Stem Cell Signalling Flashcards
What is a stem cell?
A cell which can differentiate and self renew
What cells are able to differentiate into any cell type in the body?
Embryonic stem (ES) cells and induced pluripotent stem (iPS) cells
What are the medical applications of ES and iPS cells?
Regenerative therapies
Disease remodelling
Remodelling organ toxicities
What are iPS cells?
They are embryonic like cells but they can be taken from any tissue (somatic cells)
Example of a regenerative therapy this could be used for?
Neurodegenerative disease - make new neurons
Where are ES cells derived from?
Blastocytes (pre-implantation embryos)
What does pluripotent mean?
All germ layers - ectoderm, mesoderm and endoderm
Why can ES and iPS be maintained indefinitely in vitro?
because of their ability to self renew
What type of cell cycle do ES and iPS cells have?
Fast cycling due to their constant self-renewal and therefore do not have all the checkpoints found in normal cells
What extracellular signals control stem cell self-renewal and differentiation?
GFs
Cytokines
Cell-Matrix and Cell-cell interactions
What signalling pathways control stem cell self-renewal and differentiation?
Protein kinases
E3 Ub ligases
Post translational modifications
What cell specific gene expression programmes control stem cell self-renewal and differentiation?
Transcription factors
Epigenetic modifiers
Non-coding RNAs
What are the 3 main pathways in Stem cell signal transduction?
The LIF pathway
A differentiation switch - ERK1/2 signalling
ERK5 pathway
What does LIF stand for?
Leukaemia inhibitory factor pathway
What does the LIF pathway promote?
Pluripotency and self renewal
What does ERK1/2 signalling promote?
Differentiation, not self renewal
What does ERK5 signalling promote?
Self renewal
What is LIF?
A cytokine which activates IL-6 family receptors (LIFR and IL-6R)
What were ES cells originally cultured on?
MEF ‘feeders’ layer - they secrete LIF
How does LIF induce self renewal?
LIF bind to LIFR -> dimers of LIFR and gp130 join together through a conformational change -> There is a JAK on LIFR and gp130 which are brought together -> JAKs phosphorylate each other -> JAK on LIFR phosphorylates the gp130 -> provides a tyrosine docking site -> STAT3 recruitment via its SH2 domain -> STAT3 tyrosine phosphorylation -> STAT3 forms a homodimer -> detaches from the receptor and translocates to the nucleus -> binds to DNA and recruits transcriptional activation components -> drive gene expression
What activates ERK1/2 signalling in ES cells?
Fibroblast growth factor (FGF) 4
What does ERK1/2 do in the ES cells?
Switches off the stem cell genes and induces expression of lineage specific factors
Name a TF which promotes self renewal
Nanog
Name a TF which promotes differentiation into neurons
Sox1
How does ERK1/2 activation induce differentiation?
The FGF receptor is stimulated -> SOS1 activates Ras -> Ras converted into GTP bound form -> Recruit Raf -> Raf is phosphorylated by other kinases -> Raf phosphorylates and activates MEK1/2 -> MEK1/2 phosphorylate and activate ERK1/2 -> ERK1/2 phosphorylates TFs to shut down stem cell genes, can phosphorylate other transcriptional regulators and epigenetic modifiers to induce chromatin remodelling
How is SOS regulated?
It is autoinhibited in unstimulated cells
What is SOS in a complex with in unstimulated cells?
DH
PH
REM:CDC25
GRB2
What do DH domains have and what do they bind?
Lipid binding domains
Phospholipids in the membrane
What do PH domains bind to?
Phospholipids in the membrane
What does REM:CDC25 contain?
The catalytic activity
What part of the SOS unstimulated complex is autoinhibited?
REM:CDC25
What happens to the SOS inhibitory complex when FGFR is activated?
GRB2 binds to the phospho-tyrosine binding sites on the receptor
REM:CDC25 associates with the Ras
and the other components associate with the phospholipids in the membrane
How do ERK5 induce self renewal?
Do not know what stimulates it -> Activation of MEKK2 and 3 through dimerisation and phosphorylation of each other -> Phosphorylation and activation of MEK5 -> Phosphorylation and activation of ERK5 -> ERK5 phosphorylates itself on the C-terminal region -> switches on stem cell gene transcription
