3rd Focused Meeting on PI3K Signalling and Disease225
Phosphoinositide 3-kinases and regulation
of embryonic stem cell fate
M.J. Welham1, M.P. Storm, E. Kingham and H.K. Bone
Department of Pharmacy and Pharmacology and The Centre for Regenerative Medicine, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
ES (embryonic stem) cell lines are derived from the epiblast of pre-implantation embryos and like the inner
cell mass cells from which they are derived exhibit the remarkable property of pluripotency, namely the
ability to differentiate into all cell lineages comprising the adult organism. ES cells and their differentiated
progeny offer tremendous potential to regenerative medicine, particularly as cellular therapies for the
treatment of a wide variety of chronic disorders, such as Type 1 diabetes, Parkinson’s disease and retinal
degeneration. In order for this potential to be realized, a detailed understanding of the molecular mech-
anisms regulating the fundamental properties of ES cells, i.e. pluripotency, proliferation and differentiation,
is required. In the present paper, we review the evidence that PI3K (phosphoinositide 3-kinase)-dependent
signalling plays a role in regulation of both ES cell pluripotency and proliferation.
ES (embryonic stem) cells
ES cell lines exhibit the unique property of pluripotency, i.e.
the ability to differentiate into all cell lineages comprising the
adult organism [1,2]. Pluripotency is underpinned by ES cell
In essence, self-renewal is proliferation that is accompanied
by the suppression of differentiation. Regulation of ES cell
and expand pluripotent ES cells is essential if the therapeutic
potential offered by ES cell-derived progeny to regenerative
medicine is to be realized.
Regulation of murine ES cell pluripotency
Pluripotency of mES (murine ES) cells is regulated by a
complex network of extrinsic factors, signalling pathways
and transcription factors. LIF (leukaemia inhibitory factor)
was the first cytokine shown to play a role in maintenance of
pluripotency , via activation of STAT3 (signal transducer
However, like many cytokines, LIF also activates the ERKs
(extracellular-signal-regulated kinases) ERK1 and ERK2,
which appear to promote differentiation , leading to the
suggestion that the balance between STAT3 and ERK signals
is important in determining ES cell fate . More recently
it has been demonstrated that BMPs (bone morphogenetic
proteins) BMP2 and BMP4 collaborate with LIF to facilitate
Key words: bone morphogenetic protein (BMP), embryonic stem cell (ES cell), phosphoinositide
3-kinase (PI3K), pluripotency, self-renewal.
Abbreviations used: BMP, bone morphogenetic protein; ES, embryonic stem; ERas, ES cell-
expressed Ras; ERK, extracellular-signal-regulated kinase; GSK, glycogen synthase kinase; hES,
human ES; LIF, leukaemia inhibitory factor; mES, murine ES; mTOR, mammalian target of
rapamycin; Oct-4, octamer-binding protein-4; PI3K, phosphoinositide 3-kinase; PI(3,4,5)P3,
phosphatidylinositol 3,4,5-trisphosphate; PKB, protein kinase B; PTEN, phosphatase and tensin
homologue deleted on chromosome 10; SHP-2, Src homology 2 domain-containing protein
tyrosine phosphatase 2; STAT3, signal transducer and activator of transcription 3.
1To whom correspondence should be addressed (email email@example.com).
mES cell self-renewal, via BMP2/BMP4 activation of Smad4,
inducing expression of the Id transcriptional repressors,
which actively suppress neuronal differentiation . Wnt
signalling has also been implicated, largely as a result of the
use of the small molecule BIO [6-bromo-indirubin 3?-oxime;
an inhibitor of GSK-3 (glycogen synthase kinase 3)] that
facilitates activation of the canonical Wnt signalling pathway
. The Src tyrosine kinase also appears to play a role in
maintenance of self-renewal of mES cells .
Among the transcriptional regulators, Oct-4 (octamer-
in the maintenance of mES cell pluripotency . Oct-4 is
its expression being lost upon differentiation . Nanog
(from the Norse Tir nan Og meaning ‘ever young’) was
as a homeodomain protein that can maintain pluripotency of
mES cells independently of LIF. Recent large-scale screening
studies have mapped promoters co-bound by Nanog, Oct-
4 and Sox-2 in hES cells  and Nanog/Oct-4 co-bound
promoters in murine ES cells , demonstrating that Oct-
4 and Nanog target some of the same genes in ES cells.
Ivanova et al.  have identified a further five genes, Tcl1,
Tbx3, Esrrb, Dppa4 and Unigene Mm.343880, whose down-
regulation leads to loss of pluripotency of mES cells. Further
evidence suggests that epigenetic mechanisms also play a part
in determining ES cell fate . Thus it is increasingly clear
that a network of transcription factors and other regulators
influence and control the fate of both mES and hES cells .
Regulation of ES cell proliferation
Studies of murine and Rhesus monkey ES cells have
demonstrated that the cell cycle of ES cells is not subject to
the same regulatory checkpoints as the cell cycle of somatic
cells [18–20]. mES cells transit through the cell cycle very
rapidly (∼8 h), spending as little as 1–2 h in G1-phase and as a
C ?2007 Biochemical Society