Abstract
The HIF‐1α protein plays a key role in the cellular response to hypoxia via transcriptional regulation of genes involved in erythropoiesis, angiogenesis, and metabolism. Overexpression of HIF‐1α is commonly found in solid tumors in significant association with increased patient mortality and resistance to therapy. The predominant mode of HIF‐1α regulation by hypoxia occurs at the level of protein stability. In addition to hypoxia, HIF‐1α protein stability and synthesis is regulated by nonhypoxic signals such as inactivation of tumor suppressors and activation of oncogenes. Here, we show that an increase in gene dosage may contribute to HIF‐1α mRNA and protein overexpression in a nonhypoxic environment in head and neck squamous cell carcinomas (HNSCC). Increased HIF‐1α gene dosage was found in one out of five HNSCC‐derived cell lines and three out of 27 HNSCC primary tumors. Significantly, increased gene dosage in those samples was associated with high HIF‐1α mRNA and protein levels. Normoxic overexpression of HIF‐1α protein in HNSCC‐derived cell lines was also paralleled by higher expression levels of HIF‐1α target genes. Array CGH analysis confirmed the copy number increase of HIF‐1α gene and revealed that the gene is contained within a region of amplification at 14q23‐q24.2 both in the cell line and primary tumors. In addition, FISH analysis revealed the presence of 11–13 copies on a tetraploid background in SCC2 cells. These data suggest that increased HIF‐1α gene dosage is a mechanism of HIF‐1α protein overexpression in HNSCC that possibly prepares the cells for a higher activity in an intratumoral hypoxic environment. © 2009 Wiley‐Liss, Inc.