Abstract 1053: JUNB, survival against chemotherapy.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC The long term goal of this research is to determine the early events on the pathway to chemotherapy resistance in breast cancer. Chemotherapy plays a critical role in prolonging the disease-free survival of breast cancer patients. While chemotherapy has increased survival, many progress to a therapy resistant state with limited treatment options. This study investigated the novel induction and pro-survival function of JUNB in the MCF10CA1a human breast cancer cell line. JUNB is a member of the JUN family of transcription factors which are components of the Activating Protein-1 (AP-1) transcript factor complex. AP-1 has been associated with both oncogenic and tumor suppressor functions depending on cell type and context. MCF10CA1a were derived from MCF-10A immortalized human mammary epithelial cells transfected with a mutant, constitutively active RAS construct and serial passaging in immunocompromised mice with selection for metastases. The presence of constitutive mutant RAS signaling activates downstream Mitogen Activated Protein Kinase (MAPK) and Phosphatidylinositol 3-kinases (PI3K) signaling, mimicking aberrant signal transduction pathways in clinical breast cancer. MCF10CA1a cells were treated with a lethal dose (300nM) of the chemotherapy agent, Flavopiridol (FP), a cyclin dependent kinase 9 (CDK9) inhibitor. As a CDK9 inhibitor, FP is a general inhibitor of RNA Polymerase II (Pol II) mediated gene transcription. Unexpectedly, both JUNB mRNA and protein levels increased dramatically in MCF10CA1a cells surviving FP treatment. The increase in JUNB mRNA levels was not due to increased JUNB mRNA stability or loss of function of FP because it continued to inhibit the activation of Pol II. To determine the functional role of JUNB in response to FP, JUNB levels were reduced (∼90%) in MCF10A1a cells nucleofected with JUNB siRNA. JUNB siRNA knockdown reduced the survival of FP treated MCF10ACA1a cells, consistent with a pro-survival role for JUNB. The pro-survival role of JUNB was further supported by increased detection of cleaved caspase3 in JUNB siRNA treated MCF10ACA1a cells in response to FP. In addition, SKBR3 cells, a HER2 overexpressed human breast cancer cell line, also exhibited a dramatic (∼10 fold) increase in JUNB mRNA levels in response to FP treatment. These results demonstrate that JUNB gene expression is induced in response to a lethal dose of FP. This increase suggests that JUNB may play a previously unrecognized pro-survival role in chemotherapy treated breast cancer cells. In addition, because JUNB is rapidly (within hours) induced in response to a lethal dose of FP these results suggest that JUNB induction may be among the earliest detectable events in resistance of breast cancer cells to chemotherapeutic agents. Supported by the U.S. Army Breast Cancer Research Program (JD) and P30 CA16058 (OSUCCC). Citation Format: Mellissa J. Hicks, Qiuping Hu, James DeWille. JUNB, survival against chemotherapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1053. doi:10.1158/1538-7445.AM2013-1053