(A–C) HCC cells were transfected with siRNAs against human DPP4 (si-DPP4) or with control siRNAs (Control). (A) Clonogenicity assays (right panels: quantified colony numbers and sizes; left panels: representative images) of HCC cells (Hep3B); data are summarized for Hep3B (n = 6) and PLC (n = 3). (B) Real-time cell proliferation analysis (PLC, n = 4). (C) Boyden chamber analysis of chemotactic (i.e., directed) migration of HCC cells (PLC) toward control medium or a gradient induced by recombinant NPY (100 nM) with or without combined RNAi-mediated DPP4 knockdown (n = 3). (D) Real-time proliferation analysis (xCELLigence) of HCC cells (PLC) using serum-containing (i.e., NPY-containing) culture medium and treatment with sitagliptin (1 μM) with or without cotreatment with the specific Y5R agonist BWX46 (200 nM) (n = 4; box-and-whisker plots [min to max]). (E and F) Boyden chamber analysis of HCC cells (PLC) migrating toward a gradient induced by recombinant NPY (100 nM) (E) or BWX46 (200 nM) (F) with or without cotreatment with sitagliptin (1 μM) (n = 4; box-and-whisker plots [min to max]). (G) Summary and cartoon depicting the hypothesis that DPP4-mediated NPY conversion to (more Y5R-specific) truncated NPY_3–36 results in augmented Y5R activation. Data are presented as mean ± SEM. Statistical significance was determined by ordinary 1-way ANOVA together with Dunnett’s multiple-comparisons test (C–F) or 2-tailed, unpaired t test (A and B). *P < 0.05, **P < 0.01, ****P < 0.0001.