title: Hypoxia and hypoxia-inducible factor-1 expression enhance osteolytic bone metastases of breast cancer.
abstract: Hypoxia is a common feature of solid tumors and is associated with their malignant phenotype. The transcription factor hypoxia-inducible factor-1 (HIF-1) is a major regulator of adaptation to hypoxia and is implicated in the malignant progression of cancers. Here, we studied whether hypoxia and HIF-1 expression contribute to the development of bone metastases using a well-characterized animal model of bone metastasis in MDA-MB-231 human breast cancer cells. To study the role of hypoxia in bone metastases, we tested the effects of the fusion protein (TOP3), the oxygen-dependent degradation domain of HIF-1alpha fused with HIV-TAT, and procaspase-3. TOP3 selectively induced apoptosis in hypoxic tumor cells in vitro and significantly reduced bone metastases in vivo. We next examined the role of HIF-1 in bone metastases by establishing MDA-MB-231 cells overexpressing constitutively active or dominant-negative HIF-1alpha (MDA/CA-HIF or MDA/DN-HIF, respectively). Bone metastases of MDA/CA-HIF were significantly increased with elevated number of CD31-positive blood vessels. In contrast, bone metastases were significantly reduced in MDA/DN-HIF. Because the progression of osteolytic bone metastases is due in part to the imbalance between bone formation and bone resorption, we examined the effects of hypoxia and HIF-1 on the differentiation of osteoblasts and osteoclasts. Hypoxia and CA-HIF overexpression markedly inhibited osteoblastic differentiation, whereas hypoxia increased osteoclast-like cell formation. In conclusion, these results suggest that tumor-associated hypoxia and HIF-1 expression promote the progression of bone metastases in breast cancer. Our results also suggest that hypoxia and HIF-1 lead to the development of osteolytic bone metastases by suppressing osteoblast differentiation and promoting osteoclastogenesis.
authors.affiliation: Department of Biochemistry, Graduate School of Dentistry, Osaka University, Suita, Osaka, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Hiraga
authors.forename: Shinae
authors.initials: S
authors.lastname: Kizaka-Kondoh
authors.forename: Kiichi
authors.initials: K
authors.lastname: Hirota
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Yoneda
mesh_terms: D000818:Animals; D001859:Bone Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000556:secondary*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D053148:Caspase 3 / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis* / Q000235:genetics; D007191:Indazoles / Q000494:pharmacology; D051379:Mice; D008809:Mice, Inbred C3H; D008819:Mice, Nude; D011993:Recombinant Fusion Proteins / Q000378:metabolism / Q000494:pharmacology; D014162:Transfection
chemical_list: C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007191:Indazoles; D011993:Recombinant Fusion Proteins; C498363:TOP3 fusion protein; C090937:3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole; D053148:Caspase 3