Epigenetic regulation of protein phosphatase 2A (PP2A), lymphotactin (XCL1) and estrogen receptor alpha (ER) expression in human breast cancer cells

Cancer Biol Ther. 2004 Dec;3(12):1304-12. doi: 10.4161/cbt.3.12.1458. Epub 2004 Dec 9.


Absence of the estrogen receptor alpha (ER) in human breast cancer cells is an indicator of poor prognosis, and predictive of lack of response to hormonal therapy. Previous studies in our laboratory and others have shown that epigenetic regulation, including DNA methylation and histone deacetylation, are common mechanisms leading to ER gene silencing. Through the use of pharmacologic inhibitors, 5-aza 2'deoxycytidine (AZA) and Trichostatin A (TSA), we have shown that alterations in both of these mechanisms results in synergistic reexpression of ER mRNA and functional protein. These alterations may play a larger role in stimulation of cell signaling pathways leading to ER expression. We have utilized newly developed genome wide screening microarray techniques to identify gene(s) contributing to the hormone independent phenotype and AZA/TSA mediated ER expression. From this screen, we identified and confirmed expression of 4 candidate genes (PP2A, XCL1, THY1 and NBC4) as potential regulators of the hormone independent phenotype. Expression of two genes, XCL1 and PP2A, appeared to be correlated with ER expression. PP2A expression was not changed with ER degradation using ICI 182,780 whereas XCL1 expression decreased in the presence of AZA/TSA and ICI 182,780. This suggests that PP2A may be a determinant of ER expression while XCL1 appears to be ER responsive and downstream of ER expression. These gene products may be novel targets to be further explored in the development of new therapeutics for ER negative breast cancer.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetylation / drug effects
  • Azacitidine / analogs & derivatives*
  • Azacitidine / pharmacology
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / genetics*
  • Breast Neoplasms / metabolism
  • Chemokines, C
  • DNA Methylation*
  • DNA Modification Methylases / antagonists & inhibitors
  • Decitabine
  • Epigenesis, Genetic*
  • Estrogen Receptor alpha / genetics*
  • Estrogen Receptor alpha / metabolism
  • Female
  • Gene Expression Profiling
  • Gene Expression Regulation, Neoplastic / drug effects
  • Histone Deacetylase Inhibitors
  • Humans
  • Hydroxamic Acids
  • Lymphokines / genetics*
  • Lymphokines / metabolism
  • Oligonucleotide Array Sequence Analysis
  • Phosphoprotein Phosphatases / genetics*
  • Phosphoprotein Phosphatases / metabolism
  • Protein Phosphatase 2
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Neoplasm / genetics
  • RNA, Neoplasm / metabolism
  • Receptors, Progesterone / genetics
  • Receptors, Progesterone / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sialoglycoproteins / genetics*
  • Sialoglycoproteins / metabolism
  • Tumor Cells, Cultured


  • Chemokines, C
  • Estrogen Receptor alpha
  • Histone Deacetylase Inhibitors
  • Hydroxamic Acids
  • Lymphokines
  • RNA, Messenger
  • RNA, Neoplasm
  • Receptors, Progesterone
  • Sialoglycoproteins
  • XCL1 protein, human
  • lymphotactin
  • trichostatin A
  • Decitabine
  • DNA Modification Methylases
  • Phosphoprotein Phosphatases
  • Protein Phosphatase 2
  • Azacitidine