STAT3 and cancer: To address the functional consequence of the glucosamine-induced inhibition of global protein N-glycosylation, we examined the phosphorylation (activity) of three important signaling proteins in cancer cells, STAT3 (Tyr705), AKT (Ser473) and ERK1/2 (Thr202/Tyr204) that were activated by membrane N-glycosylated receptors.