Cell culture experiments

PANC1 and MiaPaCa-2 cell lines were grown in DMEM (Lonza, Leusden, Netherlands) supplemented with fetal bovine serum (FBS) 10% (Merck, Darmstadt Germany), sodium pyruvate (1 mM) (Gibco™, Waltham, MA, USA), penicillin-streptomycin 1% (Gibco™) and amphotericin B 1% (Gibco™). For MiaPaCa-2 cells, horse serum 2.5% (Gibco™) was added to the medium. HEK-293T cells were grown in DMEM (Lonza) supplemented with FBS 10% (Merck), penicillin-streptomycin 1% (Gibco™) and amphotericin B 1% (Gibco™).

Lentiviral particles were obtained by calcium phosphate-mediated transfection of HEK-293T. HEK-293T cells were seeded and transfected with plasmids encoding proteins involved in viral packaging (pRSV-REV, pCMV-dR8.2 dvpr and pCMV-VSV-G) as well as pLenti-PGK-Empty or pLenti-PGK-mErbb2. These plasmids and their constructions are detailed in Supplementary Information. Lentiviruses were collected, filtered and concentrated with Lenti-X™ Concentrator (Clontech, Mountain View, CA, USA). Concentrated lentiviruses were added to target cells (PANC1) that were selected with hygromycin B (Sigma) at 400 µg/ml (MiaPaCa-2) or 600 µg/ml (PANC1) for 2 weeks. For Western Blot experiments and KRAS pull-down assay, PANC1 cell lines were collected 48 hours after plating. Detailed experimental protocols about Western Blot and KRAS pull-down assay can be found in Supplementary Information.