THE NEUROTROPHIC FACTORS SIGNAL TRANSDUCTION CASCADE WITH SPECIAL REFERENCE TO NGF
In principle, a pathway for activating a series of changes in the cell phenotype consists in the following stages: growth factors->growth factors receptors (tyrosine kinase) ->Ras-> kinase cascade (serine/threonine kinases) -> transcription factors -> protein expression. When a growth factor interacts with its receptor, it activates a tyrosine kinase activity. The signal passes along a cascade of kinases, in which one kinase phosphorilates a target protein, which is itself a kinase that is activated by phosphorilation. In the cascade presented above Ras is involved in making this switch. The NGF and other growth factors finally determine the expression of several proteins. A signal transduction pathway, of course, is likely to branch at several stages, so that an initial stimulus may trigger a variety of responses.