To determine whether the expression level of CTSL changed in GC cells and contributed to endothelial cells tubule formation and migration, we established an in vitro co-culture system (Supplementary Fig. 2C), in which HUVECs were indirectly cocultured with GC cells and separated from GC cells by a semipermeable membrane (pore size of 0.6 μm). The gene discussed is CTSL; the disease is gastric cancer.