Identification of a minority population in breast cancer that integrates into the vasculature and initiates metastasis. [RNA-seq]

Metastasis is responsible for the majority of cancer-related deaths1. Although single-cell RNA sequencing (scRNA-seq) has revealed considerable heterogeneity among tumor cells, identifying the cellular determinants of metastasis has remained challenging. Here, we analyzed scRNA-seq data of primary human breast tumor biopsies and identified a minority population of immature THY1+/VEGFA+ basal epithelial cells that display angiogenic features and are marked by the expression of the oncogene, LMO2. Higher levels of LMO2+ basal cells in human breast tumors correlated with endothelial content and predicted poor distant recurrence-free survival. Using MMTV-PyMT/Lmo2CreERT2 mice, we demonstrate that Lmo2 lineage-traced cells integrate into the vasculature and metastasize to the lung. In human breast tumors, knockdown of LMO2 reduced lung metastasis by affecting multiple steps required for intravasation, leading to a reduced frequency of circulating tumor cells. Mechanistically, we find that LMO2 is a binding partner of STAT3 and is required for STAT3 activation in the presence of the inflammatory cytokines, TNFa and IL6. Collectively, our study identifies a population of metastasis-initiating cells with angiogenic features and establishes the LMO2-STAT3 signaling axis as a therapeutic target in breast cancer metastasis. Overall design: Bulk RNA-sequencing profiles (n = 9) of 200,000 MDA-MB-468 cells infected with either pSicoR (control), shLMO2-1, or shLMO2-2 each in triplicates.