Abstract 3562: Protein palmitoylation in breast cancer: DHHC5 palmitoyltransferase as a potential therapeutic target

Protein S-palmitoylation is a widespread and dynamic post-translational modification that regulates protein-membrane interactions, protein-protein interactions, and protein stability. S-palmitoylation is catalyzed by members of a family of 23 palmitoyl acyl transferases, termed the DHHC family due to the presence of a common catalytic motif. The role of protein palmitoylation in cancer is largely unexplored. In our previous study, we have shown that DHHC5 palmitoyltransferase supports the growth of non-small cell lung cancer. To further investigate the role of DHHC5 in cancer, we expanded our study to include breast cancer cell lines. Stable knockdowns of DHHC5 were undertaken in 8 breast cancer cell lines (including 4 “triple-negative” breast cancer lines) as well as in two normal human mammary epithelial cell lines (HMECs) using lentiviral shRNAs. The protein levels of DHHC5 were analyzed by immunoblotting, which all showed efficient knockdown. Cell proliferation and anchorage-dependent/ independent colony formation assays indicated that DHHC5 knockdown led to cell growth arrest and decreased cell clonogenicity in most of the tested breast cancer cell lines in vitro, but not in the HMECs. BT-549, SkBr3 and T-47D cell lines were particularly dependent on DHHC5 expression, and rescue experiments involving ectopic plasmid-driven DHHC5 and its catalytic mutant DHHS expression are in progress. In vivo tumor formation assays will be carried out by injecting MCF-7 and T-47D control cells and DHHC5 stable knockdown cells as well as rescued cells subcutaneously into NOD/SCID mice. Tumor xenograft formation will be measured. As DHHC5 function is needed for optimal breast cancer cell growth, it will be important to identify physiologically relevant substrates in order to develop inhibitors of DHHC5 function. Future plans include microarray and protein kinase array analysis to identify possible signaling pathways in which DHHC5 may be involved, as well as palmitoyl-protein profiling of control and knockdown DHHC5 cell lines by mass spectrometry. Citation Format: Hui Tian, Xiaoxia Qi, Kenneth Huffman, John Minna, Sandra L. Hofmann. Protein palmitoylation in breast cancer: DHHC5 palmitoyltransferase as a potential therapeutic target. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3562. doi:10.1158/1538-7445.AM2015-3562