Stimulation of Erythropoietin Gene Transcription During Hypoxia and Cobalt Exposure

Erythropoietin, a plasma glycoprotein produced primarily by the kidney, is a growth and differentiation factor for erythroid progenitor cells. Production of renal erythropoietin is regulated by modulation of mRNA levels in response to changes in tissue oxygenation. Exposure to cobalt, a nonphysiologic stimulus for erythropoietin production, also acts by inducing mRNA accumulation. To determine whether variations in erythropoietin mRNA levels result from enhanced transcription of the erythropoietin gene, in vitro transcription reactions were performed using isolated rat kidney cell nuclei. Quantitation of specific nuclear RNAs labeled during in vitro transcription revealed active erythropoietin gene transcription in kidney nuclei from anemic-hypoxic and cobalt-treated animals while erythropoietin transcriptional activity was undetectable in normal kidney nuclei. Time course studies showed that stimulation of transcription begins between two and four hours following cobalt treatment and parallels the kinetics of mRNA and plasma erythropoietin accumulation. These results indicate that tissue hypoxia and cobalt exposure specifically enhance erythropoietin gene expression. This increase in erythropoietin production is regulated at least in part at the level of gene transcription.