Although recent evidence demonstrates that Ras causes transformation by activation of
multiple downstream pathways, the specific role of non-Raf effector pathways is presently
unknown. Although Ras causes activation of the Jun NH 2-terminal kinases (JNKs) via a Raf-
independent pathway, the contribution of JNK activation to Ras transformation and the
effector that mediates JNK activation have not been established. We observed that a
dominant negative mutant of SEK1/JNKK, an activator of JNKs, selectively inhibited …