Endosomal signaling and oncogenesis.

The endosomal system provides a route whereby nutrients, viruses, and receptors are internalized. During the course of endocytosis, activated receptors can accumulate within endosomal structures and certain signal-transducing molecules can be recruited to endosomal membranes. In the context of signaling and cancer, they provide platforms within the cell from which signals can be potentiated or attenuated. Regulation of the duration of receptor signaling is a pivotal means of refining growth responses in cells. In cancers, this is often considered in terms of mutations that affect receptor tyrosine kinases and maintain them in hyperactivated states of dimerization and/or phosphorylation. However, disruption to the regulatory control exerted by the assembly of protein complexes within the endosomal network can also contribute to disease among which oncogenesis is characterized in part by dysregulated growth, enhanced cell survival, and changes in the expression of markers of differentiation. In this chapter, we will discuss the role of proteins that regulate in endocytosis as tumor suppressors or oncogenes and how changing the fate of internalized receptors and concomitant endosomal signaling can contribute to cancer.