Epithelial-mesenchymal interactions in breast cancer: evidence for a role of nuclear localized β-catenin in carcinoma-associated fibroblasts

Inhibition of interferon-signalling halts cancer-associated fibroblast-dependent protection of breast cancer cells from chemotherapy

BACKGROUND

Triple negative breast cancers (TNBC) have poor prognoses despite aggressive treatment with cytotoxic chemotherapy. Cancer-associated fibroblasts (CAFs) are prominent in tumour stroma. Our hypothesis was that CAFs modulate chemotherapy sensitivity.

METHODS

TNBC cells and breast fibroblasts were cultured; survival after chemotherapeutics was assessed using luciferase or clonogenic assays. Signalling was investigated using transcriptomics, reporters, recombinant proteins and blocking antibodies. Clinical relevance was investigated using immunohistochemistry.

RESULTS

Breast CAFs dose-dependently protected TNBC cell lines MDA-MB-231 and MDA-MB-157, but not MDA-MB-468s, from chemotherapy. CAF-induced protection was associated with interferon (IFN) activation. CAFs were induced to express IFNβ1 by chemotherapy and TNBC co-culture, leading to paracrine activation in cancer cells. Recombinant IFNs were sufficient to protect MDA-MB-231 and MDA-MB-157 but not MDA-MB-468 cells. In TNBC patients, IFNβ1 expression in CAFs correlated with cancer cell expression of MX1, a marker of activated IFN signalling. High expression of IFNβ1 (CAFs) or MX1 (tumour cells) correlated with reduced survival after chemotherapy, especially in claudin-low tumours (which MDA-MB-231 and MDA-MB-157 cells represent). Antibodies that block IFN receptors reduced CAF-dependent chemoprotection.

CONCLUSIONS

CAF-induced activation of IFN signalling in claudin-low TNBCs results in chemoresistance. Inhibition of this pathway represents a novel method to improve breast cancer outcomes.

Multiple oncogenic roles of nuclear beta-catenin

β-Catenin is essential for embryonic development and required for cell renewal/regeneration in adult life. Cellular β-catenin exists in three different pools: membranous, cytoplasmic and nuclear. In this review, we focus on functions of the nuclear pool in relation to tumorigenesis. In the nucleus, beta-catenin functions as both activator and repressor of transcription in a context-dependent manner. It promotes cell proliferation and supports tumour growth by enhancing angiogenesis. β-Catenin-mediated signalling regulates cancer cell metabolism and is associated with tumour-initiating cells in multiple malignancies. In addition, it functions as both pro- and anti-apoptotic factor besides acting to inhibit recruitment of inflammatory anti-tumour T-cells. Thus, β-catenin appears to possess a multifaceted nuclear function that may significantly impact tumour initiation and progression.

Dermal fibroblasts induce cell cycle arrest and block epithelial-mesenchymal transition to inhibit the early stage melanoma development

Stromal fibroblasts are an integral part of the tumor stroma and constantly interact with cancer cells to promote their initiation and progression. However, the role and function of dermal fibroblasts during the early stage of melanoma development remain poorly understood. We, therefore, designed a novel genetic approach to deactivate stromal fibroblasts at the onset of melanoma formation by targeted ablation of β-catenin. To our surprise, melanoma tumors formed from β-catenin-deficient group (B16F10 mixed with β-catenin-deficient fibroblasts) appeared earlier than tumors formed from control group (B16F10 mixed with normal dermal fibroblasts). At the end point when tumors were collected, mutant tumors were bigger and heavier than control tumors. Further analysis showed that there were fewer amounts of stromal fibroblasts and myofibroblasts inside mutant tumor stroma. Melanoma tumors from control group showed reduced proliferation, down-regulated expression of cyclin D1 and increased expression of cyclin-dependent kinase inhibitor p16, suggesting dermal fibroblasts blocked the onset of melanoma tumor formation by inducing a cell cycle arrest in B16F10 melanoma cells. Furthermore, we discovered that dermal fibroblasts prevented epithelial-mesenchymal transition in melanoma cells. Overall, our findings demonstrated that dermal fibroblasts crosstalk with melanoma cells to regulate in vivo tumor development via multiple mechanisms, and the outcomes of their reciprocal interactions depend on activation states of stromal fibroblasts and stages of melanoma development.

MiR-26b is down-regulated in carcinoma-associated fibroblasts from ER-positive breast cancers leading to enhanced cell migration and invasion

Carcinoma-associated fibroblasts (CAFs) influence the behaviour of cancer cells but the roles of microRNAs in this interaction are unknown. We report microRNAs that are differentially expressed between breast normal fibroblasts and CAFs of oestrogen receptor-positive cancers, and explore the influences of one of these, miR-26b, on breast cancer biology. We identified differentially expressed microRNAs by expression profiling of clinical samples and a tissue culture model: miR-26b was the most highly deregulated microRNA. Using qPCR, miR-26b was confirmed as down-regulated in fibroblasts from 15 of 18 further breast cancers. Next, we examined whether manipulation of miR-26b expression changed breast fibroblast behaviour. Reduced miR-26b expression caused fibroblast migration and invasion to increase by up to three-fold in scratch-closure and trans-well assays. Furthermore, in co-culture with MCF7 breast cancer epithelial cells, fibroblasts with reduced miR-26b expression enhanced both MCF7 migration in trans-well assays and MCF7 invasion from three-dimensional spheroids by up to five-fold. Mass spectrometry was used to identify expression changes associated with the reduction of miR-26b expression in fibroblasts. Pathway analyses of differentially expressed proteins revealed that glycolysis/TCA cycle and cytoskeletal regulation by Rho GTPases are downstream of miR-26b. In addition, three novel miR-26b targets were identified (TNKS1BP1, CPSF7, COL12A1) and the expression of each in cancer stroma was shown to be significantly associated with breast cancer recurrence. MiR-26b in breast CAFs is a potent regulator of cancer behaviour in oestrogen receptor-positive cancers, and we have identified key genes and molecular pathways that act downstream of miR-26b in CAFs. © 2013 The Authors. Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Pharmacological modulation of beta-catenin and its applications in cancer therapy

Beta-catenin (β-catenin) is a multifunction protein with a central role in physiological homeostasis. Its abnormal expression leads to various diseases including cancer. In normal physiology, β-catenin either maintains integrity of epithelial tissues or controls transcription of various genes on extracellular instigations. In epithelial tissues, β-catenin functions as a component of the cadherin protein complex and regulates epithelial cell growth and intracellular adhesion. In Wnt signalling, β-catenin is a major transcriptional modulator and plays a crucial role in embryogenesis, stem cell renewal and organ regeneration. Aberrant expression of β-catenin can induce malignant pathways in normal cells and its abnormal activity is also exploited by existing malignant programmes. It acts as an oncogene and modulates transcription of genes to drive cancer initiation, progression, survival and relapse. Abnormal expression and function of β-catenin in cancer makes it a putative drug target. In the past decade, various attempts have been made to identify and characterize various pharmacological inhibitors of β-catenin. Many of these inhibitors are currently being investigated for their anticancer activities in a variety of cancers. The first half of this review will focus on the role of β-catenin in cancer initiation, maintenance, progression and relapse whereas the second half will briefly summarize the recent progress in development of agents for the pharmacological modulation of β-catenin activity in cancer therapeutics.

Prognostic significance of cyclin D1, β-catenin, and MTA1 in patients with invasive ductal carcinoma of the breast

BACKGROUND

To investigate markers for predicting breast cancer progression, we performed a candidate gene-based study that assessed expression change of three genes, cyclin D1, β-catenin, and metastasis-associated protein-1 (MTA1), involving in aggressive phenotypes of cancerous cells, namely hyperproliferation, epithelial-mesenchymal transition, and global transcriptional regulation.

METHODS

Specimens were from 150 enrolled female patients, with invasive ductal carcinoma, followed up for more than 10 years. mRNA expression of cyclin D1, β-catenin, and MTA1 in cancerous and noncancerous cells microdissected from the primary tumor site was determined by quantitative real-time PCR. The relationship between mRNA expression levels of the genes and clinicopathologic features was assessed by statistical analysis. Disease-free and overall survival (DFS and OS) were analyzed by Kaplan-Meier analysis with log-rank test and a multivariate Cox regression model.

RESULTS

Cyclin D1 was shown to be overexpressed in late-stage breast cancer (stage III/IV). Breast cancer with lymph node metastasis (LNM) showed significantly higher frequency of overexpressed cyclin D1, β-catenin, and MTA1 (P < 0.05). Patients carrying greater numbers of overexpressed genes had joint effects on increased risk in tumors of advanced stages (P ( trend ) = 0.03) and LNM (P ( trend ) < 0.01). In the LNM-negative group, patients whose tumors with greater number of cyclin D1, β-catenin, and MTA1 overexpressions were associated with poorer clinical outcomes, with hazard ratio of 14.79 for OS (P = 0.015) and 7.54 for DFS (P = 0.015) using multivariate Cox regression analysis during the 10-year follow-up.

CONCLUSIONS

Higher expression of cyclin D1, β-catenin, and MTA1 mRNAs in breast cancers may prove effective in predicting unfavorable outcomes of breast cancer.