Stem cell factor (SCF) plays important roles in
tumor growth and angiogenesis. However, its regulatory mechanism remains largely undefined. Here, we report that
hypoxia upregulated the expression of SCF in MCF-7
breast cancer cells in both
messenger RNA and
protein levels. When
hypoxia-inducible factor (HIF)-1 alpha expression was knocked down by RNA interference, the MCF-7 cell expression of SCF was decreased significantly. Furthermore, the
SCF receptor, c-kit phosphorylation was significantly strengthened by the condition
culture media from hypoxic MCF-7 and MCF-7-c cells. The survival of A549 cells was more dependent on SCF under
hypoxia. Analysis of SCF promoter 5'-flanking region revealed a potential
hypoxia-response element (HRE; 5'-GCGTG-3') located at -68 to -64 relative to the transcriptional start site.
Chromatin immunoprecipitation assay demonstrated that HIF-1 alpha directly bound to this region under normoxia, and this binding activity was significantly enhanced under
hypoxia. Overexpression of HIF-1 alpha significantly upregulated the expression of
luciferase reporter gene under control of the SCF promoters in both MCF-7 cells and human embryonic kidney 293 cells, but mutation of the HRE site completely blocked this effect.
Epidermal growth factor was also able to enhance the SCF expression under normoxia in MCF-7 cells, which was dependent on HIF-1 alpha. Taken together, our data demonstrated that HIF-1 alpha was a key regulator of SCF expression in
breast cancer cells.
Hypoxia and
epidermal growth factor receptor signal coexisted in the tumor microenvironment and might promote angiogenesis through HIF-1 alpha-mediated upregulation of SCF and other angiogenic factors.