Cell Signaling
A. Types of Cell Signaling
B. Intracellular Receptor Signaling: Steroid Hormones
C. Cell Surface Receptors: Types
D. Cell Surface Receptors: G-protein
linked receptors
A. Types of Cell Signaling• Three forms of signaling by secreted
molecules
– Paracrine
– Synaptic
– Endocrine
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 channel-linked
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 G-protein
– 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
• 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
SUMMARY
1. Types of Cell Signaling
2.Intracellular Receptor Signaling: Steroid Hormones
3.Cell Surface Receptors: Types
4.Cell Surface Receptors: G-protein
linked receptors