Identification of the site of inhibition of oncogenic ras-p21-induced signal transduction by a peptide from a ras effector domain.

We have previously found that a peptide corresponding to residues 35-47 of the ras-p21 protein, from its switch 1 effector domain region, strongly inhibits oocyte maturation induced by oncogenic p21, but not by insulin-activated cellular wild-type p21. Another ras-p21 peptide corresponding to residues 96-110 that blocks ras-jun and jun kinase (JNK) interactions exhibits a similar pattern of inhibition. We have also found that c-raf strongly induces oocyte maturation and that dominant negative c-raf strongly blocks oncogenic p21-induced oocyte maturation. We now find that the p21 35-47, but not the 96-110, peptide completely blocks c-raf-induced maturation. This finding suggests that the 35-47 peptide blocks oncogenic ras at the level of raf; that activated normal and oncogenic ras-p21 have differing requirements for raf-dependent signaling; and that the two oncogenic-ras-selective inhibitory peptides, 35-47 and 96-110, act at two different critical downstream sites, the former at raf the latter at JNK/jun, both of which are required for oncogenic ras-p21 signaling.