Abstract 2308: ΔNp63 promotes neuroblastoma by regulating tumor angiogenesis.

Abstract

Abstract Background: The tumor suppressor gene p63 and its family members p53/p73 have been described as critical determinants of tumorigenesis. ΔNp63, a splice variant of p63 lacking the N-terminal transactivation domain, is thought to antagonize the transcriptional regulation of the p53, p63 and p73 target genes and blocks their tumor suppressor activity. Overexpression of ΔNp63 has been observed in a number of adult human cancers, suggesting a role of this isoform in tumor formation. While some studies have proposed that ΔNp63 might simply inhibit p53 function within cells, leading to malignant transformation, we found that this model is challenged by the lack of consistent correlation between p53 mutation and ΔNp63 expression suggesting that ΔNp63 might possess a gain of function. Methods: Since expression of ΔNp63 isoforms in primary tumors has been shown to correlate with poor prognosis, we attempted to analyze their relationships with tumor angiogenesis. To test whether overexpression of oncogenic ΔNp63 in HEK-293T cells can stimulate tube formation in endothelial cells using HUVEC tube formation assay. Further, we performed gene affymetrix as well as protein micro array analysis in primary cells compared to cells overexpressed ΔNp63 isoforms. In addition, we used siRNA techniques to verify any potential role of ΔNp63 isoforms in tumor angiogenesis in vitro as well as in vivo experiments. Results: We found that overexpression of the oncogenic isoform of p53 family member ΔNp63 in HEK-293T cells resulted in stimulation of tubular structures in HUVEC cells. As 293T cells lack functional p53, these results strongly suggest a gain of function for ΔNp63. In addition, we found that ΔNp63 is overexpressed in neuroblastoma and ΔNp63 overexpression results in increasing secretion of the inflammatory cytokines interleukin-6 (IL-6) and -8 (IL-8) leading to elevated phosphorylation of STAT-3. Our further analysis showed that elevated phosphorylation of STAT-3 induced stabilization of HIF-1α protein resulting in VEGF secretion. Conclusions: We found that ΔNp63 is overexpressed in neuroblastoma and resulted in elevated secretion of the inflammatory cytokines IL-6 and -8 leading to increased STAT3 activation. Our further studies showed that elevated ΔNp63 induced stabilization of HIF-1α protein resulting in VEGF secretion in a p53 independent manner. Importantly, we show in vitro and in vivo experiments that depletion of ΔNp63 isoform by specific siRNAs significantly reduced angiogenic potential of Neuroblastoma. In summary, our study revealed the underlying molecular mechanism how ΔNp63, as a master transcription factor, modulates tumor angiogenesis in Neuroblastoma. Citation Format: Hemant K. Bid, Maren Cam, Antony Audino, Raushan Kurmasheva, Jiayuh Lin, Peter Houghton, Hakan Cam. ΔNp63 promotes neuroblastoma by regulating tumor angiogenesis. [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 2308. doi:10.1158/1538-7445.AM2013-2308