Asporin Is a Fibroblast-Derived TGF-β1 Inhibitor and a Tumor Suppressor Associated with Good Prognosis in Breast Cancer.
BACKGROUND
Breast cancer is a leading malignancy affecting the female population worldwide. Most morbidity is caused by metastases that remain incurable to date. TGF-β1 has been identified as a key driving force behind metastatic breast cancer, with promising therapeutic implications.


RESULTS
Employing immunohistochemistry (IHC) analysis, we report, to our knowledge for the first time, that asporin is overexpressed in the stroma of most human breast cancers and is not expressed in normal breast tissue. In vitro, asporin is secreted by breast fibroblasts upon exposure to conditioned medium from some but not all human breast cancer cells. While hormone receptor (HR) positive cells cause strong asporin expression, triple-negative breast cancer (TNBC) cells suppress it. Further, our findings show that soluble IL-1β, secreted by TNBC cells, is responsible for inhibiting asporin in normal and cancer-associated fibroblasts. Using recombinant protein, as well as a synthetic peptide fragment, we demonstrate the ability of asporin to inhibit TGF-β1-mediated SMAD2 phosphorylation, epithelial to mesenchymal transition, and stemness in breast cancer cells. In two in vivo murine models of TNBC, we observed that tumors expressing asporin exhibit significantly reduced growth (2-fold; p = 0.01) and metastatic properties (3-fold; p = 0.045). A retrospective IHC study performed on human breast carcinoma (n = 180) demonstrates that asporin expression is lowest in TNBC and HER2+ tumors, while HR+ tumors have significantly higher asporin expression (4-fold; p = 0.001). Assessment of asporin expression and patient outcome (n = 60; 10-y follow-up) shows that low protein levels in the primary breast lesion significantly delineate patients with bad outcome regardless of the tumor HR status (area under the curve = 0.87; 95% CI 0.78-0.96; p = 0.0001). Survival analysis, based on gene expression (n = 375; 25-y follow-up), confirmed that low asporin levels are associated with a reduced likelihood of survival (hazard ratio = 0.58; 95% CI 0.37-0.91; p = 0.017). Although these data highlight the potential of asporin to serve as a prognostic marker, confirmation of the clinical value would require a prospective study on a much larger patient cohort.


CONCLUSIONS
Our data show that asporin is a stroma-derived inhibitor of TGF-β1 and a tumor suppressor in breast cancer. High asporin expression is significantly associated with less aggressive tumors, stratifying patients according to the clinical outcome. Future pre-clinical studies should consider options for increasing asporin expression in TNBC as a promising strategy for targeted therapy.
Metastasis Research Laboratory, GIGA-Cancer, University of Liège, Liège, Belgium.
Pamela
P
Maris
Metastasis Research Laboratory, GIGA-Cancer, University of Liège, Liège, Belgium.
Arnaud
A
Blomme
Metastasis Research Laboratory, GIGA-Cancer, University of Liège, Liège, Belgium.
Ana Perez
AP
Palacios
Metastasis Research Laboratory, GIGA-Cancer, University of Liège, Liège, Belgium.
Brunella
B
Costanza
Metastasis Research Laboratory, GIGA-Cancer, University of Liège, Liège, Belgium.
Akeila
A
Bellahcène
Department of Pathology, University Hospital Liège, University of Liège, Liège, Belgium.
Elettra
E
Bianchi
Biotheque, University of Liège, Liège, Belgium.
Stephanie
S
Gofflot
Animal Facility, GIGA-Cardiovascular Sciences, University of Liège, Liège, Belgium.
Pierre
P
Drion
Metastasis Research Laboratory, GIGA-Cancer, University of Liège, Liège, Belgium; Department of Pharmacy and Health and Nutritional Sciences, University of Calabria, Arcavacata di Rende, Cosenza, Italy.
Giovanna Elvi
GE
Trombino
GIGA-Viral Vectors Platform, University of Liège, Liège, Belgium.
Emmanuel
E
Di Valentin
Department of Senology, University Hospital Liège, University of Liège, Liège, Belgium.
Pino G
PG
Cusumano
Department of Abdominal Surgery, University of Liège, Liège, Belgium.
Sylvie
S
Maweja
Department of Medical Oncology, University Hospital Liège, University of Liège, Liège, Belgium.
Guy
G
Jerusalem
Department of Pathology, University Hospital Liège, University of Liège, Liège, Belgium.
Philippe
P
Delvenne
Department of Senology, University Hospital Liège, University of Liège, Liège, Belgium.
Eric
E
Lifrange
Metastasis Research Laboratory, GIGA-Cancer, University of Liège, Liège, Belgium.
Vincent
V
Castronovo
Metastasis Research Laboratory, GIGA-Cancer, University of Liège, Liège, Belgium.
Andrei
A
Turtoi
D000818:Animals; D014408:Biomarkers, Tumor / Q000378:metabolism; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D016326:Extracellular Matrix Proteins / Q000378:metabolism* / Q000494:pharmacology*; D005260:Female; D005346:Fibroblast Growth Factors / Q000378:metabolism / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D064593:Heterografts; D006801:Humans; D053583:Interleukin-1beta / Q000494:pharmacology; D051379:Mice; D008875:Middle Aged; D011379:Prognosis; D060888:Real-Time Polymerase Chain Reaction; D012189:Retrospective Studies; D016019:Survival Analysis; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014407:Tumor Cells, Cultured
C439889:ASPN protein, human; C511592:Aspn protein, mouse; D014408:Biomarkers, Tumor; D016326:Extracellular Matrix Proteins; D053583:Interleukin-1beta; D016212:Transforming Growth Factor beta; D005346:Fibroblast Growth Factors