Newly identified aspects of tumor suppression by RB.

The retinoblastoma (RB) tumor suppressor belongs to a cellular pathway that plays a crucial role in restricting the G1-S transition of the cell cycle in response to a large number of extracellular and intracellular cues. Research in the last decade has highlighted the complexity of regulatory networks that ensure proper cell cycle progression, and has also identified multiple cellular functions beyond cell cycle regulation for RB and its two family members, p107 and p130. Here we review some of the recent evidence pointing to a role of RB as a molecular adaptor at the crossroads of multiple pathways, ensuring cellular homeostasis in different contexts. In particular, we discuss the pro- and anti-tumorigenic roles of RB during the early stages of cancer, as well as the importance of the RB pathway in stem cells and cell fate decisions.