DETERMINING IF TRUNCATED DOPAMINE AND CAMP-REGULATED PHOSPHOPROTEIN (T-DARPP) HAS ONCOGENIC POTENTIAL IN BREAST CELLS
Aracely Acevedo1, Susan Kane2, Jamil Momand1.
1California State University, Los Angeles, Los Angeles, CA, 2City of Hope, Duarte, CA.
Human breast cancers that are found to overexpress Her2 receptor tyrosine kinase are often treated with herceptin (trastuzumab), a humanized monoclonal antibody. Although cancer patients who initially respond to herceptin in combination with chemotherapy have a 5 month increase in median overall survival, the cancer usually builds up resistance. Previous studies have shown Her2+ breast cancer cell lines that acquire resistance to herceptin often overexpress a truncated isoform of Darpp-32 protein, known as t-Darpp. Darpp-32 and t-Darpp are both encoded by the PPP1R1B gene. Darpp-32 (dopamine and cAMP regulated phosphoprotein of 32kD) and t-Darpp modulate the PI3K/Akt signal transduction pathway. In this study, our objective is to determine if t-Darpp is an oncogene. Specifically, the aim is to investigate whether t-Darpp can increase anchorage independent growth of mammalian cells. Additionally, we will determine if endogenous Darpp-32 is necessary for this increased growth. To reach this goal, 4 cell lines will be stably transfected with t-Darpp: MCF10A, MCF-7, NIH3T3, and t-Drp KO MEF. Soft agar colony formation assays (transformation assays) will then be conducted using these mammalian cell lines. We hypothesize that t‐Darppoverexpression transforms all cell lines and does not require Darpp-32 for its oncogenic transformation. If so, this would confirm the oncogenicity of t-Darpp without the need for endogenous Darpp-32. Determining the oncogenicity of t‐Darpp will allow us to get a better insight in its role in the PI3K/Akt pathway and how it confers herceptin resistance in Her-2+ breast cancers.