Asporin Is a Fibroblast-Derived TGF-β1 Inhibitor and a Tumor Suppressor Associated with Good Prognosis in Breast Cancer

Abstract

BackgroundBreast 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.Methods and FindingsEmploying 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.ConclusionsOur 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.

Glycoprotein asporin as a novel player in tumour microenvironment and cancer progression

“…Soluble IL-1β, secreted by TNBC cells, was found to be responsible for inhibiting ASPN in normal and cancerassociated fibroblasts. Importantly, induced ASPN expression in MDA-MB-468 cells significantly reduced their growth and metastatic capacity in a murine model 39 . During the publication process of this review, our original article on the dual role of asporin in breast cancer progression was accepted 65 .…”

“…Importantly, IL 1β is secreted by triple-negative breast cancer cells and down-regulates ASPN expression in cancer-associated fibroblasts (CAFs) (ref. 39 ), see below. One of the homeodomain transcription factors, CUX1 (cut-like homeobox 1; previous symbol CUTL1) has been described as a target of TGFβ and as an enhancer of breast cancer cell motility and invasiveness 40 .…”

“…63,64 ). Recently, Maris and colleagues 39 described ASPN protein as a fibroblast-derived TGF-β1 inhibitor and a tumour suppressor associated with good prognosis in breast cancer. Detailed functional analyses showed that hormone receptor positive cell lines induced strong ASPN expression (both mRNA and protein) in breast fibroblasts, while triple-negative breast cancer (TNBC) cells suppressed it.…”

L’asporine : une nouvelle défense naturelle contre le cancer du sein

“…La présence d'asporine empê-chait également les cellules d'effectuer la transition épithélio-mésenchymateuse 2 (TEM) [9] (➜) et diminuait la proportion de cellules souches dans différentes lignées de cancer du sein. De plus, nous avons mis en évidence que, mécanistiquement, cet effet inhibiteur de l'asporine dépendait d'un fragment peptidique correspondant aux acides aminés 159 à 205 [8]. En utilisant deux modèles in vivo, nous avons également prouvé que la surexpression d'asporine dans des cellules 1 Cellules formant le cartilage.…”

“…L'asporine a initialement été découverte dans le cartilage articulaire où elle régule la formation de cartilage en modulant la voie de signalisation du TGF-1 [7]. Intrigués par sa localisation particulière, dans le stroma tumoral, nous avons décidé d'étudier plus en détails le rôle de cette protéine dans le contexte du cancer du sein [8].…”