However, the fact that R-Ras and R-Ras2 are activated in NF1-null MPNST cells is consistent with earlier studies indicating that neurofibromin inactivates these proteins in vitro [27] and implicating R-Ras proteins in the enhanced migration of Nf1−/− non-neoplastic Schwann cells [40]. Here, NF1 is linked to malignant peripheral nerve sheath tumor.