A regulatory protein that terminates signaling from G protein-coupled receptors, as well as stimulating other downstream signaling pathways.
abscisic acid
A plant hormone.
adenylyl cyclase
An enzyme that catalyzes the formation of cyclic AMP from ATP.
Akt
A protein-serine/threonine kinase that is activated by PIP3 and plays a key role in signaling cell survival.
autocrine signaling
A type of cell signaling in which a cell produces a growth factor to which it also responds.
autophosphorylation
A reaction in which a protein kinase catalyzes its own phosphorylation.
auxin
A plant hormone that controls many aspects of plant development.
brassinosteroid
A plant steroid hormone.
calmodulin
A calcium-binding protein.
CaM kinase
A member of a family of protein kinases that are activated by the binding of Ca2+/calmodulin.
cAMP phosphodiesterase
An enzyme that degrades cyclic AMP.
cAMP response element (CRE)
A regulatory sequence that mediates the transcriptional response of target genes to cAMP.
cAMP-dependent protein kinase
See protein kinase A.
Cdc42
A member of the Rho subfamily of small GTP-binding proteins.
cGMP phosphodiesterase
An enzyme that degrades cGMP.
corticosteroid
Steroid hormone produced by the adrenal gland.
CREB
Cyclic AMP response element-binding protein. A transcription factor that is activated by cAMP-dependent protein kinase.
crosstalk
A regulatory mechanism in which one signaling pathway controls the activity of another.
cyclic AMP (cAMP)
Adenosine monophosphate in which the phosphate group is covalently bound to both the 3′ and 5′ carbon atoms, forming a cyclic structure; an important second messenger in the response of cells to a variety of hormones.
cyclic GMP (cGMP)
Guanosine monophosphate in which the phosphate group is covalently bound to both the 3′ and 5′ carbon atoms, forming a cyclic structure; an important second messenger in the response of cells to a variety of hormones, and in vision.
cytokine
A growth factor that regulates blood cells and lymphocytes.
cytokine receptor superfamily
A family of cell surface receptors that act by stimulating the activity of intracellular protein-tyrosine kinases.
cytokinin
A plant hormone that regulates cell division.
diacylglycerol
A second messenger formed from the hydrolysis of PIP2 that activates protein kinase C.
ecdysone
An insect steroid hormone that triggers metamorphosis.
eicosanoid
A class of lipids, including prostaglandins, prostacyclins, thromboxanes, and leukotrienes, that act in autocrine and paracrine signaling.
Elk-1
A transcription factor that is activated by ERK phosphorylation and induces expression of immediate-early genes.
endocrine signaling
A type of cell-cell signaling in which endocrine cells secrete hormones that are carried by the circulation to distant target cells.
endorphin
A neuropeptide that acts as a natural analgesic.
enkephalin
A neuropeptide that acts as a natural analgesic.
epidermal growth factor (EGF)
A growth factor that stimulates cell proliferation.
ERK
A member of the MAP kinase family that plays a central role in growth factor-induced cell proliferation.
estrogen
A steroid hormone produced by the ovaries.
ethylene
A plant hormone responsible for fruit ripening.
FAK (focal adhesion kinase)
A nonreceptor protein-tyrosine kinase that plays a key role in integrin signaling.
feedback loop
A regulatory mechanism in which a downstream element of a signaling pathway controls the activity of an upstream component of the pathway.
feedforward relay
A regulatory mechanism in which one element of a signaling pathway stimulates a downstream component.
G protein
A family of cell signaling proteins regulated by guanine nucleotide binding.
G protein-coupled receptor
A receptor characterized by seven membrane-spanning α helices. Ligand binding causes a conformational change that activates a G protein.
gibberellin
A plant hormone.
glucocorticoid
A steroid produced by the adrenal gland that acts to stimulate production of glucose.
growth factor
A polypeptide that controls animal cell growth and differentiation.
GTPase-activating protein
A protein that stimulates GTP hydrolysis by the small GTP-binding proteins.
guanine nucleotide exchange factor
A protein that acts on small GTP-binding proteins to stimulate the exchange of bound GDP for GTP.
guanylyl cyclase
An enzyme that catalyzes the formation of cyclic GMP from GTP.
Hedgehog
A secreted signaling molecule that stimulates a pathway regulating cell fate during embryonic development.
heterotrimeric G protein
A guanine nucleotide-binding protein consisting of three subunits.
hormone
A signaling molecule produced by an endocrine gland that acts on cells at distant body sites.
IκB
An inhibitory subunit of NF-κB transcription factors.
immediate-early gene
A gene whose transcription is rapidly induced in response to growth factor stimulation.
inositol 1,4,5-trisphosphate (IP3)
A second messenger, formed from the hydrolysis of PIP2, that signals the release of calcium ions from the endoplasmic reticulum.
intracellular signal transduction
A chain of reactions that transmits chemical signals from the cell surface to their intracellular targets.
JAK/STAT pathway
A signaling pathway in which STAT transcription factors are activated as a result of phosphorylation by members of the JAK family of protein kinases.
Janus kinase (JAK)
A family of nonreceptor protein-tyrosine kinases associated with cytokine receptors.
leukotriene
An eicosanoid synthesized from arachodonic acid.
MAP kinase
A family of mitogen-activated protein-serine/threonine kinases that are ubiquitous regulators of cell growth and differentiation.
MEK (MAP kinase/ERK kinase)
A dual-specificity protein kinase that phosphorylates and activates members of the ERK family of MAP kinases.
membrane-anchored growth factor
A growth factor associated with the plasma membrane that functions as a signaling molecule during cell-cell contact.
mineralocorticoid
A steroid hormone produced by the adrenal gland that acts on the kidney to regulate salt and water balance.
mTOR
A protein kinase involved in regulation of protein synthesis in response to growth factors, nutrients, and energy availability.
nerve growth factor (NGF)
A polypeptide growth factor that regulates the development and survival of neurons.
neurohormone
Peptides that are secreted by neurons and act on distant cells.
neuropeptide
A peptide signaling molecule secreted by neurons.
neurotransmitter
A small, hydrophilic molecule that carries a signal from a stimulated neuron to a target cell at a synapse.
neurotrophin
A member of a family of polypeptides that regulates neuron development and survival.
NF-κB
A family of transcription factors that are activated in response to a variety of stimuli.
nonreceptor protein-tyrosine kinase
An intracellular protein-tyrosine kinase.
Notch
A transmembrane receptor in a signaling pathway that regulates cell fate as a result of cell-cell interactions during development.
nuclear receptor superfamily
A family of transcription factors that includes the receptors for steroid hormones, thyroid hormone, retinoic acid, and vitamin D3.
paracrine signaling
Local cell-cell signaling in which a molecule released by one cell acts on a neighboring target cell.
peptide hormone
A signaling molecule composed of amino acids.
phosphatidylinositide 3-kinase (PI 3-kinase)
An enzyme that phosphorylates PIP2, yielding the second messenger phosphatidylinositol 3,4,5-trisphosphate (PIP3).
phosphatidylinositol 3,4,5-trisphosphate (PIP3)
A second messenger formed by phosphorylation of PIP2.
phosphatidylinositol 4,5-bisphosphate (PIP2)
A minor phospholipid component of the inner leaflet of the plasma membrane. Hormones and growth factors stimulate its hydrolysis by phospholipase C, yielding the second messengers diacylglycerol and inositol trisphosphate.
phospholipase C
An enzyme that hydrolyzes PIP2 to form the second messengers diacylglycerol and inositol trisphosphate.
plant hormone
Member of a group of small molecules that coordinate the responses of plant tissues to environmental signals.
platelet-derived growth factor (PDGF)
A growth factor released by platelets during blood clotting to stimulate the proliferation of fibroblasts.
progesterone
A steroid hormone produced by the ovaries.
prostacyclin
An eicosanoid formed from prostaglandin H2.
prostaglandin
A family of eicosanoid lipids involved in signaling inflammation.
protein kinase A
A protein kinase regulated by cyclic AMP.
protein kinase C
Member of a family of protein-serine/threonine kinases that are activated by diacylglycerol and Ca2+ and function in intracellular signal transduction.
protein-serine/threonine kinase
A protein kinase that phosphorylates serine and threonine residues.
protein-tyrosine phosphatase
An enzyme that removes the phosphate groups from phosphotyrosine residues.
PTB domain
A protein domain that binds phosphotyrosine-containing peptides.
Rac
A small GTP-binding protein involved in regulation of the actin cytoskeleton.
Raf
A protein-serine/threonine kinase (encoded by the raf oncogene) that is activated by Ras and leads to activation of the ERK MAP kinase.
Ras
A family of small GTP binding proteins (encoded by the ras oncogenes) that couple growth factor receptors to intracellular targets, including the Raf protein-serine/threonine kinase and the ERK MAP kinase pathway.
receptor protein-tyrosine kinase
A membrane-spanning protein-tyrosine kinase that is a receptor for extracellular ligands.
retinoic acid
A signaling molecule synthesized from vitamin A.
retinoid
A molecule related to retinoic acid.
Rho
A family of small GTP-binding proteins involved in regulation of the cytoskeleton.
rhodopsin
A G protein-coupled photoreceptor in retinal rod cells that activates transducin in response to light absorption.
ryanodine receptor
A type of calcium channel in muscle and nerve cells that opens in response to changes in membrane potential.
scaffold protein
A protein that binds to components of signaling pathways, leading to their organization in specific signaling cassettes.
second messenger
A compound whose metabolism is modified as a result of a ligand-receptor interaction; it functions as a signal transducer by regulating other intracellular processes.
secondary response gene
A gene whose induction following growth factor stimulation of a cell requires protein synthesis.
serum response element (SRE)
A regulatory sequence that is recognized by the serum response factor and mediates the transcriptional induction of many immediate-early genes in response to growth factor stimulation.
serum response factor (SRF)
A transcription factor that binds to the serum response element.
SH2 domain
A protein domain of approximately 100 amino acids that binds phosphotyrosine-containing peptides.
signaling network
The interconnected network formed by the interactions of multiple signaling pathways within a cell.
Smad
A family of transcription factors activated by TGF-β receptors.
STAT protein
Member of a family of transcription factors that have an SH2 domain and are activated by tyrosine phosphorylation, which promotes their translocation from the cytoplasm to the nucleus.
steroid hormone
A member of a group of hydrophobic hormones, including estrogen and testosterone, that are derivatives of cholesterol.
testosterone
A steroid hormone produced by the testis.
thromboxane
An eicosanoid involved in blood clotting.
thyroid hormone
A hormone synthesized from tyrosine in the thyroid gland.
Toll-like receptor
Member of a family of receptors that recognize a variety of molecules associated with pathogenic bacteria and viruses.
transducin
A G protein that stimulates cGMP phosphodiesterase when it is activated by rhodopsin.
transforming growth factor β (TGF-β)
A polypeptide growth factor that generally inhibits animal cell proliferation.
tumor necrosis factor (TNF)
A polypeptide growth factor that induces inflammation and programmed cell death.
Wnt
A secreted signaling molecule that stimulates a pathway regulating cell fate during embryonic development.
