Nitric oxide (NO) is believed to play an important, but as yet undefined, role in regulating hypoxia inducible gene expression. Recently, we have reported evidence suggesting that the human insulin-like growth factor-binding protein-1 (IGFBP-1) gene is directly regulated by hypoxia through the hypoxia-inducible factor-1 pathway. The goal of the current study was to investigate NO regulation of hypoxic induction of IGFBP-1 gene expression using HepG2 cells, a model system of hepatic gene expression. We report that a NO generator, sodium nitroprusside, significantly diminishes hypoxic activation of IGFBP-1 protein and messenger ribonucleic acid expression. Furthermore, these effects are independent of guanylate cyclase/cGMP signaling, as two different inhibitors, LY 83583, a specific inhibitor of guanylate cyclase, and KT 5823, a protein kinase G inhibitor, had no effect on IGFBP-1 induction by hypoxia. Hypoxic induction of a reporter gene containing four tandemly ligated hypoxia response elements was completely blocked by sodium nitroprusside, but not by 8-bromo-cGMP, an analog of cGMP. These results suggest that NO blocks hypoxic induction of IGFBP-1 by a guanylate cyclase/cGMP-independent pathway, possibly at the level of oxygen sensing. The impaired hypoxia regulation of IGFBP-1 by nitric oxide may play a key role in the hyperinduction of IGFBP-1 observed in pathophysiological conditions such as fetal hypoxia and preeclampsia where dysregulation of NO has been observed.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Clinical Biochemistry
- Biochemistry, medical