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. Author manuscript; available in PMC: 2016 Apr 1.
Published in final edited form as: Surg Oncol Clin N Am. 2015 Jan 24;24(2):347–358. doi: 10.1016/j.soc.2014.12.011

Figure 4.

Figure 4

Simplified diagram on the regulation of the RAS superfamilty of small GTPases and the role of NF1. RAS proteins become active versus inactive if bound to GTP and GDP, respectively. Extracellular growth factor signals (red circle) are transmitted through growth factor receptors (light blue) to guanine nucleotide exchange factors (GEF), which activate RAS (red) by exchanging GDP for GTP. In contrast, GTPase activating proteins, including NF1, tend to keep RAS proteins in their inactive state (light blue). Please note the promiscuity of RAS signaling which activate several signaling pathways, including the MAPK as well as the PI3K-Akt pathway.