title: Effects of hypoxia inducible factor-1α on apoptotic inhibition and glucocorticoid receptor downregulation by dexamethasone in AtT-20 cells.
abstract: BACKGROUND
  Hypoxia inducible factor-1α (HIF-1α) is the central transcriptional regulator of hypoxic responses during the progression of pituitary adenomas. Although previous immunohistochemical studies revealed that HIF-1α is expressed in adreno-cortico-tropic-hormone (ACTH) pituitary adenomas, the role of HIF-1α remains unclear.
  
  
  METHODS
  AtT-20 cells were incubated under hypoxic conditions (1 % O2) for 12 h. HIF-1α mRNA and protein expression levels were measured by real-time PCR and western blotting, respectively. BrdU was used to determine the effects of hypoxia on cell viability. AtT-20 cells were transfected with siRNA targeting HIF-1α, followed by hypoxia (1 % O2) for 12 h. Apoptosis was determined by annexin V-FITC flow cytometry and Tdt-mediated dUTP nick end-labelling (TUNEL) assay. In addition, we examined interactions between HIF-1α, glucocorticoid receptor (GR), and dexamethasone under both normoxic and hypoxic conditions.
  
  
  RESULTS
  Hypoxia triggered the time-dependent proliferation of AtT-20 cells in association with increased HIF-1α mRNA and protein levels. However, the viability of AtT-20 cells decreased greatly when they were first transfected with HIF-1α-siRNA and then exposed to hypoxia. According to flow cytometry (annexin V-FITC and PI staining) and TUNEL analyses, a greater percentage of cells were apoptotic when transfected with HIF-1α siRNA and subsequently cultured under hypoxic conditions compared to those in the normoxia and mock groups. After AtT-20 cells were cultured in 1 % O2 and then treated with dexamethasone, HIF-1α levels significantly increased or decreased in normoxic or hypoxic conditions, respectively. Dexamethasone suppressed GR expression to a higher degree in hypoxic than normoxic conditions. Downregulation of GR by dexamethasone was greatly prevented in cells that were transfected with HIF-1α siRNA.
  
  
  CONCLUSIONS
  These findings strongly suggest that HIF-1α exerts an antiapoptotic role and participates in the downregulation of GR by dexamethasone in hypoxic AtT-20 cells.
authors.affiliation: Department of Neurosurgery, Shanghai Changzheng Hospital, Second Military Medical University, No. 415, Feng-Yang Road, Shanghai, 200003, China. christopher0708@163.com.
authors.forename: Chenran
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Department of Neurology, Huadong Hospital, Fudan University, Shanghai, 200040, China. qiangqiangshsmu@126.com.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Qiang
authors.affiliation: Department of Neurosurgery, Shanghai Changzheng Hospital, Second Military Medical University, No. 415, Feng-Yang Road, Shanghai, 200003, China. yiyijijiji@gmail.com.
authors.forename: Ying
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Department of Cardiology, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, 200127, China. iam565@126.com.
authors.forename: Liuhua
authors.initials: L
authors.lastname: Hu
authors.affiliation: Department of Neurosurgery, Shanghai Changzheng Hospital, Second Military Medical University, No. 415, Feng-Yang Road, Shanghai, 200003, China. dxuehua.73360@163.com.
authors.forename: Xuehua
authors.initials: X
authors.lastname: Ding
authors.affiliation: Department of Neurosurgery, Shanghai Changzheng Hospital, Second Military Medical University, No. 415, Feng-Yang Road, Shanghai, 200003, China. luyc305@163.com.
authors.forename: Yicheng
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Department of Neurosurgery, Shanghai Changzheng Hospital, Second Military Medical University, No. 415, Feng-Yang Road, Shanghai, 200003, China. huguohan@163.com.
authors.forename: Guohan
authors.initials: G
authors.lastname: Hu
mesh_terms: D049913:ACTH-Secreting Pituitary Adenoma / Q000235:genetics* / Q000378:metabolism; D000236:Adenoma / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D045744:Cell Line, Tumor; D003907:Dexamethasone / Q000494:pharmacology*; D015536:Down-Regulation; D005434:Flow Cytometry; D055785:Gene Knockdown Techniques; D005938:Glucocorticoids / Q000494:pharmacology*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D020287:In Situ Nick-End Labeling; D051379:Mice; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism*; D011965:Receptors, Glucocorticoid / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
chemical_list: D005938:Glucocorticoids; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D003907:Dexamethasone