title: Hypoxia regulates CD44 and its variant isoforms through HIF-1α in triple negative breast cancer.
abstract: BACKGROUND
  The CD44 transmembrane glycoproteins play multifaceted roles in tumor progression and metastasis. CD44 expression has also been associated with stem-like breast cancer cells. Hypoxia commonly occurs in tumors and is a major cause of radiation and chemo-resistance. Hypoxia is known to inhibit differentiation and facilitates invasion and metastasis. Here we have investigated the effect of hypoxia on CD44 and two of its isoforms in MDA-MB-231 and SUM-149 triple negative human breast cancer cells and MDA-MB-231 tumors using imaging and molecular characterization.
  
  
  RESULTS
  The roles of hypoxia and hypoxia inducible factor (HIF) in regulating the expression of CD44 and its variant isoforms (CD44v6, CD44v7/8) were investigated in human breast cancer cells, by quantitative real-time polymerase chain reaction (qRT-PCR) to determine mRNA levels, and fluorescence associated cell sorting (FACS) to determine cell surface expression of CD44, under normoxic and hypoxic conditions. In vivo imaging studies with tumor xenografts derived from MDA-MD-231 cells engineered to express tdTomato red fluorescence protein under regulation of hypoxia response elements identified co-localization between hypoxic fluorescent regions and increased concentration of (125)I-radiolabeled CD44 antibody.
  
  
  CONCLUSIONS
  Our data identified HIF-1α as a regulator of CD44 that increased the number of CD44 molecules and the percentage of CD44 positive cells expressing variant exons v6 and v7/8 in breast cancer cells under hypoxic conditions. Data from these cell studies were further supported by in vivo observations that hypoxic tumor regions contained cells with a higher concentration of CD44 expression.
authors.affiliation: JHU ICMIC Program, Division of Cancer Imaging Research, The Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America. bkrishn1@jhu.edu
authors.forename: Balaji
authors.initials: B
authors.lastname: Krishnamachary
authors.forename: Marie-France
authors.initials: MF
authors.lastname: Penet
authors.forename: Sridhar
authors.initials: S
authors.lastname: Nimmagadda
authors.forename: Yelena
authors.initials: Y
authors.lastname: Mironchik
authors.forename: Venu
authors.initials: V
authors.lastname: Raman
authors.forename: Meiyappan
authors.initials: M
authors.lastname: Solaiyappan
authors.forename: Gregg L
authors.initials: GL
authors.lastname: Semenza
authors.forename: Martin G
authors.initials: MG
authors.lastname: Pomper
authors.forename: Zaver M
authors.initials: ZM
authors.lastname: Bhujwalla
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D018960:Hyaluronan Receptors / Q000235:genetics / Q000378:metabolism*; D000860:Hypoxia / Q000235:genetics / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism
chemical_list: C497442:HIF1A protein, human; D018960:Hyaluronan Receptors; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D020033:Protein Isoforms