title: Genes responsive to both oxidant stress and loss of estrogen receptor function identify a poor prognosis group of estrogen receptor positive primary breast cancers.
abstract: BACKGROUND
  Oxidative stress can modify estrogen receptor (ER) structure and function, including induction of progesterone receptor (PR), altering the biology and clinical behavior of endocrine responsive (ER-positive) breast cancer.
  
  
  METHODS
  To investigate the impact of oxidative stress on estrogen/ER-regulated gene expression, RNA was extracted from ER-positive/PR-positive MCF7 breast cancer cells after 72 hours of estrogen deprivation, small-interfering RNA knockdown of ER-alpha, short-term (8 hours) exposure to various oxidant stresses (diamide, hydrogen peroxide, and menadione), or simultaneous ER-alpha knockdown and oxidant stress. RNA samples were analyzed by high-throughput expression microarray (Affymetrix), and significance analysis of microarrays was used to define gene signatures responsive to estrogen/ER regulation and oxidative stress. To explore the association of these signatures with breast cancer biology, microarray data were analyzed from 394 ER-positive primary human breast cancers pooled from three independent studies. In particular, an oxidant-sensitive estrogen/ER-responsive gene signature (Ox-E/ER) was correlated with breast cancer clinical parameters and disease-specific patient survival (DSS).
  
  
  RESULTS
  From 891 estrogen/ER-regulated probes, a core set of 75 probes (62 unique genes) responsive to all three oxidants were selected (Ox-E/ER signature). Ingenuity pathway analysis of this signature highlighted networks involved in development, cancer, and cell motility, with intersecting nodes at growth factors (platelet-derived growth factor-BB, transforming growth factor-beta), a proinflammatory cytokine (tumor necrosis factor), and matrix metalloproteinase-2. Evaluation of the 394 ER-positive primary breast cancers demonstrated that Ox-E/ER index values correlated negatively with PR mRNA levels (rp = -0.2; P = 0.00011) and positively with tumor grade (rp = 0.2; P = 9.741 x e-5), and were significantly higher in ER-positive/PR-negative versus ER-positive/PR-positive breast cancers (t-test, P = 0.0008). Regardless of PR status, the Ox-E/ER index associated with reduced DSS (n = 201; univariate Cox, P = 0.078) and, using the optimized cut-point, separated ER-positive cases into two significantly different DSS groups (log rank, P = 0.0009).
  
  
  CONCLUSIONS
  An oxidant-sensitive subset of estrogen/ER-responsive breast cancer genes linked to cell growth and invasion pathways was identified and associated with loss of PR and earlier disease-specific mortality, suggesting that oxidative stress contributes to the development of an aggressive subset of primary ER-positive breast cancers.
authors.affiliation: Buck Institute for Age Research, Redwood Boulevard, Novato, California 94945, USA. cyau@buckinstitute.org
authors.forename: Christina
authors.initials: C
authors.lastname: Yau
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Benz
mesh_terms: D001943:Breast Neoplasms / Q000175:diagnosis* / Q000235:genetics* / Q000401:mortality; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D020411:Oligonucleotide Array Sequence Analysis; D016877:Oxidants / Q000378:metabolism*; D018384:Oxidative Stress; D011379:Prognosis; D034741:RNA, Small Interfering / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000378:metabolism
chemical_list: D016877:Oxidants; D034741:RNA, Small Interfering; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone