Abstract 185: p300 and STAT3 drive YAP-independent mechanotransduction during breast cancer invasion
Authors: Lee Joanna Y. , Chang Jessica , Nam Sungmin , Lee Hong-pyo , Dominguez Antonia A. , Varma Sushama , Qi Lei S. , West Robert B. , Chaudhuri Ovijit 
Published: August 2018

Abstract
83% of non-invasive breast cancers are diagnosed as ductal carcinoma in situ (DCIS). While some DCIS tumors remain confined in the mammary duct, about half progress into invasive ductal carcinoma (IDC), when carcinoma cells break through the basement membrane (BM) into the type-1 collagen (col-1) rich stroma, a key first step towards metastasis. As 90% of cancer-related deaths are due to metastasis, preventing progression to invasive disease could significantly reduce cancer mortality. However there are no established biomarkers for invasive potential and current diagnostic methods cannot predict which DCIS cases will progress to IDC. Interestingly, increased tissue stiffness correlates with invasion and the transcriptional regulator YAP has been implicated as a mechanotransducer, largely based on 2D culture studies. To identify the drivers of DCIS progression, we encapsulated mammary epithelial cells (MECs) in 3D hydrogels with a range of stiffness and that presented either BM-ligands or col-1 containing microenvironments to the cells. RNA-seq identified the global gene expression changes induced by increased 3D culture stiffness in BM-like environments. 3SEQ analysis of breast cancer patient samples revealed that genes regulated by 3D culture stiffness were upregulated in breast cancer patients, demonstrating the relevance of 3D culture models and suggesting expression of S100A7 as a potential biomarker of breast cancer progression. Interestingly gene expression changes induced by increased 3D stiffness in BM-like environments were distinct from col-1 like environments. Col-1 exposure in stiff gels promotes expression of genes whose protein products remodel the col-1 network including FN1 and LOX. As col-1 remodeling promotes cell dissemination, this suggests that col-1 exposure following BM invasion induces pro-metastatic changes in carcinoma phenotype. Surprisingly, enhanced stiffness induced invasion in MECs independently of YAP activation in both BM-like and col-1 rich 3D hydrogels. Instead, bioinformatic analysis identified transcriptional regulators p300 and STAT3 as mediators of 3D mechanosensing. Inhibition of p300 and STAT3 in stiff 3D BM-like environments and, conversely, overexpression in soft 3D BM-like environments confirm a role during stiffness-induced proliferation. This suggests p300 and STAT3 as possible targets for preventing progression to invasive disease. While genetic alterations initiate transformation, these results reveal the miroenvironment events that initiate breast cancer invasion.
Citation Format: Joanna Y. Lee, Jessica Chang, Sungmin Nam, Hong-pyo Lee, Antonia A. Dominguez, Sushama Varma, Lei S. Qi, Robert B. West, Ovijit Chaudhuri. p300 and STAT3 drive YAP-independent mechanotransduction during breast cancer invasion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 185.