The secreted glycolytic enzyme GPI/AMF stimulates glioblastoma cell migration and invasion in an autocrine fashion but can have anti-proliferative effects

Background. Aerobic glycolysis confers several advantages to tumor cells, including shunting of metabolites into anabolic pathways. In glioblastoma cells, hypoxia induces a flux shift from the pentose phosphate pathway toward glycolysis and a switch from proliferation to migration. The mechanistic link between glycolysis and migration is poorly understood. Since glucose-6-phosphate isomerase (GPI) is identical to the secreted cytokine autocrine motility factor (AMF), we investigated whether GPI/AMF regulates glioblastoma cell invasion. Methods. The expression and hypoxic regulation of GPI/AMF and its receptor AMFR were analyzed in glioblastoma tissue and cell lines. Functional effects were studied in vitro and in xenograft models. Results. High GPI/AMF expression in glioblastomas was found to be associated with a worse patient prognosis, and levels were highest in hypoxic pseudopalisades. Hypoxia upregulated both GPI/AMF and AMFR expression as well as GPI/AMF secretion in vitro. GPI/AMF stimulated cell migration in an autocrine fashion, and GPI/AMF expression was upregulated in migratory cells but reduced in rapidly proliferating cells. Knockdown or inhibition of GPI/AMF reduced glioblastoma cell migration but in part stimulated proliferation. In a highly invasive orthotopic glioblastoma model, GPI/AMF knockdown reduced tumor cell invasion but did not prolong survival. In a highly proliferative model, knockdown tumors were even larger and more proliferative than controls; however, perivascular invasion, provoked by simultaneous bevacizumab treatment, was reduced. Conclusions. GPI/AMF is a potent motogen for glioblastoma cells, explaining in part the association between glycolysis and migration. Targeting GPI/AMF is, however, problematic, since beneficial anti-invasive effects may be outweighed by unintended mitogenic effects.