Increasing Complexity of the Ras Signaling Pathway

Ras is a key regulator of cell growth in all eukaryotic cells. Genetic, biochemical, and molecular studies inCaenorhabditis elegans, Drosophila, and mammalian cells have positioned Ras centrally in signal transduction pathways that respond to diverse extracellular stimuli, including peptide growth factors, cytokines, and hormones. The biological activity of Ras is controlled by a regulated GDP/GTP cycle. Guanine nucleotide exchange factors (GEFs1 ; RasGRF1/2 and Sos1/2) promote the formation of the active, GTP-bound form of Ras (1).