Since ST6Gal1-mediated α2,6-sialylation constitutes a well-established regulator of transmembrane receptor activation, namely by influencing receptor dimerization and membrane turnover rate, we analyzed the phosphorylation levels of 49 cancer-related RTKs in untreated and trastuzumab-treated NCI-N87 WT and ST6GAL1 K.O. cells with a human phospho-RTK array (Fig. 7D). The gene discussed is NRP1; the disease is cancer.