Revisiting the nucleolus: from marker to dynamic integrator of cancer signaling.

Key signaling pathways (such as phosphoinositide 3-kinase, Myc, and RAS) act as sensors of energy, stress, and nutrient availability and integrate these inputs to directly control ribosome production and gene expression at the translational level. This activity is normally directly coupled to cell growth, division, and survival. However, it remains poorly understood the extent to which changes in ribosome number and nucleolar integrity downstream of these key signaling pathways contribute to their oncogenic activity. Emerging studies provide interesting insight into how deregulations in RNA polymerase I activity may lead to tumorigenesis and suggest that new drugs targeting ribosomal DNA transcription may hold great promise for the treatment of cancer.