Pak to the future.

Members of the Pak family of serine/threonine kinases serve as targets for the small GTP-binding proteins Cdc42 and Rac and have been implicated in a wide range of biological activities. Recently, some exciting developments help elaborate the regulation of Pak activity and identify downstream signalling targets. These include the discovery of the Cool/Pix and Cat proteins, which modulate Pak signalling, and downstream kinases that modulate the organization of the actin cytoskeleton or gene expression. We present these recent findings and consider how these new regulators and targets could explain some of the cellular effects that have been attributed to Pak family members.