Hypoxia-Induced Snail Expression Through Transcriptional Regulation by HIF-1α in Pancreatic Cancer Cells

Intratumoral hypoxia and epithelial-mesenchymal transition are involved in tumor invasion and metastasis. This study investigated the molecular mechanisms that relay the hypoxia signal into the epithelial-mesenchymal transition and metastasis. Morphology analysis and tumor cell migration and invasion assays were performed to detect phenotypic changes of pancreatic cancer cells under normoxic and hypoxic conditions after lentiviral HIF-1 alpha shRNA transfection. Quantitative reverse transcription polymerase chain reaction, western blot, and immunohistochemistry were used to detect gene expression in pancreatic cancer cell lines and tissues or normal pancreatic tissues. Luciferase, gel shift, and ChIP assays were used to assess gene regulation. Under hypoxic conditions, these tumor cells underwent typical morphological and molecular changes to epithelial-mesenchymal transition. Moreover, Snail expression was induced by hypoxic conditions and was regulated by HIF-1 alpha expression at the transcriptional level through HIF-1 alpha-binding to the second site of hypoxia-responsive elements of the Snail gene promoter. In addition, Snail expression was associated with HIF-1 alpha expression in pancreatic cancer tissues, and expression of both was associated with tumor metastasis and poor patient survival. Our study provides key evidence that HIF-1 alpha and Snail are responsible for hypoxia-induced metastasis phenotypes in pancreatic cancer and that HIF-1 alpha and Snail expression can be used as biomarkers to predict tumor metastasis and patient survival.