Hypoxia-induced elevation in interleukin-8 expression by human ovarian carcinoma cells

The expression level of interleukin-8 (IL-8) directly correlates with the progression of human ovarian carcinomas implanted into the peritoneal cavity of nude mice, but the mechanism of induction is unknown. Because hypoxia induces expression of vascular endothelial growth factor/vascular permeability factor, which, like IL-8, is an angiogenesis-regulating molecule, we determined whether hypoxic conditions could regulate the expression of IL-8. Surgical specimens of human ovarian carcinomas were prepared for immunohistochemical and in situ hybridization analysis. Elevated levels of IL-8 mRNA and protein were found in tumor cells adjacent to necrotic zones. In vitro exposure of human ovarian carcinoma cell lines SKOV3 i.p.1 and Hey-A8 to hypoxia resulted in a time-dependent increase in steady-state levels of IL-8 mRNA (Northern blot) and in increased production and secretion of IL-8 protein (ELISA). Hypoxia-mediated transient induction of IL-8 expression could be ascribed to both an increase in IL-8 mRNA stability and transcriptional activation of the IL-8 gene promoter. Detailed functional analysis of the IL-8 promoter revealed that the sequence between -133 and -98 bp relative to the transcription initiation site was primarily responsible for IL-8 gene transcriptional activation by hypoxia. Point-mutated luciferase reporter studies indicated that AP-1 and NF-kappaB-like factor binding elements were mainly responsible for hypoxia-induced increase in IL-8 gene expression in human ovarian cancer cells, and that IL-8 transcription activation by hypoxia required the cooperation of NF-kappaB and AP-1 binding sites.