title: PRC2/EED-EZH2 complex is up-regulated in breast cancer lymph node metastasis compared to primary tumor and correlates with tumor proliferation in situ.
abstract: BACKGROUND
  Lymph node metastasis is a key event in the progression of breast cancer. Therefore it is important to understand the underlying mechanisms which facilitate regional lymph node metastatic progression.
  
  
  RESULTS
  We performed gene expression profiling of purified tumor cells from human breast tumor and lymph node metastasis. By microarray network analysis, we found an increased expression of polycomb repression complex 2 (PRC2) core subunits EED and EZH2 in lymph node metastatic tumor cells over primary tumor cells which were validated through real-time PCR. Additionally, immunohistochemical (IHC) staining and quantitative image analysis of whole tissue sections showed a significant increase of EZH2 expressing tumor cells in lymph nodes over paired primary breast tumors, which strongly correlated with tumor cell proliferation in situ. We further explored the mechanisms of PRC2 gene up-regulation in metastatic tumor cells and found up-regulation of E2F genes, MYC targets and down-regulation of tumor suppressor gene E-cadherin targets in lymph node metastasis through GSEA analyses. Using IHC, the expression of potential EZH2 target, E-cadherin was examined in paired primary/lymph node samples and was found to be significantly decreased in lymph node metastases over paired primary tumors.
  
  
  CONCLUSIONS
  This study identified an over expression of the epigenetic silencing complex PRC2/EED-EZH2 in breast cancer lymph node metastasis as compared to primary tumor and its positive association with tumor cell proliferation in situ. Concurrently, PRC2 target protein E-cadherin was significant decreased in lymph node metastases, suggesting PRC2 promotes epithelial mesenchymal transition (EMT) in lymph node metastatic process through repression of E-cadherin. These results indicate that epigenetic regulation mediated by PRC2 proteins may provide additional advantage for the outgrowth of metastatic tumor cells in lymph nodes. This opens up epigenetic drug development possibilities for the treatment and prevention of lymph node metastasis in breast cancer.
authors.affiliation: Division of Hematology, Department of Medicine, Stanford University, Stanford, CA, USA.
authors.forename: Hongxiang
authors.initials: H
authors.lastname: Yu
authors.forename: Diana L
authors.initials: DL
authors.lastname: Simons
authors.forename: Ilana
authors.initials: I
authors.lastname: Segall
authors.forename: Valeria
authors.initials: V
authors.lastname: Carcamo-Cavazos
authors.forename: Erich J
authors.initials: EJ
authors.lastname: Schwartz
authors.forename: Ning
authors.initials: N
authors.lastname: Yan
authors.forename: Neta S
authors.initials: NS
authors.lastname: Zuckerman
authors.forename: Frederick M
authors.initials: FM
authors.lastname: Dirbas
authors.forename: Denise L
authors.initials: DL
authors.lastname: Johnson
authors.forename: Susan P
authors.initials: SP
authors.lastname: Holmes
authors.forename: Peter P
authors.initials: PP
authors.lastname: Lee
mesh_terms: D001943:Breast Neoplasms / Q000473:pathology*; D049109:Cell Proliferation; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008207:Lymphatic Metastasis; D063151:Polycomb Repressive Complex 2 / Q000235:genetics / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D015854:Up-Regulation
chemical_list: D063151:Polycomb Repressive Complex 2