2015;29:23C38

2015;29:23C38. how the cell cycle and differentiation are linked has become critical to a broad swath of disciplines including regenerative medicine, cancer biology, and aging. This review will examine recent findings around the dynamic regulation between the pluripotency and cell cycle networks. Reciprocal regulation of cell cycle and pluripotency networks: Pluripotency regulation of the cell cycle The pluripotent network consists of a core set of transcription factors, including Oct4 (Pou5f1), Sox2, and Nanog, which serve to establish the undifferentiated state and the self-renewing capacity of embryonic stem (ES) cells [reviewed in 4,5]. While it is usually clear that a major role of these core transcription factors is the activation of the greater pluripotency network [6], an emerging emphasis Rabbit Polyclonal to RHOBTB3 on crosstalk with the cell cycle machinery has recently been identified (Physique 1, Table 1). Early studies of the core pluripotency network identified as a target of Oct4 and Nanog in ES cells that is central to the maintenance of pluripotency [7C9]. Myc then binds to and regulates many cell cycle genes in ES cells [10,11]. It does so in part by overcoming paused Pol II at target genes allowing for successful transcriptional elongation [12,13]. The dependency of Myc, and PI3K signaling, which also promotes pluripotency [14], can be relieved by growth in media made up of GSK3 and MEK1/2 inhibitors (2i conditions) [15]. Open in a separate window Physique 1 Means of pluripotency control of the cell cycle Table 1 Molecular Pathways which regulate pluripotency and the cell cycle in ES cells cluster, cluster, (Table 1), which in turn repress CDK inhibitors, pocket proteins, pro-differentiation miRNAs, and apoptosis [24C28]. Beyond transcriptional regulation and post-transcriptional regulation by miRNAs, post-translational modifications of key pathway members are also utilized by the cell to enforce high proliferation in ES cells. For example, the F-box protein Fbw7 (Fbxw7), a component of the SCF-type ubiquitin ligase complex, targets c-Myc for degradation and is therefore downregulated in ES cells to maintain high c-Myc protein stability [29,30]. In addition, the O-GlcNAcylation of a RINGB, a member of the polycomb repressive complex 1 (PRC1), removes PRC1 from regulatory DNA elements of cell cycle genes to promote differentiation [31]. One complication of fast cell proliferation is the potentially increased accumulation of genetic mutations due to error-prone DNA synthesis. Oct4 has been shown to directly bind to and inhibit Cdk1 resulting in a lengthening of G2 phase which allows more time for the DNA repair machinery to correct mutations [32]. Similarly, a NU 1025 axis also serves to balance the needs of the cell to maintain fast proliferation and resolve DNA damage. This occurs through the expression of signaling induces expression of the DNA-damage repair gene [28]. Reciprocal regulation of cell cycle and pluripotency networks: Cell cycle regulation of pluripotency As the core pluripotency network can control the cell cycle, there are multiple means by which cell cycle regulators control pluripotency (Physique 2). Indeed there are several examples of how the high CDK activity in ES cells may influence the pluripotency network. Loss of CDK1 in human ES cells results in a reduction of pluripotency gene expression, including the core factors OCT4, KLF4, and LIN28, and subsequently increases differentiation [33]. Additionally, these cells show increased DNA damage and ensuing apoptosis [33,34]. Comparable results were found performing chemical CDK2-inhibition in human ES cells [35]. Sox2 can be phosphorylated by Cdk2, although this is dispensable for the maintenance of pluripotency [36]. Mediator, which is NU 1025 usually controlled by Cdk8, plays an important role in the activation of genes made up of Oct4, Sox2, and Nanog bound at their enhancers by looping them to promoter regions using cohesion [4]. Rb and associated proteins can silence members of the core pluripotency network in differentiated tissues, therefore this high Cdk activity serves to block this repression on pluripotency [37C39]. Similarly, Cdk inhibitors such as p27Kip1 also silence some pluripotency factors and are themselves repressed in ES cells [23,40]. This repression of Cdk inhibitors is usually E2F4-dependent, a NU 1025 reflection of the complex transcriptional role.