Sa1993a Reduced Expression of Prostaglandin Transporter Promotes Angiogenesis in Gastric Cancer

Abstract

Background & Aims: Colorectal cancer (CRC) cells (unlike normal colonic epithelial cells) secrete VEGF, which drives these cells proliferation and promotes tumor-related angiogenesis. The mechanism(s) of increased, aberrant VEGF expression in CRC cells is not known, but is likely related to transcriptional activation of VEGF gene.We hypothesized that: 1) upregulated importin-α in CRC cells (which facilitates nuclear transport of transcription factors: HIF1α and CREB, and is essential for VEGF gene promoter activation) is the underlying mechanism for increased VEGF expression in these cells and CRC cell proliferation, and, 2) inhibition and/or silencing of importin-α in CRC cells will inhibit VEGF gene activation and CRC cell proliferation. Ivermectin is a specific inhibitor of importin α nuclear transport (Biochem J. 2012: 1;443(3):851-6). We examined whether treatment of CRC cell lines with ivermectin could inhibit CRC cell growth. Methods: We used: (a) human CRC cell lines HCT116 & HT29 and (b) normal colonic epithelial cells NCM356 & NCM460. We treated cultured CRC cells with ivermectin (50 μM, 6 hr; specific inhibitor of importin-α nuclear transport), with importin α specific siRNA or control RNA (100nM, 48 hr). Add-back studies included treatment with exogenous VEGF (20ng/ml). Studies: 1) mRNA and protein expression of importin-α and VEGF by Real-Time RT-PCR, and/or Western blotting and immunostaining, respectively; 2) VEGF secretion into culture medium by ELISA; 3) translocation of importin to the nucleus in CRC vs. normal cells; and 4) cell proliferation by BrdU assay. Results: 1) CRC cell lines express high levels of VEGF and secrete large amounts of VEGF (up to 1530 pg/ml) into culture medium at 24 hours vs. normal epithelial cells, which only secrete minimal VEGF ( 40% (p< 0.05); 3) Selective inhibition of importin-α in CRC cells using ivermectin significantly reduced VEGF expression by ~3-fold (p<0.01) and proliferation of these cells by 2.4-fold (p<0.01). Treatment with exogenous VEGF partly reversed inhibited by ivermectin cell proliferation; 4) Importin-α silencing in CRC cells significantly reduced VEGF expression and proliferation of these cells by 2.2-fold and 2fold (both p<0.01), respectively; treatment with exogenous VEGF following importin-α silencing reversed inhibition of cell proliferation by 2-fold (p < 0.01). Conclusions: 1) VEGF gene activation in CRC cells requires functional importin-α; 2) importin-α mediates increased proliferation of CRC cells; downregulation of importin-α with specific siRNA or its inhibition with specific inhibitor ivermectin inhibits CRC cell proliferation; 3) These studies suggest a potential therapeutic role of ivermectin in inhibiting CRC cell proliferation.