shRNA plasmids: shRNA-IGF-1R (1) Clone identity: NM_010513.1-3300s1c1 (TRCN0000023490):5′GCAGAATAATCTAGTCCTCAT-3′ and shIGF-1R (2) Clone identity: NM_010513.1-3656s1c1 (TRCN0000023493): 5′-CCAACGAGCAAGTTCTTCGTT-3′ cloned into the plasmid pLKO 1. (Sigma Chemical Co, Mo, USA) Control shRNA does not recognize any mouse sequence. The construct pCAG-DsRed and pCAG-GFP were generous gifts from Connie Cepko. The construct IGF-1R OPT was prepared in GeneScrip (Piscataway, NJ, USA). p110CAAX was constructed at Dr. Marta Nieto Laboratory.