Dissecting Signal Transduction in Embryonic Stem Cell Pluripotency and Cell Fate Determination

Characterized by the ability to self-renew indefinitely and differentiate into all cell lineages of an organism, embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) hold enormous promise for biomedicine. Cell fate choices in ESCs and iPSCs are regulated by a complex orchestration of multiple signaling pathways. However, only a few pathways, such as the LIF-gp130-Stat3 and BMP4-TGF-beta-Smad pathways, have been studied in maintaining ESC self-renewal. The exact signal transduction map by which cell fate changes are controlled remains poorly understood. To unravel the essential internal and external signals required for sustaining the ESC state, we conducted a short hairpin (sh) RNA screen of 104 ESC-associated phosphoregulators and identified aurora kinase A (Aurka). Depletion of Aurka resulted in compromised self-renewal and consequent differentiation. Furthermore, loss of Aurka led to an up-regulation of p53 signaling that triggered ESC differentiation. We found that Aurka phosphorylation of p53 S212 plays a major role in impairing p53-induced ESC differentiation, as well as hampering p53-mediated suppression of iPSC reprogramming. This work is the first report demonstrating that a specific phosphorylation event regulates ESC self-renewal, differentiation, and somatic cell reprogramming.;To further study the physiological role of p53 in balancing self-renewal and differentiation, we used iPSC approches to model Li-Fraumeni Syndrome (LFS). LFS is a genetically heterogeneous inherited cancer syndrome characterized by germline p53 mutations that cause multiple early-onset tumors in affected patients. We used iPSCs derived from LFS patients and directed differentiation to create a "disease in a dish" model of human LFS-associated osteosarcoma to elucidate the underlying pathogenesis and aberrant signals caused by these p53 mutations.;Collectively, our results elucidate that novel signal transduction pathways play a crucial role in balancing ESCs self-renewal and differentiation. Such work will aid in identifying novel therapeutic targets for future ESC/iPSC-based clinical therapies.