signaling pathway

(noun)

Signal pathways occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response. There are two stages in this process:A signaling molecule activates a specific receptor protein on the cell membrane.A second messenger transmits the signal into the cell, eliciting a physiological response.In either step, the signal can be amplified. Thus, one signaling molecule can cause many responses.

Related Terms

Examples of signaling pathway in the following topics:

  • Binding Initiates a Signaling Pathway

    • Ligand binding to cell-surface receptors activates the receptor's intracellular components setting off a signaling pathway or cascade.
    • After the ligand binds to the cell-surface receptor, the activation of the receptor's intracellular components sets off a chain of events that is called a signaling pathway or a signaling cascade .
    • A single pathway can branch off toward different endpoints based on the interplay between two or more signaling pathways.
    • Another complicating element is signal integration of the pathways in which signals from two or more different cell-surface receptors merge to activate the same response in the cell.
    • An example of ligand initiated signaling pathways is when epidermal growth factor (EGF) binds to its receptor.

  • Cell Signaling and Cell Growth

    • Cell signaling pathways play a major role in cell division.
    • Activation of RTKs initiates a signaling pathway that includes a G-protein called RAS, which activates the MAP kinase pathway described earlier.
    • In addition, uncontrolled cell growth leads to cancer; mutations in the genes encoding protein components of signaling pathways are often found in tumor cells .
    • Signaling pathways control cell growth.
    • These pathways are controlled by signaling proteins, which are, in turn, expressed by genes.

  • Toll-Like Receptors

    • In addition, random germline mutagenesis with ENU has been used to decipher the TLR signaling pathways.
    • Four adapter molecules are known to be involved in signaling.
    • TLR signaling is divided into two distinct signaling pathways, the MyD88-dependent and TRIF-dependent pathway.
    • TRIF activates the kinases TBK1 and RIP1, which creates a branch in the signaling pathway.
    • Signaling pathway of Toll-like receptors.

  • Methods of Intracellular Signaling

    • Signaling pathway induction activates a sequence of enzymatic modifications that are recognized in turn by the next component downstream.
    • The induction of a signaling pathway depends on the modification of a cellular component by an enzyme.
    • One of the most common chemical modifications that occurs in signaling pathways is the addition of a phosphate group (PO4–3) to a molecule such as a protein in a process called phosphorylation .
    • The activation of second messengers is also a common event after the induction of a signaling pathway.
    • A-kinase regulates many vital metabolic pathways.

  • Termination of the Signal Cascade

    • Signal cascades convey signals to the cell through the phosphorylation of molecules by kinases.
    • Ligand binding to the receptor allows for signal transduction through the cell.
    • The chain of events that conveys the signal through the cell is called a signaling pathway or cascade.
    • Signaling pathways are often very complex because of the interplay between different proteins.
    • The aberrant signaling often seen in tumor cells is proof that the termination of a signal at the appropriate time can be just as important as the initiation of a signal.

  • Interferons

    • STAT activation initiates the most well-defined cell signaling pathway for all IFNs, the classical Janus kinase-STAT (JAK-STAT) signaling pathway.
    • In this pathway, JAKs associate with IFN receptors and, following receptor engagement with IFN, phosphorylate both STAT1 and STAT2.
    • In addition to the JAK-STAT pathway, IFNs can activate several other signaling cascades.
    • Both type I and type II IFNs activate a member of the CRK family of adaptor proteins called CRKL, a nuclear adaptor for STAT5 that also regulates signaling through the C3G/Rap1 pathway.
    • The phosphatidylinositol 3-kinase (PI3K) signaling pathway is also regulated by both type I and type II IFNs.

  • Cell Signaling and Cellular Metabolism

    • Metabolic regulation also allows organisms to respond to signals and interact actively with their environments.
    • Two closely-linked concepts are important for understanding how metabolic pathways are controlled.
    • Firstly, the regulation of an enzyme in a pathway is how its activity is increased and decreased in response to signals.
    • For example, an enzyme may show large changes in activity (i.e. it is highly regulated), but if these changes have little effect on the rate of a metabolic pathway, then this enzyme is not involved in the control of the pathway.
    • The result of one such signaling pathway affects muscle cells and is a good example of an increase in cellular metabolism.

  • Visual Processing

    • Visual signals are processed in the brain through several different pathways.
    • Within the nerves, different axons carry different parts of the visual signal.
    • When visual signals leave the thalamus, they travel to the primary visual cortex at the rear of the brain.
    • From the visual cortex, the visual signals travel in two directions.
    • Finally, there is the pathway from the retina to the suprachiasmatic nucleus (SCN) of the hypothalamus.

  • Neural Mechanisms (Cortex)

    • The processes that drive its functions aren't fully understood, but it works by sending signals to the spinal cord, which sends signals to the muscles it controls, such as the diaphragm and the accessory muscles for respiration.
    • This neural pathway is called the ascending respiratory pathway.
    • Note that voluntary respiratory nerve signals in the ascending respiratory pathway can be overridden by chemoreceptor signals from involuntary respiration.
    • During periods of perceived danger or emotional stress, signals from the hypothalamus take over the respiratory signals and increase the respiratory rate to facilitate the fight or flight response.
    • These three types of nerves continue the signal of the ascending respiratory pathway from the spinal cord to stimulate the muscles that perform the movements needed for respiration.

  • Proteolytic Degradation

    • The recognition of this ubiquitin signal by the proteasome results in degradation of the protein into its amino acids, which are then recycled and reused for the synthesis of new proteins.
    • The proteasomal degradation pathway is the major pathway utilized to ensure proteolytic degradation .
    • The lysosomal pathway, in comparison to the proteasomal pathway, is typically non-selective.
    • Schematic of the proteolytic degradation pathway that utilizes proteasomal complexes.
    • The protein is tagged with several ubiquitin signals that target the proteasome.