To validate our proteomic analysis, we examined the sialylated state of integrin β4 (ITGB4), that has been recently reported as ST3GAL1-sialylated target24, and of 3 receptor tyrosine kinases (RTKs) that have been linked to melanoma progression: AXL receptor (also known as UFO)25, nerve growth factor receptor (NGFR) (known also as CD271)26, and epidermal growth factor receptor (EGFR)27,28, that are expressed in melanoma cells at variable levels (Supplementary Fig. 7a). The gene discussed is AXL; the disease is melanoma.