POLYPEPTIDE GROWTH-FACTORS - STRUCTURE, FUNCTION AND MECHANISM OF ACTION

Polypeptide growth factors are a diverse group of hormone-like agents that regulate growth and differentiation through cell surface receptor s. They are generally represented by homologous families containing se veral members with distinct overlapping receptor interactions and henc e, responsive tissue specificities. Similarly, their receptors are als o clustered in family groups of sequence-related proteins. The neurotr ophin group, characterized by its typical prototypical member nerve gr owth factor (NGF), has four members which interact variably with three receptors of the trk family. The activation of their tyrosine kinases initiates the characteristic responses. In PC12 cells, stimulation by NGF leads to activation of non-receptor tyrosine kinases and several phospholipid dependent pathways. The sum of these signals induce a var iety of immediate early response genes that govern the phenotypic resp onse However, the minimum pathway (and its essential components) is no t yet fully defined.