Signaling to p53: ribosomal proteins find their way.

Inherently disparate cell growth and division, which are intimately coupled through a delicate network of intracellular and extracellular signaling, require ribosomal biogenesis. A number of events imparting instability to ribosomal biogenesis can cause nucleolar stress. In response to this stress, several ribosomal proteins bind to MDM2 and block MDM2-mediated p53 ubiquitination and degradation, resulting in p53-dependent cell cycle arrest. By doing so, the ribosomal proteins play a crucial role in connecting deregulated cell growth with inhibition of cell division. The ribosomal protein-MDM2-p53 signaling pathway provides a molecular switch that may constitute a surveillance network monitoring the integrity of ribosomal biogenesis.