Cell signaling

Cells communicate and respond to the extracellular environment through a process designated signal transduction. Signal molecules bind to transmembrane receptors that span the cell membrane. The interaction of signal molecules with components of receptors located outside the cell modifies the intracellular components of the receptors. An environmental signal is thereby transduced into a cascade of regulatory steps that control genes which control cell proliferation and specialized properties of cells.

In some signaling pathways, scaffold proteins assemble signaling molecules into complexes for the initial passage of information from the transmembrane receptor to relay and adaptor proteins. Subsequent steps in the signaling process amplify and integrate signals. A chain of intracellular signaling proteins processes regulatory information through the cytoplasm and into the cell nucleus to activate or suppress genes. In other signaling pathways the regulatory cascades are abbreviated. The transduction of regulatory information from the intracellular component of the transmembrane receptor is more direct, circumventing intermediary steps in information transfer. At an early stage in the signaling process a signaling protein enters the nucleus and interacts directly with genes to modify expression.

Many cancer cells exhibit defects in one or more steps of signaling cascades that alter control of
cell growth, specialized cell properties, cell–cell communication, cell motility, and cell adhesion. The components of signaling pathways that are modified in tumor cells are targets for treatments that are effective and specific.