Figure 2.

Signaling Pathways. A simplified overview of signal transduction pathways altered in CSCs. In the CSC literature, an emphasis has been placed on those with a role to play in normal development (Wnt, Hedgehog, Notch). Gene expression that follows stimulation or activation of a given receptor is shown (e.g., Wnt). In some instances, subsequent crosstalk with particular pathways is noted (TNF). Additionally, a tumor cell must produce energy and essential metabolites such as nucleotides, fatty acids, and amino acids as building blocks for maintenance. Oxygen gradients are also crucial and likely vary within any given region of a tumor. Growth factors, extracellular matrix and hormones are not depicted, but provide a context in which the signal transduction pathways act.