Background: Breast cancers can be subgrouped into ER-positive and ER-negative breast cancers according to their estrogen receptor status. Clinical data has shown that ER-negative breast cancers are aggressive and have a poor prognosis; however, few effective targeted treatments are available for these cancers. A human kinome study conducted in our lab has identified 52 kinases highly expressed in ER-negative breast tumors. One of these kinases, DAPK-1, was selected for further study. Death-associated protein kinase-1 (DAPK-1) mediates cell death through P53-dependent or -independent pathways. In this study, we investigated the role of DAPK-1 in regulating growth and death in ER-negative breast cancer. Methods: To perform expression and survival analysis of DAPK-1 in breast tumors, we used data from VandeVijver, Desmedt and Ivshina datasets. Inducible DAPK-1 knockdown cell lines were constructed through pTRIPZ lentiviral system. Anchorage-independent growth was performed in soft agar. Colonies were enumerated after 15-30 days. Xenograft experiments were performed in nude mice by injecting 5×106 cells per mice. Results: Our gene expression analysis found that high DAPK-1 expression correlated significantly with ER-negative breast cancers. Survival analysis showed that high DAPK-1 expression is associated with worse clinical outcome. Using an inducible DAPK-1 knockdown system, we found that depletion of DAPK-1 suppressed anchorage-dependent and -independent growth of ER-negative P53 mutant cells but not P53 wildtype cells. We next investigated whether DAPK-1 suppression inhibits tumor growth in mouse xenograft experiments. Results of in vivo experiments demonstrated that DAPK-1 suppression inhibited the growth of ER-negative breast tumors but not ER-positive breast tumors. Through a siRNA study in an expanded panel of breast cancer cell lines, we found that the sensitivity of cell lines to DAPK-1 knockdown is dependent on ER and P53 status. ER-negative breast cancer cell lines with P53 mutations are very sensitive to DAPK-1 knockdown, while ER-positive, P53 wildtype breast cancer cell lines are resistant to DAPK-1 knockdown. To determine if p53 dysfunction can sensitize breast cancer cell lines to DAPK-1 suppression, we depleted P53 expression in MCF7 and found an increased sensitivity to DAPK-1 knockdown, indicating that MCF7 growth becomes partially addicted to DAPK-1 after P53 dysfunction. Conclusion: DAPK-1 is an essential growth regulator of ER-negative breast cancer cells, but not of ER-positive, P53 wildtype breast cancer cells in vitro and in vivo. These results suggest that P53 dysfunction causes breast cancer cells to become addicted to DAPK-1 signaling pathway for their growth. Our results show that DAPK-1 has a dual role in regulating breast cancer proliferation and apoptosis depending on the status of P53. This study is supported by a PROMISE grant (KG081694) from the Susan G. Komen for the Cure Foundation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 82. doi:1538-7445.AM2012-82