Increase in gene dosage is a mechanism of HIF‐1α constitutive expression in head and neck squamous cell carcinomas

Abstract

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

Reactive Oxygen Species-generating Mitochondrial DNA Mutation Up-regulates Hypoxia-inducible Factor-1α Gene Transcription via Phosphatidylinositol 3-Kinase-Akt/Protein Kinase C/Histone Deacetylase Pathway

“…Actually, we and others have reported the up-regulation of HIF-1␣ mRNA in some tumor types (8 -10). Although the precise mechanism of HIF-1␣ gene activation is largely unknown, an increase in gene dosage is reported as one of the mechanisms of constitutive up-regulation of HIF-1␣ mRNA expression (9,10).…”

Interplay between receptor tyrosine kinases and hypoxia signaling in cancer

“…Signaling by EGFR has been shown to increase the level of HIF-1α in a variety of cancer cell types, including prostate cancer, head and neck squamous cell carcinoma (HNSCC), NSCLC and breast cancer [104][105][106][107]. Additionally, various studies reported that EGFR activity upregulates HIF-1α also under normoxic conditions [104,[107][108][109][110], however, there are controversial data aiming to explain as how this event is mediated.…”

“…Additionally, various studies reported that EGFR activity upregulates HIF-1α also under normoxic conditions [104,[107][108][109][110], however, there are controversial data aiming to explain as how this event is mediated. On one hand, few studies indicate that EGF increases both HIF-1α mRNA and protein levels [111].…”

“…Similar to other RTKs, EGFR activation triggers multiple signal transduction pathways, including the phosphatidylinositol 3-kinase (PI3K)/AKT pathway [113] and the RAS/RAF/mitogenactivated protein kinase (MAPK) pathway [114]. Besides oxygen, ROS and particular Krebs cycle metabolites such as fumarate and succinate [115] have also been demonstrated to regulate prolyl-hydroxylase activity-mediating HIF-1α stabilization under normoxic conditions [107,116]. H 2 O 2 has been shown to induce EGF-stimulated activation of PI3K/AKT signaling in ovarian cancer cells.…”

“…A more limited number of studies has examined the impact of MAPK signaling on HIF-1α expression. Some reports suggest that inhibition of the MAPK pathway does not alter EGFR-induced expression of HIF-1α [112], whereas others reported that inhibition of MAPK reduces basal HIF-1α activity through potential phosphorylation events [107].…”