Subcellular distribution of S100A4 and its transcriptional regulation under hypoxic conditions in gastric cancer cell line BGC823.

It is well known that S100A4 is overexpressed in many tumors and involved in tumor invasion and metastasis. But the regulation of it is ill understood. We previously found that hypoxia mimicking cobalt chloride (CoCl(2)) enhanced the mRNA and protein expressions of the S100A4 gene in the gastric cancer cell line BGC823. In this study we found that S100A4 also displayed increased expression in BGC823 cells after exposure to real hypoxia (2.5% O(2)) as that by CoCl(2) treatment. Moreover, S100A4 protein showed different subcellular distribution under real hypoxia compared with that by CoCl(2) treatment or in normoxic conditions. To investigate the underlying molecular mechanism by which hypoxia regulates the expression of S100A4, we analyzed the regulatory sequences of the genes by bioinformatics and found a putative hypoxia responsive element (HRE) motif in the first intron of S1004. Furthermore, luciferase reporter assay showed that it is responsive to hypoxia. Electrophoretic mobility shift assay and chromatin immunoprecipitation assays demonstrated that hypoxia-inducible factor 1 (HIF-1) binds to the functional HRE in vitro and in vivo. The results provide evidence that S100A4 is a hypoxia-inducible gene, whose transcription is stimulated at least partly through the interaction of HIF-1 and HRE located at +329 to +334 of S100A4.