Download IX. Cell Signaling

Cell Signaling
A.
B.
C.
D.
Types of Cell Signaling
Intracellular Receptor Signaling: Steroid
Hormones
Cell Surface Receptors: Types
Cell Surface Receptors: G-protein
linked receptors
A.
Types of Cell
Signaling
• Direct cell-cell signaling vs.
signaling via secretion
A.
Types of Cell
Signaling
• Cell surface receptors vs.
Intracellular receptors
A.
Types of Cell
Signaling
• Three forms of signaling by secreted
molecules
– Paracrine
– Synaptic
– Endocrine
A.
Types of Cell
Signaling
• Gap junctions
A.
Types of Cell
Signaling
• The same signal can produce different
effects in different cells
A.
Types of Cell
Signaling
• Proper signaling generally depends
on a signal molecule being degraded
rapidly
A.
Types of Cell
Signaling
• Types of Signals based on
Where they Bind
– To an intracellular receptor:
e.g. Steroid hormones
– To a cell-surface receptor: G-protein
linked, enzyme-linked, or ion channellinked
B. Intracellular Receptor
Signaling: Steroid Hormones
• Overview of Steroid Hormone Action:
– Steroid hormone (small, hydrophobic) is
secreted by glandular cells and released into
bloodstream (usually transported via shuttle
proteins)
– The hormone enters the cytoplasm of cells
– In the cytoplasm of target cells, the hormone
binds to steroid hormone receptor protein
B. Intracellular Receptor
Signaling: Steroid Hormones
• Overview of Steroid . . . (cont.):
– The steroid-receptor conplex is translocated
into the nucleus, where it activates the
transcription of the primary response genes
– Transcription of the primary response genes,
followed by translation, results in the
production of primary response proteins
B. Intracellular Receptor
Signaling: Steroid Hormones
• Overview of Steroid . . . (cont.):
– The primary response proteins usually inhibit
further transcription of their own genes, and
they may activate transcription of secondary
response genes.
C. Cell Surface Receptors:
Types
• Three known classes of cell surface
receptors
– Ion channel-linked, G-protein-linked,
Enzyme-linked
– An activated cell-surface receptor
triggers a phosphorylation cascade
D. Cell Surface Receptors:
G-protein linked
receptors
• Largest family of cell surface
receptors
– Different ones respond to a wide variety
of mediators including different
hormones, neurotransmitters, local
mediators
– Examples: Receptors to epinephrine,
acetylcholine, serotonin
B.
G-linked Receptors
• What do G-protein receptors do?
– G-protein receptors activate trimeric Gprotein
– Activated G-protein alters the cellular
concentration of a “second messenger”:
usually cyclic AMP or Ca2+
– The second messenger activates a protein
kinase enzyme
– The protein kinase phosphorylates
another enzyme and alters its activity
B.
G-linked Receptors
• Trimeric G-proteins disassemble
when activated
– Three chains: a, b, and g
 a chain binds and hydrolyzes GTP
 b & g chains form a tight complex bg that
anchors G-protein to the plasma
membrane
B.
G-linked Receptors
• Trimeric G-proteins disassemble
when activated
– Inactive G-protein has a bound GDP
– When activated: GDP dissociates, new
GTP is bound
– This causes a to dissociate from bg
 a binds to adenylate cyclase, altering its
activity
– Gs protein stimulates activates adenylate
cyclase, Gi inhibits it
B.
G-linked Receptors
• Action of epinephrine on glycogen
metabolism
– Epinephrine (adrenaline) is released
from the adrenal gland in times of stress.
It has two overall actions on glycogen
metabolism: it inhibits glycogen
synthesis, and it promotes glycogen
breakdown
– This is mediated by a protein
phosphorylation cascade