Macrophages Mediate a Switch between Canonical and Non-Canonical Wnt Pathways in Canine Mammary Tumors

Magdalena Król,Mikołaj Perszko,Karolina Romanowska,Małgorzata Gajewska,Elisabetta Manuali,Tomasz Motyl,Agata Homa,Karol Pawłowski,Eva Hellmen,Kinga Majchrzak,Marta Pietrzak,Joanna Mucha,Małgorzata Bulkowska,Alicja Majewska,Roger Chammas

doi:10.1371/journal.pone.0083995

Abstract

ObjectiveAccording to the current hypothesis, tumor-associated macrophages (TAMs) are “corrupted” by cancer cells and subsequently facilitate, rather than inhibit, tumor metastasis. Because the molecular mechanisms of cancer cell–TAM interactions are complicated and controversial we aimed to better define this phenomenon.Methods and ResultsUsing microRNA microarrays, Real-time qPCR and Western blot we showed that co-culture of canine mammary tumor cells with TAMs or treatment with macrophage-conditioned medium inhibited the canonical Wnt pathway and activated the non-canonical Wnt pathway in tumor cells. We also showed that co-culture of TAMs with tumor cells increased expression of canonical Wnt inhibitors in TAMs. Subsequently, we demonstrated macrophage-induced invasive growth patterns and epithelial–mesenchymal transition of tumor cells. Validation of these results in canine mammary carcinoma tissues (n = 50) and xenograft tumors indicated the activation of non-canonical and canonical Wnt pathways in metastatic tumors and non-metastatic malignancies, respectively. Activation of non-canonical Wnt pathway correlated with number of TAMs.ConclusionsWe demonstrated that TAMs mediate a “switch” between canonical and non-canonical Wnt signaling pathways in canine mammary tumors, leading to increased tumor invasion and metastasis.Interestingly, similar changes in neoplastic cells were observed in the presence of macrophage-conditioned medium or live macrophages. These observations indicate that rather than being “corrupted” by cancer cells, TAMs constitutively secrete canonical Wnt inhibitors that decrease tumor proliferation and development, but as a side effect, they induce the non-canonical Wnt pathway, which leads to tumor metastasis.These data challenge the conventional understanding of TAM–cancer cell interactions.

Highlights

Interactions between various cell types within tumor microenvironments influence development, progression, and metastasis
We demonstrated that Tumor-associated macrophages (TAMs) mediate a ‘‘switch’’ between canonical and non-canonical Wnt signaling pathways in canine mammary tumors, leading to increased tumor invasion and metastasis
These observations indicate that rather than being ‘‘corrupted’’ by cancer cells, TAMs constitutively secrete canonical Wnt inhibitors that decrease tumor proliferation and development, but as a side effect, they induce the non-canonical Wnt pathway, which leads to tumor metastasis

Summary

Introduction

Interactions between various cell types within tumor microenvironments influence development, progression, and metastasis. A prevalent hypothesis suggests that macrophages are corrupted by cancer cells and subsequently contribute to tumor progression instead of tumor inhibition [7,10]. This mechanism comprises a paracrine signaling loop between tumor cells and TAMs that involves various chemokines and cytokines [9]. These factors secreted by cancer cells contribute to down-regulation of both expression of major histocompatibility complex class II and macrophage ability to present antigen. ‘‘corrupted’’ TAMs secrete various growth factors that facilitate the spread of cancer cells into blood vessels, lymph nodes, and distal organs [11]

Methods

Results

Conclusion