Abstract A35: Insulin and hypoxia-inducible factor-1 cooperate to increase the viability of pancreatic cancer cells

Abstract

Abstract Insulin receptor (IR) and hypoxia-inducible factor-1 (HIF-1) master two different intracellular signaling pathways. Both the pathways regulate growth, glycolysis, migration and angiogenesis in cancer. We hypothesized that the IR and HIF-1 pathways are interrelated to each other in pancreatic cancer cells. To test this hypothesis, we designated 45 athymic mice to six tumor-carrying groups (6-7 mice per group) and an intact control group (n=5). All tumor carriers were subject to one of the following conditions: (i) injection of beta-cell-toxin streptozotosin (SZ) before cancer induction, (ii) daily injection of insulin after cancer induction, and (iii) no treatment other than cancer induction. In a 12-week experiment, wild-type MiaPaCa2 human pancreatic cancer cells and HIF-1-null si-MiaPaCa2 cells were implanted orthotopically. When wild-type cells were used, the resulting groups were mice(wt-sz), mice(wt-in), and mice(wt-un). When si-MiaPaCa2 cells were used, the resulting groups were mice(si-sz), mice(si-in), and mice(si-un). In the end of the experiment, insulin was determined in pancreas and plasma by radioimmunoassay. Tumor viability was assessed by histology and Western blots. We found that pancreatic insulin was decreased in all tumor carriers except mice(wt-in), which suggests that tumor carriage per se impaired pancreatic beta-cells. When plasma insulin was determined, significant decreases were seen in mice(wt-sz) and mice(si-sz). Thus, SZ treatment caused additional damage on pancreatic beta-cells and thereby decreased plasma insulin. When glucose and lactate were determined in the plasma, decreased glucose and increased lactate were seen in four out of six tumor-carrying groups. These changes may be due to an uncontrolled glycolysis in cancer cells (also known as the Warburg effect). When tumors were weighed, the biggest ones came from mice(wt-in). Necrosis was seen in all tumors, but tumors from mice(wt-un) had the least necrosis. It suggests that normal pancreas is the best environment for insulin-HIF-1 cooperation. We performed Western blots to determine IR, hexokinase-II (HK-II, a glycolytic enzyme), and vascular endothelial growth factor (VEGF) in tumor grafts. HK-II and VEGF are known to be regulated by HIF-1. In addition, HK-II and VEGF are also known to be involved in IR-motivated signaling cascades. In the present study, insulin injection in mice(wt-in) and mice(si-in) increased IR expression. However, increased HK-II and VEGF expression were only seen in tumors from mice(wt-in) but not mice(si-in). This suggests that HIF-1 is a prerequisite for insulin to stimulate glycolysis and angiogenesis. Finally, we determined caveolin-1 in tumors. Caveolin-1 is an IR regulator, and caveolin-1 gene is regulated by HIF-1. In this study, we found that wild-type tumors had greater caveolin-1 expression than HIF-1-null tumors. In conclusion, insulin and HIF-1 systems cooperate to give survival advantage to pancreatic cancer cells. HIF-1 expression is a prerequisite for insulin to stimulate pancreatic cancer cells. HIF-1 is also necessary for pancreatic cancer cells to express caveolin-1. Citation Format: Yue Chen, Dapeng Zhang, Lihua Cui, Feng Wang. Insulin and hypoxia-inducible factor-1 cooperate to increase the viability of pancreatic cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A35.