Abstract C299: Functional differences of mutant p53's expressed in MCF10A cells and their contribution to breast carcinogenesis.

Recent high-throughput tumor sequencing has confirmed a striking prevalence of somatic TP53 mutations in breast cancer (∼35% overall), usually associated with basal-like tumors. Patients with these aggressive tumors have worst clinical outcome, fewer treatment options and respond poorly to current therapies. Successful treatment of basal cancer patients may require a combined approach that addresses known cancer protein pathways, e.g, p53, as well as modifier pathways that collaborate with these driver pathways to cause cancer. For this, we are developing a functional screen to analyze the importance of co-driver mutations and find alternative targets that may offer target therapy for these breast cancer patients. Mutations in TP53 can induce dominant negative effects on wild-type (WT) p53 protein, including enhanced tumor growth, increased cell migration, invasion and metastasis. Dominant mutations do not necessarily lead to a null phenotype. Different p53 mutations result in gain-of-function phenotypes such as distinct patterns of growth, tumorigenicity and protein interactions, which suggest that individual TP53 mutations result in distinct cellular programs. We hypothesized that unique TP53 mutations would have distinct functional effects on the hallmarks of cancer. To study this, we generated MCF10A and HMEC-htert stable cells expressing the ten most frequent breast cancer mutations located in the DNA binding domain of TP53. Ectopic expression of p53 in stable cells has been confirmed by qRT-PCR and we are currently investigating the phenotypic changes associated with these mutations in several hallmarks of cancer such as 1) epithelial to mesenchymal transition (EMT), 2) migration 3) invasion 4) escape from apoptosis and 5) proliferation. Compared with wt-p53, the p53G245S, p53R248Q, p53Y234C and p53H179R mutants displayed a mesenchymal phenotype characterized by the presence of slug and a disrupted B-catenin and E-cadherin staining. Interestingly these same mutants were more invasive. Indeed, p53R248Q was one of the most resistant to apoptosis; follow by p53Y234C, which may suggest that these two mutations are the most aggressive. This also suggests that different mutants have different downstream effects like p53G245S and p53H179R, which are the most sensitive to apoptosis. In conjunction, these preliminary data suggest that different TP53 mutations result in distinct cellular programs. As soon as we complete the assay development we will set up the screen to determine the role of the co-drivers. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C299. Citation Format: Laura G. Gonzalez-Malerva, Seron Eaton, Anasuya Pal, Donald Chow, Mayra Guzman, Eva Amouzougan, Hongwei Yin, Jin Park, Karen Anderson, Joshua LaBaer. Functional differences of mutant p539s expressed in MCF10A cells and their contribution to breast carcinogenesis. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C299.