Functional Compensation Between Myc and PI3K Signaling Supports Self-Renewal of Embryonic Stem Cells

Abstract

c-Myc and phosphatidylinositol 3-OH kinase (PI3K) both participate in diverse cellular processes, including cell cycle control and tumorigenic transformation. They also contribute to preserving embryonic stem cell (ESC) characteristics. However, in spite of the vast knowledge, the molecular relationship between c-Myc and PI3K in ESCs is not known. Herein, we demonstrate that c-Myc and PI3K function cooperatively but independently to support ESC self-renewal when murine ESCs are cultured under conventional culture condition. Interestingly, culture of ESCs in 2i-condition including a GSK3b and MEK inhibitor renders both PI3K and Myc signaling dispensable for the maintenance of pluripotent properties. These results suggest that the requirement for an oncogenic proliferation-dependent mechanism sustained by Myc and PI3K is context dependent and that the 2i-condition liberates ESCs from the dependence of this mechanism. STEM CELLS

Proliferation, survival and metabolism: the role of PI3K/AKT/mTOR signalling in pluripotency and cell fate determination

“…In mESCs, increasing evidence suggests that PI3K promotes the retention of ESC properties mainly through the inhibition of two downstream pathways: the mitogen-activated protein kinases/extracellular signal-regulated kinase (MAPK/ERK) pathway and the GSK3 signalling pathway. This is consistent with the finding that PI3K signalling is dispensable in naive mESC 2i culture conditions in which both MAPK/ERK and GSK3 pathways are suppressed (Hishida et al, 2015). Active MAPK/ERK signalling is a key requirement for mESCs to undergo differentiation (Ying et al, 2008); thus, inhibition of MAPK/ERK signalling by LIF-induced PI3K may contribute to the maintenance of pluripotency even though the exact mechanisms by which PI3K inhibits MAPK/ERK are unclear (Paling et al, 2004).…”

Membrane translocation of t-SNARE protein syntaxin-4 abrogates ground-state pluripotency in mouse embryonic stem cells

“…In addition to morphological changes, the syntaxin-4-triggered inactivation of PI3K/Akt signaling is a plausible differentiation cue, as this signaling pathway reportedly mediates the upregulation of genes involved in self-renewal43, retention of transcription factors for maintenance of stemness23, and inhibition of Wnt/MAPK- induced differentiation signals in ES cells155. However, ES cells failed to upregulate the differentiation marker brachyury in response to an Akt inhibitor, despite a significant downregulation of the stemness factor zscan4 .…”

Crosstalk between stem cell and cell cycle machineries

“…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 containing GSK3β and MEK1/2 inhibitors (2i conditions) [15]. …”

“…Indeed there are many proteins that coordinately link both processes, such as Rb and p53 [37,38,57]. Many signaling pathways can also simultaneously induce rapid proliferation and the core pluripotency gene network [15,62]. In ES cells it does appear, though, that there may be conditions in which cell cycle regulation and pluripotency may be uncoupled [37,63].…”