The growth response to androgen receptor signaling in ERα-negative human breast cells is dependent on p21 and mediated by MAPK activation.
BACKGROUND
Although a high frequency of androgen receptor (AR) expression in human breast cancers has been described, exploiting this knowledge for therapy has been challenging. This is in part because androgens can either inhibit or stimulate cell proliferation in pre-clinical models of breast cancer. In addition, many breast cancers co-express other steroid hormone receptors that can affect AR signaling, further obfuscating the effects of androgens on breast cancer cells.


METHODS
To create better-defined models of AR signaling in human breast epithelial cells, we took estrogen receptor (ER)-α-negative and progesterone receptor (PR)-negative human breast epithelial cell lines, both cancerous and non-cancerous, and engineered them to express AR, thus allowing the unambiguous study of AR signaling. We cloned a full-length cDNA of human AR, and expressed this transgene in MCF-10A non-tumorigenic human breast epithelial cells and MDA-MB-231 human breast-cancer cells. We characterized the responses to AR ligand binding using various assays, and used isogenic MCF-10A p21 knock-out cell lines expressing AR to demonstrate the requirement for p21 in mediating the proliferative responses to AR signaling in human breast epithelial cells.


RESULTS
We found that hyperactivation of the mitogen-activated protein kinase (MAPK) pathway from both AR and epidermal growth factor receptor (EGFR) signaling resulted in a growth-inhibitory response, whereas MAPK signaling from either AR or EGFR activation resulted in cellular proliferation. Additionally, p21 gene knock-out studies confirmed that AR signaling/activation of the MAPK pathway is dependent on p21.


CONCLUSIONS
These studies present a new model for the analysis of AR signaling in human breast epithelial cells lacking ERα/PR expression, providing an experimental system without the potential confounding effects of ERα/PR crosstalk. Using this system, we provide a mechanistic explanation for previous observations ascribing a dual role for AR signaling in human breast cancer cells. As previous reports have shown that approximately 40% of breast cancers can lack p21 expression, our data also identify potential new caveats for exploiting AR as a target for breast cancer therapy.
The Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins University School of Medicine, Baltimore, MD, USA. bpark2@jhmi.edu
Joseph P
JP
Garay
Bedri
B
Karakas
Abde M
AM
Abukhdeir
David P
DP
Cosgrove
John P
JP
Gustin
Michaela J
MJ
Higgins
Hiroyuki
H
Konishi
Yuko
Y
Konishi
Josh
J
Lauring
Morassa
M
Mohseni
Grace M
GM
Wang
Danijela
D
Jelovac
Ashani
A
Weeraratna
Cheryl A
CA
Sherman Baust
Patrice J
PJ
Morin
Antoun
A
Toubaji
Alan
A
Meeker
Angelo M
AM
De Marzo
Gloria
G
Lewis
Andrea
A
Subhawong
Pedram
P
Argani
Ben H
BH
Park
D000726:Androgen Antagonists / Q000494:pharmacology; D000728:Androgens / Q000494:pharmacology; D000813:Anilides / Q000494:pharmacology; D001943:Breast Neoplasms; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019938:Cyclin D1 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D047628:Estrogen Receptor alpha / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D006801:Humans; D020935:MAP Kinase Signaling System; D015741:Metribolone / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology; D011944:Receptors, Androgen / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D014105:Tosyl Compounds / Q000494:pharmacology; D015854:Up-Regulation
D000726:Androgen Antagonists; D000728:Androgens; D000813:Anilides; C530104:CCND1 protein, human; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; D009570:Nitriles; D011944:Receptors, Androgen; D011994:Recombinant Proteins; D014105:Tosyl Compounds; D019938:Cyclin D1; D015741:Metribolone; C053541:bicalutamide; D048049:Extracellular Signal-Regulated MAP Kinases