The unique transcriptional response produced by concurrent estrogen and progesterone treatment in breast cancer cells results in upregulation of growth factor pathways and switching from a Luminal A to a Basal-like subtype.
BACKGROUND
In breast cancer, progesterone receptor (PR) positivity or abundance is positively associated with survival and treatment response. It was initially believed that PR was a useful diagnostic marker of estrogen receptor activity, but increasingly PR has been recognised to play an important biological role in breast homeostasis, carcinogenesis and metastasis. Although PR expression is almost exclusively observed in estrogen receptor positive tumors, few studies have investigated the cellular mechanisms of PR action in the context of ongoing estrogen signalling.


METHODS
In this study, we contrast PR function in estrogen pretreated ZR-75-1 breast cancer cells with vehicle treated ZR-75-1 and T-47D breast cancer cells using expression microarrays and chromatin immunoprecipitation-sequencing.


RESULTS
Estrogen cotreatment caused a dramatic increase in the number of genes regulated by progesterone in ZR-75-1 cells. In T-47D cells that have naturally high levels of PR, estrogen and progesterone cotreatment resulted in a reduction in the number of regulated genes in comparison to treatment with either hormone alone. At a genome level, estrogen pretreatment of ZR-75-1 cells led to a 10-fold increase in the number of PR DNA binding sites detected using ChIP-sequencing. Time course assessment of progesterone regulated genes in the context of estrogen pretreatment highlighted a series of important regulatory pathways, including those driven by epithelial growth factor receptor (EGFR). Importantly, progesterone applied to cells pretreated with estradiol resulted in switching of the PAM50-determined intrinsic breast cancer subtype from Luminal A to Basal-like, and increased the Oncotype DX® Unscaled Recurrence Score.


CONCLUSIONS
Estrogen pretreatment of breast cancer cells increases PR steady state levels, resulting in an unequivocal progesterone response that upregulates key members of growth factor pathways. The transformative changes progesterone exerts on the breast cancer subtype suggest that these subtyping tools should be used with caution in premenopausal women.
Cancer Biology Group, The Basil Hetzel Institute for Translational Health Research, School of Medicine, The University of Adelaide, DX465701, 28 Woodville Road, Woodville South, 5011, South Australia, Australia. Eleanor.need@adelaide.edu.au.
Eleanor F
EF
Need
Dame Roma Mitchell Cancer Research Laboratories and Adelaide Prostate Cancer Research Centre, The University of Adelaide, Adelaide, South Australia, Australia. Luke.selth@adelaide.edu.au.|Freemasons Foundation Centre for Men's Health, The University of Adelaide, Adelaide, South Australia, Australia. Luke.selth@adelaide.edu.au.
Luke A
LA
Selth
Cancer Biology Group, The Basil Hetzel Institute for Translational Health Research, School of Medicine, The University of Adelaide, DX465701, 28 Woodville Road, Woodville South, 5011, South Australia, Australia. Trotta.andrew@gmail.com.|Present address: Icahn School of Medicine at Mount Sinai, Department of Oncological Sciences, Manhattan, New York, USA. Trotta.andrew@gmail.com.
Andrew P
AP
Trotta
Cancer Biology Group, The Basil Hetzel Institute for Translational Health Research, School of Medicine, The University of Adelaide, DX465701, 28 Woodville Road, Woodville South, 5011, South Australia, Australia. Damien.leach@adelaide.edu.au.
Damien A
DA
Leach
Cancer Biology Group, The Basil Hetzel Institute for Translational Health Research, School of Medicine, The University of Adelaide, DX465701, 28 Woodville Road, Woodville South, 5011, South Australia, Australia. lauren.giorgio@gmail.com.
Lauren
L
Giorgio
Cancer Biology Group, The Basil Hetzel Institute for Translational Health Research, School of Medicine, The University of Adelaide, DX465701, 28 Woodville Road, Woodville South, 5011, South Australia, Australia. melol@adam.com.au.
Melissa A
MA
O'Loughlin
Solid Cancer Regulation Research Group, The Basil Hetzel Institute for Translational Health Research Discipline of Surgery, The University of Adelaide, South Australia, Australia. Eric.smith@adelaide.edu.au.
Eric
E
Smith
School of Medicine, Department of Surgery, The University of Adelaide, Adelaide, South Australia, Australia. grantley.gill@adelaide.edu.au.
Peter G
PG
Gill
School of Medicine at The Queen Elizabeth Hospital, University of Adelaide, South Australia, Australia. wendy.ingman@adelaide.edu.au.|Robinson Research Institute, University of Adelaide, South Australia, Australia. wendy.ingman@adelaide.edu.au.
Wendy V
WV
Ingman
Centre for Cancer Research, Westmead Millennium Institute, University of Sydney Medical School, Westmead, New South Wales, 2145, Australia. dinny.graham@sydney.edu.au.
J Dinny
JD
Graham
Cancer Biology Group, The Basil Hetzel Institute for Translational Health Research, School of Medicine, The University of Adelaide, DX465701, 28 Woodville Road, Woodville South, 5011, South Australia, Australia. grant.buchanan@adelaide.edu.au.|Freemasons Foundation Centre for Men's Health, The University of Adelaide, Adelaide, South Australia, Australia. grant.buchanan@adelaide.edu.au.
Grant
G
Buchanan
D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology*; D045744:Cell Line, Tumor; D066246:ErbB Receptors / Q000096:biosynthesis*; D004967:Estrogens / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D061986:MCF-7 Cells; D011374:Progesterone / Q000008:administration & dosage*; D011980:Receptors, Progesterone / Q000096:biosynthesis; D015533:Transcriptional Activation / Q000187:drug effects* / Q000502:physiology; D016896:Treatment Outcome; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D004967:Estrogens; D011980:Receptors, Progesterone; D011374:Progesterone; C512478:EGFR protein, human; D066246:ErbB Receptors