Derived Neurotrophic Factor), NT-4 (for Neurotrophin-4) and NT-3 (for Neurotrophin-3). While TrkA mediated the effects of NGF, TrkB is bound and activated by BDNF , NT-4 and NT-3. Further, TrkC binds and is activated by NT-3. TrkB binds BDNF and NT-4 more strongly than it binds NT-3. TrkC binds NT-3 more strongly than TrkB does. There is one other NT-3 receptor family besides the Trks (TrkC & TrkB), called the "LNGFR" (for "low affinity nerve growth factor receptor"). As opposed to TrkC, the LNGFR plays a somewhat less clear role in NT-3 biology. Some researchers have shown the LNGFR binds and serves as a "sink" for neurotrophins. Cells which express both the LNGFR and the Trk receptors might therefore have a greater activity - since they have a higher "microconcentration" of the neurotrophin. It has also been shown, however, that the LNGFR may signal a cell to die via apoptosis - so therefore cells expressing the LNGFR in the absence of Trk receptors may die rather than live in the presence of a neurotrophin. It has been demonstrated that NTRK3 is a dependence receptor, meaning that it can be capable of inducing proliferation when it binds to its ligand NT-3, however, the absence of the NT-3 will result in the induction of apoptosis by NTRK3. Role in disease With the past of the years, lot of studies have shown that the lack or deregulation of TrkC or the complex TrkC:NT-3 can be associated with different diseases. One study have demonstrated that mice defective for either NT-3 or TrkC display severe sensory defects. These mice have normal nociception, but they are defective in proprioception, the sensory activity responsible for localizing the limbs in space. The reduction of TrkC expression has been observed in neurodegenerative diseases, including Alzheimer's (AD), Parkinson's (PD), and Huntington's diseases (HD). The role of NT-3 was also therapeutically studied in models of amyotrophic lateral sclerosis (ALS) with loss of spinal cord motor neurons that express TrkC Moreover, it has been shown that TrkC plays a role in cancer. The expression and function of Trk subtypes are dependent on the tumor type. For example, in neuroblastoma, TrkC expression correlates with a good prognosis, but in breast, prostate and pancreatic cancers, the expression of the same TrkC subtype is associated with cancer progression and metastasis. Role in cancer Although originally identified as an oncogenic fusion in 1982, only recently has