Down-regulation of Phosphoglucose Isomerase/Autocrine Motility Factor Expression Sensitizes Human Fibrosarcoma Cells to Oxidative Stress Leading to Cellular Senescence

Abstract

Phosphoglucose isomerase/autocrine motility factor (PGI/ AMF) is a housekeeping gene product present in all cells, is an essential enzyme of catabolic glycolysis and anabolic gluconeogenesis, and regulates tumor cell growth and metastasis. Because glycolytic enzyme up-regulation of expression contributes to glycolytic flux, leading to increased of cell growth and a resistance to cellular stress of normal fibroblasts whereas downregulation of PGI/AMF leads to mesenchymal-to-epithelial transition in tumor cells, we examined the involvement of PGI/ AMF in overcoming cellular senescence in cancer cells. PGI/ AMF cellular expression in HT1080 human fibrosarcoma was down-regulated by small interfering RNA methodology, which resulted in an increased sensitivity to oxidative stress and oxidative stress-induced cellular senescence. Signaling analysis revealed that the senescence pathway involving p21 cyclin-dependent kinase inhibitor was up-regulated in PGI/AMF knockdown cells and that superoxide dismutase is the upstream regulator protein of p21-mediated cellular senescence. A specific inhibitor of PGI/AMF induced cellular senescence and p21 expression in tumor cells exposed to an oxidative stress environment. Taken together, the results presented here suggest that PGI/AMF is involved in oxidative stress-induced cellular senescence and should bring novel insights into the control of cellular growth leading to a new methodology for cancer treatment.Cellular senescence, e.g. the loss of proliferative capacity of cells leading to terminal differentiation (1), is a cellular response to stresses, including oxidative stress, DNA damage, and oncogene activation (2-4). Once cells have entered senescence, they display several characteristic changes in morphology, physiology, and gene expression resulting in an increased activity of senescence-associated ␤-galactosidase (SA ␤-gal; Refs. 4 and 5), 2 and cellular senescence is thought to act as a cancer suppressor phenomenon regulated in part by tumor suppressor genes. Because cancer cells have overcome the limits to proliferation imposed by the cellular senescence machinery, it was speculated to be an attractive target for cancer therapy (6, 7). Phosphoglucose isomerase (PGI; EC 5.3.1.9) is a housekeeping cytosolic enzyme of sugar metabolism present in all cells and plays a key role in both glycolysis and gluconeogenesis pathways. It catalyzes the reversible aldose-ketose isomerization of D-glucose-6-phosphate to D-fructose-6-phosphate and in the recycling of hexose-6-phosphate in the pentose phosphate pathway (8). PGI is a secretable protein that extracellularly behaves as a cytokine following binding to its seven-transmembrane receptor (gp78/AMFR; Ref. 9). Molecular cloning and sequencing have identified PGI as an autocrine motility factor (AMF), which is originally identified as a major cell motility-stimulating factor associated with cancer progression and metastasis (8, 10, 11). PGI/AMF was independently identified as neuroleukin that promotes growth of embryonic spinal and s...

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