title: Isolation and characterization of a metastatic hybrid cell line generated by ER negative and ER positive breast cancer cells in mouse bone marrow.
abstract: BACKGROUND
  The origin and the contribution of breast tumor heterogeneity to its progression are not clear. We investigated the effect of a growing orthotopic tumor formed by an aggressive estrogen receptor (ER)-negative breast cancer cell line on the metastatic potential of a less aggressive ER-positive breast cancer cell line for the elucidation of how the presence of heterogeneous cancer cells might affect each other's metastatic behavior.
  
  
  METHODS
  ER positive ZR-75-1/GFP/puro cells, resistant to puromycin and non-tumorigenic/non-metastatic without exogenous estrogen supplementation, were injected intracardiacally into mice bearing growing orthotopic tumors, formed by ER negative MDA-MB-231/GFP/Neo cells resistant to G418. A variant cell line B6, containing both estrogen-dependent and -independent cells, were isolated from GFP expressing cells in the bone marrow and re-inoculated in nude mice to generate an estrogen-independent cell line B6TC.
  
  
  RESULTS
  The presence of ER negative orthotopic tumors resulted in bone metastasis of ZR-75-1 without estrogen supplementation. The newly established B6TC cell line was tumorigenic without estrogen supplementation and resistant to both puromycin and G418 suggesting its origin from the fusion of MDA-MB-231/GFP/Neo and ZR-75-1/GFP/puro in the mouse bone marrow. Compared to parental cells, B6TC cells were more metastatic to lung and bone after intracardiac inoculation. More significantly, B6TC mice also developed brain metastasis, which was not observed in the MDA-MB-231/GFP/Neo cell-inoculated mice. Low expression of ERα and CD24, and high expression of EMT-related markers such as Vimentin, CXCR4, and Integrin-β1 along with high CD44 and ALDH expression indicated stem cell-like characteristics of B6TC. Gene microarray analysis demonstrated a significantly different gene expression profile of B6TC in comparison to those of parental cell lines.
  
  
  CONCLUSIONS
  Spontaneous generation of the novel hybrid cell line B6TC, in a metastatic site with stem cell-like properties and propensity to metastasize to brain, suggest that cell fusion can contribute to tumor heterogeneity.
authors.affiliation: Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio, Texas, United States of America.
authors.forename: Keya De
authors.initials: KD
authors.lastname: Mukhopadhyay
authors.forename: Abhik
authors.initials: A
authors.lastname: Bandyopadhyay
authors.forename: Ting-Tung A
authors.initials: TT
authors.lastname: Chang
authors.forename: Abdel G
authors.initials: AG
authors.lastname: Elkahloun
authors.forename: John E
authors.initials: JE
authors.lastname: Cornell
authors.forename: Junhua
authors.initials: J
authors.lastname: Yang
authors.forename: Beth A
authors.initials: BA
authors.lastname: Goins
authors.forename: I-Tien
authors.initials: IT
authors.lastname: Yeh
authors.forename: Lu-Zhe
authors.initials: LZ
authors.lastname: Sun
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000473:pathology*; D001859:Bone Neoplasms / Q000556:secondary; D001932:Brain Neoplasms / Q000556:secondary; D001943:Breast Neoplasms / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002469:Cell Separation / Q000379:methods*; D002471:Cell Transformation, Neoplastic; D005260:Female; D006801:Humans; D051379:Mice; D009362:Neoplasm Metastasis; D014411:Neoplastic Stem Cells / Q000473:pathology; D011960:Receptors, Estrogen / Q000378:metabolism*
chemical_list: D011960:Receptors, Estrogen