RPS6KB1 and neoplasm: However, the fact that Raf‐1 is able to facilitate tumour development through mechanisms other than MEK/ERK signalling is evident by identification of other Raf‐1 targets.7 Ribosomal protein S6 kinase (p70S6K) is a well‐characterized downstream target of the mammalian target of rapamycin (mTOR) for its role in protein biosynthesis.