Tgf-Beta Regulates Cxcl1 Expression In Mammary Carcinoma Associated Fibroblasts Through Novel Smad2/3-And Hgf/C-Met-Dependent Mechanisms.

CXCL1 is a chemokine secreted by macrophages, neutrophils, epithelial cells and fibroblasts, and plays a role in inflammation and wound healing. Enhanced expression of CXCL1 in tumor epithelium is associated with cell invasion, angiogenesis in melanoma, bladder, ovarian and breast cancer. However, little is known about CXCL1 expression in tumor stroma. Through analysis of gene expression data, our studies reveal that high RNA levels of CXCL1 in breast tumor stroma is associated with increased rate of recurrence and shorter relapse-free survival. We noticed decreased secretion levels of TGF-β and increased secretion of CXCL1 in tumor derived fibroblasts. Increased CXCL1 expression was also observed in mammary fibroblasts in which the TGF-β type II receptor was knocked out. By immunohistochemistry analysis we found that expression of CXCL1 inversely correlated with expression of TGF-β, phosphorylated-Smad2 and phosphorylated-Smad3 in breast tumor stroma. We hypothesized that TGF-β suppresses CXCL1 expression in breast fibroblasts. Our goal for this project was to determine the molecular mechanisms through which TGF-β suppresses CXCL1 expression using mammary fibroblasts derived from MMTV-PyVmT mammary tumor model. Treatment of fibroblasts with recombinant TGF-β decreased CXCL1 transcription and secretion by up to 85% over time, as determined by RT-PCR and ELISA. SiRNA silencing of TGF-β signaling transducers, Smad2 and Smad3, increased CXCL1 transcription and secretion in mammary fibroblasts. In addition, TGF-β suppressed expression of HGF, a factor that enhanced CXCL1 expression in mammary fibroblasts. Knockdown of HGF or treatment of fibroblasts with c-Met inhibitors reduced CXCL1 expression. These data indicate TGF-β suppresses CXCL1 expression through Smad2/3-dependent mechanisms. As a secondary mechanism, TGF-β suppresses CXCL1 expression through down-regulation of HGF/c-Met signaling. This is the first report to characterize the mechanisms of CXCL1 expression in mammary fibroblasts and demonstrate a clinical relevance for CXCL1 expression in breast cancer stroma. Citation Format: An Zou, Diana Lambert, Henry Yeh, Wei Bin Fang, Nikki Cheng. TGF-β regulates CXCL1 expression in mammary carcinoma associated fibroblasts through novel Smad2/3- and HGF/c-Met-dependent mechanisms.. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr A62. doi:10.1158/1538-7445.CHTME14-A62