Figure 1. Functional surfaceome analysis identified SDC1 as a KRAS*-dependent surface protein important for tumor maintenance.

a, Experimental design for the functional surfaceome analysis. Differentially expressed surface proteins upon Kras^G12D inactivation were identified via SILAC-based proteomic analysis. In vivo loss-of-function screening was subsequently conducted with a custom barcoded lentiviral shRNA library targeting the Kras*-dependent surfaceome. Depletion was observed relative to reference population. b, Top 10 canonical signaling pathways identified with IPA analysis of differentially expressed surface proteins upon Kras* activation; n=3 biologically independent samples, enrichment score (Enrich) and P-value (two-sided Fisher) reported. c, Rank of common top-scoring hits from three independent iKras p53^L/+ tumor cell lines: RSA/LogP-based cutoff is heatmapped against corresponding quantification rank from SILAC-based proteomic analysis. d, Heavy and light spectra of representative SDC1 peptide show membrane SDC1 in presence (Heavy) or absence (Light) of Kras^G12D in iKras p53^L/+ tumor cells. e, SDC1 levels of iKras p53^L/+ tumor cells in presence (ON) or absence (OFF) of doxycycline were measured by FACS analysis (Top) and quantification of fluorescence intensity is shown (Bottom). REON: cells were grown in absence of doxycycline for 48 hours followed by doxycycline treatment for 24 hours (n=3 biological replicates; data are mean + s.d.; P-values were determined by paired two-sided Student’s t-test). f, Three-week-old iKras p53^L/+ mice received doxycycline-containing water for 1/3/7 weeks (W) to induce premalignant lesions or for 9 weeks to induce invasive PDAC (T), then doxycycline was withdrawn for 1/2/7 days (D). SDC1 in pancreatic or tumor tissues was analyzed by IHC (scale bar: 200 μm). Arrows indicate areas magnified in the inserts. d-f: Representative experiments from three independent experiments.