Increase in Gene Dosage is a Mechanism of HIF-1α Constitutive Expression in Head and Neck Squamous Cell Carcinomas

The HIF-1 alpha 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-1 alpha is commonly found in solid tumors in significant association with increased patient mortality and resistance to therapy. The predominant mode of HIF-1 alpha regulation by hypoxia occurs at the level of protein stability. In addition to hypoxia, HIF-1 alpha 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-1 alpha mRNA and protein overexpression in a nonhypoxic environment in head and neck squamous cell carcinomas (HNSCC). Increased HIF-1 alpha 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-1 alpha mRNA and protein levels. Normoxic overexpression of HIF-1 alpha protein in HNSCC-derived cell lines was also paralleled by higher expression levels of HIF-1 alpha target genes. Array CGH analysis confirmed the copy number increase of HIF-1 alpha 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-1 alpha gene dosage is a mechanism of HIF-1 alpha protein overexpression in HNSCC that possibly prepares the cells for a higher activity in an intratumoral hypoxic environment. (C) 2009 Wiley-Liss, Inc.