BACKGROUND In 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. METHODS We 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. RESULTS We 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. CONCLUSION In 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.

中文翻译：

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GREM1与转移相关，并预测ER阴性乳腺癌患者的预后不良。

背景技术在乳腺癌中，骨形态发生蛋白（BMP）信号传导的激活和BMP拮抗剂水平的升高已与肿瘤的进展和转移相关。然而，BMPs及其拮抗剂的同时上调，以及两者都促进肿瘤侵袭性的事实似乎是矛盾的，并且尚未完全被理解。方法我们分析了4T1小鼠乳腺肿瘤模型的转移性66cl4和非转移性67NR细胞系的转录组，以寻找促进转移的因子。CRISPR / Cas9基因编辑用于同一细胞系中的机理研究。此外，我们分析了从公共数据集获得的人类乳腺癌活检组织中的基因表达模式，以评估共表达以及与临床结果的可能关系。结果我们发现，与67NR相比，在66cl4的细胞和原发性肿瘤中，编码gremlin1的BMP拮抗剂Grem1和配体Bmp4的mRNA水平均显着上调。在这个模型中，grcllin1在66cl4中的消耗可能会削弱向肺的转移。此外，我们发现与67NR细胞相比，Grem1的表达与66cl4细胞中几种干细胞标志物的上调相关。在小鼠模型和患者中，GREM1的表达均与细胞外基质的组织，胶原蛋白的形成，生物合成和修饰有关。重要的是，GREM1的高表达预示着雌激素受体阴性乳腺癌患者的不良预后。对大量患者队列的分析表明，在超过一半的患者的活检中，编码BMP拮抗剂的基因的扩增和相应转录本的升高是明显的，并且分泌的BMP拮抗剂比SMAD信号的细胞内抑制剂更为频繁。结论总之，我们的结果表明GREM1与转移相关，并预测ER阴性乳腺癌患者的预后不良。Gremlin1可能代表一种新的治疗靶点。