GREM1 is associated with metastasis and predicts poor prognosis in ER-negative breast cancer patients

Ulrike Neckmann,Jiang Ren,Geir Bjørkøy,Toril Holien,Rolf I Skotheim,Sen Zhao,Bjarne Johannessen,Eivind Almaas,Martina Hall,Camilla Wolowczyk,Peter Ten Dijke

doi:10.1186/s12964-019-0467-7

Abstract

BackgroundIn breast cancer, activation of bone morphogenetic protein (BMP) signaling and elevated levels of BMP-antagonists have been linked to tumor progression and metastasis. However, the simultaneous upregulation of BMPs and their antagonist, and the fact that both promote tumor aggressiveness seems contradictory and is not fully understood.MethodsWe analyzed the transcriptomes of the metastatic 66cl4 and the non-metastatic 67NR cell lines of the 4T1 mouse mammary tumor model to search for factors that promote metastasis. CRISPR/Cas9 gene editing was used for mechanistic studies in the same cell lines. Furthermore, we analyzed gene expression patterns in human breast cancer biopsies obtained from public datasets to evaluate co-expression and possible relations to clinical outcome.ResultsWe found that mRNA levels of the BMP-antagonist Grem1, encoding gremlin1, and the ligand Bmp4 were both significantly upregulated in cells and primary tumors of 66cl4 compared to 67NR. Depletion of gremlin1 in 66cl4 could impair metastasis to the lungs in this model. Furthermore, we found that expression of Grem1 correlated with upregulation of several stem cell markers in 66cl4 cells compared to 67NR cells. Both in the mouse model and in patients, expression of GREM1 associated with extracellular matrix organization, and formation, biosynthesis and modification of collagen. Importantly, high expression of GREM1 predicted poor prognosis in estrogen receptor negative breast cancer patients. Analyses of large patient cohorts revealed that amplification of genes encoding BMP-antagonists and elevation of the corresponding transcripts is evident in biopsies from more than half of the patients and much more frequent for the secreted BMP-antagonists than the intracellular inhibitors of SMAD signaling.ConclusionIn conclusion, our results show that GREM1 is associated with metastasis and predicts poor prognosis in ER-negative breast cancer patients. Gremlin1 could represent a novel target for therapy.

Highlights

In breast cancer, activation of bone morphogenetic protein (BMP) signaling and elevated levels of bone morphogenetic proteins (BMPs)-antagonists have been linked to tumor progression and metastasis
Grem1 is highly expressed in the metastatic 66cl4 cells and elevated GREM1 in tumor biopsies correlates with reduced relapse-free survival in patients Cancer cells’ ability to metastasize may be affected by factors that are secreted by the cancer cells or by factors secreted by cells in the tumor microenvironment (TME)
Using RNA-sequencing (RNA-seq), we compared the transcriptomes of cells grown in culture and isolated from primary tumors in mice and we focused on transcripts encoding matrisome-associated extracellular matrix (ECM) affiliated proteins (164 genes) and secreted factors (363 genes) as defined by Naba et al [30]

Summary

Introduction

Activation of bone morphogenetic protein (BMP) signaling and elevated levels of BMP-antagonists have been linked to tumor progression and metastasis. Members of the transforming growth factor β (TGF-β) family, including the TGF-βs, activins, nodal, bone morphogenetic proteins (BMPs), and growth and differentiation factors (GDFs), play important roles in tumor progression and formation of metastases [1]. These signaling molecules have pleiotropic effects in cancer, as seen with TGF-β signaling, which has been linked to both tumor suppression and tumor promotion depending on the tumor stage [2, 3]. Understanding the role of TGF-β family members in cancer and the development of TGF-β targeted therapies have been hampered by the complex interplay of these signaling molecules with intracellular SMAD-inhibitors and extracellular BMP-antagonists. Dand, known as Coco, facilitated formation of lung metastases in the 4T1 mammary tumor model by blocking lung-derived BMPs [8], whereas gremlin promoted stem cell maintenance in both glioma [9] and colorectal cancer [10]

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