Abstract 3341: Inhibiting the destruction of the oncogene ZNF217 promotes breast cancer metastasis to lung

The oncogene and transcription factor ZNF217 is overexpressed in 20-30% of breast cancers. Its overexpression correlates strongly with poor prognosis in patients and causes accelerated tumor progression, metastasis, and chemoresistance in vivo. While several studies have examined the regulation of ZNF217 at the gene and mRNA levels, little is known about how ZNF217 is regulated as a protein. In this study we identify the regions of ZNF217 that are required for protein turnover and other cancer phenotypes, including increased invasion and metastasis. Due to the high expression and aberrant localization of ZNF217 in some human breast tumors, both ZNF217 protein expression levels and localization of ZNF217 may be critical determinants of ZNF2179s function in vivo. To investigate the role of ZNF217 protein on cancer progression, we first examined ZNF217 protein expression in human breast tumors by Western analysis. In addition to full-length ZNF217 protein, smaller ZNF217 proteins were detected and were even more prominent than full-length ZNF217 in both human breast tumors and cell lines, but the importance of these smaller isoforms remains unknown. To investigate the function of the smaller ZNF217 proteins and to determine the requirements of the regions of ZNF217 protein to promote breast cancer, we examined the consequences of removing regions of ZNF217 using truncation mutants overexpressed in human breast cancer cells. As a structure-function analysis, we tested both truncation mutants and full-length ZNF217 for their ability to promote phenotypes usually associated with ZNF217 overexpression, including protein turnover, increased branching of organoids, tumor burden, and metastasis. For protein turnover, these mutants were expressed in breast cancer cells and treated with cycloheximide to inhibit protein synthesis. This assay identified the regions of ZNF217 required for ZNF217 protein turnover. Further analysis of the sequence in this region identified a putative destruction box required for the protein turnover. We next determined which regions of ZNF217 are required for organoid branching and metastatic tumor burden. Both the N-terminus and C-terminus of ZNF217 were required for organoid branching. Interestingly, the same region identified to be required for ZNF217 protein turnover was not required for metastatic tumor burden. In fact, overexpression of breast cancer cells expressing stabilized ZNF217 truncation mutants significantly increased the metastatic tumor burden in vivo when assayed by tail vein injection. These results suggest that regulation of ZNF217 protein expression may be clinically valuable in generating a clinical assay used to generate personalized treatment strategies for patients with advanced metastatic breast cancer and high ZNF217 expression. Citation Format: Beth Facchine, Junmin Wu, Megan Fabry, Matt Messana, William Kaliney, Laurie Littlepage. Inhibiting the destruction of the oncogene ZNF217 promotes breast cancer metastasis to lung [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 3341.