Targeting the GD3 acetylation pathway selectively induces apoptosis in glioblastoma

Abstract

The expression of ganglioside GD3, which plays crucial roles in normal brain development, decreases in adults but is upregulated in neoplastic cells, where it regulates tumor invasion and survival. Normally a buildup of GD3 induces apoptosis, but this does not occur in gliomas due to formation of 9-O-acetyl GD3 by the addition of an acetyl group to the terminal sialic acid of GD3; this renders GD3 unable to induce apoptosis. Using human biopsy-derived glioblastoma cell cultures, we have carried out a series of molecular manipulations targeting GD3 acetylation pathways. Using immunocytochemistry, flow cytometry, western blotting, and transwell assays, we have shown the existence of a critical ratio between GD3 and 9-O-acetyl GD3, which promotes tumor survival. Thus, we have demonstrated for the first time in primary glioblastoma that cleaving the acetyl group restores GD3, resulting in a reduction in tumor cell viability while normal astrocytes remain unaffected. Additionally, we have shown that glioblastoma viability is reduced due to the induction of mitochondrially mediated apoptosis and that this occurs after mitochondrial membrane depolarization. Three methods of cleaving the acetyl group using hemagglutinin esterase were investigated, and we have shown that the baculovirus vector transduces glioma cells as well as normal astroctyes with a relatively high efficacy. A recombinant baculovirus containing hemagglutinin esterase could be developed for the clinic as an adjuvant therapy for glioma.

Glycosylation in cancer: mechanisms and clinical implications

“…RTKs are located in glycolipidenriched microdomains, and changes in gangliosides modify the molecular composition and the structure of glycolipid-enriched microdomains, leading to modifications in the location and organization of RTKs in the cellular membrane and altered activation 53,169 . Further regulation of specific ganglioside GD3 due to formation of 9-O-acetyl GD3 that renders GD3 unable to induce apoptosis has been shown in gliomas 170 .…”

Hallmarks of glycosylation in cancer

“…GD3 expression is upregulated in neoplastic cells where it regulates tumour invasion and survival [73]. Although an increase in GD3 would normally induce apoptosis, in glioblastomas addition of an acetyl group to the terminal sialic acid (to produce 9-O-acetyl GD3) makes GD3 unable to induce apoptosis, thus promoting tumour survival [74]. Ceramide accumulation also plays a role in programmed cell death [75].…”

TargetingO-Acetyl-GD2 Ganglioside for Cancer Immunotherapy

“…In tumor cells, such as melanoma, O -acetyl-GD3 seems to contribute to tumor cell proliferation [76]. In glioblastoma, it may also promote tumor cell survival [77]. Similar observations were reported in acute lymphoblastic leukemia cells [74, 78] in which O- acetyl-GD3 seems further to contribute to their drug resistance capacity [79].…”

“…Importantly, the evidence for the antiapoptotic functions of O -acetyl-GD3 in the above studies remains indirect. In addition to the effects of mAbs specific for O -acetyl-GD3 [68, 72, 73, 80], they consist of the effects induced by the addition of O -acetyl-GD3 into cells [74, 75] and the effect of the viral 9- O -acetylesterase [69, 76, 77, 79]. …”

“…Therefore, it is not excluded that the mechanisms evidenced in these studies also involved O- acetyl-GD2. Hence, O -acetyl-GD2 may behave very similarly to GD2 in mediating apoptosis in the GD2/ O AcGD2-expressing tumor cells [81, 83–85], in disagreement with the antiapoptotic role evidenced for O- acetyl-GD3 [74, 77–79]. …”