Abstract 3089: The role of p63 regulation during epithelial to mesenchymal transition (EMT) and subsequent accumulation of malignant features of primary immortalized prostate cells

A family of transcription factors is constituted by p53, p63 and p73. Unlike p53, which is expressed in response to environmental stress, p63 (TP73L) is constitutively expressed at high levels in a variety of epithelial tissues including prostate. Our genome-wide gene expression analysis identified p63 as one of the most consistently under-expressed genes in prostate cancer samples compared to matched benign prostate tissue. All benign prostate samples including benign prostate hyperplasias (BPH) exhibited high p63 expression. Two alternative p63 promoters generate two different N-terminal variants, TA or ΔN which contains and lacks the transactivating domain, respectively. Differential splicing generates multiple additional isoforms. The activity and interactions of the different isoforms remain unresolved. Using isoform-specific TaqMan real-time quantitative PCR assays, we have found that ΔNp63α is the predominant isoform in prostate tissues, but the other isoforms are detectable. Our group has established a new experimental cell culture model based upon primary, immortalized prostate epithelial cells (EP156T cells), where p63 was found to be shut-down as EP156T cells underwent epithelial-to-mesenchymal transition (EMT) to become EPT1 cells. Subsequently, EPT2 cells were derived from EPT1 cells and p63 stayed shut-down. EPT2 cells had acquired several malignant features in contrast to the progenitors, including anchorage independent growth in soft agar and ability to grow at much higher density in monolayers. To dissect the role of p63 in EMT and in gene expression modules associated with carcinogenesis, we have stably re-expressed the predominant isoform ΔNp63α in both EPT1 and EPT2 cells using retroviral vector transductions. Microarray analysis shows that p63 re-expression leads to re-expression of genes participating in several cell-junction components, such as hemidesmosomes, focal adhesions and gap junctions. These genes were down-regulated during EMT. There were also morphological changes and a decreased ability to migrate following p63 re-expression. This indicates that ΔNp63α re-expression might result in a partial mesenchymal-to-epithelial transition (MET). The present focus is to identify co-factors that may act complementary or synergetically with p63 to induce a complete MET in EPT1 cells and to identify p63 target genes and regulatory cross-talk with relevance for anti-cancer strategies. 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 3089. doi:10.1158/1538-7445.AM2011-3089