Abstract 833: S100A4 interacts with p53 in the nucleus promoting its degradation.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Background. S100A4 is a calcium binding protein which has no known enzymatic activity, but it exerts its function by binding and regulating other molecules, among which have been described Myosin and p53. S100A4 has been shown to be upregulated in several types of cancers, correlating with poor prognosis and metastasis. In a previous study (Orre et al., 2007), S100A4 has been shown to be involved the cellular response to ionizing irradiation in a p53 dependent manner; our aim here was therefore to investigate the cellular interaction partners of S100A4 in response to p53 and then, based on this data, to further elucidate the cellular function of S100A4. Observations. Nutlin-3A is a compound that specifically stabilizes p53 through inhibiting the interaction between p53 and mdm2. We could show an interaction between S100A4 and p53 via immunoprecipitation in the NSCLC cell line A549 (which has a high expression of S100A4 and a wild-type p53), and that this interaction is increased after Nutlin-3A treatment. The interaction has been independently confirmed via Proximity Ligation Assay, showing as well that the protein complexes are localized in the nucleus. Since this interaction increased after inhibition of the mdm2-p53 interaction, we hypothesized that S100A4 could be involved in regulation of p53 degradation; therefore we generated two cell lines from A549, infected with S100A4 shRNA (shS100A4) or an Empty Vector shRNA (shEV) as a control. Knockdown of S100A4 resulted in stabilization of p53 and transactivation of p53 transcriptional targets; it also resulted in higher sensitivity to cisplatin-mediated apoptotic cell death, measured as a drop in mitochondrial membrane potential, caspase-3 activation and AV/PI assay. We confirmed this finding by an independent method using transient S100A4 down regulation via siRNA; this resulted in an increase in p53 level and of p21 and MDM2 level in A549 adenocarcinoma cells. S100A4 siRNA resulted also in p53-dependent growth arrest, that was reversed after co-transfecting p53 siRNA. Conclusions. Our data show that S100A4 interacts with p53 increasing its degradation, resulting in higher cell viability and lower apoptosis after cisplatin treatment. A possible correlation in patients between S100A4 overexpression and cisplatin resistance could be used to drive treatment selection. Citation Format: Lukas Orre, Elena Panizza, Vitaliy Kaminskyy, Torbjorn Graslund, Boris Zhivotovsky, Janne Lehtio. S100A4 interacts with p53 in the nucleus promoting its degradation. [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 833. doi:10.1158/1538-7445.AM2013-833