In addition to enzymes, some studies have considered the impact of abnormal glycosylated proteins themselves on downstream signaling pathways; for example, as highly glycosylated proteins, MUC4 is overexpressed in GBM cell lines and tissues, while ectopic MUC4 expression can promote GBM cell proliferation and invasion characteristics by regulating EGFR expression (Fig. 2c) [9]. This evidence concerns the gene MUC4 and glioblastoma.