Lentiviral clones expressing shRNAs directed against human ADSL (TRCN0000078271, TRCN0000078272), human GMPS (TRCN0000045939, TRCN0000045940), human PRPS1 (TRCN0000010123, TRCN0000010125), murine Adsl (TRCN0000120128, TRCN0000339620), murine Gmps (TRCN0000251162, TRCN0000251160), murine Prps1 (TRCN0000024886, TRCN0000024888), human MYC (TRCN0000039640, TRCN0000039642), human GLUT3 (TRCN0000043616, TRCN0000043615) or a control shRNA that has no targets in either human or mouse genome (shCont: SHC002) were obtained from Sigma-Aldrich (St. Louis, MO). shRNAs with non-overlapping sequences that had the best relative knockdown efficiency were used for all experiments. Lentiviral overexpression plasmid for human MYC was generated by cloning the ORF with the N-terminal Flag into the pCDH-MCS-T2A-Puro-MSCV vector (System Biosciences)51 (link). Lentiviral particles were generated in 293FT cells in Neurobasal complete medium (Life Technologies) with cotransfection with the packaging vectors pCMV-dR8.2 dvpr and pCI-VSVG (Addgene) using standard calcium phosphate transfection.