Pi3k/Akt-Induced Stabilization Of Fuse Binding Proteins (Fbps) In Liver Cancer Cells

Far upstream element-binding proteins (FBPs) represent a family of transcription factors, which are highly overexpressed in the majority human liver cancer (hepatocellular carcinoma; HCC). Nuclear accumulation of FBP-1, -2, and -3 in HCC cells support cell proliferation and migration. However, the mode of FBP dysregulation in HCC cells has not been defined so far. Genomic alterations of the fubp (FBP-1; chr. 1p31.1), khsrp (FBP-2; chr. 19.p13.3), and fubp3 (FBP-3; 9p34.11) gene loci in primary human HCCs were determined by matrix-comparative genomic hybridization (CGH). In order to identify specific stimuli of FBP enrichment, different human HCC cell lines were cultured under different cell density and hypoxic conditions or treated with growth factors (e.g., TGFs, IGF-II), chemical inhibitors (e.g., AG1478, SB203580, MEK1/2, sorafenib, and PI3K inhibitors), and gene-specific siRNAs (e.g., Akt1-3, rictor, raptor). The in vivo relevance of the findings was confirmed using HCC mouse models (e.g., Mdr2-/- animals) and human HCC tissue specimens (immunohistochemistry and western blotting). Only few genomic gains were found for all FBP family members in human HCC samples (e.g., 6% for fubp). In vitro, inhibition of EGFR (by AG1478) or administration of the multi-kinase inhibitor sorafenib reduced FBP protein levels. Furthermore, inhibition of the PI3K/Akt/mTOR pathway revealed strong effects on FBP protein half-live without significant impact on FBP transcription. Other pathways or stimuli only caused minor effects on FBP expression (e.g., p38 or Raf1 inhibition). These findings were confirmed in mouse HCC models with high-level expression of FBPs, where injection of sorafenib or rapamycin significantly diminished FBP amounts. Reduction of FBP concentrations after inhibition of the PI3K/Akt/mTOR pathway was rescued after inhibition of caspase-3/-7 activity. Lastly, a significant correlation between pAkt and nuclear FBP expression was detected in human HCC tissues. These results demonstrate that activation of the PI3K/Akt/mTOR signalling axis is responsible for increased stabilisation of FBPs in human HCC cells. Elevated FBP half-live is at least partly mediated through crosstalk between the PI3K/Akt/mTOR pathway and caspase activity. These data are important for a deeper understanding of how druggable upstream regulators may affect FBP bioavailability in hepatocarcinogenesis. Citation Format: Jana Samarin, Ilan Stein, Elad Horwitz, Xin Chen, Mona Malz, Eli Pikarsky, Diego Calvisi, Peter Schirmacher, Kai Breuhahn. PI3K/AKT-induced stabilization of FUSE binding proteins (FBPs) in liver cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2157. doi:10.1158/1538-7445.AM2015-2157