Abstract 1135: PPAPDC1B isoform 2, a new candidate oncogene within the 8p11-12 amplicon induces a proliferative advantage in breast cancer

Abstract

Abstract The 8p11-12 genomic region is amplified in about 10-15% of human breast cancer and may be associated with poor prognosis. Earlier, we used genomic analysis of copy number and gene expression to perform a detailed analysis of the 8p11-12 amplicon for identifying candidate oncogenes in breast cancer. We identified phosphatidic acid phosphatase type 2 domain containing 1B (PPAPDC1B) as one of the candidate oncogenes based on statistical analysis of copy number increase and over expression. Recently, fine-mapping of this locus, and the updated human genomic database has shown there may be more than 3 splicing variants of PPAPDC1B. We measured the expression status of all 3 individual PPAPDC1B isoforms in breast cancer cell lines by real-time quantitative RT-PCR and western blot. Interestingly, the short splicing variant /isoform2 is the dominant over-expressed form in SUM44 and SUM52 breast cancer cell lines that harbor the 8p11-12 amplicon. The PPAPDC1B gene encodes a novel type of transmembrane phosphatidate phosphatase with an acid-PPc domain with broad lipid phosphate substrate specificity. This suggests that PPAPDC1B may play a role in cell signaling and lipid metabolism. The PPAPDC1B isoform 2 is predicted to have an inactive acid-PPc domain due to truncation of mRNA. To address the question of whether PPAPDC1B possesses transforming properties, and to functionally characterize the different isoforms, we established lentiviral expression constructs of full-length PPAPDC1B as well as the short isoform. MCF10A cells were infected with equalized viral titer of lentiviral vectors and assayed for alterations in growth rates, colony formation and growth factor-independent proliferation. Cell proliferation assays indicated that over expression of PPAPDC1B isoform 2 enhanced cell proliferation more dramatically than full-length PPAPDC1B. Furthermore, colony formation assay showed that MCF10A cells over expressing PPAPDC1B isoform 2 formed large highly proliferative colonies compared with control cells. All of the isoforms of PPAPDC1B could induce insulin-like growth factor-independence in MCF-10A cells, but not independence of EGF. Thus, our data suggest that PPAPDC1B isoform 2 is a candidate oncogene from the 8p11 region that can induce a proliferative advantage in subset of breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1135. doi:10.1158/1538-7445.AM2011-1135