title: Opposing effects of Runx2 and estradiol on breast cancer cell proliferation: in vitro identification of reciprocally regulated gene signature related to clinical letrozole responsiveness.
abstract: OBJECTIVE
  To assess the clinical significance of the interaction between estrogen and Runx2 signaling, previously shown in vitro.
  
  
  METHODS
  MCF7/Rx2(dox) breast cancer cells were treated with estradiol and/or doxycycline to induce Runx2, and global gene expression was profiled to define genes regulated by estradiol, Runx2, or both. Anchorage-independent growth was assessed by soft-agar colony formation assays. Expression of gene sets defined using the MCF7/Rx2(dox) system was analyzed in pre- and on-treatment biopsies from hormone receptor-positive patients undergoing neoadjuvant letrozole treatment in two independent studies, and short-term changes in gene expression were correlated with tumor size reduction or Ki67 index at surgery.
  
  
  RESULTS
  Reflecting its oncogenic property, estradiol strongly promoted soft-agar colony formation, whereas Runx2 blocked this process suggesting tumor suppressor property. Transcriptome analysis of MCF7/Rx2(dox) cells treated with estradiol and/or doxycycline showed reciprocal attenuation of Runx2 and estrogen signaling. Correspondingly in breast cancer tumors, expression of estradiol- and Runx2-regulated genes was inversely correlated, and letrozole increased expression of Runx2-stimulated genes, as defined in the MCF7/Rx2(dox) model. Of particular interest was a gene set upregulated by estradiol and downregulated by Runx2 in vitro; its short-term response to letrozole treatment associated with tumor size reduction and Ki67 index at surgery better than other estradiol-regulated gene sets.
  
  
  CONCLUSIONS
  This work provides clinical evidence for the importance of antagonism between Runx2 and E2 signaling in breast cancer. Likely sensing the tension between them, letrozole responsiveness of a genomic node, positively regulated by estradiol and negatively regulated by Runx2 in vitro, best correlated with the clinical efficacy of letrozole treatment.
authors.affiliation: Department of Biochemistry, Institute for Genetic Medicine, USC Epigenome Center, Keck School of Medicine of the University of Southern California, Los Angeles, California 90033, USA.
authors.forename: Nyam-Osor
authors.initials: NO
authors.lastname: Chimge
authors.forename: Sanjeev K
authors.initials: SK
authors.lastname: Baniwal
authors.forename: Jingqin
authors.initials: J
authors.lastname: Luo
authors.forename: Simon
authors.initials: S
authors.lastname: Coetzee
authors.forename: Omar
authors.initials: O
authors.lastname: Khalid
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Berman
authors.forename: Debu
authors.initials: D
authors.lastname: Tripathy
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Ellis
authors.forename: Baruch
authors.initials: B
authors.lastname: Frenkel
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D017322:Clinical Trials, Phase II as Topic; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics* / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D004958:Estradiol / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005455:Fluorescent Antibody Technique; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D000077289:Letrozole; D009570:Nitriles / Q000627:therapeutic use; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D014230:Triazoles / Q000627:therapeutic use
chemical_list: D000970:Antineoplastic Agents; D050659:Core Binding Factor Alpha 1 Subunit; D009570:Nitriles; D014230:Triazoles; D004958:Estradiol; D000077289:Letrozole