NT-4 is a member of the structurally related neurotrophin family of proteins, which includes β-NGF, BDNF and NT-3 (1). NT-4 is expressed in a number of cell types and tissues, including neuronal cells, normal breast epithelial cells, melanocytes, activated T cells, and granulocytes (1-5). NT-4 is required for the development of peripheral sensory neurons (6,7). NT-4 may be important for the development of long term memory (8). Increased NT-4 expression in melanoma cells promotes cell proliferation and migration (5). NT-4 is secreted from cells as a precursor protein, which is proteolytically cleaved into the mature form (1). NT-4 signaling is mediated through two distinct receptors, the neurotrophin receptor p75NTR and the Trk tyrosine kinase receptor TrkB. While all neurotrophins bind to the p75NTR receptor, NT-4 preferentially binds to the TrkB receptor (1).
