Regulation of the Erythropoietin Gene: Evidence That the Oxygen Sensor Is a Heme Protein

TLDR

Erythropoietin (Epo) is produced in kidney and liver in response to hypoxia, stimulating red blood cell production. The study proposes that a ligand‑dependent conformational change in a heme protein mediates hypoxia, cobalt, and nickel‑induced Epo production. Using Hep3B cells, the authors show that Epo regulation is physiologic, requires new protein synthesis before hypoxia‑ or cobalt‑induced mRNA increases, and is driven by a heme‑protein conformational change. Hypoxia, cobalt, and nickel chloride all increase Epo mRNA and protein via a common pathway, and inhibition by carbon monoxide or blocking heme synthesis confirms a heme protein’s essential role in oxygen sensing.

Abstract

Erythropoietin (Epo), the hormone that stimulates red blood cell production, is synthesized in the kidney and liver in response to hypoxia. The human hepatoma cell line Hep3B regulates its production of Epo in a physiologic manner. Either hypoxia or cobalt chloride markedly increases expression of Epo mRNA as well as production of biologically active and immunologically distinct Epo protein. New protein synthesis is required before the induction of increased levels of hypoxia- or cobalt-induced Epo mRNA. Hypoxia, cobalt chloride, and nickel chloride appear to stimulate Epo production through a common pathway. The inhibition of Epo production at low partial pressures of oxygen by carbon monoxide provides evidence that a heme protein is integrally involved in the oxygen-sensing mechanism. This hypothesis is further supported by the finding that when heme synthesis is blocked, hypoxia-, cobalt-, and nickel-induced Epo production are all markedly inhibited. A model is proposed in which a ligand-dependent conformational change in a heme protein accounts for the mechanism by which hypoxia as well as cobalt and nickel stimulate the production of Epo.