title: Silencing hypoxia-inducible factor-1alpha inhibits cell migration and invasion under hypoxic environment in malignant gliomas.
abstract: Malignant gliomas are characterized by active invasiveness, necrosis, and vascular proliferation. These pathological features have been speculated to be caused by tissue hypoxia. Hypoxia-inducible factor-1 (HIF-1), which is controlled by rapid stabilization of the HIF-1alpha subunit, is a pivotal transcriptional factor in the cellular response to hypoxia. Although many studies have described the relationship between tumor angiogenesis and hypoxic environment, the roles of HIF-1 in cell invasion have been barely elucidated in malignant gliomas. We investigated the role of HIF-1alpha in the motile and invasive activities of human glioma cells under hypoxia. Four malignant glioma cell lines, U87MG, U251MG, U373MG, and LN18, were cultured under 21 and 1% oxygen concentration. Expression of HIF-1alpha under hypoxia was observed to be much higher than that under normoxia in all cell lines. Introducing HIF-1alpha-targeted small interfering RNA (HIF-1alpha siRNA) into the glioma cell lines resulted in downregulation of HIF-1alpha expression, and significantly suppressed glioma cell migration in vitro. Furthermore, invasiveness was significantly reduced in the cells transfected with HIF-1alpha siRNA compared with those transfected with the control siRNA. Co-culture of glioma spheroids and rat brain slices showed that HIF-1alpha siRNA-transfected glioma cells failed to invade the surrounding normal brain tissue in an organotypic brain slice model. These effects of HIF-1alpha siRNA were more conspicuous under hypoxia than under normoxia. In addition, under hypoxic conditions, the level of matrix metalloproteinase (MMP)-2 mRNA was upregulated, and that of tissue inhibitor of metalloproteinase (TIMP)-2 was downregulated in all glioma cell lines. Treatment with HIF-1alpha siRNA resulted in downregulation of MMP-2 mRNA and upregulation of TIMP-2 mRNA. Furthermore, the enzyme activities of MMP-2 and MMP-9, both of which were activated by hypoxia, decreased with the introduction of HIF-1alpha siRNA. These findings suggest that overexpression of HIF-1alpha induced by hypoxic stress is an essential event in the activation of glioma cell motility through alteration of invasion-related molecules. Targeting the HIF-1alpha molecule may be a novel therapeutic strategy for malignant gliomas.
authors.affiliation: Department of Neurosurgery, Ehime University School of Medicine, Shitsukawa, Toon, Ehime 791-0295, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Fujiwara
authors.forename: Kou
authors.initials: K
authors.lastname: Nakagawa
authors.forename: Hironobu
authors.initials: H
authors.lastname: Harada
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Nagato
authors.forename: Koji
authors.initials: K
authors.lastname: Furukawa
authors.forename: Mikio
authors.initials: M
authors.lastname: Teraoka
authors.forename: Toshimoto
authors.initials: T
authors.lastname: Seno
authors.forename: Keizo
authors.initials: K
authors.lastname: Oka
authors.forename: Shinji
authors.initials: S
authors.lastname: Iwata
authors.forename: Takanori
authors.initials: T
authors.lastname: Ohnishi
mesh_terms: D001932:Brain Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002465:Cell Movement / Q000235:genetics*; D015536:Down-Regulation; D005910:Glioma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D000860:Hypoxia / Q000235:genetics / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors* / Q000235:genetics; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D009361:Neoplasm Invasiveness; D034741:RNA, Small Interfering / Q000494:pharmacology; D019716:Tissue Inhibitor of Metalloproteinase-2 / Q000378:metabolism
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering; D019716:Tissue Inhibitor of Metalloproteinase-2; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9