Induction of Invasive Basal Phenotype in Triple-Negative Breast Cancers by Long Noncoding RNA BORG

TL;DR

This paper shows that high levels of a gene called BORG are linked to more aggressive triple-negative breast cancers and could lead to new treatments.

Contribution

The study identifies BORG as a novel long noncoding RNA driver of invasive basal phenotype in triple-negative breast cancers.

Findings

High BORG expression is associated with invasive tumor behavior and poor therapy response in triple-negative breast cancers.

BORG induces pathways linked to basal tumor and epithelial-mesenchymal transition features in human and mouse models.

BORG expression varies widely across breast cancer subtypes and correlates with aggressive tumor traits.

Abstract

Breast cancer remains a major health issue in the United States and around the world. While progress has been made in curing most types of breast cancer, there are currently no effective cures for a subtype called ‘triple-negative’ breast cancer. We have identified a gene named BORG that, based on experiments in cultured human cells and mice, plays an important role in triple-negative breast cancer. Here, we study the function of this gene in a large group of human triple-negative breast cancers and show that when the level of expression of this gene is high, tumors become more invasive and develop ‘triple-negative’-like properties. Even in non-triple-negative tumors, high levels of expression of this gene are associated with more aggressive tumor behavior and poor response to therapy. Based on these validation studies in human tumors, we hope to leverage mechanistic vulnerabilities in BORG action to one day advance novel therapeutic strategies to alleviate hard-to-cure triple-negative breast tumors.

Background/Objectives: Long noncoding RNAs (lncRNAs) are known to play key roles in breast cancers; however, detailed mechanistic studies of lncRNA function have not been conducted in large cohorts of breast cancer tumors, nor has inter-donor and inter-subtype variability been taken into consideration for these analyses. Here we provide the first identification and annotation of the human BORG lncRNA gene. Methods/Results: Using multiple tumor cohorts of human breast cancers, we show that while BORG expression is strongly induced in breast tumors as compared to normal breast tissues, the extent of BORG induction varies widely between breast cancer subtypes and even between different tumors within the same subtype. Elevated levels of BORG in breast tumors are associated with the acquisition of core cancer aggression pathways, including those associated with basal tumor and pluripotency phenotypes and with epithelial–mesenchymal transition (EMT) programs. While a subset of BORG-associated pathways was present in high BORG-expressing tumors across all breast cancer subtypes, many were specific to tumors categorized as triple-negative breast cancers. Finally, we show that genes induced by heterologous expression of BORG in murine models of TNBC both in vitro and in vivo strongly overlap with those associated with high BORG expression levels in human TNBC tumors. Conclusion: Our findings implicate human BORG as a novel driver of the highly aggressive basal TNBC tumor phenotype.

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