HYPOXIA INDUCES AP-1-REGULATED GENES AND AP-1 TRANSCRIPTION FACTOR-BINDING IN HUMAN ENDOTHELIAL AND OTHER CELL-TYPES

Hypoxia results in differential expression of specific genes in certain cell types. In endothelial cells, hypoxia. activates several genes that are known to be inducible by transcription factor AP-1. including endothelin-l and platelet-derived growth factor-B (PDGF-B). In this study we demonstrated that other AP-1-inducible genes are activated by hypoxia in these cells, including collagenase IV anti c-jun, and sought to correlate the activation of genes by hypoxia with the activation of transcription factor AP-1. Depending upon the type of cell studied, hypoxic exposure resulted in the induction of AP-1 transcription factor DNA-binding activity with wide variations in levels of binding. The magnitude of activation of transcription factor AP-1 by hypoxia did not always strictly correlate with the level of induction of AP-1-inducible genes. This finding indicates a requirement for additional mechanisms of controlling transcription beyond the simple activation of AP-1 factor DNA-binding activity for the activation of AP-l-inducible genes during hypoxia. Hypoxia has been reported to lower the intracellular redox potential. The effect of redox state changes on AP-1 transcription factor activity and on the activation of AP-1-inducible genes was also studied. PDTC, a potent reducing agent, activated the AP-I transcription factor in HeLa cells. and also resulted in increased accumulation of c-jun mRNA in these cells. In contrast to PDTC-mediated activation of the AP-1 transcription factor and the subsequent induction of the AP-1-regulated c-jun gene, hypoxic activation of AP-1 transcription factor binding to its cognate DNA sequence did not activate the c-jun gene in HeLa cells, thus documenting distinct differences in signals generated by the reducing intracellular microenvironments created by hypoxia and PDTC. These results demonstrate the induction of. AP-1 transcription factor activity by hypoxic environments. but suggest that additional factors or cell-specific signals are involved in the regulation of hypoxia-induced genes.