Short definitions of cell-signaling terms used across autocrine.com. For fuller explanations see the Autocrine Signaling guide and the articles.
- Autocrine signaling
- Signaling in which a cell secretes a ligand that acts on receptors of the same cell.
- Paracrine signaling
- Signaling in which a ligand diffuses a short distance to act on neighbouring cells.
- Endocrine signaling
- Signaling by hormones released into the bloodstream to act on distant target cells.
- Juxtacrine signaling
- Contact-dependent signaling between adjacent cells, for example Notch-Delta signaling.
- Intracrine signaling
- Action of a signaling molecule inside the cell that produced it, without secretion.
- Ligand
- A molecule that binds specifically to a receptor, such as a growth factor, cytokine or hormone.
- Receptor
- A protein, usually on the cell surface or in the cytoplasm/nucleus, that binds a ligand and transmits a signal.
- Receptor tyrosine kinase (RTK)
- A cell-surface receptor whose intracellular domain phosphorylates tyrosine residues after ligand binding; examples include EGFR, PDGFR, FGFR, VEGFR and IGF1R.
- Dimerization
- Pairing of two receptor molecules after ligand binding, a key activation step for many RTKs and cytokine receptors.
- Autophosphorylation
- Phosphorylation of a kinase by itself or its partner in a receptor dimer, creating docking sites for signaling proteins.
- Growth factor
- A secreted protein that stimulates cell growth, proliferation, survival or differentiation, such as EGF, PDGF, FGF, VEGF or IGF.
- Cytokine
- A small secreted protein that regulates immune and inflammatory responses, such as interleukins, interferons and TNF.
- EGFR
- Epidermal growth factor receptor (ERBB1/HER1), an RTK activated by EGF, TGF-alpha and related ligands; frequently involved in autocrine loops in carcinomas.
- TGF-alpha
- Transforming growth factor alpha, an EGFR ligand often co-expressed with EGFR in tumour cells.
- TGF-beta
- Transforming growth factor beta, a cytokine that signals through serine/threonine kinase receptors and SMAD proteins; distinct from TGF-alpha.
- IL-2
- Interleukin-2, a cytokine produced by activated T cells that drives their own proliferation, a textbook autocrine loop.
- CD25 (IL-2R alpha)
- The high-affinity alpha chain of the IL-2 receptor, up-regulated on activated and regulatory T cells.
- JAK-STAT pathway
- Cytokine-receptor signaling in which Janus kinases phosphorylate STAT transcription factors, which then move to the nucleus.
- MAPK/ERK pathway
- The Ras-Raf-MEK-ERK kinase cascade that links many growth factor receptors to gene expression and proliferation.
- PI3K/AKT/mTOR pathway
- A signaling axis downstream of RTKs that promotes cell survival, growth and metabolism.
- Wnt/beta-catenin pathway
- A developmental pathway in which Wnt ligands stabilise beta-catenin, which then activates target genes; important in stem cells and colorectal cancer.
- SMAD proteins
- Transcription factors that carry TGF-beta and BMP signals from the receptor to the nucleus.
- Second messenger
- A small intracellular molecule, such as cAMP, Ca2+ or IP3, that relays and amplifies a receptor signal.
- Negative feedback
- A mechanism in which pathway output dampens its own activation, for example ERK phosphorylating upstream components.
- Receptor internalization
- Uptake of ligand-bound receptors into the cell by endocytosis, which can end or redirect signaling.
- Monoclonal antibody
- A laboratory-made antibody that binds one target, used to block ligands or receptors (for example cetuximab against EGFR).
- Tyrosine kinase inhibitor (TKI)
- A small-molecule drug that blocks the kinase activity of a receptor or intracellular kinase.
- Ligand trap
- A soluble receptor-based protein that binds and neutralises a ligand before it reaches its receptor.