Regulation of Runx1 in triple negative breast cancer

SOFIA MARIA SOSA; MARÍA SOL RECOUVREUX; LUCIANA ROCHA-VIEGAS; VIRGINIA DANSEY; SANTIAGO RODRIGUEZ SEGUI; PABLO ECHEVERRÍA; NATALIA RUBINSTEIN

Congreso; Mammary Gland Gordon Conference; 2018

Recently, we have shown that RUNX1 could be involved in the aggressiveness of ER-/PR- breast tumor. Briefly, we reported that RUNX1 is able to promote oncogene expression (RSPO3) and to down regulate tumor suppressor gene expression (GJA1) in a Forkhead box P3 (FOXP3)-dependent manner. Interestingly, RUNX1 has been reported to correlate with poor patient prognosis in human samples of TNBC. Nevertheless, RUNX1 participation in each breast cancer subtype is still under debate. With the aim to find new target genes regulated by RUNX1 in mammary tumor epithelial cells we studied a database of RUNX1 ChIP-seq obtained from human T lymphocyte. This database was combined and curated with expression microarrays obtained from human mammary normal and breast cancer samples. This analysis reveals that RUNX1 has the potential to positively regulate SOX4, and also to down regulate tumor suppressor genes like FST and GALTN6. At this point it is important to underline that RUNX1 is able to up or down regulate gene expression depending on the cofactors associated to the target promoter. Consequently, we performed ChIP assays on MDA-MB-231 and T47D cell lines that validated this predictive model. Attractively, FST has been previously described as a negative regulator of EMT in claudin-low and metastatic tumours. Furthermore, SOX4 has been identified as a master gene able to control EMT by Ezh2 gene regulation. Remarkably, we found that Runx1 gene expression and its transcriptional activity is significantly up regulated in murine tumor cell lines treated with TGFβ (2 ng/ml) during 7 days. Even more, by blocking RUNX1 transcriptional activity we demonstrated that this transcription factor is necessary for MDA-MB321 and LM3 cell lines migration. With the aim of studying how RUNX1 gene expression could be externally regulated we found several potential DNA binding sites for glucocorticoid receptor (GR), among others. It has been shown that high GR expression on TNBC samples correlates with a reduced overall survival and a shorter metastasis-free survival in chemotherapy-treated patients. Additionally, it has been described that activation of GR induces EMT and CSC renovation on TNBC cell lines. Interestingly, our data shows that RUNX1 mRNA is significantly up regulated in tumor cell lines treated with dexa (10-7M). Moreover, mifepristone-treated cells (10-7M) show a significant down regulation (around 50%) of RUNX1 gene expression. Altogether, our data suggest that RUNX1 gene expression is regulated during EMT and by GR activation and it could be considered a new molecular target in TNBC.