a barrier to cellular reprogramming.

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Available from: Laure Blouin, Sep 26, 2014
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    • "Hippo signaling also plays a role in cellular differentiation. MST1/2 are essential components of differentiation, and inactivation of Hippo signaling leads to the induction pluripotent stem cells [56]. In mouse cell culture models, YAP expression is associated with the maintenance of embryonic stem cells, and the reduction of nuclear YAP corresponds with differentiation [42,57]. "
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    ABSTRACT: Understanding the molecular nature of human cancer is essential to the development of effective and personalized therapies. Several different molecular signal transduction pathways drive tumorigenesis when deregulated and respond to different types of therapeutic interventions. The Hippo signaling pathway has been demonstrated to play a central role in the regulation of tissue and organ size during development. The deregulation of Hippo signaling leads to a concurrent combination of uncontrolled cellular proliferation and inhibition of apoptosis, two key hallmarks in cancer development. The molecular nature of this pathway was first uncovered in Drosophila melanogaster through genetic screens to identify regulators of cell growth and cell division. The pathway is strongly conserved in humans, rendering Drosophila a suitable and efficient model system to better understand the molecular nature of this pathway. In the present study, we review the current understanding of the molecular mechanism and clinical impact of the Hippo pathway. Current studies have demonstrated that a variety of deregulated molecules can alter Hippo signaling, leading to the constitutive activation of the transcriptional activator YAP or its paralog TAZ. Additionally, the Hippo pathway integrates inputs from a number of growth signaling pathways, positioning the Hippo pathway in a central role in the regulation of tissue size. Importantly, deregulated Hippo signaling is frequently observed in human cancers. YAP is commonly activated in a number of in vitro and in vivo models of tumorigenesis, as well as a number of human cancers. The common activation of YAP in many different tumor types provides an attractive target for potential therapeutic intervention.
    Clinical and Translational Medicine 07/2014; 3(1):25. DOI:10.1186/2001-1326-3-25
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    • "Importantly, the somatic cell is not a tabula rasa and expresses genes that antagonize reprogramming, as has been shown for tumor suppressors (p53, INK4a/ARF, LATS2) (Kawamura et al., 2009; Qin et al., 2012; Zhao et al., 2008) and H3K9 methyltransferases (SETDB1, SUV39H, EHMT2) (Chen et al., 2013). In addition, focused RNAi screens have revealed other pathways that act as barriers to reprogramming, such as TGF-b signaling (Samavarchi-Tehrani et al., 2010), H3K79 methylation by DOT1L (Onder et al., 2012), or protein ubiquitination (Buckley et al., 2012). "
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    ABSTRACT: Reprogramming of somatic cells to induced pluripotent stem cells (iPSCs) holds enormous promise for regenerative medicine. To elucidate endogenous barriers limiting this process, we systematically dissected human cellular reprogramming by combining a genome-wide RNAi screen, innovative computational methods, extensive single-hit validation, and mechanistic investigation of relevant pathways and networks. We identify reprogramming barriers, including genes involved in transcription, chromatin regulation, ubiquitination, dephosphorylation, vesicular transport, and cell adhesion. Specific a disintegrin and metalloproteinase (ADAM) proteins inhibit reprogramming, and the disintegrin domain of ADAM29 is necessary and sufficient for this function. Clathrin-mediated endocytosis can be targeted with small molecules and opposes reprogramming by positively regulating TGF-β signaling. Genetic interaction studies of endocytosis or ubiquitination reveal that barrier pathways can act in linear, parallel, or feedforward loop architectures to antagonize reprogramming. These results provide a global view of barriers to human cellular reprogramming.
    Cell 07/2014; 158(2):449-61. DOI:10.1016/j.cell.2014.05.040 · 32.24 Impact Factor
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    • "While we currently do not understand the long term consequences of sustained YAP/TAZ inhibition, the central role of YAP/TAZ in mammalian stem cells is undeniable [31]. YAP and TAZ are critical regulators of stem cell pluripotency in murine [124] and human cells [125,126]. Thus, although YAP/TAZ depletion has the potential to inhibit cancer stem cell expansion in a clinical setting [97], it is very likely that YAP/TAZ inhibition would also negatively affect essential stem cell pools in non-cancerous tissues. In summary, increased YAP/TAZ activities are associated with stem cell expansion that is coupled with inhibition of differentiation, while reduction of YAP/TAZ activities results in the opposite effect. "
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    ABSTRACT: The Hippo tumour suppressor pathway co-ordinates cell proliferation, cell death and cell differentiation to regulate tissue growth control. In mammals, a conserved core Hippo signalling module receives signal inputs on different levels to ensure the proper regulation of YAP/TAZ activities as transcriptional co-activators. While the core module members MST1/2, Salvador, LATS1/2 and MOB1 have been attributed tumour suppressive functions, YAP/TAZ have been mainly described to have oncogenic roles, although some reports provided evidence supporting growth suppressive roles of YAP/TAZ in certain cancer settings. Intriguingly, mammalian Hippo signalling is also implicated in non-cancer diseases and plays a role in tissue regeneration following injury. Cumulatively, these findings indicate that the pharmacological inhibition or activation of the Hippo pathway could be desirable depending on the disease context. In this review, we first summarise the functions of the mammalian Hippo pathway in tumour formation, and then discuss non-cancer diseases involving Hippo signalling core components with a specific focus on our current understanding of the non-cancer roles of MST1/2 and YAP/TAZ. In addition, the pros and cons of possible pharmacological interventions with Hippo signalling will be reviewed, with particular emphasis on anti-cancer drug development and regenerative medicine.
    Clinical and Translational Medicine 07/2014; 3(1):22. DOI:10.1186/2001-1326-3-22
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