Hypoxia-inducible factor-1 up-regulates the expression of Toll-like receptor 4 in pancreatic cancer cells under hypoxic conditions

Background & aims: Hypoxia is a common characteristic of solid tumors. Recent studies confirmed that Toll-like receptor 4 (TLR4) plays a significant role in cancer invasion and progression. In this study, the correlation between the expression of TLR4 and the change of the protein level of Hypoxia-inducible factor-1 alpha (HIF-1 alpha) was studied. Methods: We examined 84 human pancreatic cancer tissues for expression of HIF-1 alpha and TLR4 proteins. Panc-1 cells were exposed to normoxia (20% O-2) or hypoxia (<1% O-2) or treated with CoCl2. TLR4 protein was analyzed by flow cytometry and immunostaining. Growth studies were conducted on cells with the HIF-1 alpha inhibition isolated from stable transfected cell lines. Finally, TLR4 protein was detected by immunohistochemistry in vivo tumors. Results: There was a positive correlation between TLR4 and HIF-1 alpha protein in pancreatic cancer tissues. Hypoxic stress induced TLR4 mRNA and protein expression in Panc-1 cells. Cells transfected with HIF-1 alpha siRNA showed attenuation of hypoxia stress-induced TLR4 expression. In vivo growth decreased in response to TLR4 and HIF-1 alpha inhibiton. Transient HIF-1 alpha siRNA treatment could effectively curb tumor growth in vivo. Conclusion: These results suggest that TLR4 expression in pancreatic cancer cells is up-regulated via HIF-1 alpha in response to hypoxic stress and underscore the crucial role of HIF-1 alpha-induced TLR4 in tumor growth. Copyright (C) 2012, IAP and EPC. Published by Elsevier India, a division of Reed Elsevier India Pvt. Ltd. All rights reserved.