Regulation of STAT-dependent pathways by growth factors and cytokines

Polypeptide growth factors and cytokines elicit their effects by activating specific cell-surface receptors, thereby initiating signaling cascades that culminate in the induction of specific subsets of genes. Initially identified as the primary mediators of interferon-dependent signaling, JAKs and STATs are now known to be utilized by many different extracellular signaling proteins. In this report we describe how JAK-STAT pathways transduce signals initiated by both cytokines and growth factors, focusing on how specificity is achieved through STAT-receptor interactions and on how receptor-associated kinases function in STAT activation. We also summarize current information on interactions between signaling pathways, particularly STAT-Ras cross-talk and the relative importance of these two pathways in regulating the transcription of target genes.