title: Hypoxia enhances tumor stemness by increasing the invasive and tumorigenic side population fraction.
abstract: Although advances have been made in understanding the role of hypoxia in the stem cell niche, almost nothing is known about a potentially similar role of hypoxia in maintaining the tumor stem cell (TSC) niche. Here we show that a highly tumorigenic fraction of side population (SP) cells is localized in the hypoxic zones of solid tumors in vivo. We first identified a highly migratory, invasive, and tumorigenic fraction of post-hypoxic side population cells (SPm([hox]) fraction) in a diverse group of solid tumor cell lines, including neuroblastoma, rhabdomyosarcoma, and small-cell lung carcinoma. To identify the SPm((hox)) fraction, we used an "injured conditioned medium" derived from bone marrow stromal cells treated with hypoxia and oxidative stress. We found that a highly tumorigenic SP fraction migrates to the injured conditioned medium in a Boyden chamber. We show that as few as 100 SPm((hox)) cells form rapidly growing tumors in vivo. In vitro exposure to hypoxia increases the SPm((hox)) fraction significantly. Quantitative real-time polymerase chain reaction and immunofluorescence studies showed that SPm((hox)) cells expressed Oct-4, a "stemness" gene having a potential role in TSC maintenance. In nude mice xenografts, SPm((hox)) cells were localized to the hypoxic zones, as demonstrated after quantum dot labeling. These results suggest that a highly tumorigenic SP fraction migrates to the area of hypoxia; this migration is similar to the migration of normal bone marrow SP fraction to the area of injury/hypoxia. Furthermore, the hypoxic microenvironment may serve as a niche for the highly tumorigenic fraction of SP cells.
authors.affiliation: Department of Pediatric Laboratory Medicine, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada.
authors.forename: Bikul
authors.initials: B
authors.lastname: Das
authors.forename: Rika
authors.initials: R
authors.lastname: Tsuchida
authors.forename: David
authors.initials: D
authors.lastname: Malkin
authors.forename: Gideon
authors.initials: G
authors.lastname: Koren
authors.forename: Sylvain
authors.initials: S
authors.lastname: Baruchel
authors.forename: Herman
authors.initials: H
authors.lastname: Yeger
mesh_terms: D000818:Animals; D018288:Carcinoma, Small Cell / Q000473:pathology; D045744:Cell Line, Tumor; D003094:Collagen / Q000737:chemistry; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004338:Drug Combinations; D006801:Humans; D000860:Hypoxia; D007797:Laminin / Q000737:chemistry; D008175:Lung Neoplasms / Q000473:pathology; D051379:Mice; D008954:Models, Biological; D009368:Neoplasm Transplantation; D014411:Neoplastic Stem Cells / Q000166:cytology*; D009447:Neuroblastoma / Q000473:pathology; D018384:Oxidative Stress; D011509:Proteoglycans / Q000737:chemistry; D012208:Rhabdomyosarcoma / Q000473:pathology
chemical_list: D017077:Culture Media, Conditioned; D004338:Drug Combinations; D007797:Laminin; D011509:Proteoglycans; C059485:matrigel; D003094:Collagen