Breast cancer normalization induced by embryonic mesenchyme is mediated by extracellular matrix biglycan

Abstract

Some epithelial cancers can be induced to revert to quiescent differentiated tissue when combined with embryonic mesenchyme; however, the mechanism of this induction is unknown. Here we combine tissue engineering, developmental biology, biochemistry and proteomics approaches to attack this problem. Using a synthetic reconstitution system, we show that co-culture of breast cancer cells with embryonic mesenchyme from early stage (E12.5-13.5) mammary glands decreases tumor cell proliferation while stimulating acinus differentiation, whereas cancer-associated fibroblasts (CAFs) fail to produce these normalizing effects. When insoluble extracellular matrices (ECMs) were isolated from cultured early stage (E12.5-13.5) embryonic mammary mesenchyme cells or E10 tooth mesenchyme and recombined with mammary tumor cells, they were found to be sufficient to induce breast cancer normalization including enhanced expression of estrogen receptor-α (ER-α). In contrast, ECM from later stage (E14.5) mammary mesenchyme and conditioned medium isolated from mesenchymal cell cultures were ineffective. Importantly, when the inductive ECMs produced by early stage embryonic mammary mesenchyme were scraped from dishes and injected into fast-growing breast tumors in mice, they significantly inhibited cancer expansion. Proteomics analysis of the detergent insoluble ECM material revealed several matrix components that were preferentially expressed in the embryonic ECMs. Analysis of two of these molecules previously implicated in cancer regulation--biglycan and tenascin C--revealed that addition of biglyan can mimic the tumor normalization response, and that siRNA knockdown of its expression in cultured embryonic mesenchyme results in loss of the ECM's inductive activity. These studies confirm that embryonic mesenchyme retains the ability to induce partial breast cancer reversion, and that its inductive capability resides at least in part in the ECM protein biglycan that it produces.

Insights into the key roles of proteoglycans in breast cancer biology and translational medicine

“…Indeed, high levels of biglycan expression are associated with increased risk of esophageal squamous cell carcinoma [157], significant clinical outcome of pancreatic adenocarcinoma [167], enhanced gastric cancer invasion [183], and breast cancer normalization [184]. It is well established that breast cancer cells slow their growth and differentiate when associated with embryonic mesenchyme.…”

“…Notably, when the matrix secreted by embryonic mammary mesenchyme was injected into fast-growing breast carcinoma in mice, there was a marked reduction of growth. Proteomics analysis of this mesenchyme ECM showed biglycan as a major constituent [184]. Moreover, addition of soluble biglycan was capable of evoking the tumor normalization response, and RNAi-mediated depletion of biglycan expression in cultured embryonic mesenchyme abolished the ECM’s inductive activity [184].…”

“…Proteomics analysis of this mesenchyme ECM showed biglycan as a major constituent [184]. Moreover, addition of soluble biglycan was capable of evoking the tumor normalization response, and RNAi-mediated depletion of biglycan expression in cultured embryonic mesenchyme abolished the ECM’s inductive activity [184]. Thus, biglycan has a novel biological activity within the embryonic mammary mesenchyme that leads to partial breast cancer reversion.…”

Matricellular proteins as regulators of cancer metastasis to bone

“…Bone marrow stromal cell-derived biglycan may have similar anti-bone metastatic functions as decorin. Biglycan in an ECM scaffold produced by mammary mesenchyme cells can “normalize” breast cancer cells in vitro [34]. In addition, decreased biglycan is found in paired bone metastases compared to primary tumors in breast cancer patients [35].…”

Biomimetic Tissue–Engineered Systems for Advancing Cancer Research: NCI Strategic Workshop Report

“…Ingber (Harvard University, Cambridge, MA, USA) emphasized in a keynote presentation the importance of the tumor microenvironment and showed that local changes in extracellular matrix (ECM) remodeling and cell mechanics actively contribute to tumor initiation and progression. He also showed that breast cancer cell growth and spheroid architecture are normalized when mixed with normal embryonic mesenchyme or with the critical ECM component biglycan in either 3D Matrigel or in collagen I gels (1). This insight on the tumor microenvironment was applied in the context of human ‘organs-on-chips’: cell culture devices containing micrometer-sized chambers seeded with live cells that then recapitulate the specialized multicellular architectures, tissue-tissue interfaces, physicochemical microenvironments, and vascular perfusion necessary to capture complex organ-level functions and human disease processes in vitro (2), (3).…”