Genome-wide analysis of aromatase inhibitor-resistant, tamoxifen-resistant, and long-term estrogen-deprived cells reveals a role for estrogen receptor.
Acquired resistance to either tamoxifen or aromatase inhibitors (AI) develops after prolonged treatment in a majority of hormone-responsive breast cancers. In an attempt to further elucidate mechanisms of acquired resistance to AIs, MCF-7aro cells resistant to letrozole (T+LET R), anastrozole (T+ANA R), and exemestane (T+EXE R), as well as long-term estrogen deprived (LTEDaro) and tamoxifen-resistant (T+TAM R) lines were generated. This is the first complete panel of endocrine therapy-resistant cell lines, which were generated as multiple independent biological replicates for unbiased genome-wide analysis using affymetrix microarrays. Although similarities are apparent, microarray results clearly show gene signatures unique to AI-resistance were inherently different from LTEDaro and T+TAM R gene expression profiles. Based on hierarchical clustering, unique estrogen-responsive gene signatures vary depending on cell line, with some genes up-regulated in all lines versus other genes up-regulated only in the AI-resistant lines. Characterization of these resistant lines showed that LTEDaro, T+LET R, and T+ANA R cells contained a constitutively active estrogen receptor (ER)alpha that does not require estrogen for activation. This ligand-independent activation of ER was not observed in the parental cells, as well as T+EXE R and T+TAM R cells. Further characterization of these resistant lines was performed using cell cycle analysis, immunofluorescence experiments to visualize ER subcellular localization, as well as cross-resistance studies to determine second-line inhibitor response. Using this well-defined model system, our studies provide important information regarding differences in resistance mechanisms to AIs, TAM, and LTEDaro, which are critical in overcoming resistance when treating hormone-responsive breast cancers.
Masri
Selma
S
Department of Surgical Research, Division of Information Sciences, Beckman Research Institute of the City of Hope, Duarte, California, USA.
Phung
Sheryl
S
Wang
Xin
X
Wu
Xiwei
X
Yuan
Yate-Ching
YC
Wagman
Lawrence
L
Chen
Shiuan
S
D001141:Aromatase / Q000737:chemistry* / Q000378:metabolism; D047072:Aromatase Inhibitors / Q000494:pharmacology*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects; D047369:Chromatin Immunoprecipitation; D019008:Drug Resistance, Neoplasm; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism*; D004967:Estrogens / Q000172:deficiency*; D005260:Female; D005455:Fluorescent Antibody Technique; D020869:Gene Expression Profiling; D015894:Genome, Human; D006801:Humans; D046228:Microarray Analysis; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013629:Tamoxifen / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D047072:Aromatase Inhibitors; D047628:Estrogen Receptor alpha; D004967:Estrogens; D012333:RNA, Messenger; D013629:Tamoxifen; D001141:Aromatase