Biological process

extrinsic apoptotic signalling pathway in absence of ligand

The series of molecular signals in which a signal is conveyed from the cell surface to trigger the apoptotic death of a cell. The pathway starts with withdrawal of a ligand from a cell surface receptor, and ends when the execution phase of apoptosis is triggered.

dependence receptor signaling pathway

For dependence receptors, absence of a ligand or withdrawal of a ligand from a receptor acts as a signal. An example of 'extrinsic apoptotic signaling pathway in absence of ligand' is withdrawal of a growth factor such as NGF, even if traditionally apoptosis induced via growth factor withdrawal has been classified as an instance of intrinsic apoptosis. See an example in PMID:19767770. Ligands whose withdrawal or absence induce apoptosis should be annotated to GO:2001239 'regulation of extrinsic apoptotic signaling pathway in absence of ligand', rather than to the pathway term itself. Examples of gene products that may be annotated to GO:0097192 'extrinsic apoptotic signaling pathway in absence of ligand' include dependence receptors such as DCC or UNC5B, which relay lethal signals in the absence of their ligand (netrin-1). In the case of DCC and UNC5B, the signaling proceeds through the assembly of a DRAL- and TUCAN- (or NLRP1-) containing caspase-9-activating complex or by the dephosphorylation-mediated activation of death-associated protein kinase 1 (DAPK1) by UNC5B-bound protein phosphatase 2A (PP2A), respectively. DAPK1 can mediate the direct activation of executioner caspases or favor MOMP (reviewed in PMID:21760595). Also see PMID:21172653 (annotations to UNC5B and PR65beta, UniProt symbols O08722, PPP2R1B and P30154).