Carcinogenesis Advance Access published online on March 13, 2008
Carcinogenesis, doi:10.1093/carcin/bgn066
Hypoxia-inducible factor (HIF)-1
directly enhances the transcriptional activity of stem cell factor (SCF) in response to hypoxia and epidermal growth factor (EGF)
1 The State Key Laboratory of Experimental Hematology, Institute of Hematology and Hospital of Blood Diseases, Chinese Academy of Medical Sciences and Peking Union of Medical College, Tianjin, China
2 National Engineering Research Centers of Cell Products, AmCellGene Co. Ltd, TEDA, Tianjin, China
3 TEDA Life and Technology Research Center, Institute of Hematology, Chinese Academy of Medical Sciences, TEDA, Tianjin, China
# Corresponding Author: Dr. Zhong Chao Han, Institute of Hematology, Chinese Academy of Medical Sciences & Peking Union Medical College, 288 Nanjing Road, Tianjin 300020, China, Tel.: 86-22-27317273; Fax: 86-22-27317273; E-mail: zchan{at}amcellgene.com
Stem cell factor (SCF) plays important roles in tumor growth and angiogenesis. However, its regulatory mechanism remains largely undefined. Here we report that hypoxia up-regulated the expression of SCF in MCF-7 breast cancer cells in both mRNA and protein levels. When HIF-1
expression was knocked down by RNA interference, the SCF cells expression of SCF was decreased significantly. Furthermore, the SCF receptor, c-kit phosphorylation was significantly strengthened by the condition culture media (CCM) 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 (ChIP) assay demonstrated that HIF-1 directly bound to this region under normoxia, and this binding activity was significantly enhanced under hypoxia. Overexpression of HIF-1 significantly up-regulated the expression of luciferase reporter gene under control of the SCF promoters in both MCF-7 cells and HEK-293 cells, but mutation of the HRE site completely blocked this effect. EGF was also able to enhance the SCF expression under normoxia in MCF-7 cells, which was dependent on HIF-1. Taken together, our data demonstrated that HIF-1 was a key regulator of SCF expression in breast cancer cells. Hypoxia and EGFR signal co-existed in the tumor microenvironment and might promote angiogenesis through HIF-1-mediated up-regulation of SCF and other angiogenic factors.
Key Words: HIF • MCF-7 • SCF • EGF
* These authors contributed equally to the work.
Received October 16, 2007; revised February 16, 2008; accepted February 29, 2008.