ABSTRACT
Growth factors, polypeptide signaling molecules that play a prominent role in intercellular communication, are critical regulators o f cell growth, prolifer ation, differentiation, and survival (reviewed in Ref. 1). Growth factors include both soluble and membrane-anchored polypeptides acting in an autocrine or paracrine manner (1,2). Cytokines that specifically regulate hematopoiesis and immune cell function represent a special functional class o f growth factors that will not be covered in this chapter. Growth factors exert their effects by binding to specific cell-surface receptors, triggering a cascading network o f events that transduce the extracellular signal to the nucleus, resulting in altered gene expression and the characteristic growth factor response (re viewed in Refs. 3-6). Activation or modulation o f the activity o f various intracellular signal-transducing molecules, often by phosphorylation/dephosphorylation, is a central theme in the mechanism by which growth factors effect a response (reviewed in Refs. 3 and 6).
