title: DEC2 expression is positively correlated with HIF-1 activation and the invasiveness of human osteosarcomas.
abstract: BACKGROUND
  Osteosarcoma is the most common malignancy of bone. HIF-1 (hypoxia-inducible factor 1) activation is critical for the metabolic reprogramming and progression of solid tumors, and DEC2 (differentiated embryonic chondrocyte gene 2) has been recently reported to suppress HIF-1 in human breast and endometrial cancers. However, the roles of HIF-1 and DEC2 in human osteosarcomas remain unclear.
  
  
  METHODS
  We evaluated the correlation of DEC2 and HIF-1 expression to the prognosis, and studied the roles of DEC2 and HIF-1 activation in the invasiveness of osteosarcoma. Multiple approaches including immunohistochemical staining of clinical osteosarcoma tissues, siRNA-based knockdown and other molecular biology techniques were used. Particularly, by using a repetitive trans-well culture-based in vitro evolution system, we selected a more invasive subpopulation (U2OS-M) of osteosarcoma cells from U2OS and used it as a model to study the roles of DEC2 and HIF-1 in the invasiveness of osteosarcoma.
  
  
  RESULTS
  We found that the expression of DEC2 was positively correlated with HIF-1α levels, and HIF-1α expression positively correlated with poor prognosis in osteosarcomas. DEC2 knockdown in osteosarcoma cell lines (U2OS, MNNG and 143B) attenuated HIF-1α accumulation and impaired the up-regulation of HIF-1 target genes in response to hypoxia. Compared with the low invasive parental U2OS, U2OS-M showed higher levels of DEC2 expression which were confirmed at both mRNA and protein levels. Importantly, we found that the increased DEC2 expression resulted in a more rapid accumulation of HIF-1α in U2OS-M cells in response to hypoxia. Finally, we found that HIF-1 activation is sufficient to upregulate DEC2 expression in osteosarcoma cells.
  
  
  CONCLUSIONS
  Taken together, whereas DEC2 was found to promote HIF-1α degradation in other types of tumors, our data indicate that DEC2 facilitates HIF-1α stabilization and promotes HIF-1 activation in osteosarcoma. This implies that DEC2 may contribute to the progression and metastasis of human osteosarcoma by sensitizing tumor cells to hypoxia. On the other hand, HIF-1 activation may contribute to the expression of DEC2 in osteosarcoma. This is the first demonstration of a novel DEC2-HIF-1 vicious cycle in osteosarcoma and a tumor-type specific role for DEC2.
authors.affiliation: Department of Orthopedics, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, No.600, Yishan Road, Shanghai, 200233, China. zzuhutu@163.com.
authors.forename: Tu
authors.initials: T
authors.lastname: Hu
authors.affiliation: Department of Orthopedics, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, No.600, Yishan Road, Shanghai, 200233, China. hen0@163.com.
authors.forename: Nengbin
authors.initials: N
authors.lastname: He
authors.affiliation: Huazhong University of Science and Technology, Wuhan, China. yys1994429@outlook.com.
authors.forename: Yunsong
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Departments of Biology, Pathology & Laboratory Medicine, Drexel University CoAS, 3245 Chestnut St, PISB 417, Philadelphia, PA, 19104, USA. chengqian.yin@drexel.edu.
authors.forename: Chengqian
authors.initials: C
authors.lastname: Yin
authors.affiliation: Departments of Biology, Pathology & Laboratory Medicine, Drexel University CoAS, 3245 Chestnut St, PISB 417, Philadelphia, PA, 19104, USA. nianli.sang@drexel.edu.|Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, USA. nianli.sang@drexel.edu.
authors.forename: Nianli
authors.initials: N
authors.lastname: Sang
authors.affiliation: Department of Orthopedics, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, No.600, Yishan Road, Shanghai, 200233, China. tjyqc@163.com.
authors.forename: Qingcheng
authors.initials: Q
authors.lastname: Yang
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics*; D001859:Bone Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D006801:Humans; D000860:Hypoxia / Q000235:genetics / Q000378:metabolism; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D012516:Osteosarcoma / Q000235:genetics* / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D011379:Prognosis; D055550:Protein Stability; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering; C422085:BHLHE41 protein, human