SAT-333 CCAAT Enhancer Binding Protein Β(C/EBPΒ)-induced Axl in Early Breast Cancer Progression

Ductal carcinoma in situ (DCIS) is a nonobligatory precursor to invasive breast cancer that accounts for up to 30% of all diagnosed breast cancers. It is estimated that over half of all DCIS patients are overtreated with surgery and possible radiation due to our inability to identify which DCIS patients are at risk to progress. The goal of these studies is to understand the mechanisms of localized invasion during DCIS progression, which may ultimately lead to the identification of predictive biomarkers to help guide treatment decisions. Our laboratory has shown that the receptor tyrosine kinase Axl is an important mediator of DCIS cell invasion, however, the transcriptional mechanisms regulating Axl are largely unknown. C/EBPβ is a transcription factor that regulates mammary gland development and is deregulated in breast cancer. Our data show that the protein isoform LIP is increased in DCIS patients that progress to invasive cancer. We hypothesize that C/EBPβ-LIP promotes DCIS progression by activating Axl in high risk patients. Overexpression of C/EBPβ-LIP in MCF10AT or MCF10ADCIS.com cells increased Axl mRNA and protein expression, while C/EBPβ-LAP1 inhibited Axl. Furthermore, C/EBPβ-LIP induced cell proliferation and migration, and Axl knockdown decreased LIP-induced proliferation. As numerous CEBP sites can be found in the Axl promoter, we performed promoter assays and found that all C/EBPβ protein isoforms (LAP1, LAP2, LIP) can activate the Axl promoter. To determine whether C/EBPβ-LIP promotes progression in vivo, we will use a human-in-mouse intraductal injection model (MIND) utilizing LIP-overexpressing MCF10ADCIS.com cells to assess changes in localized invasion in the presence or absence of Axl inhibitors. These studies will define a novel mechanism that promotes DCIS progression and may ultimately have critical implications for the prevention and treatment of DCIS. These studies supported by Susan G Komen and NCI RO1 grants.