N-glycosylation of CD24 mediates cell motility but inhibits cell proliferation in colorectal cancer

Abstract

CD24 confers features of stemness and enhances cell motility in colorectal cancer. It contains numerous O-glycosylation sites but just two putative N-glycosylation sites. The study aimed to mutate N-glycosylation as it thought to be important in mediating many glycoproteins’ function. Site-directed mutagenesis performed to mutate N-glycosylation sites by converting asparagine residues to glutamine. Each site was mutated individually (CD24N36Q and CD24N52Q) and in combination (CD24N[36,52]Q) and were overexpressed in HCT116 and SW480 cell lines. The effect of the mutant CD24 on cell viability, cell motility and induction of downstream targets was compared to wild-type CD24 and empty vector control (EVC). Overexpression of the individually mutated clones increased cell motility compared to EVC but was significantly less than that induced by CD24WT. Overexpression of the double mutant clone resulted in near-complete abrogation of cell motility induction. Unexpectedly, the expression of mutant clones (single and double) increased cell viability. Analysis of downstream targets and F-actin staining demonstrated reduced induction of known CD24 targets by mutant vectors and reduced epithelial-mesenchymal transition. In conclusion, each N-glycosylation site on CD24 contributes partially to induce motility by CD24, and these are additive. Loss of the N-glycosylation results in an unexpected gain of proliferative function. Highlights CD24 is a heavily glycosylated molecule that contains two N-glycosylation sites, and these contribute to the activation of downstream targets and induction of cell motility Each N-glycosylation site contributes partially, and their effects appear to be additive The N-glycosylation sites may exert an inhibitory effect on cell proliferation Much of the CD24 activity is mediated through post-transcriptional effects