STATs and MAPKs: obligate or opportunistic partners in signaling.

Ligand binding to cellular receptors initiates a series of signal transducing cascades that are essential to cellular responses. The Ras pathway is activated in response to a variety of ligands and has been extensively studied. More recently, a novel family of transcription factors (Stats) has been found to be activated in response to many ligands. Three recent publications have presented evidence to suggest that these two pathways converge at the level of modulation of Stat function by phosphorylation by MAP kinases. However, each proposes radically different models that are not easily reconciled but invite further experimentation.