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

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.

Relationship between the inflammatory tumor microenvironment and different histologic types of canine mammary tumors

“…Regarding the macrophages, a higher number of these cells were found in malignant tumors with better prognosis (CMT), but no relationship with survival, invasion and metastasis was observed. These findings contradict what was pointed out by Król et al (2011Król et al ( , 2014 and Raposo et al (2014), who verified that an increase of tumor associated macrophages (TAMs) was related to increased invasion and metastasis and decreased survival in patients, which are characteristics of more aggressive neoplasms. However, it is important to point out that, in the present study, immunohistochemistry technique was not used to identify and differentiate subpopulations of M1 or M2 macrophages.…”

Leveraging Naked Mole Rat (Heterocephalus glaber) Comparative Genomics to Identify Canine Genes Modulating Susceptibility to Tumorigenesis and Cancer Phenotypes

“…Conserved tumorigenesis orthologs implicated in this tumor type include CTNNB1 and PTEN [59] while least conserved orthologs associated with canine mammary tumors include BRCA1 [4] AND [60], BRCA2 [61], MUC1 [62], and KLF4 [63]. Interestingly, tumor associated macrophages (TAMs) have been implicated in modulating tumor invasion and metastasis in this cancer type [64].…”

MicroRNA and cancer: a focus on mammary tumors in female dogs

“…Studies on miRNAs in canine mammary tumors are scarce, particularly regarding metastatic progression (BULKOWSKA et al, 2017). Few studies have investigated the global miRNA expression profile in in vitro models of canine breast cancer (KRÓL et al, 2014;LUTFUL et al, 2015;OSAKI et al, 2016). Some studies evaluated miRNA expression in different phases of tumorigenesis using canine breast tissue and reported several differentially expressed miRNAs (BOGGS et al, 2008;VON DEETZEN et al, 2014;BULKOWSKA et al, 2017).…”

“…A study based on miRNA expression profiles in in vitro models of canine breast cancer investigated miRNA expression in a co-culture of canine mammary tumor cells with tumor-associated macrophages and observed changes in expression patterns, suggesting that the tumor microenvironment may affect miRNA expression (KRÓL et al, 2014).…”