Abstract 3299: Maternal embryonic leucine zipper kinase is critical for the growth and migration of triple negative breast cancer cells

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background: Breast cancer constitutes 30% of all new cancer cases in women. Despite steady decrease in breast cancer mortality, the lack of therapeutic targets is still a major problem. While the hormone-receptor positive (ER+) and human epidermal growth factor receptor 2-positive (HER2+) breast cancers respond to current targeted therapies, no targeted therapy is available for the treatment of triple negative breast cancer (TNBC), which lacks the expression of ER alpha (ER), progesterone receptor (PR), and HER2-receptor. Hence, there is an urgent need for effective targets against this sub-type of breast cancer. Previous studies in our laboratory used gene expression profiling of human breast cancers to identify kinases overexpressed in ER-negative breast cancers. One of these highly expressed kinases is the maternal embryonic leucine-zipper kinase (MELK). MELK is a serine/threonine protein kinase known to have a role in cell cycle progression, apoptosis and DNA repair. The purpose of this study was to test the hypothesis that MELK is required for the growth and migration of TNBC. Methods: RNA and protein was isolated from a panel of TNBC and ER-positive breast cancer cell lines and MELK expression was quantified by qPCR and immunoblotting. To determine whether MELK regulates cell growth, ER-positive and TNBC cell lines were transfected with siRNA targeting MELK and cell number was measured by manual counting. Anchorage-independent growth was measured using soft agar assays. Effect on migration and invasion was determined using Boyden Chamber assays. Immunostaining with actin-phalloidin was performed on MELK knockdown cells to determine effect of MELK loss on the cytoskeleton. Results: MELK mRNA and protein levels were significantly higher in TNBC cell lines compared to ER-positive breast cancers. Knockdown of MELK suppressed growth (≥50% growth inhibition) in six TNBC cell lines but had no effect on growth of six ER positive cell lines. Colony formation was also greatly reduced in TNBC cell lines but was not affected in ER positive cell lines upon siRNA knockdown of MELK. In addition, knockdown of MELK reduced migration of three TNBC cell lines (MDAMB231, MDAMB468 and Hcc70) but had no effect on the ER-positive cell line (MCF7). Decreased staining of actin filaments was observed in cell lines where migration was reduced upon MELK knockdown suggesting a role of MELK in formation of actin cytoskeleton. Current studies are focused on understanding how MELK regulates the cell growth and migration in TNBC. Conclusions: MELK is an important growth regulator of TNBC, but not of ER positive breast cancers. Our results indicate that MELK promotes cell migration in TNBC cells. These findings suggest that MELK is a promising target for the treatment of TNBC. Supported by a Susan G. Komen for the Cure Promise Grant (KG081694), and the John Charles Cain Award. Citation Format: Nidhi Batra, Corey Speers, Ivan Uray, Abhijit Mazumdar, Anna Tsimelzon, Susan Hilsenbeck, Gordon Mills, Powel Brown. Maternal embryonic leucine zipper kinase is critical for the growth and migration of triple negative breast cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3299. doi:10.1158/1538-7445.AM2014-3299