NIH 3T3 fibroblasts stably transformed with a constitutively active isoform of p21 ^Ras , H-Ras ^V12 (v-H-Ras or EJ-Ras), produced large amounts of the reactive oxygen species superoxide (·O ₂ ⁻ ). ·O ₂ ⁻ production was suppressed by the expression of dominant negative isoforms of Ras or Rac1, as well as by treatment with a farnesyltransferase inhibitor or with diphenylene iodonium, a flavoprotein inhibitor. The mitogenic activity of cells expressing H-Ras ^V12 was inhibited by treatment with the chemical antioxidant N -acetyl-L-cysteine. Mitogen-activated protein kinase (MAPK) activity was decreased and c-Jun N-terminal kinase (JNK) was not activated in H-Ras ^V12 -transformed cells. Thus, H-Ras ^V12 -induced transformation can lead to the production of ·O ₂ ⁻ through one or more pathways involving a flavoprotein and Rac1. The implication of a reactive oxygen species, probably ·O ₂ ⁻ , as a mediator of Ras-induced cell cycle progression independent of MAPK and JNK suggests a possible mechanism for the effects of antioxidants against Ras-induced cellular transformation.

RAS proteins (KRAS4A, KRAS4B, NRAS and HRAS) function as GDP–GTP-regulated binary on-off switches, which regulate cytoplasmic signaling networks that control diverse normal cellular processes. Gain-of-function missense mutations in RAS genes are found in ∼25% of human cancers, prompting interest in identifying anti-RAS therapeutic strategies for cancer treatment. However, despite more than three decades of intense effort, no anti-RAS therapies have reached clinical application. Contributing to this failure has been an underestimation of the complexities of RAS. First, there is now appreciation that the four human RAS proteins are not functionally identical. Second, with >130 different missense mutations found in cancer, there is an emerging view that there are mutation-specific consequences on RAS structure, biochemistry and biology, and mutation-selective therapeutic strategies are needed. In this Cell Science at a Glance article and accompanying poster, we provide a snapshot of the differences between RAS isoforms and mutations, as well as the current status of anti-RAS drug-discovery efforts.