HIF-1α Promotes the Metastasis of Esophageal Squamous Cell Carcinoma by Targeting SP1

Background: In microenvironment of malignant tumors, Hypoxia-Inducible Factors (HIF), most importantly HIF-1alpha, play an important role in regulation of adaptive biological response to hypoxia, promoting angiogenesis and metastasis. However, the underlying mechanism that HIF-1alpha regulates metastasis needs to be further clarified. Methods: The expressions of HIF-1alpha and SP1 were detected in 182 samples of esophageal squamous cell carcinoma (ESCC) and adjacent normal tissues by immunohistochemistry (IHC), and the correlation between the expression levels of HIF-1alpha and SP1 was analyzed. The expression of HIF-1alpha in ESCC cell lines TE1 and KYSE30 was then detected using qRT-PCR and western blot. The potential binding sites of HIF-1alpha on the SP1 promoter were analyzed using UCSC and JASPAR databases, verified by chromosomal immunoprecipitation (ChIP) assay and qRT-PCR. The effects of HIF-1alpha and SP1 on ESCC cell migration and invasion were then tested with Transwell and Matrigel experiments. Results: The expression of HIF-1alpha in cancer tissues is higher than adjacent normal tissues, and is correlated with metastasis, recurrence and poor prognosis. Upon silencing HIF-1alpha by siRNA, the invasion and migration ability of ESCC cells were significantly inhibited, which could be restored by the overexpression of SP1. Hypoxic conditions significantly increased the expression of HIF-1alpha and SP1 at both protein and mRNA levels in ESCC cells. HIF-1alpha enhanced SP1 transcription through binding to the promoter region. The expression of protein and mRNA levels of SP1 was decreased by silencing HIF-1alpha in cells. In contrast, overexpression of HIF-1alpha significantly increased the mRNA and protein levels of SP1. The expression of SP1 in ESCC was positively correlated with the protein expression of HIF-1alpha and poor prognosis. Conclusion: The results of our study indicate that HIF-1alpha promotes metastasis of ESCC by targeting SP1 in a hypoxic microenvironment. Further study on this mechanism may elucidate the possibility of HIF-1alpha and SP1 as new targets for the treatment of ESCC.