Biology Reference
In-Depth Information
Chemokines,
hormones,
transmitters
(e.g., interleukins,
serotonin)
Survival factors
(e.g., IGF 1)
Growth factors
(e.g., TGF α, EGG)
Extracellular
matrix
GPCR
Integrins
RTK
RTK
cdc42
Fyn/Shc
Wnt
PLC
Grb2/SOS
Dishevelled
GSK-3 β
PI3K
G-Protein
Ras
Raf
MEK
FAK
Src
Akt
PKC
NF-kB
Adenylate
cyclase
Hedgehog
Akk α
APC
PKA
MEKK
MAPK
MKK
β -catenin
Cytokines
(e.g., EPC)
IkB
JAKs
STAT3,5
TCF
Myc: Mad:
Max Max
ERK
JNKs
β -catenin:TCF
Bd-xL
Fos
Jun
Cytochrome C
Caspase 9
CREB
CyclD
Gli
p16
Rb
CDK4
p15
E2F
Gene regulation
CydE
CDK2
p27
Caspase 8
Apoptosis
ARF
p21
Cell
proliferation
mdm2
FADD
Bd-2
p53
Bad
Abnormality
sensor
Mt
Bax
FasR
Bim
Death factors
(e.g. Fasl, Tnf)
Figure 2.12 An overview of major signal transduction pathways.
Source : From http://en.wikipedia.org/wiki/File:Signal_transduction_v1.png .
cells' epigenetic control of gene expression enable the organism to maintain homeo-
static values of variables despite the disturbances caused by the interference of exter-
nal and internal agents.
The last element of the signal cascade acts as a ligand for the receptor molecule
to which it binds. When the ligand has a low molecular weight (e.g., steroids and
retinoic acids), it passes through the cell and nuclear membranes, where it binds
to a specific nuclear receptor. The ligand changes the conformation of the nuclear
receptor, transforming it into an active form of the TF that binds to specific regula-
tory sequences by inducing the expression of a specific gene. However, since they
are too big to allow them to travel through the cell membrane, most protein ligands
(e.g., hormones and growth factors) bind to their specific cell membrane receptors.
The binding of the ligand changes the conformation of the intracellular part of the
receptor molecule, thus activating it and triggering sequential events in the elements
of the transduction pathway that ends with the activation of one gene or a number of
genes ( Figure 2.13 ). The receptors serve the cell as antennae for capturing extracel-
lular signals.
All major transduction pathways in metazoans are activated by extracellular sig-
nals such as hormones, growth factors, ECM proteins, and neurotransmitters, which
in turn are neurally regulated. The overwhelming majority of these signals are the
final elements of signal cascades originating in the nervous system. All hormones of
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