title: Loss of pigment epithelium-derived factor: a novel mechanism for the development of endocrine resistance in breast cancer.
abstract: BACKGROUND
  Despite the benefits of endocrine therapies such as tamoxifen and aromatase inhibitors in treating estrogen receptor (ER) alpha-positive breast cancer, many tumors eventually become resistant. The molecular mechanisms governing resistance remain largely unknown. Pigment epithelium-derived factor (PEDF) is a multifunctional secreted glycoprotein that displays broad anti-tumor activity based on dual targeting of the tumor microenvironment (anti-angiogenic action) and the tumor cells (direct anti-tumor action). Recent studies indicate that PEDF expression is significantly reduced in several tumor types, including breast cancer, and that its reduction is associated with disease progression and poor patient outcome. In the current study, we investigated the role of PEDF in the development of endocrine resistance in breast cancer.
  
  
  METHODS
  PEDF mRNA and protein levels were measured in several endocrine-resistant breast cancer cell lines including MCF-7:5C, MCF-7:2A, and BT474 and in endocrine-sensitive cell lines MCF-7, T47D, and ZR-75-1 using real-time PCR and western blot analyses. Tissue microarray analysis and immunohistochemistry were used to assess the PEDF protein level in tamoxifen-resistant breast tumors versus primary tumors. Lentiviruses were used to stably express PEDF in endocrine-resistant breast cancer cell lines to determine their sensitivity to tamoxifen following PEDF re-expression.
  
  
  RESULTS
  We found that PEDF mRNA and protein levels were dramatically reduced in endocrine-resistant MCF-7:5C, MCF-7:2A, and BT474 breast cancer cells compared with endocrine-sensitive MCF-7, T47D, and ZR-75-1 cells, and that loss of PEDF was associated with enhanced expression of pSer167ERα and the receptor tyrosine kinase rearranged during transfection (RET). Importantly, we found that silencing endogenous PEDF in tamoxifen-sensitive MCF-7 and T47D breast cancer cells conferred tamoxifen resistance whereas re-expression of PEDF in endocrine-resistant MCF-7:5C and MCF-7:2A cells restored their sensitivity to tamoxifen in vitro and in vivo through suppression of RET. Lastly, tissue microarray studies revealed that PEDF protein was reduced in ~52.4% of recurrence tumors (31 out of 59 samples) and loss of PEDF was associated with disease progression and poor patient outcome.
  
  
  CONCLUSIONS
  Overall, these findings suggest that PEDF silencing might be a novel mechanism for the development of endocrine resistance in breast cancer and that PEDF expression might be a predictive marker of endocrine sensitivity.
authors.forename: Rifat
authors.initials: R
authors.lastname: Jan
authors.forename: Min
authors.initials: M
authors.lastname: Huang
authors.forename: Joan
authors.initials: J
authors.lastname: Lewis-Wambi
mesh_terms: D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use*; D017209:Apoptosis / Q000235:genetics; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D047628:Estrogen Receptor alpha / Q000235:genetics; D005136:Eye Proteins / Q000096:biosynthesis / Q000235:genetics*; D005260:Female; D006801:Humans; D061986:MCF-7 Cells; D051379:Mice; D008819:Mice, Nude; D009414:Nerve Growth Factors / Q000096:biosynthesis / Q000235:genetics*; D034622:RNA Interference; D012333:RNA, Messenger / Q000096:biosynthesis; D034741:RNA, Small Interfering; D020218:Response Elements / Q000235:genetics; D015843:Serpins / Q000096:biosynthesis / Q000235:genetics*; D013629:Tamoxifen / Q000627:therapeutic use*; D046888:Tissue Array Analysis; D014161:Transduction, Genetic; D023041:Xenograft Model Antitumor Assays; D000099174:Pigment Epithelium-Derived Factor
chemical_list: D018931:Antineoplastic Agents, Hormonal; D047628:Estrogen Receptor alpha; D005136:Eye Proteins; D009414:Nerve Growth Factors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D015843:Serpins; D013629:Tamoxifen; D000099174:Pigment Epithelium-Derived Factor