Abstract 3869: SOCS3-mediated regulation of inflammatory cytokines in triple-negative breast cancer
Authors: Korkaya Hasan , Ouzounova Maria , Kim Gwangil , Quraishi Ali , Davis April , Tawakkol Nader , Korkaya Sumeyye , Wicha Max S. 
Published: May 2015

We demonstrated that knock-down of tumor suppressors p53 and PTEN in mammary epithelial MCF10A cells (called MCF10A-p53-PTEN-) results in generation of aggressive tumors. Furthermore MCF10A-p53-PTEN- cells also display an increased EMT phenotype as well as expansion of cancer stem cell (CSC) population. Utilizing Affymetrix gene expression analyses, we confirmed that malignant MCF10Ap53-PTEN- cells displayed a gene expression pattern which closely resembled that of the basal/claudin molecular subtype with the TN. This subtype is previously characterized by the expression of EMT and stem cell genes.

The Inflammatory cytokines IL6 and TGF-β have been found to regulate stem cells and EMT. Consistent with these data, we found that MCF10A-p53-PTEN- cells secreted significantly higher levels of IL6 (&gt;1000 fold) and TGF-β (&gt;200 fold) compared to parental or single gene deleted cells. Furthermore combined deletion of p53 and PTEN compared to single gene knockdown resulted in transformation of MCF10A cells generating aggressive metastatic tumors in NOD/SCID mice.

IL6 is a key regulator of inflammatory responses and orchestrates these physiological functions by controlling the SOCS3 mediated Stat3/NF-κB pathway. Consistent with these reports, we demonstrated that SOCS3 is abundantly expressed in MCF10A cells where it negatively regulates the IL6 feedback loop. Unexpectedly, we found that SOCS3 protein was undetectable in MCF10A-p53-PTEN- cells. Basal/claudin-low breast cancer cell lines that display an activated IL6 feedback loop also had low SOCS3 protein levels. Furthermore, we found a similar discordance between SOCS3 protein and mRNA levels in primary basal/claudin-low breast cancer samples as demonstrated by immunochemistry utilizing a primary breast cancer tissue array. Together these findings suggest that loss of SOCS3 protein expression allows for maintenance of the IL6 mediated inflammatory feedback loop in aggressive/metastatic TN breast cancers. We found that MCF10A-p53-PTEN- cells displayed increased proteasome activity as evidenced by SOCS3 protein accumulation upon proteasome inhibition. Proteolytic degradation of SOCS3 protein in turn is controlled by constitutive activation of the IL6 mediated Stat3/NF-κB pathway.

We demonstrate that enforced expression of SOCS3 or IL6 pathway inhibition interfering with this loop through IL6R blockade repress the CSC population, reducing the tumor growth and metastasis in mouse xenografts. These studies provide a strong rationale for development of IL6 pathway-targeting agents for the treatment of TNBC, an aggressive disease that currently lacks molecularly targeted therapeutics.

Citation Format: Hasan Korkaya, Maria Ouzounova, Gwangil Kim, Ali Quraishi, April Davis, Nader Tawakkol, Sumeyye Korkaya, Max S. Wicha. SOCS3-mediated regulation of inflammatory cytokines in triple-negative breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3869. doi:10.1158/1538-7445.AM2014-3869